Treatment of a small boxy room - REW file attached

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Treatment of a small boxy room - REW file attached

#1

Postby Greyhound » Sat, 2021-Dec-25, 23:57

Hi all and Merry Christmas!

I'm finally getting around to implementing treatment for a small-ish basement room in which I hope to do some basic tracking, mixing, and reviewing. I've had some rudimentary treatment in the past (corner traps and wall panels) but this was ripped out during some construction work requiring the entire area to be gutted :( . The main application is to prepare guide tracks for remote collaboration and some passable demo materials for sharing on social media. Mainly acoustic guitar and vocals but also some spoken word. I do understand I am looking at some significant compromises, and the priority is for a room that is pleasant to play music (and speak) in.

The dimensions of the room are rather unfortunate, with horizontal dimensions of 12' x 12' and a 7' ceiling (I'm not truncating the fractional part - the dimensions are within an eighth of an inch of those figures). In it's 'naked' state it sounds ***bad***!! Forget about tracking or mixing - it's hard to even have a phone call. It is fairly well soundproofed, with double 5/8" sheetrock on the walls and three layers of sheetrock with resilient channel on the ceiling. Three out of four interior walls are bounded by thick concrete foundation walls, and the fourth wall with an adjoining room is on resilient channel. If nobody is walking around upstairs, the soundproofing (in both directions) is more than adequate for my purposes.

In the past (before our foundation was demolished) I had a detailed treatment plan but did not have the chance to implement it. I can provide more details of the treatment plan but first wanted to upload the REW mdat file with measurements from the untreated room. I did my best to follow the detailed instructions posted on this forum, but am using a UMIK-1 mic so not sure if a sound card loopback made sense.

Before getting into more details, I would be grateful for any comments on the 'baseline' REW files (ie to make sure I haven't screwed up the setup somehow).

Thanks in advance and hope everyone is having a wonderful Christmas.

gh
Attachments
Baseline Room Tests No Treatment.mdat
A hopefully valid set of baseline measurements
(21.16 MiB) Downloaded 858 times
Baseline Room Tests No Treatment.mdat
A hopefully valid set of baseline measurements
(21.16 MiB) Downloaded 858 times



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Treatment of a small boxy room - REW file attached

#2

Postby Greyhound » Sun, 2021-Dec-26, 10:18

Here are some CAD views showing the general shape of the room. As noted above, the primary horizontal dimensions are 12' x 12' with a 7' ceiling. There are two windows on the "right" wall and a small doorway alcove on the "left". There is also a small bulkhead along the "left" wall/ceiling for ductwork. Left/right is in reference to listening position facing "front" wall.

Plan view from top:

(listener's "front" wall is to the left in this 2D view; the window wall, door wall, and listener "front" wall are backed by 12" concrete; black dots inside room are ceiling attachment points for resilient channel)

Room2D-plan.png


3D views showing windows and door arrangement. The door alcove extends beyond the 12' dimension for the rest of that wall. Note small bulkhead above door alcove.

Room3D-1.png


Room3D-2.png



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Treatment of a small boxy room - REW file attached

#3

Postby Greyhound » Sun, 2021-Dec-26, 10:30

and here are some screen grabs from REW showing room dimensions (door alcove on listener left is omitted here):

Room-dimensions2.png
Room-dimensions2.png (47.67 KiB) Viewed 25400 times
Room-dimensions2.png
Room-dimensions2.png (47.67 KiB) Viewed 25400 times


Room-dimensions1.png


Room-dimensions3.png


The monitor/listening positions here are somewhat arbitrary and based on the natural position when sitting at a desk. The monitors are Focal Solo6 - sealed in back with a "front laminar port". There is no subwoofer and I'm not sure if one would even make sense in such a small room.

The predicted room modes are very easy to trigger, with pronounced peaks and near-perfect nulls for the lower ones (based on walking around in untreated room).



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Treatment of a small boxy room - REW file attached

#4

Postby Greyhound » Sun, 2021-Dec-26, 10:44

Here are some photos of the room in its current untreated state. Note that the baseline REW measurements were done without the insulation materials in the room (I moved them in for temporary storage after doing the measurements).

Note the large desk along the "front" wall. It is about 10' long. The idea was to minimize other furniture in the room. The couch should stay in the position shown if at all possible acoustically.

Room-view1.jpeg


This view shows the door alcove and small bulkhead:

Room-view2.jpeg


Here is a view of the current monitor placement. I realize that affixing them to the desk is not ideal and am open to other placement options. The small wedge in front of the monitor can hold 19" rack mount gear or serve as a lecturn/music stand. I built the desk and can modify if required.

Room-speaker.jpeg


The black sheets leaning against two of the walls are Manson Akousti Liner R, which is similar to Owens Corning 703. I have 16 sheets (1" thick) and was planning to use them for facing of 4" ceiling traps as well as 4" and 8" traps along the walls. Traps would be filled with Owens Corning R12 (pink) behind the Akousti Liner. Plan is to put 19" deep bass traps from floor to ceiling in back corners.



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Treatment of a small boxy room - REW file attached

#5

Postby Greyhound » Sun, 2021-Dec-26, 11:04

Here is the material I can get locally for filling traps:

Room-OCR12.jpeg


This is the most convenient format, at 3.5" thick, as it can be used in 4" wall/ceiling traps and doubled for use in 8" wall traps (faced with 1" of the Akousti Liner).



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Treatment of a small boxy room - REW file attached

#6

Postby Greyhound » Sun, 2021-Dec-26, 18:04

Here is the spectrogram with bare walls and minimal furniture, as shown in the photos (minus the insulation):

Spectrogram-baseline.png


Below is the spectrogram after (temporarily) leaning the insulation sheets against the right and rear walls, plus a bale of R12 fiberglas in the left rear corner (as shown in photos above):

Spectrogram-insulation.png


The same mic position and REW/audio settings were used for both. I am only showing the right speaker here - the left is similar but with some small differences.



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Treatment of a small boxy room - REW file attached

#7

Postby Greyhound » Mon, 2021-Dec-27, 13:34

Apologies as I'm realizing this thread might have been more appropriate in the "Recording Studio Acoustics and Treatment" section, since the room structure has already been designed and built.



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Treatment of a small boxy room - REW file attached

#8

Postby Soundman2020 » Mon, 2021-Dec-27, 18:09

Hi there "greyhound", and Welcome to the forum! :thu:

Wow! That's a pretty darn good set o initial posts, with all the details and doubts about your studio.

Your thread is fine in the "Design" section of the forum, since you are sort-of still in the design stage, for the acoustic treatment. I could move it to another section if you want, but I don't have a problem with it being here.

OK, on to comments!

The dimensions of the room are rather unfortunate, with horizontal dimensions of 12' x 12' and a 7' ceiling
Ouch! That's not a good arrangement... Square footprint with a low ceiling. That's a bit of a challenge, for sure!

In it's 'naked' state it sounds ***bad***!! Forget about tracking or mixing - it's hard to even have a phone call.
To be expected!

first wanted to upload the REW mdat file with measurements from the untreated room. I did my best to follow the detailed instructions posted on this forum, but am using a UMIK-1 mic so not sure if a sound card loopback made sense.
It's fine. For USB mics, you don't need to do the loopback, since there is no soundcard involved in the mic input, so there's nothing to connect to.

I downloaded your MDAT file, and it' looks valid, so you did it right!

Before getting into more details, I would be grateful for any comments on the 'baseline' REW files (ie to make sure I haven't screwed up the setup somehow).
Your data looks good, and matches what can be expected for your room. for a 12 foot square, theory predicts a major modal issue at 47 Hz. Your REW data agrees:
Greyhound_REW-Baseline-WF--15..500.png


It also predicts another modal issue for the vertical axis at about 81 Hz: Check:
Greyhound_REW-Baseline-WF--15..500--hilite-82Hz.png


Also, a big modal dip at around 140 Hz.. check!
Greyhound_REW-Baseline-WF--15..500--hilite-139Hz.png


... and several other things that are very evident in your MDAT. So yeah. I'd say that you got a very valid reading, you are doing it right, and it matches reality quite well.

Left/right is in reference to listening position facing "front" wall.
:thu: Correct! some people get confused about the right way to refer to the walls in a room: You got it spot on. The front wall is, indeed, the one where the speakers: the wall you face when you are seated, mixing. real wall is behind you, left wall on your left, right wall on your right. That stays the same regardless of which way you happen to be looking in the room. Even if you turn your seat around 180°, the names are still the same as for when you are seating "normally". if you turn your seat around, you are now facing the rear wall, the left wall is on your right, and the right wall is on your left.

and here are some screen grabs from REW showing room dimensions
I realize that you did that mostly to show room dimensions and rough layout, but there's some issue with your speaker/mix position layout that should be fixed, to optimize acoustic response.

The monitor/listening positions here are somewhat arbitrary and based on the natural position when sitting at a desk.
I wrote some stuff about speaker placement a couple of years back, that you might find helpful: Speaker setup, and the equilateral triangle

The monitors are Focal Solo6
:thu: Those are nice! I've designed a couple of rooms with those. They can work very well.

There is no subwoofer and I'm not sure if one would even make sense in such a small room.
ANY size room can benefit from a sub! I've been meaning to write an article about that for a while, but never got around to it. There are several reasons why a sub is an excellent idea for a control room, or any size. In fact, subs are even more useful in small rooms, than they are in large ones....

Here are some photos of the room in its current untreated state. Note that the baseline REW measurements were done without the insulation materials in the room (I moved them in for temporary storage after doing the measurements).
Right! I figured that none of that was in the room for the tests. There's also several things you could do with your furniture that would benefit the room, and the acosutic response at the mix position.

Note the large desk along the "front" wall. It is about 10' long.
It's actually too big for that room. The desk should be as small as you can possibly live with, and any outboard gear you need can be mounted into the desk itself. The desk also needs to be as "open" as possible, so that it has the least effect on the room response. Large flat surfaces are a bad idea in a control room, in general. Here's a desk I design I use often in control rooms I design for clients. It can be adapted to different situations, fairly easily (eg, room size, console size, rack space, etc.) The Soundman M1 studio desk I'm not saying you should copy that, but it does embody the concepts that you could consieder.

Also, I'd suggest getting your speakers off the desk and onto stands placed behind the desk, up against the front wall. In a small room, ou want the speakers as close as you can get them to the front wall. to minimize the SBIR problem-

The couch should stay in the position shown if at all possible acoustically.
Probably OK, if you need it. I could say a lot about couches, but I'm running out of time for today!

This view shows the door alcove and small bulkhead:
Both of those are fine: they are actually in pretty good locations, as they leave space for the treatment you will need.

Here is a view of the current monitor placement. I realize that affixing them to the desk is not ideal and am open to other placement options.
Right: Having your speakers firmly attached to the desk creates a whole series of problems that can be minimized by getting them off the desk. There are issues such as vibrations, comb-filtering, improper acoustic loading, projection into quarter-space, and even early-early sound (sound that arrives at your ears BEFORE the direct sound form the speakers). Not a good thing, if you can avoid it.

and was planning to use them for facing of 4" ceiling traps
With a 7' ceiling, you don't have a lot of space up there for a good cloud. I'm thinking that your best bet would be some type of acoustic coupler grid over an absorber with very good low frequency characteristics. I think Glenn actually has a design like that that I saw somewhere in one of the rooms he did. I may be wrong: I think it was Glenn....

as well as 4" and 8" traps along the walls.
Right, but only in the first reflection points, probably.

Plan is to put 19" deep bass traps from floor to ceiling in back corners.
19" isn't very much, to be honest. It's certainly better than nothing! But to get down into the 47 Hz range, youa re going to need something a lot deeper than that! You might even need a membrane trap, or perhaps a large Helmholtz type trap (needs careful design!). The wavelength for 47 Hz is 24 feet (half-wave is 12 feet), so you are going to need something substantial to deal with that mode: And since your room is exactly square (down to the nearest 1/8"!), that's going to be a nasty mode. You will likely need to target that in all four vertical corners, as well as along the side walls. I'm thinking that maybe deep superchunks in the corners plus tuned traps on the walls would be a good approach. Theoretically, you can get some trapping in about 10 inches thickness, but more is better.
Here is the material I can get locally for filling traps:
Do you have the acosutic specs for that? If not, maybe ask the manufacturer for whatever specs they have for it?

Overall, you have a tough room to deal with (You actually didn't need me to tell you that! You already know... :) ) But by optimizing the room layout and treating it heavily, you should be able to make it usable.

I know of some studio designers who won't even attempt to do a room such as yours: they have their own set of "minimum" requirements, and if your room doesn't meet all of them, then won't touch it. But to me that's a rather arrogant approach, and very disheartening for the poor guy who has no other options! ANY room is better than no room at all, when you just have to mix, and ANY room can benefit from treatment, to a certain extent. Your room isn't terribly bad: just not optimal. I have successfully designed and treated even smaller rooms (the smallest so far is 97 square feet, compared to your 144 square feet), so there is hope for your place! I sometimes wonder if those designers who won't touch rooms outside a certain range just don't know how to deal with small rooms, or are scared of even trying! Or maybe they don't want to be associated with a room that isn't perfect.... Not me! All I can say is that smaller rooms are harder to treat, really small rooms are really hard to treat, but any room can sound better with suitable treatment, and most rooms in a typical home can be at least somewhat usable when treated well (with the possible exceptions of broom closets and Harry Potter style cupboards... ). Your room is certainly not in that category, and stands a pretty good chance of being quite acceptable!


- Stuart -



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Treatment of a small boxy room - REW file attached

#9

Postby Greyhound » Tue, 2021-Dec-28, 00:49

Thanks very much for the detailed response!

Soundman2020 wrote:Source of the post Hi there "greyhound", and Welcome to the forum! :thu:

Wow! That's a pretty darn good set o initial posts, with all the details and doubts about your studio.

Your thread is fine in the "Design" section of the forum, since you are sort-of still in the design stage, for the acoustic treatment. I could move it to another section if you want, but I don't have a problem with it being here.


Ok great I wasn't sure - the initial incarnation of this studio was based on a John Brandt design in 2014. I think I mentioned earlier that I completed the structure and ventilation, which provided very good isolation, but then had to demolish everything before completing the treatment . :cry:.

The structure has been rebuilt, and although I would have liked to stretch the room and lower the floor this would have created a host of other headaches.

Ouch! That's not a good arrangement... Square footprint with a low ceiling. That's a bit of a challenge, for sure!


Yes - I think if you wanted to build a room to demonstrate room modes and standing waves then this would be it! I've had friends come walk around in the room while I played a 47Hz sine wave and they think it's some kind of magic trick! I should charge admission :lol:

At one point during our work it had a much higher ceiling but then the isolation wasn't so great :lol:

IMG_3678.jpeg

(the studio room is on the far left in this photo)

It's fine. For USB mics, you don't need to do the loopback, since there is no soundcard involved in the mic input, so there's nothing to connect to.

I downloaded your MDAT file, and it' looks valid, so you did it right!


Ok super thanks! I didn't think it would be relevant to calibrate for a mic preamp (or line input) that isn't used, but wondered if there could be some DAC characteristic that needs accounting for. The interface I'm using is an SSL2+ (nothing fancy but assume it should work for this purpose).

I can see the value of an XLR measurement mic for things like the "walking mic" test and will try to snag one at some point.

Your data looks good, and matches what can be expected for your room. for a 12 foot square, theory predicts a major modal issue at 47 Hz. Your REW data agrees:
It also predicts another modal issue for the vertical axis at about 81 Hz: Check:
Also, a big modal dip at around 140 Hz.. check!
... and several other things that are very evident in your MDAT. So yeah. I'd say that you got a very valid reading, you are doing it right, and it matches reality quite well.


It is very helpful to be walked through that, highlighting the main issues!

I realize that you did that mostly to show room dimensions and rough layout, but there's some issue with your speaker/mix position layout that should be fixed, to optimize acoustic response.

I wrote some stuff about speaker placement a couple of years back, that you might find helpful: Speaker setup, and the equilateral triangle


Thanks I will read through that!

Those are nice! I've designed a couple of rooms with those. They can work very well.


I quite like the Focal Solo6, having had the chance to demo them along with a number of other comparable speakers in a well treated space at a local studio. My hope was also that the extended frequency response of these would help with room tuning.

ANY size room can benefit from a sub! I've been meaning to write an article about that for a while, but never got around to it. There are several reasons why a sub is an excellent idea for a control room, or any size. In fact, subs are even more useful in small rooms, than they are in large ones....


That is good to know - there is a lot of fluff about this on various forums so would love to see a rigorous article.

It's actually too big for that room. The desk should be as small as you can possibly live with, and any outboard gear you need can be mounted into the desk itself. The desk also needs to be as "open" as possible, so that it has the least effect on the room response. Large flat surfaces are a bad idea in a control room, in general. Here's a desk I design I use often in control rooms I design for clients. It can be adapted to different situations, fairly easily (eg, room size, console size, rack space, etc.) The Soundman M1 studio desk I'm not saying you should copy that, but it does embody the concepts that you could consieder.


That's a good point - the desk is kind of ridiculous and I'm open to downsizing. I could probably recycle the materials into something like your design.

Also, I'd suggest getting your speakers off the desk and onto stands placed behind the desk, up against the front wall. In a small room, ou want the speakers as close as you can get them to the front wall. to minimize the SBIR problem-


Ok it's great to get clear guidance on that, thanks. Again there is a lot of fluff about this online with contradictory advice but I believe you because you are working with a rigorous testing method and real-world experience.

Probably OK, if you need it. I could say a lot about couches, but I'm running out of time for today!


Sometimes I have to sleep there lol.

Right: Having your speakers firmly attached to the desk creates a whole series of problems that can be minimized by getting them off the desk. There are issues such as vibrations, comb-filtering, improper acoustic loading, projection into quarter-space, and even early-early sound (sound that arrives at your ears BEFORE the direct sound form the speakers). Not a good thing, if you can avoid it.


No problem to get them off the desk - I'm convinced! Any recommendation regarding wall stand vs floor stand?

With a 7' ceiling, you don't have a lot of space up there for a good cloud. I'm thinking that your best bet would be some type of acoustic coupler grid over an absorber with very good low frequency characteristics. I think Glenn actually has a design like that that I saw somewhere in one of the rooms he did. I may be wrong: I think it was Glenn....


John's design specified a cloud comprised of 4" thick traps with a coupling grid ("space coupler") below. This would still give just enough headroom for the taller members of my family.

Right, but only in the first reflection points, probably.


John's design had all walls covered in traps, but they were to be slatted traps which may be pertinent to this approach. He has posted this design here: https://www.jhbrandt.net/wp-content/uploads/2020/12/208.pdf

19" isn't very much, to be honest. It's certainly better than nothing! But to get down into the 47 Hz range, youa re going to need something a lot deeper than that! You might even need a membrane trap, or perhaps a large Helmholtz type trap (needs careful design!). The wavelength for 47 Hz is 24 feet (half-wave is 12 feet), so you are going to need something substantial to deal with that mode: And since your room is exactly square (down to the nearest 1/8"!), that's going to be a nasty mode. You will likely need to target that in all four vertical corners, as well as along the side walls. I'm thinking that maybe deep superchunks in the corners plus tuned traps on the walls would be a good approach. Theoretically, you can get some trapping in about 10 inches thickness, but more is better.


Again apologies for not providing more details initially. The design was based on a corner trap of John's design that incorporates diffusive and absorptive elements along with waveguides. I don't think I can copy his plans here but the general idea is shown in a studio example published at this link: https://aws1.discourse-cdn.com/business4/uploads/psaudio/original/3X/c/3/c30426832d2b2fdb9eaefe7895fea60b7e221300.jpeg

It is the corner trap for which the top is fully visible, showing three openings and the ends of vertical waveguide panels. The interior is filled entirely with Owens Corning R13 or equivalent.

Do you have the acosutic specs for that? If not, maybe ask the manufacturer for whatever specs they have for it?


Owens Corning do not include acoustic specs in their data sheet for this product. The closest thing I could find was on Bob Gold's page for R11 at 3.5" thickness mounted directly on the wall:

125Hz -> 0.34
250Hz -> 0.85
500Hz -> 1.09
1000Hz -> 0.97
2000Hz -> 0.97
4000Hz -> 1.12
NRC -> 0.95

Overall, you have a tough room to deal with (You actually didn't need me to tell you that! You already know... :) ) But by optimizing the room layout and treating it heavily, you should be able to make it usable.

I know of some studio designers who won't even attempt to do a room such as yours: they have their own set of "minimum" requirements, and if your room doesn't meet all of them, then won't touch it. But to me that's a rather arrogant approach, and very disheartening for the poor guy who has no other options! ANY room is better than no room at all, when you just have to mix, and ANY room can benefit from treatment, to a certain extent. Your room isn't terribly bad: just not optimal. I have successfully designed and treated even smaller rooms (the smallest so far is 97 square feet, compared to your 144 square feet), so there is hope for your place! I sometimes wonder if those designers who won't touch rooms outside a certain range just don't know how to deal with small rooms, or are scared of even trying! Or maybe they don't want to be associated with a room that isn't perfect.... Not me! All I can say is that smaller rooms are harder to treat, really small rooms are really hard to treat, but any room can sound better with suitable treatment, and most rooms in a typical home can be at least somewhat usable when treated well (with the possible exceptions of broom closets and Harry Potter style cupboards... ). Your room is certainly not in that category, and stands a pretty good chance of being quite acceptable!


Thank you for the kind and optimistic words! I have been encouraged by the improvement from just the partial treatment I was able to do in the past, and look forward to a more complete implementation!



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Treatment of a small boxy room - REW file attached

#10

Postby Soundman2020 » Tue, 2021-Dec-28, 05:04

but then had to demolish everything before completing the treatment
Wow! That photo says it all. That was some pretty major work you had to do there! Floor and foundations mostly gone, and the entire place just held up on jacks! :shock: :!: Glad you got through that OK. Whew!

I quite like the Focal Solo6, having had the chance to demo them along with a number of other comparable speakers in a well treated space at a local studio. My hope was also that the extended frequency response of these would help with room tuning.
The Focal Solo, Twin and Trio speakers all use basically the same concept, and I do like them. Here's a room I did some years ago with the Trios:
FrKCAUS--complete-soffits-Focal-trios.jpg
Interestingly, the floor area of that room is exactly the same as yours, at 144 square feet, and the room height and width are also identical: 12'7" in this case, 12' in your case. (the 7" discrepancy vs. 144 ft2, is due to this room not being square, but rather more of a truncated trapezoid). Here's some of the final REW measurements from the completed room, so you can feel a bit more confident about your room.

Frequency response, full spectrum, 12 Hz to 22 KHz:
FrKCAUS-REW-FR-12-22k--1..3-FINAL.png


Impulse response:
FrKCAUS--REW--IR--180ms--R.png


Full spectrum waterfall plot:
FrKCAUS-REW-WF-12-23k-FINAL.png


Waterfall plot of just the low end and low mids (12Hz to 500 Hz):
FrKCAUS-REW-WF-12-500-FINAL.png


I'm not sure if your room can get all the way to those results, since I designed that room specifically from the ground up to achieve those results, but as I said before, you should be able to get very usable response in your room. (PS: there's a sub in that room! It is part of the acosutic tuning, not just there for extending the low end. Subs are great for dealing with some stubborn acosutic issues, such as large modal issues at 47 Hz for example... :) ).

That is good to know - there is a lot of fluff about this on various forums so would love to see a rigorous article.
Darn! Now you are pushing me to write it! :) I guess I'll have to sit down and do that, one of these days...

the desk is kind of ridiculous and I'm open to downsizing. I could probably recycle the materials into something like your design.
The design isn't complex, and it's fairly easy to build. In fact, that same room above used this desk design:
FrKCAUS--M1-desk-with-racked-gear-B_SML.jpg


Ok it's great to get clear guidance on that, thanks. Again there is a lot of fluff about this online with contradictory advice but I believe you because you are working with a rigorous testing method and real-world experience.
I feel another article coming along.... :)

No problem to get them off the desk - I'm convinced! Any recommendation regarding wall stand vs floor stand?
The very, very best thing you can do for pretty much any speakers in pretty much any room, is to flush-mount them: That's the single greatest acoustic gift you can give your room, and your speakers. flush-mounting eliminates or greatly reduces many of the artifacts created by having speakers in a room, simply because flush-mounting (or "soffit mounting") removes the speaker from the room! Thus, all of the bad stuff, such as edge diffraction around the speaker, front wall SBIR, power imbalance, baffle-step response, etc. simply goes away, because all of that is a consequence of the speaker being in the room. When the speaker is not in the room any more, but rather flush with the "wall" surface, all of that stuff, just goes away completely or is reduced considerably. The only drawback is that building the "soffit" modules to do that is a bit more complex than just putting speakers on a stand, and costs more too, but the benefits are well worth it, if you can spare the extra money and effort. As you can see, the Focals in that room above are flush-mounted.... I needed to do that to get the ruler-flat results you see in the graphs. That would not have been possible if those speakers were in the room. Flush mounting speakers in a proper RFZ type room, is the best way to get a room working well, in my opinion (and in my experience). Perhaps a few other studio designers might disagree, and prefer their own methods, but you can't argue with the results! Those of us who do base our designs around the RFZ concept, can consistently get results such as those in the graphs above. Of course, we don't use the exact same original RFZ design, since that is both patented and out of date. We add out own extensions and modifications to the original concept, based on updated research of room acoustics. The results speak for themselves. I'm not aware of any other room design concept that can boast similar results.

John's design specified a cloud comprised of 4" thick traps with a coupling grid ("space coupler") below. This would still give just enough headroom for the taller members of my family.
That sounds like what I have in mind. It's a good compromise when you don't have enough height to put in a proper hard-backed and properly angled cloud.

The design was based on a corner trap of John's design that incorporates diffusive and absorptive elements along with waveguides.
I must ask him why he insists on calling those things "waveguides"! The guy who originally invented them was Tom Hidley, way back in the 70's I think, and he christened them "acoustic hangers", so that's what they should be called: John Sayers 8and others) then carried on that tradition using the same name, and so do most other studio designers. John Sayers used them extensively in many of his designs, and perfected methods for optimizing them. John Brandt seems to be one of the very few who use the term "waveguide", but its only partly correct. Technically, hangers do have some waveguide properties, but that's not all they do! There's several other things going on at once, with the waveguide principle being just one of them. "Acoustic hanger" is a better moniker, to my way of thinking. After all, in wave theory, the entire purpose of a "waveguide" is to move energy efficiently form one point to another while MINIMIZING losses! The concept of an acoustic hanger is that you want to MAXIMIZE losses... The purpose of a group of acoustic hangers is to dissipate as much unwanted energy as possible in a certain frequency band, not to guide it from point A to point B: Yes, there is a waveguide function going on, helping to achieve that, but it isn't the only process. Sometimes they are also called simply "wideband absorbers", but that's confusing because there are also other types of wideband absorbers that do not use hangers.

Anyway, I just added a couple of documents to the forum's "document library" (Useful reference documents for designing and building a studio ) about acoustic waveguides, that you might find interesting. One is about waveguides in HVAC, the other is more about waveguides in speakers. They are the last two documents, right at the bottom of the list.

There's also a research paper somewhere about how acoustic hangers actually work, from about ten years ago. I think it was from a university in Spain, or maybe Germany. They went to a Tom Hidley style control room, stuck a bunch of instruments inside and around the hangers, and took a whole lot of measurements, then analyzed all the data. They proposed about a dozen or so different theories about how those hangers might actually work, including the waveguide effect, but also the horn effect, porous absorption, panel resonance, cavity resonances, and several others, then set to work figuring our which ones were actually operating. They discarded some as not being relevant, and highlighted others. I think there were four or five major ones that they found to be in operation, and only one of those was the waveguide principle. Very interesting. I'll see if I can find it.

I don't think I can copy his plans here but the general idea is shown in a studio example published at this link: https://aws1.discourse-cdn.com/business ... 21300.jpeg
I get the idea, but that rear wall in that image would not be suitable for your room: That will only work well for a large room, since there is a minimum distance for placing numeric-based diffusers with respect to your ears: that distance is ten feet, and was discovered by the guys who "literally" wrote the book on numeric-sequence diffusers: Cox and D'Antonio (their book is titled "Acoustic Absorbers and Diffusers": These two guys pretty much defined and invented the entire diffuser industry, based on earlier work by people like Schroeder, but they took it a whole lot further, working out the theory and equations that describe how diffusers work. Their book is an interesting read, if you are interested in detailed in-depth acosutic theory! One thing they discovered, is this:
QRD-Diffusion-lobing--pattern-graph-SML-ENH-2.PNG
That shows the "lobing" patterns and general uneven distribution of the wave field in front of a diffuser. They found that its not until about ten feet away from the face of the diffuser that you start getting a truly smooth, even diffuse field, regardless of how the diffuser is tuned. In fact, for some tuning parameters, the distance can be more than ten feet, but it will always be at least 10 feet for a QRD. It's a consequence of the math. So, numeric-sequence diffusers are only suitable for rooms that are large enough to have at least ten feet between the diffuser and the ears of anyone in the room doing critical listening. Since your entire room is only 12 feet long, numeric sequence diffusers on the rear wall are not really an option.

Thank you for the kind and optimistic words! I have been encouraged by the improvement from just the partial treatment I was able to do in the past, and look forward to a more complete implementation!
I'm sure you room can be good! With careful acosutic design, it can probably be VERY good!

- Stuart -



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#11

Postby gullfo » Tue, 2021-Dec-28, 11:42

Soundman2020 wrote:Source of the post numeric-sequence diffusers are only suitable for rooms that are large enough to have at least ten feet between the diffuser and the ears of anyone in the room doing critical listening

there are numeric options for "diffusive" effects though. QRD are particularly known for the lobing and as some deeper 2D types. however smaller units (high frequencies) and be used in several locations in the room to adjust "room feedback" and not present significant lobing effects. flat and open "diffusers" (quoted to avoid too much debate on diffusion vs scattering) like MLS, Slat-Slot absorbers, Boggy diffusers, etc can all provide diffusive effects without significant lobing (the word significant because in practice, all the "stuff" that ends up in a room contributes to the room scattering/diffusion effects - we measure as impulse responses).



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Postby Soundman2020 » Tue, 2021-Dec-28, 12:35

gullfo wrote:Source of the post etc can all provide diffusive effects without significant lobing
True, but the device in the photo that Greyhound linked too, is a QRD (or maybe a PRD). That's why I mentioned that something like what was in the photo would not be suitable for his 12 foot long room.

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#13

Postby Greyhound » Tue, 2021-Dec-28, 15:09

Thanks guys for the discussion on this point.

The diffuser specified by John is a PRD - it is described in detail on his web site:

https://www.jhbrandt.net/wp-content/uploads/2018/09/Prime_523_Two_Dimensional_Primitive_Root_Diffusors.pdf

Because this would take considerable effort to build, I am very grateful for the feedback in regards to my specific room before I make the investment!



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Postby Soundman2020 » Tue, 2021-Dec-28, 16:56

Because this would take considerable effort to build,
Yup! Not to mention that it will take nearly a foot of your room length... A useful version of that thing is at least 10" deep, probably 14" or more, plus some more for the support structure, and deep bass trapping behind it... That's a lot of space to lose on your back wall... plus, it weighs a ton! There's a lot of wood in there.

As Glenn mentioned, there are other ways of achieving diffusion in small rooms, that are less intrusive and less problematic. My guess is that John provides that for larger rooms, such as the one shown in your initial link, where there's a long distance between the device and the ears of the listeners on the client couch.

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#15

Postby Greyhound » Tue, 2021-Dec-28, 18:52

Soundman2020 wrote:Source of the post
Because this would take considerable effort to build,
Yup! Not to mention that it will take nearly a foot of your room length... A useful version of that thing is at least 10" deep, probably 14" or more, plus some more for the support structure, and deep bass trapping behind it... That's a lot of space to lose on your back wall... plus, it weighs a ton! There's a lot of wood in there.

As Glenn mentioned, there are other ways of achieving diffusion in small rooms, that are less intrusive and less problematic. My guess is that John provides that for larger rooms, such as the one shown in your initial link, where there's a long distance between the device and the ears of the listeners on the client couch.

- Stuart -


Thanks Stuart and Glenn!

The other thing is that the PRD would have been against the only wall in the room is hanging on resilient channel (since it abuts an adjoining room not separated by concrete). This would have posed challenges for anchoring it along with the bass trapping.




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