"high damping tends to make the room sound smaller, not bigger"
I'm not sure now that it would make it sound smaller, but I doubt bigger. To me a highly damped room doesn't sound right. Not what I am looking for.
But I should also say that the indirect field can only be defined by timing and the other two concepts are steady state.
It is a common mistake to overdamp a room, and more so when the overdamping involves only high frequencies. My experience is that a combination of acoustic measures works well, so absorption, diffusion and bass trapping combined, at the appropriate places. Especially for smaller rooms, but unfortunately it takes valuable space and therefore people tend to stick with only absoption. Sometimes that is sufficient if the room is too lively.
For a practical example of compromises, I'll share my setup (basement). Built-in shelving divides the space from a laundry room, a structural wall is behind and to the left of listeners, and a 3 ft wall on the right open to the rest of the basement space. I'm using some hybrid absorber/ Diffusors along the left wall, and absorption behind the seating. The room is about 10D x 20W ignoring the shelving, which is an additional 2' or so of depth. Drop ceiling w acoustic tiles at just over 7' (7'6 or so to the actual structure). Orange triangles are speaker locations (lots of toe in as it's all CD from 1k+ and 700+ on the L/R). Subs are 4x12" between the speaker locations; honestly it's the easiest space for bass I've ever worked with so let's ignore those.
My solution below allows for decent delay and /or attenuation/diffusion on early reflections on everything but rear wall where I'm only using damping. I'm likely to add some diffusion atop the 3' wall, as while the diffusors help, there's still an audible "open" and "closed" side.
So, in such an instance, do you: Build a system into the shelving (Studio infinite baffle style) to allow the listener to move forward a foot or two? Accept lateral asymmetry with near boundaries (left wall placement)? Accept the rear wall being close and damp it (the way I am)?
My solution below allows for decent delay and /or attenuation/diffusion on early reflections on everything but rear wall where I'm only using damping. I'm likely to add some diffusion atop the 3' wall, as while the diffusors help, there's still an audible "open" and "closed" side.
So, in such an instance, do you: Build a system into the shelving (Studio infinite baffle style) to allow the listener to move forward a foot or two? Accept lateral asymmetry with near boundaries (left wall placement)? Accept the rear wall being close and damp it (the way I am)?
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I would set the system up to point along the greater length, sit 1/2 way back, use high DI speakers and toe them in. Same thing I do in my room, about the same aspect ratio almost exactly the same dimensions (without built in shelving. I would certainly loose the shelving.
Perhaps the (messy) pic below helps clarify. The shelving is kind of here to stay without a full-scale remodel; it's floor to ceiling and constructed of 2x4s and 3/4" ply for the first 3' of height, then has 2 areas with only short shelving above. The 3' tall half-wall (and the right surround) is behind where the photo was shot. Previously I had the system configured as you'd described- the far wall here where the diffusors are was the "gear" wall, and the listening chair in the middle of the space. 2 big shortcomings with that layout, asymmetrical sidewalls close to the (rather wide at 24") mains, and surround placement. 2ch is my priority but surround placement and seating for 2 with 10' width were the straws that broke the camel's back. I can squeeze a loveseat in with both seats at least 5' from the surrounds this way, but along the long axis, I'm stuck with rear surrounds only, which don't blend to front (I'd rather have side only vs. side and rear).
Happy to discuss any of the speakers but perhaps in a different thread as not a one of them is a 2 way here.
Happy to discuss any of the speakers but perhaps in a different thread as not a one of them is a 2 way here.
Floyd Toole used to say that one should never sit with a wall close behind you. I would concur with that.
Sure absorption helps, but completely eliminating the issues is very difficult. You have to live with what you have. I would look to getting some open cell foam as thick as possible, but at least 6 inches. Make sure that its open cell (25-35 ppi - easy to blow into.) I made this suggestion once but the guy got closed cell foam - a complete disaster. I would use a very large piece, at least 2' x 2' - even then the issues will still persist. You will get all kinds of reflection's and diffractions from this piece as well. Remember that the edges of this are a discontinuity and will diffract (very short delayed ones - best not round, reduce symmetry - round with offset?
Sure absorption helps, but completely eliminating the issues is very difficult. You have to live with what you have. I would look to getting some open cell foam as thick as possible, but at least 6 inches. Make sure that its open cell (25-35 ppi - easy to blow into.) I made this suggestion once but the guy got closed cell foam - a complete disaster. I would use a very large piece, at least 2' x 2' - even then the issues will still persist. You will get all kinds of reflection's and diffractions from this piece as well. Remember that the edges of this are a discontinuity and will diffract (very short delayed ones - best not round, reduce symmetry - round with offset?
I guess the only way is to be AT the wall, but that is not very practical lol
This is a problem in a lot of European houses.
In the Netherlands it's about 80-90% of all living rooms.
As a joke I sometimes just say why manufactures just don't put a 30-55Hz EQ dip in any amplifier, period.
It doesn't solve the problem, but it at least make the first mode less noticeable.
Anyway, back to the higher region again.
Proper damping material behind you most certain helps, the problem is, most people don't like it AT ALL for speech or just general room acoustics.
It feels and sounds extremely unnatural to have so much absorption right next to your ear.
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Yes, exactly, even the solution creates more problems. Our ears want to hear sound from behind us, otherwise, it's not natural. But neither is a very short time delay. As I said, there are no really good solutions.
Having actually had this problem, I striped the wall behind me and filled it with damping and then put felt over that - the whole wall. That was reasonable, but I quickly gave up on that and moved to a different room where i could use a larger extension behind me. Same system, but the change was much better.
Yes this is also a solution, but you cannot sit too close in front of a back wall with diffusers, because they require some distance from a source or listener to work. It seems that the 3D diffusers work better in closer proximity, but the listener still need to be plm 3' (1m) from the back wall for them to work. It conserves the energy in the room so the room will not sound dull as you would expect with absorbing material on the back wall (from the listener).
Great perspectives, thank you for sharing. I'm stuck with the installed shelving for now as it has integral lighting and electric and covers up structural members; a full remodel would be needed to eliminate them (losing that space by just covering up isn't really an option, too many records and electronics). Accordingly, "We're gonna need a bigger boat" behind the listeners. Current pyramid foam is 24"x72"x4", a holdover from the old "short wall" setup.
I think I'll ask the wife about some pictures to use and brute force it with these- https://www.gikacoustics.com/product/acoustic-art-panels-6-inch/ Making really nice-looking treatments would take some significant time and I'd rather be working on speakers or listening.
I can get about 2' away from the wall before the driver integration and SQ start deteriorating. Ideally the space would simply be larger, but absent a larger house this is the biggest space besides the living room.
I think I'll ask the wife about some pictures to use and brute force it with these- https://www.gikacoustics.com/product/acoustic-art-panels-6-inch/ Making really nice-looking treatments would take some significant time and I'd rather be working on speakers or listening.
I can get about 2' away from the wall before the driver integration and SQ start deteriorating. Ideally the space would simply be larger, but absent a larger house this is the biggest space besides the living room.
That's right ...
I don't have a 'specifically damped' listening room, but it is not that 'live' either.
What I do have is a Yamaha DSP-E580 that I sometimes use to dial up a 'room sound-field' I want.
Is this true when we look at the transfer function of perception? Would it not be possible for THD to be below the limits of perception, yet FM or AM to be above the lower threshold of perception. Could we have high levels of THD but AM and FM are not causing perceivable distortion?
Non linear distortion can also be a result of break up? What else can cause outside of excursion itself?
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This is not strictly the case. The breakup resonance might increase the level of a harmonic, and this is also directionally dependent. Breakup does not cause harmonic distortion.
What's your definition of breakup?
Normally this means when the frequency response just collapses.
But often people use the same term for material resonances, like the ringing peak of an aluminum or ceramic cone.
Those most definitely can be seen in the distortion plots.
..because they amplify sound mechanically, amplify distortion products generated in the driver motor and thus appear as peak in distortion plot
You can see distortion peak disappear if you put passive notch filter in series with the driver, but it stays if you put notch filter in parallel with the driver.Both filters would reduce current from (voltage) amplifier through voice coil at breakup frequency leveling acoustic frequency response of the system, but only the increased series impedance reduces current from driver motor distortion mechanisms. If the distortion was from the breakup itself, it would disappear in acoustic measurements with both filters.
The breakup amplifies (or attenuates, depending on angle you observe at) any current through voice coil in acoustic domain, I imagine the beakup as mechanical amplifier.
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