Designing The Perfect Listening Room

[AudiocRaver]

This is a little bit blue-sky, but I will be implementing as much of these ideas as I can into my new Listening Room/Home Theater.

The main innovation is the L/R asymmetry at LF, while remaining L/R symmetrical at MF and HF. The purpose is to place the LP where LF modes are minimized.

Also, in theory, if reflections are all handled properly,there should be an ideal speaker position which applies to all speaker types, except for toe (angle) adjustments.

Design Features:

• BEST OF BOTH WORLDS:
  • L/R Golden Mean dimension ratios (1.618:1) at Modal Frequencies
  • L/R Symmetry above Modal Frequencies
• “Treatment Walls” are 2x10 framing with insulation, inner surface of Treatment Walls can be varied to change HF/LF room crossover freq
• Exterior Walls also covered with framing and sound absorption material
• POTENTIAL DOWNSIDE: unsure about directional characteristics of sounds between ~80 Hz and ~200 Hz, but can vary the room crossover freq if need to
• First Reflection "Trap”
• No Parallel Surfaces at HF
• Not intended to eliminate LF modes, but extensive damping at LF to tighten bass
• Treatment Surfaces:
  • Front of room: Absorption plus Selective Diffusion
  • Selective Diffusion = NO EARLY ENERGY on reflection path from speaker is directed toward the LP
  • Rear of room: Diffusion
• Proof of concept version easily changed with unfinished appearance, final version can have more finished appearance, still be changeable

 

[Sonnie Parker]

This should be interesting. Have you looked at any of the Cardas guides: http://www.cardas.com/room_setup_main.php

 

[NBPK402]

Question... What would happen if the front and rear walls were Curved? Would this help break up the sound Waves? What if the front and rear walls were like this \__/ ?

 

[AudiocRaver]

Curved front and/or rear walls would work well, they are just harder to implement.

Sonnie, the Cardas guide is a good one that I have referred to often, and there are certain aspects of that design that would be implemented in my "ideal room." But the left/right symmetry is always assumed for a good soundstage, and places the LP in a bad place for L/R modes. My approach is an attempt to place the LP at a more ideal location for the L/R room modes without sacrificing soundstage. The non-parallel walls are also more "studio control room" like, to support soundstage perfection.

 

[NBPK402]

When you sat harder to implement... do you mean harder to measure and TREAT? We could build it, but would it be better, and what the positives, and negatives are if we build it.

 

[AudiocRaver]

I meant harder to build. Not impossible,, especially for the woodworkers among us. But not as easy as a straight wall.

Also, no real advantage that I can think of over non-parallel surfaces.

 

[Peter Loeser]

This looks like a very promising plan. I don't see any reason you couldn't accomplish all aspects. If I understand correctly, your angled walls (along left and right sides) act as treated reflective surfaces a defined distance above and below ear height, with the top and bottom open to allow bass to travel beyond them? So you're picking an optimal LP based on bass response, then building an optimal "room" for HF response around that position. That's very creative... never thought of doing that.

I actually had planned to implement what you're calling a "first reflection trap" on either side in my new build if my layout allows for it. I like your terminology for that feature.

I take it your two angled reflective surfaces up front will be "tuned" for SS&I?

What are your plans for sub usage/positioning?

Very interested to see this project develop.

 

[Jack]

Very interesting design Wayne and I really hope you can accomplish what you set out to do. May I ask about the dotted line on the right side of the room, is this a partial wall ? I only ask because the room sits to the left side of the center line and I am quite sure you have a good reason for this. Otherwise the cautionary tale of room symmetry i hear so often from the big boys out there would not be correct in these plans. I do like your other ideas though....oh if we could all build form scratch.

Good Luck, with your intensity I am sure it will come to pass.

 

[AudiocRaver]

Clarifying:

• The angled treatment walls left and right are floor to ceiling, but open enough that bass goes through. Bass in the range where modes are a problem is very difficult to "stop", so I will make no attempt to stop those modes from occurring. The acoustical treatment material in the treatment wall and on the inside of the outer wall surfaces will damp those modes so they die very quickly, also make them less "sharp" by mechanically softening the resonant Q.
• By being off-L/R center at low frequencies, the LP is away from the dreaded L/R "center spot" where the effect of modes is worst. IOW, let the modes occur, ,just make sure you sit where they don't affect you, and then make sure you damp them down so they die quickly and don't affect image clarity.
• Room symmetry is vital at frequencies where sound sounds directional to human ears. So, above 80 Hz or so, the Treatment Walls provide that symmetry.
• The dotted line on the right only represents the "symmetry equivalence" accomplished by the Treatment Walls.

 

[Leonard Caillouet]

Can't wait to see this implemented. What are the overall dimensions of the space?

 

[AudiocRaver]

I take it your two angled reflective surfaces up front will be "tuned" for SS&I?

What are your plans for sub usage/positioning?

Yes the reflective surfaces are for SS&I. I am still thinking about subwoofer positions.

Can't wait to see this implemented. What are the overall dimensions of the space?

I wish I knew the dimensions. Still deciding on that.

The space will be rectangular, not sure if the longer dimension will be front to back or width-wise. Or if the smaller dimension can be opened up with an LVL beam that will allow removal of a support pole that is currently right in the way.

 

[Sonnie Parker]

I guess I may end up having to make a trip up there and help you work this out huh?

Hmmm... I don't know though... no system to listen to while I'm there?

 

[Matthew J Poes]

I hope nobody mines me reviving this thread.

I've had thoughts in the past about creating first reflection traps myself. I actually had a different idea originally which was to build a room with a large raised floor (12" or so) that is acoustically open at/near the first reflection point of the speakers, and to dot he same with the ceiling. That the area would then covered with something acoustically transparent, possibly a grate. The idea would be that it would trap and absorb the low frequencies that enter the openings. I later realized that such an approach would likely not work as I had anticipated and instead the opening would operate as both a broadband absorber at high frequencies but as a tuned resonant absorber at lower frequencies. That without careful calculations this behavior could be unpredictable. I've experimented a little with tuned absorbers that rely on an undamped or mostly undamped spring-mass system and as such had a higher Q than may have been desirable, but high efficiency. What I found was that these experiments yielded very strange and unpredictable results. While sometimes I would find I am absorbing resonances, other times I was creating them, in some cases causing later reverberant energy to be nearly as high as the initial signal.

Do you worry that the edges of the first reflection trap could actually cause worse problems due to diffraction around the edge of the wall cavity?

Since the angled walls will be timber framed and I assume drywalled, do you have concern about the impact on LF modes? I know I've read a number of opinions on this. Some argue that angled walls fix tons of problems, others stating it actually leads to very unpredictable behavior in the modal region that can be harder to treat. I'd think even if that is true you can always rely on measurements to target any modal problems that arise.

What about the initial premise that absorbing first reflections completely is a good thing? I thought that in the work by Harman, they actually found first reflections to be critical to the imaging and our perception of space. That removing them would be bad. I believe Toole usually quotes work that was done in anechoic chambers to prove this idea.

I myself go back an forth. I read his books and look at the Harman papers and remove all my first reflection absorbers. I listen, I measure, I think, its ok but I'm hearing and seeing issues. Then I put them back and think, it sounds better, those issues I hear and see are gone, but some weirdness still exists. In my current space, which has significant acoustic design and treatment (but is soundproof and thus the shell is HIGHLY reflective, I sometimes find some phasie behavior in the imaging with some songs. it's much worse without first reflection absorbers, but still present and in some cases, sometimes more distracting with the absorbers. My current approach is to use curved absorbers as even with absorbers it is common for some sound, especially at higher frequencies, to still be reflected. I plan to try diffusers in place of the first reflection absorbers next to see if I like that any better. While I've heard and used diffusers before (and have MLS diffusers in my room now), I've actually never heard or used them at first reflection points. In my younger years my acoustic mentor had taught me to use diffusers in ways that I now think might have been too restrictive. He felt there only value is behind the listener and sometimes between the monitors. He never used them on ceilings or side walls and treated it as a hard and fast rule. I never questioned it until recently. I'm really curious to try it in precisely those two locations.

 

[Allen Rumbaugh]

I have had excellent results with ceiling mounted diffusers both at the first ceiling reflection point and directly overhead of the listening position. You can see on of my designs at www.hilltopstudio.com it is control room A over the engineer position, a 2' wide by 8' long with a 14.5" depth. It is flush mounted in the ceiling covered with grey Guilford of Maine cloth. Large diffusers have a profound impact on the entire listening range including the low bass.

 

[Matthew J Poes]

I have had excellent results with ceiling mounted diffusers both at the first ceiling reflection point and directly overhead of the listening position. You can see on of my designs at www.hilltopstudio.com it is control room A over the engineer position, a 2' wide by 8' long with a 14.5" depth. It is flush mounted in the ceiling covered with grey Guilford of Maine cloth. Large diffusers have a profound impact on the entire listening range including the low bass.

That is a great looking studio space. You do good work.

Wow! 14.5” deep diffusers! Those would do a great job across the board. Unfortunately I and many others simply don’t have the ceiling height to accommodate that. I’ve been in studios with large overhead diffusers and very much appreciate what they can do. I currently use an MLS diffuser in a cloud over the first reflection point of my theater and have plans to add something with temporal diffusion like a qrd over the remaining ceiling space between the MLS and first row of seats.

The majority of my experience with diffusers is in recording spaces and performance halls. I have a feeling that diffusers at the first reflection points in a listening room/theater that is suitably dry to begin with would be the best form of treatment as long as the diffuser is sufficiently deep to diffuse down into the 500hz or less range. I plan to do some experiments along these lines in the future.

If you are willing it might be nice to share some measurements from your two studios. I be people would find it informative to see what a well treated mixing space looks like.

 

[Allen Rumbaugh]

I have a hot dog performer that measures 70" wide and 10.5" deep. Its height can be tailored to the installation to a max of 41" fabric covered to 48" bare. Would that fit anywhere? It has been used both in the rear wall and overhead so far....

 

[Matthew J Poes]

I have a hot dog performer that measures 70" wide and 10.5" deep. Its height can be tailored to the installation to a max of 41" fabric covered to 48" bare. Would that fit anywhere? It has been used both in the rear wall and overhead so far....

Ok I’ll admit it, I have no idea what a hot dog performer is? Is it a kind of diffuser?

 

[Allen Rumbaugh]

Ok, I guess it sort of a southern expression a "hot dog" is analogous to something that "kicks " or dominates the competition. That is what I am trying to convey.

 

[Matthew J Poes]

Ok, I guess it sort of a southern expression a "hot dog" is analogous to something that "kicks " or dominates the competition. That is what I am trying to convey.

Yeah Im a Yank. born and raised in New York, moved to Chicago. I don't know southern turns of speech.

So what is this hot dog exactly? It's a design for a diffuser or a diffuser that's actually adjustable. I'm curious.

 

[Allen Rumbaugh]

Here is a couple of them on the back wall of this media room. It is a very high performance diffuser that I will put up against any competitor. It is a hot dog of a diffuser!

 

[DrDyna]

Here is a couple of them on the back wall of this media room. It is a very high performance diffuser that I will put up against any competitor. It is a hot dog of a diffuser!

Do you have any pics of how they're made internally?

I'm trying to amass a collection of acoustic management devices, I need to build some.

 

[Allen Rumbaugh]

Well, here is a picture of a bare diffuser that is similar to my best design. I can supply the bare product at a very attractive price. It would be difficult for you to duplicate, because the material I use is made to my specifications (high density) and is not sold on the open market. Additionally the variables in the quadratic residue equation have been chosen using Zen acquired through a lifetime of experience. I have analyzed my competitors, their choices are literally made to make products easy to ship. I only care about performance so the choices I have made (high prime designs, greater depth) make a product that is large, but will easily outperform several of the smaller units put together

, so the choice is yours. My company motto is "Do it right the first time."

 

[DrDyna]

Well, here is a picture of a bare diffuser that is similar to my best design. I can supply the bare product at a very attractive price. It would be difficult for you to duplicate, because the material I use is made to my specifications (high density) and is not sold on the open market. Additionally the variables in the quadratic residue equation have been chosen using Zen acquired through a lifetime of experience. I have analyzed my competitors, their choices are literally made to make products easy to ship. I only care about performance so the choices I have made (high prime designs, greater depth) make a product that is large, but will easily outperform several of the smaller units put together, so the choice is yours. My company motto is "Do it right the first time."

Cool!

I'm sorry, I didn't realize a product was for sale. I won't bug you about it anymore