Attic Shaped Studio

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endorka
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Attic Shaped Studio

#1

Postby endorka » Tue, 2019-Sep-24, 15:20

Hello folks,

I've been visiting several well know acoustics forums for years, and studied them and some written literature intently before designing my studio in 2015. I planned it to the best of my ability at the time and built a significant number of DIY bass traps. Those and some thinner panels from my previous apartment room studio formed the bulk of the acoustic treatment. A friend with considerable expertise helped with the final positioning and optimizing of the panels.

Over the last four years I've made incremental improvements, some based on theory learning, some from experience recording, mixing and mastering there. My fascination and study with acoustics continues, and I now feel ready to make some bigger improvements. I'll detail the current state in this post, and put my plans for improvement in subsequent ones in this thread.

The studio is on the second floor of our detached house. We moved here in 2015. It's a modern timber frame construction with a pleasing block cladding, built by the previous owner (a professional builder) for his family. The studio is in the "attic" and the walls are part sloping along one dimension. I quoted attic because it isn't really - the house was designed and built this way, so has proper sized stairs, landings, doors and so on. Even before treatment the studio room had appealing acoustics.


exterior - balcony.png


Before acoustic treatment;

empty room.png


The house is at the bottom of the "U" in a town cul de sac. The studio faces south onto our garden, then a very dense wooded area. The wooded area is dense with tall trees and undergrowth. It's really nice to look out on when working, especially in summer when the leaves are all present. Beyond that is a road, then more wooded areas and some housing. After that it's pretty much park, farms and countryside. South is at the top of the page.

studio-plan-768x487.png


My initial plan was to to use it for composing, writing arrangements and recording single or small groups of instruments and vocals associated with this. Guitars, strings, horns, light percussion etc. This comprised most of my work at the time.

Not long after completion though, a jazz composer I had played bass for asked if he could record his band here. Drums, sax, guitar and bass, all to be recorded live. I figured we could do it all in room 1, gave our neighbours advance warning of potential noise and promised them it would end 5pm at the latest. I spoke to them the day after, and happily they didn't hear a thing. In our garden you could hear there was a band playing, but it wasn't bad at all.

Since then I've been blessed that many other people have recorded, mixed and mastered here, and my love of music production and recording has grown with the studio. Much of my work in the last few years has been in producing, recording, mixing and mastering. Most of it comes by word of mouth or musical associations from my bass playing or arrangements. I've constantly developed the studio and my skills to do the best I can for these projects.

The vast majority of work goes on in room 1. Writing, arranging, recording, mixing, mastering. I often have production input into recordings, and being in the same room as the musicians & songwriters is hugely beneficial.

Dimensions of this room are 4.95 x 3.5 x 2.29m. Here's the current state of acoustic treatment;

current acoustic panels 2.png


current acoustic panels 3.png


current acoustic panels 4.png


current acoustic panels 5.png


current acoustic panels 6.png


current acoustic panels 7.png


The beige panels are mostly 600mm wide, open frame and filled with 100mm thick Rockwool RW5, mineral wool of 100kg/m3 density. In retrospect perhaps not the best choice for bass absorption due to high gas flow resistivity of ~60 x 10³, although there are some who reckon it's ok at 100mm thickness. These charts that show reasonable absorption properties in the low end;

Rockwool Absorption.PNG


The grey panels with blue trim were from a large TV studio that was relocating. They are 1080 x 600 x 45 mm perforated metal faced and filled with absorbent material. The have an open back, and the studio had them fastened to a wall butting up against each other. Presumably some sort of resonant properties were in force in that configuration. I haven't used them that way yet, just covered the open backs with cloth and hung them on the walls and ceiling, some with an air gap.

The biggest and loudest entity so far has been a six piece rock group, initial tracks recorded with them all playing at once. For this I routed cabling through the eaves into room 2 to gain an additional room with decent sound isolation. The landing is similarly routed for "drum room mics" and is also useful for guide vocals. There are XLRs to the room below, which I've employed to isolate a large bass guitar cab. A guitar cable is routed this way too so the bass player can stay in room 1 with the drums. All these rooms have returns, sends and talkback / listenback from the main room for recording monitoring. It's a nice system that works really well.

Room 2 is a guest room, and usually used for relaxing and getting a cup of tea or what have you in between takes during sessions. In practice it's only been used for recording by larger groups or when there is a requirement for serious isolation between sound sources. I use gobos to make temporary acoustic treatment in this case.

I've recorded a large range of instruments in room 1, the quietest a gently bowed violin with a Blumlein pair of ribbon mics 4' away. Loudest is drums, recorded occasionally, perhaps once every two months. I keep these to 9-5 hours as much as possible.

For an idea of how and what, on my website there are photos of the studio and some sessions in progress, and also some videos and audio of music made there;

https://www.jenclarkmusic.com/producer/music-studio/

The walls are plasterboard. The floor in rooms 1 and 2 is real wood about 16mm thick on top of standard floorboards also about 16mm thick. Most doors in the house are sturdy and heavy with a solid plasterboard core. On the main studio door, I've added "batwing" perimeter seals on the sides & top and a drop leaf seal on the bottom. It's pretty effective. The wall sockets are mostly flush mounted into holes cut in the plasterboard. For further sound leak control I intend to fill or cover up these holes with 18mm MDF and mount the sockets in surface pattress boxes instead.

The balcony from room 1 is a Velux roof terrace, triple right handed;

https://www.velux.co.uk/products/roof-w ... of-terrace

I've not been able to determine which version of glazing is installed, but they are double glazed and seem to have quite effective acoustic isolation. It's likely to be either the 35 or 37dB version. There are vents at the top of each window set that can be opened or closed. Good for air circulation. It's pretty quiet with them open, very quiet when closed.

I sent pink noise through a bass amp on a riser in the centre of room 1 pointing towards the windows / balcony. It measured 105dB at a distance of 1m. All measurement C weighted, slow. Levels in some relevant adjoin spaces were;

Floor 2:
Studio Landing: 79.5 dB
Room 2: 62 dB

Floor 1:
Rooms below studio room 1: 70 dB
Rooms below & across from room 1: 54.5 dB
Room beyond that: 47dB

Ground floor:
Living room (below room 1): 56.5 dB
Kitchen (across from room 1): 55.5 dB (only just audible)
Garage (converted, built in to house): 46 dB (only audible if you really really concentrate and seek it out)

Boundary to neighbour: 61dB

I also did a test at 98dB in the studio, which went to 66dB on the balcony.

Ambient level in most rooms is 42 dB. Ground floor is a little louder, especially the kitchen. The garden was about 55 dB in utter stillness, which wasn't very often. Most of the time there is bird song, distant traffic, wind in the trees, and general neighbourhood noise, and the boiler coming on or what have you. Anything of that type was pretty much comparable to the 105dB source.

Some practical observations from over the years;

- I mix around 80 dB, which isn't heard at all in the rooms of the ground floor, and only in the rooms directly under room 1 on the first floor.
- Drums and brass are the only instruments audible in some rooms of the ground floor. You don't hear them at all in the garage.
- With a full rock band playing, drums in room 1, guitar and percussion in room 2, you hear nothing in the garage.
- I played a snare drum track at "actual volume" through some monitors in room 2, and listened in our garden to the North of the house. You couldn't hear anything.

In a nutshell: in terms of sound transmission, the current state is working.

Although the diagram says "live" room 1, it's really more of a control room with a large booth at the back. My understanding was that the room is too small to give a useful diffuse sound field for recording, so I designed it to reduce unwanted room sound influence and nasty specular reflections. For recording I tend to place the musicians and mics at back of the room, which is very absorptive. The wooden floor and windows at the front ping back a bit of ambience. I can reduce this with a cardioid mic, or bring it in a bit more with a figure 8. Sometimes e.g. for acoustic guitars I put up MDF panels to get some reflections back.

The acoustic is dry but very pleasant. The vast majority of people really enjoy it. Entrance is through the house from a suburban type cul de sac, then the hall and up the stairwell which is quite reverberant. When you enter the studio there's a sudden change of sound environment and view through the glass bay onto the sunny wooded area. It really is sudden and dramatic - a bit like when they walk into the holodeck on Star Trek! It really helps people get focused into the mood for making music in a professional way, and still catches me by surprise too ever now and then.

The large glass area acts as natural bass trap. The angled section reflects sound downwards then hopefully more or less into the insignificance / reverb zone. The vertical panes don't seem to cause much of a problem in practice, and it's easy to put 4x2' baffles on their ledge if they do. We tested drum overhead recordings with these baffles and without. There wasn't a huge amount of difference, just a tiny bit more ambience without them, and it was actually very pleasant. So I keep the panes clear now, apart from the middle vertical one behind the computer monitor.

There are two water based central heating radiators in opposite corners: a mixed blessing. They ring and are very difficult to dampen down, and interfere with the placing of corner straddling bass traps. But if they weren't there they would have to be somewhere else and be more annoying and conspicuous when boxed in. At least they are in "dead space" in the corners. I didn't have time to box and vent them in properly in the initial design, but will fix it on this iteration of improvements.

Running out of attachment space - I'll continue in the next post.



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Re: Attic Shaped Studio

#2

Postby endorka » Tue, 2019-Sep-24, 18:16

The Genelec 8030a monitors are up against window as close as practical. I plan to move them out of this position, but include details and measurements for general reference.

Nearfields.png


The acoustic axis is a bit above ear height, but the correct ear height position didn't give as good an acoustic response. The angles and protusions in that area give me the unease, and there are some phase flips / SBIR issues evident. Monitor bass tilt is not applied - there is some boost above flat but I like it. My mixes are not light on bass so presumably it's ok. I suspect it is giving something of a B&K curve. The bass extends deeper than monitor specs of 55hz, and I am concerned about free lunch problems :-) There's a 600Hz issue suspect SBIR, but I can't really fit any absorption behind speaker.

There's something of an HF rise. I have EQ in my monitor signal path to bring this down a bit in line with a B&K curve.

R spl and phase.png

L spl and phase.png

LR spl and phase.png

R impulse.png

R filtered IR.png

R spectrogram.png

R waterfall.png

LR RT60.png


This nearfield positioning is giving an exaggerated picture of the bass decay time in the RT60 graph, maybe due to corners / internal angles in that area? The room doesn't sound at all like this when you are in it. Below I've attached some graphs from a midfield monitor position that I hope to use for soffit mounting. It is much more balanced, and coincides with what my ears and recordings tell me. Kick drums and amplified bass guitar are very tight and focused in this room.

R soffit monitor RT60.png

R soffit monitor SPL and phase.png

R soffit monitor spectrogram.png


There are some SBIR / phase flips happening, hopefully placing the speakers in soffits will sort them out.

Edited to attach REW mdat and Sketchup files.

onwards to some improvement plans...
Attachments
2-9-2019 window bay placement.mdat
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2-9-2019 window bay placement.mdat
(5.91 MiB) Downloaded 278 times
Studio Room 1 and 2 - original config.skp
(10.74 MiB) Downloaded 281 times
Studio Room 1 and 2 - original config.skp
(10.74 MiB) Downloaded 281 times



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Re: Attic Shaped Studio

#3

Postby endorka » Tue, 2019-Sep-24, 18:30

The main problems I've identified are;

1) Difference in response between left and right speakers in the frequency and time domains. No doubt the lesser treated "radiator corners" are partly responsible for this.

2) RT60 decays too quickly in highs. Room volume is 31 cubic metres (1094 cubic feet), so according to ITU BS.1116-3 specs for control rooms the reverberation time should be 0.17s. For live room use, I'm a huge fan of dry warm 70's type recordings, and love to hear the real sounds of instruments. At the moment I'm totally getting this in recordings, but a little more ambience wouldn't hurt would it? I could always deploy additional absorbent gobos if I really wanted the ultra dry sound back.

3) Some room modes could be tamed more.

4) The current monitor placement is not ideal. While it does free up a lot of space in the room for recording, the right monitor is in the way of the door to the balcony. They are also in direct sunlight, so in summer I have to keep them covered. I have also several acoustic concerns about their placement. I initially had the monitors in a midfield placement further into the room. It solved the above issues, but suffered from considerable SBIR.

5) Acoustic treatment in general has too much surface are and density and not enough depth.

6) Room 1 gets too hot on sunny summer days. In Scotland this is not very often - probably only a month or so in summer is uncomfortable. The rest of the year is no problem at all.

7) Noise levels from outside in and inside out are acceptable, but with a little effort I think some small but worthwhile reductions for transmission of certain sounds within the house could be made.

An exact budget for improvements is difficult to ascertain, but I hope to be making music here for many, many years to come, so a long term improvement plan with incremental improvements as time and budget allows is just fine. I'm open to suggestions. Happily, the studio has ongoing projects into next year so it would be ideal if I could make changes in short bursts or even in parallel with music making.

I've spent the last three months studying the Everest book and acoustics forums in detail, and have made some designs that will hopefully bring significant improvements. I'll put these in several following posts over the next few days, and welcome your comments!

Cheers!
Jennifer



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Re: Attic Shaped Studio

#4

Postby Soundman2020 » Tue, 2019-Sep-24, 18:49

WOW! I mean really, REALLY wow! :shock: :D :yahoo:

That's a fantastic first post, Jennifer, and an amazing way to kick off the new forum! Thanks so much for joining up, and for starting the ball rolling like that. You have set a great example for how to post on the forum.... I'm hoping all other new members will follow your lead. :thu:

Now, let me get my breath back, so I can start replying to your post and the questions you raise....

I downloaded the SKP and MDAT files, so let a take a look at those, then read over your mammoth post again...

- Stuart -



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Re: Attic Shaped Studio

#5

Postby endorka » Tue, 2019-Sep-24, 18:52

Excellent! I'm just preparing a followup, and it's all about soffits :-)

Cheers,
Jennifer



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Re: Attic Shaped Studio

#6

Postby endorka » Tue, 2019-Sep-24, 20:04

First order of business is getting these monitors into soffits. Hopefully this will directly or indirectly solve or contribute to solving many of problems 1-5.

The room has a curious combination of really working for this in many ways, but against it a little bit too. The following is the culmination of many iterations of design. It manages to violate very few of Stuart's "15 rules of soffits", restated here for completeness;

1) The speakers should not go in the corner, nor on the line that divides the corner. In other words, if your walls intersect at 90 °, then draw a line out from each corner at 45°, and stay away from that: don't put your speaker exactly on that line, since it implies that you'll be getting the same artifacts from the side walls as from the front wall. Put your speakers either outside or inside of those lines. More commonly you'll want your speakers "inside" those lines (more towards the center line of the room).

2) The "38% of room depth rule" is not a rule, but it is a useful guideline for a starting point. You'll generally want to have your listening position a bit closer to the front wall than that location, but do be aware that you might be getting into problematic SBIR territory there. (You can treat that, to a certain extent).

3) Keep the mix position away from 25% and 50% of room depth, and try to stay between about 32% and 44%

4) You can angle your speakers differently than the "textbook" 30° angle: Anything in the range 25° to about 35° will work well under most circumstances.

5) Keep the speakers as far apart as possible, while not violating rules 1 and 4.

6) Keep the mix position at a good distance from the speakers, within the range of about 1m to about 5m. Further away is usually better.

7) Don't put the speakers at 25% of the room width: that's a modal null for some frequencies, and a peak for others. Try something more like 28% to 34%.

8 ) Make the front baffle of your soffit as wide and tall as you can, within reason. The width should be at least three times the diameter of your low frequency driver. In other words, if you have a speaker with an 8" woofer, then you want the soffit baffle to be at least 24" (60cm) wide. Wider is better.

9) Do not put your speaker in the middle of the soffit baffle: Offset in both directions. In other words, the distances from the acoustic center of the speaker to each edge of the baffle should be very different, by at least 20%. So for example if your speaker axis is 30cm from one side of the baffle, it should be more than 36cm from the other side, less than 24cm from the bottom edge, and more than 44cm from the top edge. (Rough distances, for illustration only...). Larger differences are generally better.

10) Make the baffle as massively heavy as you can, and as rigid as you can.

11) Make the structure inside the soffit (the framing that holds the baffle and speaker in place) as rigid and massive as you can.

12) Mount the speaker inside an enclosure box that is either a very tight fit, in order to keep the speaker rigidly fixed in place, or mount it on suitable rubber pads, to completely decouple it from the the box. Carefully choose the properties and dimensions of that rubber, to make sure the speaker is still decoupled down to at least one octave below the speaker's low cut-off frequency.

13) Take into account that speakers need a lot of space behind them for cooling, and a path through the soffit for cooling air to flow.

14) Rear-ported speakers need special attention: Do not overload the rear port, acoustically, with an enclosure box that is too small, or un-ventilated, or un-damped.

15) Damp the hell out of the soffit interior! Fill it entirely with suitable damping if you want, except for the cooling path.


So here is the proposed design;

soffits 1.png

soffits 2.png


I've already determined the mix position to be a good one - it was where I was in a previous midfield monitor arrangement. It's 2.04m from the front, a bit further than theoretical 38% but it was really good there.

There's a radiator in the left corner. The soffit completely encloses it apart from some circular holes to allow air in at the bottom and out at the top, and also access to the radiator valve control. If heat buildup proves to be a problem perhaps a vent to the top of the soffit would help. Or I could just keep the radiator switched off, there is another in the room anyway.

Next to the radiator are a bunch of sockets and pattress boxes for routing audio and computer signal cables to the landing and room 2.

The speakers are further apart than desired in rule (7), but they are not in a null. It does mean that the must be angled in at 45 degrees to hit the mix position properly. I realise this will narrow the sweet spot, but that's ok.

soffits 4.png


I've sketched the frames with 38 x 63 mm stud wood. 38 x 89 mm is readily available, but my mitre saw blade isn't quite large enough to cut steep angles on this in one go. It'll do straight across though, so if there is benefit to be had from moving to 89 mm wide, I'm happy to change it to that.

The entire box will be stuffed with light fluffy insulation.

Very occasional access to the cables and radiator behind the left soffit is require, so it will not be attached directly to the walls. I'll make it like a piece of furniture that can be slid in and out to give access.

The monitor boxes are from the official Genelec recommendations for flush mounting. The monitors are Genelec 8030A. Genelec claim the isopods do a reasonable job of vibration transfer reduction, although I suspect it won't be as good as properly floating them. I have some thoughts about floating designs if this is the case. In the meantime, I kept things simple by sticking to the original design. I've substantially oversized the soffits to allow future upgrades to Genelec 8050 or Neumann KH310 or others of similar size.

Genelec 8030 flush mount diagram;
8030 flush fitting - updated with all dimensions.png


Here are the recessed baffles fitted. Considering 25mm MDF for this. They'll be covered with insulation, I've been checking out Knauf 50mm Earthwool RS45 Universal Insulation Slab for this purpose.
soffits 5.png


Knauf insulation and front baffle fitted, also 25mm MDF.
soffits 6.png


Fabric cloth covered frames to finish;
soffits 7.png


Determining the size of the front baffle (including the recessed portion) and hole for speaker was a little tricky. The portion of the front wall that isn't a window is about 4.5 cm longer on the left side than the right. This means that the baffle width on the right is 82cm, on the left 88cm. It seems logical that the monitors should be the same distance from the front of the room, so the distance from acoustic axis to baffle edge closest to centre of the room is kept constant. The most optimum I could come up with was the following;

Left horiz 37 51 vert 64 80 cm
Right horiz 37 45 vert 64 80 cm

And rule (9) about 20% increase from acoustic axis on each successive edge is maintained.

However, with the baffle extending that high it pretty much closes off the triangular hole above the soffit, useful for bass trapping, venting and so on. So I reduced the top dimension a bit in these designs. A substantial portion of the width goes directly into the diagonal room wall anyway, so hopefully it won't have too detrimental an effect.

Here are some reflection simulations done in Amray;

Plan view 1st reflections; absorption will be required on the side wall at the reflection point. Splayed walls at this point is not really an option because of the room door;
plan view - 1st reflections.PNG
plan view - 1st reflections.PNG (16.49 KiB) Viewed 8963 times
plan view - 1st reflections.PNG
plan view - 1st reflections.PNG (16.49 KiB) Viewed 8963 times


Plan view 2nd reflections; looks like the absorption will have to extend quite close to the soffits. Back wall will be absorbant so no worries there.
plan view - 2nd reflections.PNG
plan view - 2nd reflections.PNG (43.17 KiB) Viewed 8963 times
plan view - 2nd reflections.PNG
plan view - 2nd reflections.PNG (43.17 KiB) Viewed 8963 times


Side view, 1st reflections; sloping ceiling forms a natural cloud - nice!
side view - 1st reflections.PNG
side view - 1st reflections.PNG (12.54 KiB) Viewed 8963 times
side view - 1st reflections.PNG
side view - 1st reflections.PNG (12.54 KiB) Viewed 8963 times


But care must be taken - move a little bit back and the reflection will get you;
side view - 1st reflections - warning.PNG
side view - 1st reflections - warning.PNG (14.98 KiB) Viewed 8963 times
side view - 1st reflections - warning.PNG
side view - 1st reflections - warning.PNG (14.98 KiB) Viewed 8963 times


A small could takes care of it;
side view - 1st reflections - cloud.PNG
side view - 1st reflections - cloud.PNG (13.12 KiB) Viewed 8963 times
side view - 1st reflections - cloud.PNG
side view - 1st reflections - cloud.PNG (13.12 KiB) Viewed 8963 times


Side view, 2nd reflections; cloud and/or ceiling absorber will be required.
side view - 2nd reflections.PNG
side view - 2nd reflections.PNG (23.93 KiB) Viewed 8963 times
side view - 2nd reflections.PNG
side view - 2nd reflections.PNG (23.93 KiB) Viewed 8963 times


Edited to add Sketchup file.

More ideas to follow....
Attachments
Studio Room 1 and 2 - soffits.skp
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Studio Room 1 and 2 - soffits.skp
(10.92 MiB) Downloaded 253 times



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Re: Attic Shaped Studio

#7

Postby endorka » Tue, 2019-Sep-24, 21:41

Next is to address the rear wall. First off, make a deeper absorbing trap across the rear vertical portion; this one is 30cm deep; would light fluffy filling be a good choice here?

rear wall bass trap.png


Next get the diagonal wall and corners; the left one will need to have some kind of ventilation built in for the radiator. Tentative plan is to replace the Rockwool RW5 in the corner panels with something less dense, and fill up the gaps between the panel and corners with light fluffy. I could introduce an air gap behind the diagonal wall panels as well. This sketch is pretty rough, but should give a general idea;
rear wall bass trap 2.png

rear diagonal bass traps.png


Then the ceiling. There are some of the thinner grey panels on the ceiling at the moment; they are not doing a good job. The 100mm thick panels with an air gap should do a better job;
Studio Room 1 and 2 - ceiling trapping.png

Studio Room 1 and 2 - ceiling trapping 2.png


With the soffits and this all in place, I am aiming for better low end absorption with less surface area, and hopefully there will be a bit more high frequencies left in the room. Hopefully problems 1, 2, 3 & 5 will have been substantially addressed.

Once this is done, the next bit would be the side walls. Other than speaker reflection points it is difficult to predict what might be required at that stage just now I think!

Cheers,
Jennifer



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Re: Attic Shaped Studio

#8

Postby endorka » Tue, 2019-Sep-24, 21:50

And finally for this evening, some real photos and a REW file with the scans posted earlier and the estimated soffit position.

There's also a sweep of the empty room done almost four years ago. It was with an uncalibrated ECM8000, and I hadn't even calibrated the volume of the sweep. I recall it being much louder than the 80dB sweeps though.

This was from a while back - I no longer have panels covering the lower vertical portions of the windows. The windows offer sufficient bass trapping, and reflections back from them are no big deal, indeed they can be quite beneficial. The monitors are in the "midfield" position; I really liked it, but the SBIR issues were significant.
Jennifer-Clark-Studio-Control-Area.jpg


It looks a bit like this now on an "arranging day" :-)
8030s window bay - small.jpg


The other end of the room;
Jennifer-Clark-Studio-Live-Room-1.jpg


And room 2;
Jennifer-Clark-Studio-Live-Room-2.jpg


Cheers,
Jennifer
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extra REW sweeps.mdat
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Re: Attic Shaped Studio

#9

Postby endorka » Wed, 2019-Sep-25, 10:40

Figuring out the room modes has been an interesting challenge. For sure the angled non-parallel walls help reduce flutter echos and the like, and have some other beneficial acoustic properties. But they make studying the modal behaviour somewhat challenging.

The bottom cuboidal portion of the room seems to support modes in the usual manner. Beyond that things get interesting. I spent quite a bit of time trying to explain the behaviour, and can't resist going back to it every now and then. Here are some guestimates and rough notes from many sweeps over the last few years; not all modes are fully pronounced in all sweeps. Take these with a pinch of salt, as every time I thought I finally had a handle on the behaviour, some other result came along to contradict it :-)


39 Hz & 40 Hz. These appear to be 2 primary length nodes. Perhaps caused by walls on either side of the window giving less length at the left and right of the room? Wavelength difference gives about 30cm, but taking into account the slope on the diagonal that could be about right. The modes come from the vertical portions of the walls only, but apply when I listen from floor to ceiling. The slope portion doesn't seem to influence this, presumably because the surfaces are not facing each other directly so no standing wave.

NOTE: There could also be a tangential sloping portions of ceiling / length mode. Going lengthwise bouncing off diagonal walls and the middle of the room floor. The length is about 4.5m here (not measured exactly) but this could account for the double peaks around 40Hz. The glass will be quite effective at leaking it out though, so should act as some sort of bass trap.

43 Hz empirically seems length related. Equivalent to 3.9m. Not sure where it is coming from.
44.7 Hz (3.81m) seems length related (no difference when moving across and down) but null is more towards rear.

49 Hz width. Null is perhaps a little stronger over to right side. Or more bass trapping? Due to block wall on other side of partition there? It hangs on at a low level for a very low time!!!

55 Hz ?

62 Hz tangential length / width.

66 Hz length / width tangential? quite small effect.

68 Hz ?

76 Hz (2.25m) wavelength suggests height but seems to have an effect in some places on width/length too. Perhaps due to odd shape and bass trapping to varying degrees.

79 Hz secondary length
86 Hz Tangential length / height OR (unlikely?) secondary length shorter distance

89 Hz tangential width / height

94 Hz length / width tangential

97 Hz length / height /width oblique

101 Hz secondary width

120 Hz tertiary length

~148 Hz - a combination of axial width 3rd, height 2nd and an oblique

160 Hz 4th length



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Re: Attic Shaped Studio

#10

Postby Soundman2020 » Wed, 2019-Sep-25, 14:44

Alright! I've been working my way through your epic post, and I've got some comments.

First, great job on what you have accomplished so far! Congratulations on a really nice looking studio, and on the work you have done in there. I took at looks at your website, and it's quite impressive.

First, a quick mention of isolation: You aren't getting much within the house, which is understandable, and improving that considerably would be a big deal, so as long as you are OK with what you are getting, I would just leave it the way it is. You might consider isolating Room 2 better, if you need better separation of instruments/vocals in your tracking, since isolating that room looks like it could be easier than isolating the CR... but once again, if you are happy with the isolation you have now, there's probably no need for that. Your plans for the improvements you mentioned (see below) should get you a few dB improvement, already... hopefully enough for what you need.

The wall sockets are mostly flush mounted into holes cut in the plasterboard. For further sound leak control I intend to fill or cover up these holes with 18mm MDF and mount the sockets in surface pattress boxes instead.
:thu: Another option is something called "putty packs" or "putty pads": adding mass around the outlet box itself, sort of spreading the leaf around the sides and back of the box. However, you need access to the interior of the wall to do that properly, so that's likely not an option. But you might want to consider that just to fill up the box itself with mass, before you put the MDF on top for the surface-mount system.

it's really more of a control room with a large booth at the back. My understanding was that the room is too small to give a useful diffuse sound field for recording,
Right! A room has to be pretty to big to have a truly diffuse field, in the strict acoustical sense. "Big" as in concert-hall size... :shock: For small rooms, you can still get interesting semi-diffuse effects, though, in various ways. And since you have a wide variety of acosutic situations with the type of work you do, I'm wondering if some variable acoustic devices might be a good option for you.

Something like this, maybe: Example of a variable acoustic device.

That would give you more flexibility in your control room: you could tune it one way for mixing, and another way for tracking, for example.

For recording I tend to place the musicians and mics at back of the room, which is very absorptive. The wooden floor and windows at the front ping back a bit of ambience. I can reduce this with a cardioid mic, or bring it in a bit more with a figure 8. Sometimes e.g. for acoustic guitars I put up MDF panels to get some reflections back.
... or you could make your life easier, with swinging, sliding, flipping or rotating devices that are permanently in place, but can vary the response of the room as needed! :)

There are two water based central heating radiators in opposite corners: a mixed blessing.
Any chance of getting rid of those completely, and replacing them with a mini-split system? I'm not so sure it's a good idea to box them in... depending on how hot they get.

I'm going to do the same you did, and segment my reply into several smaller posts...

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Re: Attic Shaped Studio

#11

Postby Soundman2020 » Wed, 2019-Sep-25, 17:09

OK, part #2 of my reply! On to the speakers now...

Genelec 8030a: Nice! I like those. Should be a good match for your room as well. And they can be flush-mounted! :) More on that later...

Monitor bass tilt is not applied - there is some boost above flat but I like it. My mixes are not light on bass so presumably it's ok. I suspect it is giving something of a B&K curve.
I the low end, yes, but you also have a strange rise in the middle of the high end, around 7k roughly... That's the opposite of B&K. There should be a general, gentle slide in the high end, about 3 dB down at 20 kHz. So that's one thing you should probably look at: flattening your Frequency response curve a bit more in the high end.

The bass extends deeper than monitor specs of 55hz, and I am concerned about free lunch problems
Have you considered adding a pair of subs? The 8030's are nice, but as you say they don't go down very low, and most of your music has a good load of lows in it.... Subs could also be an easy fix for some of the other problems in your acoustic response. (OK, make that "relatively easy"... your room has a strange shape...)

There's a 600Hz issue suspect SBIR, but I can't really fit any absorption behind speaker.
600 Hz is rather high to be SBIR. It's more likely to be a reflections of some type, or an effect from some surface close to the speakers, or the listening position. To get an SBIR dip at 600 Hz, the front face of the speaker would need to be only about 15cm from the front wall. Also, your front wall is segmented and angled... so I don't think that's what you are seeing at 600 Hz.

There's a sharp phase rotation at around 600 Hz on both speakers, suggesting that this is a reflection, but it's different: for the left speaker its at around 590 Hz, while for the right its around 615 Hz. That suggests that you also have a symmetry issue in the front of the room. My guess is the glass in the windows, or it might also be the side walls. To check if that's the issue, you could temporarily place a large piece of insulation in various locations around the speakers and run REW tests, to see if that changes the dip.

Edited to attach REW mdat
You seem to be using an older version of REW: most of your measurements seem to have been taken with 5.19 Beta 03, but the current version is 5.20 Beta 23. You might want to consider upgrading. There's some new stuff in the latest versions, as well as some bug fixes, and some parts of it now run faster.

1) Difference in response between left and right speakers in the frequency and time domains.
Right! I noticed that. It's not terrible (I've see worse!), but there's room for improvement.

2) RT60 decays too quickly in highs. Room volume is 31 cubic metres (1094 cubic feet), so according to ITU BS.1116-3 specs for control rooms the reverberation time should be 0.17s. For live room use, I'm a huge fan of dry warm 70's type recordings, and love to hear the real sounds of instruments. At the moment I'm totally getting this in recordings, but a little more ambience wouldn't hurt would it?
Right. It's a little too dry for a control room, and since you also want to track a variety of instruments in there, adding a bit of life would be a good idea. Some musicians find it hard to play well in a dry room: they like to hear a bit of room reverberance, to play better.

I could always deploy additional absorbent gobos if I really wanted the ultra dry sound back.
Or you could make some variable-acoustic devices...

3) Some room modes could be tamed more.
Definitely.

4) The current monitor placement is not ideal.
Yup! Agreed! I'm looking in my crystal ball, and seeing some flush-mount soffits in your future.... :)

6) Room 1 gets too hot on sunny summer days. In Scotland this is not very often - probably only a month or so in summer is uncomfortable. The rest of the year is no problem at all.
Perhaps that's another reason why you might want to consider removing the radiators, and going with a mini-split? It cools in summer, and heats in winter... and also controls humidity.

I'm open to suggestions. Happily, the studio has ongoing projects into next year so it would be ideal if I could make changes in short bursts or even in parallel with music making.
Entirely possible! Especially if you have a place where you can build devices completely, outside of the studio, then bring them in for testing.

... to be continued ...



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Re: Attic Shaped Studio

#12

Postby endorka » Thu, 2019-Sep-26, 19:31

Thank you for the swift and very enlightening reply Stuart. It's incredibly helpful. I'll post some answers now, hopefully it won't interrupt your flow of posts.

Soundman2020 wrote:First, a quick mention of isolation: You aren't getting much within the house, which is understandable, and improving that considerably would be a big deal, so as long as you are OK with what you are getting, I would just leave it the way it is. You might consider isolating Room 2 better, if you need better separation of instruments/vocals in your tracking, since isolating that room looks like it could be easier than isolating the CR...


Indeed! Instruments in room 2 have good enough isolation - I recorded mandolin in there with a fairly close omni condenser, with drums recording in room 1. It was surprisingly good. The biggest issue has been bleed from room 2 onto the landing. On one recording, tambourine in room 2 got into the guide vocal mic in the landing, and made mixing a little tricky when we decided to use a guide vocal take in the final mix. Spill from drums in room 1 into the guide vocal mic was far less pervasive. As you say, isolating room 2 a bit more will help. I reckon some batwing gasket style seals and a drop seal in the room 2 door, like I have to room 1, will solve this sufficiently.

The wall sockets are mostly flush mounted into holes cut in the plasterboard. For further sound leak control I intend to fill or cover up these holes with 18mm MDF and mount the sockets in surface pattress boxes instead.
:thu: Another option is something called "putty packs" or "putty pads": adding mass around the outlet box itself, sort of spreading the leaf around the sides and back of the box. However, you need access to the interior of the wall to do that properly, so that's likely not an option. But you might want to consider that just to fill up the box itself with mass, before you put the MDF on top for the surface-mount system.


I've never come across these before, they are total genius! Cheap, effective, and make the property safer too. I will make it so. I can access the interior of some walls through a large panel on the landing leading into the eaves. There are similar panels in room 2, so I easily can get some there too. Happy days. Room 1 has 18 sockets, 8 of which are 2 gang, quite a large area effectively open acoustically, so it seems well worth doing.

for small rooms, you can still get interesting semi-diffuse effects, though, in various ways. And since you have a wide variety of acosutic situations with the type of work you do, I'm wondering if some variable acoustic devices might be a good option for you.

Something like this, maybe: Example of a variable acoustic device.


These are awesome, I'd be well up for that. The configuration with extended HF decay would be excellent for acoustic guitar recording, and I could see them in various positions depending on e.g. vocal type, range in a given song, and sound required. Even in terms of "pre mixing", placing things in the background by emphasizing the lows and attenuating the highs and so on. With that and the different characteristics of different microphones, the possibilities will be huge.

There are two water based central heating radiators in opposite corners: a mixed blessing.
Any chance of getting rid of those completely, and replacing them with a mini-split system? I'm not so sure it's a good idea to box them in... depending on how hot they get.


The heated water is sent from the boiler on the ground floor at 70 degrees centigrade. By the time it gets to the 2nd floor it will be a little cooler. It's possible to run it a little hotter, but we don't.

Boxing radiators in seems to be ok, and is very commonplace here. You see wooden radiator covers everywhere, particularly for larger / older style of radiators. Here's a typical example;

radiator-cabinet-oak-veneer-large-david-fearn-440x240.jpg
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I've done a lot of thought about various solutions to the HVAC situation, and it all gets a bit tricky. Part of the difficulty is that it never gets that hot in Scotland, so air con is very rare in domestic properties. I literally don't know anyone who has it in their house. So the prospect is full of fear, uncertainty and doubt. It can certainly be done, but a tentative enquiry suggested it is very specialised, would be incredibly expensive and require building code notification. I don't think this was for a mini split though.

Here's an interesting observation though: every room in the house is really comfortable even in the hottest days of summer, apart from the studio. I measured the temperature on a hot day here: 20 degrees centigrade outside, 30 inside the studio. The hottest it gets here outside is about 27 degrees, and that for probably only a day or two each year. The heat buildup in room 1 is due to the greenhouse effect of all these South facing windows. If I open some windows for long enough, the room gets close to ambient outside temperature, and all is well heatwise, if not acoustically :-)

So since it is sufficient to get the inside temperature close to outside temperature, perhaps no actual cooling is required? Would it be possible to achieve this with increased airflow from inside to outside via fan driven ventilation for example?

Cheers,
Jennifer



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Re: Attic Shaped Studio

#13

Postby endorka » Thu, 2019-Sep-26, 20:43

Soundman2020 wrote:Genelec 8030a: Nice! I like those. Should be a good match for your room as well. And they can be flush-mounted! :) More on that later...


I really like them too, so that is good news :-)

Monitor bass tilt is not applied - there is some boost above flat but I like it. My mixes are not light on bass so presumably it's ok. I suspect it is giving something of a B&K curve.
I the low end, yes, but you also have a strange rise in the middle of the high end, around 7k roughly... That's the opposite of B&K. There should be a general, gentle slide in the high end, about 3 dB down at 20 kHz. So that's one thing you should probably look at: flattening your Frequency response curve a bit more in the high end.


I made a typo, sorry! I meant to write "there is some <b>bass</b> boost above flat but I like it" :-)

For several years now I've reduced the high end to something like B&K by applying an EQ curve in the monitor FX path of my DAW. It doesn't apply to the master buss or headphones, only the monitors. I tuned it by ear, so it likely starts cutting at lower frequencies than a standard B&K would, presumably to compensate for that 7k rise. That 7k rise is bizarre, there seems to be considerable phase rotation at the start and end of it too. As you say it would be so much better to tackle this by sorting the room and speaker placement out.

Reaper B and K.PNG


Have you considered adding a pair of subs? The 8030's are nice, but as you say they don't go down very low, and most of your music has a good load of lows in it.


I've thought about subs, especially after reading Bob Katz' advocacy of them in his "Mastering Audio" book. A pair of Genelec 7050s would certainly be cheaper than upgrading to 8050 or Neumann KH310 mains - used ones appear ever now and then for very good prices. The only concern I have is that by having them on the floor they'll increase transmission of noise around the rest of the house. If this is the case, do you think placing them on smaller version of these risers would help? Or would they reduce the effectiveness of the sub?

http://www.digistar.cl/Forum/viewtopic.php?f=6&t=9

I'd also like to keep a path through the studio to the balcony door clear if possible - would a sub likely have to be placed there? I don't mind stepping over gear to get there, but it's not ideal for other people. I could always fashion something like temporary wooden "steps" over it if placement there is unavoidable.

Wacky thought: is it possible to put the subs into the soffits somehow?

balcony door.png
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There's a 600Hz issue suspect SBIR, but I can't really fit any absorption behind speaker.
600 Hz is rather high to be SBIR. It's more likely to be a reflections of some type, or an effect from some surface close to the speakers, or the listening position. To get an SBIR dip at 600 Hz, the front face of the speaker would need to be only about 15cm from the front wall. Also, your front wall is segmented and angled... so I don't think that's what you are seeing at 600 Hz.

There's a sharp phase rotation at around 600 Hz on both speakers, suggesting that this is a reflection, but it's different: for the left speaker its at around 590 Hz, while for the right its around 615 Hz. That suggests that you also have a symmetry issue in the front of the room. My guess is the glass in the windows, or it might also be the side walls. To check if that's the issue, you could temporarily place a large piece of insulation in various locations around the speakers and run REW tests, to see if that changes the dip.


The left and right side walls are slightly different sizes, so it could be that. Or it could be one speaker is positioned slightly differently than the other. I'll see if I can figure it out.

2) RT60 decays too quickly in highs. Room volume is 31 cubic metres (1094 cubic feet), so according to ITU BS.1116-3 specs for control rooms the reverberation time should be 0.17s. For live room use, I'm a huge fan of dry warm 70's type recordings, and love to hear the real sounds of instruments. At the moment I'm totally getting this in recordings, but a little more ambience wouldn't hurt would it?
Right. It's a little too dry for a control room, and since you also want to track a variety of instruments in there, adding a bit of life would be a good idea. Some musicians find it hard to play well in a dry room: they like to hear a bit of room reverberance, to play better.

I could always deploy additional absorbent gobos if I really wanted the ultra dry sound back.
Or you could make some variable-acoustic devices...


Yes! :D

I'm looking in my crystal ball, and seeing some flush-mount soffits in your future.... :)


Music to my ears :-)

I'm open to suggestions. Happily, the studio has ongoing projects into next year so it would be ideal if I could make changes in short bursts or even in parallel with music making.
Entirely possible! Especially if you have a place where you can build devices completely, outside of the studio, then bring them in for testing.


Our built in garage is exactly that place, it's converted and I use it as a gym & workshop.

Exciting times!

Cheers, and thanks again for all your help.



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Re: Attic Shaped Studio

#14

Postby Soundman2020 » Fri, 2019-Sep-27, 16:06

endorka wrote:Thank you for the swift and very enlightening reply Stuart. It's incredibly helpful. I'll post some answers now, hopefully it won't interrupt your flow of posts.
:thu:


As you say, isolating room 2 a bit more will help. I reckon some batwing gasket style seals and a drop seal in the room 2 door, like I have to room 1, will solve this sufficiently.
Take a look at Zero International for that type of thing. They have a bunch of seals specifically designed for studio doors and windows in their catalogue. You should be able to get what you need there. Particularly look at the adjustable seals, that you can tweak after they are installed: doors and windows can sag, warp, swell, shrink, etc. over time from gravity and from changes in the weather, so it's great to have the ability to just pull out a screwdriver and fix that in seconds, if needed. Yes, there's stuff is expensive, but I've found it to be good. Hopefully they have a distributor near you.

I've never come across these before, they are total genius! Cheap, effective, and make the property safer too. I will make it so.
You sound a bit like a trekkie there" "Make it so, Mr. Sulu..." :)

Room 1 has 18 sockets, 8 of which are 2 gang, quite a large area effectively open acoustically, so it seems well worth doing.
If you have the access, then definitely! 18 holes in your wall is certainly degrading for isolation. Here's a scary graph to give you nightmares: it shows how much isolation you lose from very small holes/cracks/gaps in your wall. Hard to read... I wish I had a higher res version. But note that the top two curves are for cracks that total 0.01% and 0.02% of the wall area.

loss-through-tiny-cracks-and-reduction-effect-of-small-gaps-on-TL.jpg
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These are awesome, I'd be well up for that. The configuration with extended HF decay would be excellent for acoustic guitar recording, and I could see them in various positions depending on e.g. vocal type, range in a given song, and sound required. Even in terms of "pre mixing", placing things in the background by emphasizing the lows and attenuating the highs and so on. With that and the different characteristics of different microphones, the possibilities will be huge.
That's the idea! The room those are in is roughly similar in size to your "Room #2". It's around 24m2. It's the general-purpose smaller tracking room at Studio Three Productions:

RDMS--Studio-3-Variable-acoustic-room-birdseye-view.jpg


(Link to the actual studio: https://www.studio3productions.com/ )

Probably a little larger than your room, but still in the same ball-park.


I've done a lot of thought about various solutions to the HVAC situation, and it all gets a bit tricky. Part of the difficulty is that it never gets that hot in Scotland, so air con is very rare in domestic properties. I literally don't know anyone who has it in their house. So the prospect is full of fear, uncertainty and doubt. It can certainly be done, but a tentative enquiry suggested it is very specialised, would be incredibly expensive and require building code notification. I don't think this was for a mini split though.
I can understand the fear of the unknown, not wanting "to boldly go where no man in Scotland has gone before", but really, installing a mini-split isn't such a big deal. I have three in my house: two small 9000 btu units, and a larger 18000 btu unit. That bigger one I installed myself, with help from my brother-in-law. The only bit I didn't do, was charging the system with gas, as that needs specialized tools. But installing the actual indoor unit, the compressor, the pipe bundle that links them, and the electrical work, was all DIY, and not hard.

That said, if you don't need it, then you don't need it! However, do take into account that as you increase your isolation by sealing up all those tiny air gaps around electrical boxes, doors, windows, etc., you will also be sealing up all the air paths into and out of the rooms. That has consequences for air quality, in several ways: First, you sort of need oxygen to carry on living... it seems to be important to us humans... dunno why! :) Each time you take a breath, you use up some of the oxygen in the room. Second, is CO2 build-up (along with other nasty gasses, and odors....). Third is humidity: with each breath you exhale, you are dumping a lot of water vapor into the room air. In a typical room that isn't sealed, there's plenty of tiny air paths to deal with all of those, but in a well-isolated room, there are no air paths at all: it's like Las Vegas: what happens in your room, stays in your room! If you isolate well, then you likely will need some form of minimal HVAC system, to provide enough fresh air, remove enough stale air, and control the humidity.

Your rooms are reasonably large, so it would take a few hours to become unpleasant, but being in a room full of musicians playing hard, after having garlic bread, bean-on-toast, and beer, for lunch, and perhaps a drummer who forgot to shower since last week... well, use your imagination!

Las time I was in Scotland, I do recall seeing a bit of rain, fog, and other humid things... especially the areas close to rivers, lakes, and the ocean.

Not trying to scare you, but it's a real issue in an isolated room. The more you isolate, the more this becomes an issue. Many people looking at serious studio building for the first time do tend to underestimate the HVAC situation. Some assume that they can just open the door or window to "fix it", but that's not realistic: if you have to open the door, then you no longer have isolation! Plus you get sudden swings in temperature and humidity when you do that, and some mics (as well as some musical instruments) are sensitive to changes in ambient temperature and humidity... so the later take won't sound the same as the earlier take, and the musicians will spend more time re-tuning than playing... (OK; so I exaggerate a little... but the point is valid)

It's something you might want to think about, for the future. Maybe you'll find that you never actually need to do it, but you should be aware of the potential problem.

If I open some windows for long enough, the room gets close to ambient outside temperature, and all is well heatwise, if not acoustically :-)
Bingo! Yup, that's my point exactly...

Would it be possible to achieve this with increased airflow from inside to outside via fan driven ventilation for example?
Definitely possible for ventilation, but humidity might still be an issue. A mini-split can be set to do many things: heat when the room is cold, cool it down when the room is hot, dehumidify it when its neither hot nor cold but getting muggy, and just plain circulate air otherwise. If there's not too many freezing days or boiling hot days, you would probably have it set to humidity control most of the time, but for that one day in mid-summer when you have half a dozen hot sweaty musicians in there, jamming away wildly, you would probably want to set it to do some serious cooling. A duct-and-fan system is definitely going to be needed anyway, if you seal the room airtight for better isolation, and there are methods for dealing with the hug gaping holes in the walls where the ducts go through: you need to put "silencer boxes" on those wall penetrations to allow the air to get through but block the sound.

Perhaps what you could do is to look at just ventilation for now, but do it in such a way that you can add a mini-split later, if the need arises. Don't paint yourself into a corner! For example, have the register where the fresh air comes in directly above where you would install the mini-split in the future, so the fresh air would be sucked right in to the mini-split, to be cooled / heated / dehumidified before it goes into the room. Etc.

- Stuart -



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Re: Attic Shaped Studio

#15

Postby Soundman2020 » Fri, 2019-Sep-27, 22:23

Still playing catch-up on Jennifer's epic post! ;)

endorka wrote:First order of business is getting these monitors into soffits. Hopefully this will directly or indirectly solve or contribute to solving many of problems 1-5.
Soffits! Yes! Definitely! My favorite subject...

For sure flush-mounting your speakers will improve lots of stuff in your room. No doubt.

The following is the culmination of many iterations of design. It manages to violate very few of Stuart's "15 rules of soffits", restated here for completeness;
I should probably update that: I wrote that a while back, and there's room for improvement... If I have time tomorrow, I'll do a new version in the reference area... Stay tuned....

So here is the proposed design;
The basic concept looks good! Just some caveats, and ideas for tweaking that...

I've already determined the mix position to be a good one - it was where I was in a previous midfield monitor arrangement. It's 2.04m from the front, a bit further than theoretical 38% but it was really good there.
To be certain, there's a procedure I developed that I call the "walking mic" technique, and I'll post some instructions for doing that, but the basic idea is that you set up the speakers where you think they will be best, then test a whole bunch of locations with a REW test at each one, all along the room center-line, at ear-height, from the front to the back, at very small intervals (5cm between steps, in a complicated room). Then you bang your head against the wall, scream and shout, cry a bit... for a few hours as you slowly work your way through mountains of REW data, to understand not just where the best location is, but also what the individual problems are: which ones are SBIR, which ones are modal, which ones are reflections, etc. THEN you choose the best mix position location based on that, and repeat the test, but this time moving the speakers, not the mic. Slide them further apart and closer together, in small increments, to find the best location for them... then repeat the mic test one more time. That's a "relatively" fast method for finding the best layout.

It does mean that the must be angled in at 45 degrees to hit the mix position properly. I realise this will narrow the sweet spot, but that's ok.
I would try to shoot for less than 45° if you can. It looks to me like it might be possible. I developed a dynamic tool for Sketchup that helps me lay out rooms, and I'll try find time to apply that to your room, to see what I can come up with... but I'm pretty tight on time right now!


I've sketched the frames with 38 x 63 mm stud wood. 38 x 89 mm is readily available, but my mitre saw blade isn't quite large enough to cut steep angles on this in one go. It'll do straight across though, so if there is benefit to be had from moving to 89 mm wide, I'm happy to change it to that.
Thicker. For a successful soffit, your framing needs to be just as tough and rigid and massive as you can make it. Thin stuff is too flexible. I often use 2x6 framing for soffits, which is 38x140 in metric. You might not need that in your case, since the soffits are not very tall, but I'd suggest that you beef them up a bit with more framing members.

Also, use the space under the speaker shelf inside the soffit, for bass trapping. Hangers are good there. And the area above the speaker too, but because of the ceiling shape you won't be able to do hangers there. Maybe membrane traps? Or just deep, thick absorption.

The entire box will be stuffed with light fluffy insulation.


Very occasional access to the cables and radiator behind the left soffit is require, so it will not be attached directly to the walls. I'll make it like a piece of furniture that can be slid in and out to give access.
Or put a door on it... or move your patch bay onto the side wall of the soffit, or perhaps in a recessed "niche" in the side of the soffit. Lots of options, to keep your patching options simple, and let the soffit do what it needs to do.

The monitor boxes are from the official Genelec recommendations for flush mounting.
You know, I really like Genelec, both for their great speakers and also for their great documentation, but their flush-mount kits are something I've never been able to figure out! Leaving the speaker half outside the baffle, poking out by several inches? Hmm.... :shock: :?: And to be even more honest, I've never seen anyone actually mount their speakers like that.

Here's how I do it with Genelecs:

JKDNM--Genelec-8050--Soffited-S47b.jpg


JKDNM--Genelec-8050--Soffited-S47.jpg


JKDNM--Genelec-8050--Soffited-S47c.jpg


In other words, when I want to flush-mount them, then I mount them flush! :)

Genelec claim the isopods do a reasonable job of vibration transfer reduction, although I suspect it won't be as good as properly floating them.
Very correct! Speakers move and vibrate in all three directions, at once, all over, top, bottom, sides, front, back. Just putting pads under them isn't enough when they are soffited. I have a proprietary method for fully floating them, which is the sensible way to do it, to minimize transmission into the soffit itself. I'm not a big fan of the "bolt the speaker down tightly in a rigid box" method. I prefer to fully float the speaker. But as I say, it's a proprietary method that's taken me years to perfect, so I can't really just put it out there in public!. Sorry.

In the meantime, I kept things simple by sticking to the original design.
Some people prefer to do that: as I mentioned above, I'm not a big fan. There's lots of "downside" to that, and not much "upside"...

I've substantially oversized the soffits to allow future upgrades to Genelec 8050 or Neumann KH310 or others of similar size.
Smart move! I developed a method for doing that too, allowing you to easily swap out one speaker for another without having to tear down half the soffit to to do it. I used that in Studio 3 Productions, and the owner is really glad I did: soon after we mounted his original Genelecs like that, he decided on a major upgrade to Eve Audio SC-407's, and thanks to the removable system, studio downtime was for the entire swap was just a couple of hours. Then just a few weeks ago, one of the 407s went flak on him, but he had it out in a few minutes, ready to send off for repair. It's a great idea to make the soffits oversized to do that, but there's a couple of things you need to take into account: all speakers have their acoustic axis in a different location, so you need to have some method for raising of lowering the speaker to account for that, as well as moving it left/right, such that the axis of the new speaker ends up where the axis of the old speaker was. Important! Etc...


Considering 25mm MDF for this.
Too thin: not enough mass. I usually build up the baffle from several layers, and aim for the highest surface density I can get, with the least thickness. There are ways of doing that too... :)


They'll be covered with insulation, I've been checking out Knauf 50mm Earthwool RS45 Universal Insulation Slab for this purpose.
Yep, but you are forgetting something! You need a ventilation path up the rear of the speaker, plus some "air" around it. Don't wrap the poor thing in a blanket! That's another reason why I prefer the "floated" system: you can leave space for air to circulate around the speaker, keeping the temperature even all over, as well as the acosutic response. Some people think that this ventilation isn't necessary, but do the math. Speakers are about 0.5% efficient. Maybe 1% efficient, or perhaps 2% for a really good design. In other words, to get 1 acoustic watt out of your speaker, you need to pump in 100 or maybe 200 electrical watts into it. So if you are putting in 200, and getting out 1, where does the other 199 watts go? Yup, you guessed it: wasted as heat. That heat has to go somewhere! So you need to vent the rear of the speaker. OK, so 1 acoustic watt implies a level of about 100 dB SPL, but you mix lower than that (smart move!), and the Genelecs are pretty efficient, but even so your speakers could be putting out 50 watts of heat, or more, if you are running them at normal levels for long periods.

You did mention venting later on, I noticed, but since it isn't shown in the images, I thought it better to mention it here... and the "why" as well, for others who might be following your thread.

(oh, and there's a method for ventilating the speaker! :) )

Determining the size of the front baffle (including the recessed portion) and hole for speaker was a little tricky. The portion of the front wall that isn't a window is about 4.5 cm longer on the left side than the right. This means that the baffle width on the right is 82cm, on the left 88cm.
:shock: Red flag! Symmetry is critical, so you'll need to work on that to get your soffits identical.... You currently do have a difference between your left and right channels, so it would be a good idea to aim to fix that in your soffit setup...

It seems logical that the monitors should be the same distance from the front of the room, so the distance from acoustic axis to baffle edge closest to centre of the room is kept constant. The most optimum I could come up with was the following;

Left horiz 37 51 vert 64 80 cm
Right horiz 37 45 vert 64 80 cm
I haven't checked that in your SketchUp model, but Ill try to find time to do that.

However, with the baffle extending that high it pretty much closes off the triangular hole above the soffit, useful for bass trapping, venting and so on. So I reduced the top dimension a bit in these designs. A substantial portion of the width goes directly into the diagonal room wall anyway, so hopefully it won't have too detrimental an effect.

Here are some reflection simulations done in Amray;
I'm not sure if you've seen this tool in the "Downloads" area: viewtopic.php?f=9&t=2 You might find it useful for figuring out your soffits and treatment.

absorption will be required on the side wall at the reflection point. Splayed walls at this point is not really an option because of the room door;
Right. Make that absorption thick, and light. Or maybe layered, with lower density insulation in front, and heavier stuff behind.

looks like the absorption will have to extend quite close to the soffits. Back wall will be absorbant so no worries there.
:thu:


Side view, 1st reflections; sloping ceiling forms a natural cloud - nice!
True, but I would still put some treatment on that. Only higher frequencies give you true specular reflections: the lower you go, the more "blurry" the reflection is. Plus, you do seem to have some strange modal stuff going in with those angle parts of your room. That's in addition to what you showed in your diagram, with a little absorption in the "corner" up there. It will need to be thicker than you are showing in any case.


More ideas to follow....
Phew! I'm glad I got to the end of this post! My fingers are getting tired.... :)

More "catching up" later....


- Stuart -




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