Acoustic panel placement, where are they most effective

Discussion in 'Audio Hardware' started by Phono Groove, Jul 5, 2019.

  1. Phono Groove

    Phono Groove Forum Resident Thread Starter

    Montreal, Quebec
    If I were to place only 2 acoustic panel absorbers ( 24”x 48” ) where exactly would they be most effective to tame high frequencies if I were to choose only one place to put them in a listening room?

    1- Against the wall rear of left & right speakers
    2- Mounted on wall left and right sides of listening room
    3 - Rear wall behind listening position
    4- Ceiling
  2. CoolJazz

    CoolJazz Forum Resident

    Eastern Tennessee
    Could also be important to consider where there are apposing open reflective walls, slapping sound back and forth.

    How close you are to the rear wall could also influence the more reflective places too.

  3. Phono Groove

    Phono Groove Forum Resident Thread Starter

    Montreal, Quebec
    My couch is placed 2 feet from rear wall and that is where I sit. Distance between the speakers and me are 7 feet ( the rear wall is made up of 3 large glass windows about 2 meters high! ) I am wondering weather I could benefit from putting two absorption panels right on the windows and cover it with my curtains for aesthetic purposes , I suspect the glass might be the biggest culprit, please correct me if im wrong!
  4. CoolJazz

    CoolJazz Forum Resident

    Eastern Tennessee
    Being that close to glass, yes, that's the place to start.

    I'd suggest though that you look for a heavier fabric curtain with extra backing material intended to reduce heat transfer when pulled closed. That way, you can have them open when not listening or at least partly closed when listening and pretty effectively dampening the reflections without blocking the windows completely where panels are placed.

    If you can do that, then you're free to use the pair of panels in other locations, breaking up larger flat surfaces that are reflective.

    I found curtains that were thicker and nice looking. A pair for each of three windows. It took effort to put up a support and long pole above, but well worth it. I'm setting reversed from what you describe and am able to look out those windows then. My back is to the room entrance doorway about the same 3 foot or so away. I've a larger room and use about a half a dozen home made absorbing panels made with Owens Corning 703 and hung away from the wall a couple inches to maximize effectiveness.

    The room is a very important component! Well worth listening to it and treating as a whole. Dampen enough but not too much.

    Robert C and timind like this.
  5. chervokas

    chervokas Forum Resident

    If the wall is two feet behind your listening, absorption behind your head will be almost essential, especially broadband absorption -- not Sonex foam or even 2" fiberglass, but 4" fiberglass at least. If that wall behind you is windows, that'll be especially true (you can probably also get away with heavy cotton gathered curtains and used the panels on first reflection points). But if the rear wall is only 2 feet behind your head, glass or not, absorption there will help with a bunch of ills.

    When it comes to brightness, the culprit can be many things including flutter echo (clap your hands and walk around the room -- do you hear a "ping" sort of echo? That's flutter echo from parallel reflective surfaces and it'll be a source of brightness and it'll mess up your imaging too. Break up long stretched of parallel reflective surfaces
    Cyclone Ranger likes this.
  6. Hipper

    Hipper Forum Resident

    Herts., England
    The only real answer is for you to experiment.

    You may or may not have significant ceiling reflections. It depends on your speaker's dispersion pattern - how high and wide the sound spreads.

    To find where reflections are occurring you need to imagine them as light rays reflecting off a mirror. Indeed there is the mirror test - you sit in your listening chair and someone else moves a mirror about on the relevant wall until you can see the speaker. That's the first reflection point.
    Morbius likes this.
  7. Optimize

    Optimize Forum Resident

    Great test.
    But if you are at the listening position and look at the mirror at the right wall you will be able to see two speakers along the wall. The right and the left one. So there is two first reflection points on the right wall. One from the left speaker and the other from the right speaker.

    And the same goes for the left side. But there is only 2 panels.

    But maybe by putting them horizontal then we can cover 4 first reflection points?

    If you want to aim for that.. ..but one off those reflection points may be beneficial. Keep reading..

    I think that the first reflection point (that is the strongest) from example the left speaker to the right wall and then going first to your right ear. Is one of the nastiest ones. Because it has the furthest distance to travel and will therefore the highest delay. And no 2 is that it is the left channel information that is faulty going to your right ear!

    In opposite to the right speaker and the right ear. The first reflection to a nearby wall will cause a slight delay but it may be so low delay that it do not interfere with your brain. That may also be one of the contribution factors that we may precive that the sound is coming past and beyond to the right of the right speaker! (Broader sound stage)
    I precive sound as coming in-between my right speaker and the first reflection point. And I like to think it is the reflection point that is contributing for this.

    When we are talking about first reflection points then the ceiling is otherwise a unused and maybe a idea. But if you have horns they tend to minimise sound dispersion up and down. Then I would go for the 4 walls instead at ear height.

    And when you have only two panels I would use them horizontal and at ear height that may get the most out of the limited total coverage area they have for the room.
    bever70 likes this.
  8. Phono Groove

    Phono Groove Forum Resident Thread Starter

    Montreal, Quebec
    This is how I have my living room setup, this is the view at the listening position, please note in back I am sitting 2 feet away from 3 large windows that cover almost the entire space of the couch. As you can see I am experimenting with the 2 absorption panels. At the rear of the speakers they are very effective at creating better sounding bass, the panels at the resr took care of boomyness and everything sounds tighter but , high frequencies are still there.
    My issue is this: because my setup is placed at the far right of the room and not at equal distance from the left and right walls, would placing a panel to the left and right actually absorb those early reflections even though the left panel would be placed far away onto the left wall?
    Last edited: Jul 6, 2019
    timind likes this.
  9. DaveyF

    DaveyF Forum Resident

    La Jolla, Calif
    How do you think the large flat panel TV affects the sound of your system? It is a wonderful source for reflection, glare, vibration and on so forth. :sigh:
  10. Riotvan

    Riotvan Well-Known Member

    The Netherlands
    That only matters if your back is close to a wall that is very reflective in my experience. I agree with @chervokas that putting a big fat broadband absorber behind the listening position(at ear height) will help quite a bit. Think i see a leather couch as well, that is not doing any favours either.
  11. Optimize

    Optimize Forum Resident

    I do not know. But you have a wall to the right there you have first/early reflection points.
    But on the left there is a open space.
    To battle that somewhat treat the right wall with the absorption panels.

    Then the reflections will minimise and it will be like a artificial acoustical opening to the right also.
    It is like the left when there is the open space.
  12. Dave

    Dave Esoteric Audio Research Specialist™

    Greater Vancouver
    Can you cover the windows behind the couch with fabric drapes or a thick sheet perhaps? I have a similar situation with glass patio doors behind and this solution eliminated those harsh reflective treble frequencies.
  13. jeffmackwood

    jeffmackwood Forum Resident

    Get more panels!
  14. Doctor Fine

    Doctor Fine Audio Expurdt

    Free Speech Land


    I have a dozen Sonex portable panels I use to look for trouble spots in a room.
    Then I remove as many until it gets too hard and too much reflection.
    It USUALLY helps the most to put them INSIDE in between the main speakers leaving an open "hole" in the dead center to help locate the phantom middle channel which a good stereo mix will have.
    A little reflection in the right place is a good thing.
    Another problem may be immediate first reflections like having a speaker NEXT to a wall.
    The wall reflected sound will KILL the timing of the main speaker output and try to compete in loudness with what the speaker is doing.
    So in that case you place the panel right where the first bounce occurs to help kill the bounced audio.
    You want to hear cleanly.
    Experimentation required...
    In any event it can help a lot to NOT put your gear right between the main speakers.
    This flat area of wall in between the speakers is CRITICAL in producing a three dimensional holographic "image."
    If your gear is smack in the middle of the speakers the gear will distort the center "fill."
    The answer is to locate your gear away from in between your speakers.
    OR put it all in a cabinet with a flat exterior so the reflected sound will be coherent.
    In my case I then OPEN the cabinet and trap even MORE center energy right between the mains.
    This really punches out the center fill and makes singers sound three dimensional.
    It is how they make a good sounding theater stage.
    It is called "the proscenium effect."
    Experiment to get it.
    Sometimes large furniture can help kill echo just as much as acoustic tile!
    My two cents.

  15. Lets say absorption in my 13x18 room is done and sounds great. Where do I put Diffusers lik Gik or other tall or wide panels. Never get a clear answer.
    My room is very much in the Cardas rectangular room arrangement with the the Golden ratio setup and sounds right. My seat is about 2 feet from back wall.
    Where do 2 or 4 diffuser panels about 4ft tall or others about 3ft wide be best placed? Thanks, John M.
  16. DaveyF

    DaveyF Forum Resident

    La Jolla, Calif
    Wrong. The Large glass panel in that location will severely limit imaging and depth reproduction.
  17. Riotvan

    Riotvan Well-Known Member

    The Netherlands
    That's just some old audiophile myth everyone keeps paroting. Blaming their overly reflective room on the tv. Treating the first reflection points will do far more for imaging and soundstage.
  18. Hipper

    Hipper Forum Resident

    Herts., England
    I've just been reading the third edition of Floyd Toole's Sound Reproduction, so I'm a bit full of what he tells us! What follows is my interpretation!!!

    I'm not one for reflections off side walls. I've experimented and don't like them (my solution is to put a panel, on feet, immediately on the outside of each speaker - not on the side wall. This stops both first and second reflections). However Toole says that in tests most people prefer them. And he offers interesting evidence to why this might be.

    Side wall reflections. Your ear will receive the direct sound from your speaker, and it will also receive the same sound reflected off the side wall. If that reflection is received relatively undamaged apart from reduced loudness (because of extra distance travelled and some absorption at the wall) and within a certain time limit (perhaps up to 50 milliseconds) it will be added to the direct sound by the brain. However only the direct sound gives you the source. In other words the side wall reflection will not give you any directional cues so will not give you a sense of space. If the reflection is damaged, or takes longer to get to your ear, it will have spatial information and will be a new sound. To me that means it will muddy what you should be hearing but give you a wider soundstage. In my set up that is what seems to happen hence I prefer no reflections.

    Toole discusses the phantom image and how it is weakened by 'interaural crosstalk' of the speakers. Your left ear hears not only the direct sound from left speaker but also sound from the right speaker. The latter has to travel slightly further to get round your head and so arrives slightly later at your ear. This leads to comb filtering and is noticeable by a large dip (perhaps 6 to 10dB) at about 2kHz. However if you have side wall reflections this can partly fill that dip.

    So choice of side wall reflections depends on all these factors and therefore you need to experiment to find how it sounds to you in your room.
    timind and The Pinhead like this.
  19. CoolJazz

    CoolJazz Forum Resident

    Eastern Tennessee
    I can take 15" screens that are on articulating arms on either side in a studio, turn them to point directly at your ears (right-left, up-down) and make it sound like you've put on headphones! The amount of reflection from a flat glass surface no bigger than those is very interesting. It's no myth!

    I've shown this to others and left them open mouthed at the amazing stereo headphone effect it creates.


    PS...and the speakers in this case were well behind those monitors, so it's all indirect sound they were bouncing.
    Riotvan and DaveyF like this.
  20. DaveyF

    DaveyF Forum Resident

    La Jolla, Calif
    Wrong again. See Cool Jazz's post above.
  21. Leigh


    I would pick 2. Side wall reflections first. I have 12 or so panels in my dedicated room. It's pretty dry, and that's the way I like it. I see a lot of rooms that look like they sound like echo chambers to me! If you clap, there should be a pretty quick decay.

    I would not worry about the TV. It's not much different than having just drywall there. Think about it; your speakers are firing away from that back wall. It's probably the least of your concerns.
    Kyhl and bever70 like this.
  22. Chazro

    Chazro Forum Resident

    West Palm Bch, Fl.
    I've looked into the GIK panels. The company offers consultations. You provide the dimensions & layout of yr room, and they'll provide product AND placement recommendations. Can't possibly ask for a clearer answer!;)
    timind and apesfan like this.
  23. The Pinhead

    The Pinhead SUDACA ROÑOSO

    There are plenty of Youtube tutorials that teach you how to DIY framed rockwool panels. I had them made for less than the material, bought separetely, would have cost, but this is Argentina. That size is the same I use. Dunno about your room dimensions but you'll need at least 4 of them. 2 on the wall behind your head (but space them evenly; they don't need to cover all the wall, or be both placed behind your head only).

    The idea is to absorb part of the reflections, not deaden the whole room.

    The other 2 you should place at the first reflection point. If the ceiling is reasonably high, forget about it.
  24. Riotvan

    Riotvan Well-Known Member

    The Netherlands
    Ok interesting, when i switched from a screen between my monitors to a broadband panel the effect was subtle. I noticed treating the sides and ceiling absorbtion more clearly. Perhaps it has to do with me using mostly nearfield setups?
    Kyhl likes this.
  25. Thomas_A

    Thomas_A Forum Resident

    Uppsala, Sweden
    I have ended up with treatment only behind the speakers. I never liked treatment of the wall behind me or the sidewalls. Other than that I have a carpet, fabric sofas with pillows, paintings and various decorations on the wall, a small IKEA coffee table stuffed with soft things (pillows, blankets). The damping panels are located behind the speakers and I have a hard surface between the speakers (TV).

    This works fine, although I would like to cover more of the wall behind the speakers with panels but not possible due to WAF.

    The danger with damping to much reflections is that there may be too few reflections left that may sound annoying.

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