Small control room design mk2

#31

Hi Paul
It’s definitely a good point. The difficulty is finding the right way to manage the step down on the way in, as it’s around 35cm. I’m not sure how effective a step on its own would be and I’m fairly sure a step down immediately after a door is a building regs no no, which might matter in the future.

It might be possible to raise the height of some of the ceiling modules at the back but the joists will be at a fixed height regardless.

I think I’m going to have to build the room and see what it’s like without the raised area first.

Cheers
Gareth

#32

Hi

I've been working on the soffit design/speaker positioning whilst waiting for my room to be waterproofed (happening this week!). After a frustrating few hours messing about with Sketchup and Amray I gave up and reverted to pencil and paper. This way I could easily move around a scale drawing of my monitors.

Meeting each of the design rules that Stuart posted is really hard in my room, and I've had to ignore one of them in order to get the speakers wide apart enough.

I've ended up with the speakers at 26.7 degrees (!), 55% of the room width apart (1.78m) and therefore 22.5% of the room from each side wall (0.75m). This has pushed my seating position back to 37% of the room length at 2.06m.

This means the speakers are close to the 25% of width that is to be avoided, and also close to the 45 degree line from the corner that is to be avoided. However they are close rather than on those things!
I ran this through Amray and it showed some reflections bouncing off the sides and back to me:

...so I've added some soffit wings which move those first reflections out of the way. I'm not sure about this - the walls are inside out so having absorption at the left and right mirror points is easy enough. I may build without the wings first and see how I get on..

Does anyone have a view on this element of the design? I read countless threads on here and on John Sayers' forum yesterday but couldn't find many details on other's speaker placement when in soffits. In some ways having such a blank canvas is difficult!

Thanks
Gareth

#33

garethmetcalf wrote:Source of the post ...so I've added some soffit wings which move those first reflections out of the way. I'm not sure about this - the walls are inside out so having absorption at the left and right mirror points is easy enough. I may build without the wings first and see how I get on..

I have a soffit thread on JS atm and I got this helpful reply from Paulus87:

"The reason for using soffit wings in a fully authentic RFZ design is to deflect the energy to a diffuser on the rear wall where it can be reflected back in to the room, lower in level and diffused, creating the appropriate initial time delay gap. This is supposed to create a nice "blooming" of the sound and helps to keep the room lively in stead of dead.

However, that is just one design criteria. There is no need to follow such an (IMO) outdated design. I do not see how or why ANY reflections, no matter how low in level or smeared, are beneficial to the engineer, personally I only want to hear the true, direct sound from the speakers with absolutely no colouration from the environment."

Worth keeping in mind

#34

It strikes me as slightly odd. The reason the wings would be added, as Gareth shows in the 2nd image in his post above, is to avoid reflections bounding off the side walls to the listening position. To then suggest that adding a real wall diffuser so that the refelctions can reach the listening position seems like a cleverl bit oif snake oil.

It is a pity that Stuart is not here to explain this as RFZ rooms are his speciality.

#35

Thanks both.

I think that quote from the JS forum is probably accurate in a large control room. My understanding is that diffusion doesn't work properly unless the room is above a certain size, because in a smaller room there isn't enough of a time gap between direct sound and reflected sound for the ears/brain to perceive the difference. That may be what that person was trying to get at regarding the RFZ concept.

However in my space the soffit wings would be bouncing the first reflections away from my ears, and then likely they would hit absorption somewhere else in the room. I am not sure whether this poses an advantage over just having absorption at the end of the main soffit fronts.

The bit about not wanting any reflections is odd though, because with no reflections you'd be in an anechoic chamber which is horrible (I studied at Salford University where they have one). There is an ideal amount of reverberation/reflection in a control room so you therefore need some reflective surfaces. I suspect the poster is referring therefore to a live end/dead end style control room where the dead end is where the speakers and engineer are located.

Hmm interesting.

Gareth

#36

garethmetcalf wrote:Source of the post However in my space the soffit wings would be bouncing the first reflections away from my ears, and then likely they would hit absorption somewhere else in the room. I am not sure whether this poses an advantage over just having absorption at the end of the main soffit fronts.

Yeah this was my thinking. I figured that sound reflected off the wings would be easier to absorb at the rear wall as it's weaker than if you simply absorbed it at the 1st reflection point.
I went without wings in the end because the 1st reflections with wings were still too close to the listening position for comfort (shouldn't be less than a foot apparently), & it looks like yours are as well

Like you said you'll still have the option to add them if need be.

#37

garethmetcalf wrote:Source of the postMy understanding is that diffusion doesn't work properly unless the room is above a certain size, because in a smaller room there isn't enough of a time gap between direct sound and reflected sound for the ears/brain to perceive the difference.

20ms is often said to be the minimal time gap from hearing the original sound to hearing reflections. That will equate to 7 metres (23 feet) that the reflected sound needs to travel more than the direct sound. Hence larger rooms or very clever diffusion.

#38

Starlight wrote:Source of the post It is a pity that Stuart is not here to explain this as RFZ rooms are his speciality.

He's back!!!!

Yes, you are right: Angled soffit wings do indeed help to re-direct sound from the side walls, towards the rear of the room. If the wings were not there, the sound would have reflected off the side walls to the mix pos, causing all kinds of undesirable issues. The wings change the reflection angle, so it does not get to the mix position, but rather heads back past it, towards the rear of the room.

So what happens at the rear of the room? Depends on the room! If the room is large enough, then diffusion is a good option. The goal, as always, is that the returned energy is low enough in intensity, delayed long enough, and diffuse enough, that by the time it gets back to your ears, it doesn't do "nasty stuff". By "nasty stuff", I mean that it does not mess with the psycho-acoustic response of your ears and brain. If it did, it would "confuse" your sense of directionality, and also your sense of frequency response, because those two are interconnected: mess with one, and you automatically mess with the other, because of the way your ears work.

So, if you can delay the returned sound by at least 20 ms (30ms is better), and get it down by at least 10 db (some say 20: I agree. 30 is a better goal, but really hard to achieve!), and with good, smooth, even diffusion, that that's wonderful! Your room will sound great, natural, clear, etc.

But that is not possible in a small room.

Firstly, in a small room, the rear wall is too close to get a 20ms delay (30 ms is better), second putting a numeric-based diffuser on a close rear wall is going to do more harm than good as your ears will not be far enough away for the artifacts to have smoothed out. Third, you probably won't be able to get the level down enough either.

Thus, for small rooms, the best option is absorption on the rear wall, to just kill as much as possible of that returned field, so it at least gets down by maybe 20 dB or so. Perhaps combing with some NON-numeric based diffusion, such as my favorite: polys. Of the right size and shape, of course, and in the right location. A nicely done poly can still give you back a bit of liveness in a sort-of diffuse field, so the room doesn't sound too dull.

- Stuart -

#39

garethmetcalf wrote:Source of the post The bit about not wanting any reflections is odd though, because with no reflections you'd be in an anechoic chamber which is horrible (I studied at Salford University where they have one). There is an ideal amount of reverberation/reflection in a control room so you therefore need some reflective surfaces. I suspect the poster is referring therefore to a live end/dead end style control room where the dead end is where the speakers and engineer are located.

Right. With an RFZ, you DO want some reflections... just not specular reflections! You want some low-level diffuse field coming back after a suitably long time, if possible, or a lower level field if the room isn't big enough.

One interesting thing about a well-designed RFZ style room, is that it doesn't sound dead or diffuse from YOUR point of view, at the mix position: when you speak, or someone else speaks behind you, or next to you, you can hear them naturally, you hear yourself naturally, and they hear you naturally, without it sounding "dull" or "lifeless"... even if the room is heavily treated with absorption! Why? Because you are not the loudspeaker! YOUR point of view and the SPEAKERS' point of view, are very different things: you are facing the front of the room, which is mostly reflective ad close by, but the speakers are facing the rear of the room, which is mostly diffusive/ absorptive / far away. Sound from the speakers "sees" the back of the room, which mutes, diffuses, and delays the sound before it gets back to your ears. But your own voice "sees" the front of the room (as do others around you, facing forward), where the sound is reflected pretty much the same way it would be if you were sitting in a "normal" room in your house, such as the living room, bedroom, kitchen, etc. You are facing a set of hard, solid, rigid surfaces that send your voice back to you, as it would in those other rooms. But the speakers see a very different acoustic scenario. So what you hear from your own voice and that of others, sounds good, while when you listen to the speakers, you ONLY hear the speakers, with just the right acoustic return to keep your brain happy.

That's the goal, at least. Not so easy to achieve in small rooms, but with careful planning and design, you can get some very decent results. Even in very small rooms.

- Stuart -

#40

After several months of using my room I thought it would be a good time for an update about the next steps in the design.

The first thing is that I am enjoying using the room and in the main producing mixes that are balanced. The Neumann KH310 monitors are so forgiving (not flattering, just very able) that everything can sound good, so you can quickly get used to the tonality of a track even though it's slightly off, so referencing is of course very important. However it’s a nice space to work in and I’m sure it’ll look great once I finish.

All along my plan had been to get the room up and running following the basic principles I understood, with general bass trapping in the form of hangers across the rear wall and under the soffits, and an absorbent ceiling (as it's quite low). From there I was going to revise the design and implement any further treatment and possibly digital tuning once all that treatment steps have been exhausted.

Current status:
Reverb time

Left and right SPL

Left and right individual readings overlay (left is green, right is brown)

Waterfall

I'd been lucky enough to get a grant from the Arts Council in the UK to 'improve my creative practice' and part of that was furthering my knowledge of acoustics. Unfortunately this money had to be spent this year, and as Stuart is busy catching up with other projects from when he was unwell, I ended up contacting two acoustics consultants to get their views on next steps for my room.

This was a really interesting exercise so I thought I'd share on this forum the outcomes of my conversations. I contacted two because I was interested if they would have different proposals and as you’ll see there are some areas that both agreed on, and others where they have quite different opinions.

I shared my latest REW readings and room dimensions with consultant 1 and explained how the space is constructed. I asked for advice on further flattening the response and the reverb time dip. Summary of consultant 1 views of issues:

1. Axial modes at 62, 106 and 153Hz that correlate with the dimensions of the room (5.5m x 3.25m x 2.25m)
2. Shape - he said that because my room has parallel walls that the low frequency peaks will be too sharp to deal with precisely with tuned traps, and at best the shape of the peak will be from a triangle to more of a W, as tuned traps have a bell curve response
3. Too much absorption in the mid band
4. The HVAC design, having some exposed foil ducting between inner and outer room, would potentially influence LF performance
5. He noted that there is a 600-650Hz dip which he has seen before with these Neumann monitors - likely around a crossover point
6. The ‘bass trap’ that I currently have in the position of a cloud (which is an a GIK acoustics 244 panel I had in the loft https://gikacoustics.co.uk/product/gik- ... echnology/) was also something he’d noted issues in the 500-600Hz area before. The recommendation was to remove this and see if it had an impact.
7. Soffit mounts – he thought these were a bad idea and was concerned they’d introduced a range of problems:
a. insufficiently rigid monitor support (as the speakers could be potentially energising the whole soffit wall construction) – to get this right for soffit mounting he recommended concrete block and cement was needed
b. potential causing the 490Hz dip (or possibly rear wall trapping, or both)
c. speakers not being able to operate in free field as they’d been designed to

The main recommendations were to:
1. Remove the soffit mount wall and construct speaker stands out of MDF entirely filled with sand
2. Build a fake wall to give the look of the soffit wall, if desired
3. Add 4 hard panels to the ceiling angled to reflect the sound towards the centre of the room. This is to add some reverberation back to the room
4. Remove the hangers at the rear wall and replace with tuned traps to deal with the axial modes identified. Designs for these were provided. I explained that the graphs showed the hangers had reduced RT in the lower frequencies and that I was concerned taking them out completely would bring some of this back. However I guess the tuned traps would by design take out the most offending reverberations/ringing, and being bell shaped they’d also reduce surrounding frequencies so the net result could be the same as the hangers.

The second consultant was a one hour video call consultation where we discussed the following:
1. From my measurements he identified a major peak at 53Hz (40% energy) that needed a tuned trap to absorb at the rear wall (or two tuned traps side by side). He suggested my hangers could be halved in length so they hang above the tuned traps. Whilst he referred me to a website to design the trap sizing (and drilled hole spacing across the front) we discussed that it needed to be built out of two layers of MDF, air tight into the room, with the back of the trap actually at the back of the room, and the sides, top and bottom of trap caulked to room surfaces.
2. We then discussed the issue of parallel versus splayed walls and he was of the opinion that parallel are better because they’re easier to model and design around
3. The soffit walls – consultant 2 was also not a fan of soffit walls and he also recommended solid stands build from MDF and sand filled. He recommended a fabric ‘wall’ built to mimic the soffit wall and the whole space behind filled with absorption
4. His design philosophy is 100% absorption behind and around the monitors, and this could mean less general absorption at the back of the room. He also spends a lot of time modelling the speaker positioning and said the height can make a huge difference to phase issues.

I had a bit of a ‘aha’ moment when speaking to consultant 2 around the sharp 100Hz dip, because this dip wasn't there before treatment went in. He told me this was likely a phase issue, because as standing waves and frequencies are absorbed, the interactions between the remaining frequencies bouncing around cause phase interactions which move up and down the frequency range as treatment is introduced. He advised using the room modeller in REW to see whether changing the amount of absorption on the ceiling etc would affect the 100Hz null.

This is absolutely what happened, as can be seen in this overlay graph - it's great when theory clicks and is reflected in practice:

This graph also demonstrates that the hangers have turned the 62Hz peak into a dip (so I guess that's a phase issue too), and resolved quite an issue around 73Hz, but that before the hangers 140Hz was fine and now there's a dip!

Summary of these interactions:
• Both consultants share the same opinion about soffit mounting and would recommend removing it. Consultant 1 did note that this would be an unpopular proposal with me (after the effort gone in to construction) so suggested I do other things first and review their impact.
• Both also propose tuned traps, although at different frequencies.
• They have different opinions about room design: splayed or non splayed walls. I should imagine this difference of opinion is endemic across studio designers! Either way it's irrelevant as I'm not rebuilding. For what it's worth I'm of the opinion that splayed walls are a bad idea in a control room.

What am I going to do?
A bit at a time, and nothing major in a hurry as the room is usable!! I think I’m going to explore various sizing options for tuned traps at the back, across the floor level, and then hopefully I could leave the hangers hanging part way down. Alongside this I will see if I can figure out how to use the REW room modeller.

Any thoughts?

#41

If you are producing mixes that are balanced and are enjoying working in the room, why would you even consider creating more work and undoing the soffits ? The goal is always to arrive at a point where your mixes translate. Also, is your soffit a legit hard "flushmount" - speakers floated on springs and not touching the baffle anywhere ? If so, then those acousticians are likely selling you a bill of goods. The concern about transmitting energy to the structure is null if you floated them properly. And the whole "free field" argument is just acoustician doublespeak IMO, meaning he's likely just set in his ways and takes a one size fits all approach to his clients.

IMO you'd be taking a step backwards because a legit flushmount soffit is the best case scenario for a number of reasons, SBIR being the big one. Unless you are actually unhappy with the room "as-is" I would suggest taking the approach of not undoing anything and simply doing further tweaks to try and make it better.

#42

Do you have any room measurements with the speakers in place but before the soffit build? If so this might help establish a before / after analysis of the effect of the soffit build. From memory, when people have done this, the effect is usually an objective and subjective improvement over the equivalent free standing position.

Your observations about the KH310s being flattering is interesting, as I think I mentioned if I ever make my fortune I'd get those. This is the opposite to the Genelec 8030s I have, which are incredibly unforgiving. To the extent that I don't really enjoy listening to some music I love on them as they expose too many flaws in the sound or mix quality.

Cheers!
Jennifer

#43

Hi both and thanks for your thoughts.

The soffit mount was done as well as I could and the speakers floated using sorbothane hemispheres, with the choices of hemisphere done using advice from the company I bought them from. I 'think' therefore that the speakers are isolated from the structure. I don't plan to remove the soffits to be honest, but thought it was interesting to share the feedback from these acoustic consultants.

@Jennifer - the graphs below show before and after the soffit mounts and associated treatment in that wall.

SPL before and after soffit mount:

Waterfall before soffit:

Waterfall after soffit:

In regards to the Neumann speakers, they are not flattering, rather what they do is allow you to tune into anything you're listening to in a way that it can start to sound normal. Whether that's a good or bad thing I don't know, but they are great speakers to me and my mixes are coming out well.

In terms of the room the only issues I'm really having is that one or two mixes were overcooked in the bottom end and I've not realised until I've checked in the car or on headphones. So I am seriously debating building some tuned traps for the rear wall in place of the hangers. If I do this I'll keep the hangers somewhere in case the room was better before, so they could be put back!! Not high on my priority list right now but maybe in the new year.

For reference - waterfall with rear wall and ceiling (ie all treatment):

As you can see across all three waterfall plots things improve after each step, but I just wonder if I can do something more to smooth things out with some tuned traps.

#44

I see no evidence of the soffit structure resonating and pumping out additional sound at certain frequencies in these waterfall charts. I imagine it would be obvious if it was. Looks like you did a good job there.

Presumably your mixes are bass heavy because of compensating for the dips in the low frequency response. Is it possible that SBIR is the cause of this, at least in part? Floor bounce in particular?

Cheers,
Jennifer

#45

That’s what I’d been wondering - are the dips around 60, 100 and 150 causing me to accentuate those frequencies? This is why I’m considering the proposal to build tuned absorbers at these frequencies.

In fact, I thinking about it there was one track in particular and I bet I have the version 1 mix saved. I should analyse it to see which frequencies are pronounced in case it correlates somehow.

I suppose floor bounce is possible - I do have some more of those GIK absorbers in the loft so maybe I could drop them on the floor and see what happens.

Going back to the soffits, there is evidence that things change in the low mid, with a couple of dips between 400 and 600, however before soffits there was quite a peak there so one bad thing has been replaced with another. I do think that on balance they’ve had a positive effect, particularly on the waterfall plot.

Cheers
Gareth

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