Absorption tweaks

Discussion in 'Audio Hardware' started by hazyj, Oct 15, 2018.

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  1. hazyj

    hazyj Active Member Thread Starter

    Location:
    Berkeley
    When you decide to add absorptive material to your listening room, what do you use and where do you place it?
     
  2. Kyhl

    Kyhl On break

    Location:
    Savage
    That is a very broad question and the answers are equally broad.

    In a nutshell, treat the bass with broadband absorption and the rest of the frequencies come along for the ride.

    Places to start, get a mic and download Room EQ Wizard, and graph the room. Us it to identify your problem frequencies.
    Adjust placement of the speakers and the listening position as best as reasonably possible. Make sure the listening position isn't on a bass mode.
    Identify the problem null frequencies and play them back while walking around the room identifying where their corresponding mode occurs, hopefully along a wall and place the absorptive treatments in those locations.

    There is no reason to place absorption where it isn't needed. That mainly separates you from your money while raising the possibility of overly deadening the room.

    Last places, add something to first reflection points. If they are far enough away from the listener and speakers, go with diffusion. If not, add more broadband absorption. This doesn't need to be as thick but I'd still opt for 4" panels.

    For on wall absorption, use some sort of thick (4" - 6") batting, roxul, fiberglass, or cotton. Foam is less effective. For deep bass modes, the thicker the absorption the better. If you can get away with putting three feet of absorption in a corner to tame a 35hz mode, go for it.
     
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  3. Thouston

    Thouston Forum Resident

    Location:
    Mattoon, IL
    If you are not worried about ascetics, egg cartons are effective for diffusion.
     
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  4. hazyj

    hazyj Active Member Thread Starter

    Location:
    Berkeley
    Broad question yes - that was intended. Very broad question - not at all. Important question? Absolutely.
     
  5. DyersEve726

    DyersEve726 Schmo Diggy

    Location:
    Michigan, USA
    It's a pretty safe bet that treating your corners with 4+ inches of rigid fiberglass or Safe n Sound insulation will give you favorable results. It's pretty easy to frame them out and cover with a porous material. I use black burlap, but some might think that's tacky looking. I don't mind it. I added some stained wood trim to make it look a little more like furniture. Here's one of my traps.

    [​IMG]
     
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  6. timind

    timind phorum rezident

    Simple answer is:
    1. Absorption at first reflection points between the listening spot and speakers.
    2. Bass traps in corners to absorb bass.

    For more information, google is your friend as there are too many places to list.

    As for what to use? I say commercial products are the way to go as they aren't a whole lot more expensive than the DIY pieces I've made.
     
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  7. hazyj

    hazyj Active Member Thread Starter

    Location:
    Berkeley
    Schmo - great answer. Have you also experimented with absorption at first reflection point(s) on the ceiling? I assume you also have heavy carpeting at first reflection on the floor?
     
  8. hazyj

    hazyj Active Member Thread Starter

    Location:
    Berkeley
    Thuston - maybe egg cartons stacked and adorned with well attached fabric? Maybe a good n cheap design for good absorption if all the bottoms are cut off - quick and easy to do with a small circular saw I think.
     
  9. DyersEve726

    DyersEve726 Schmo Diggy

    Location:
    Michigan, USA
    I haven't bothered with first reflection points yet. I could actually hear the overloading of bass specifically in that corner, so I tackled that first. It made an impressive difference. I haven't even made the one for the other side yet...it's sadly just two bats of safe n sound wrapped in a sheet at the moment, lol. I do have wall to wall carpet+padding and a large six inch thick panel of Corning 703 directly behind the listening position. One of my first posts on this site was to get help on figuring out what was wrong with my room, and you'll get some great answers if you're more specific about your room size, shape, listening position, speaker position, and what issues you're hearing. That panel behind the listening position was very specific to my needs and room restrictions.

    An easy testing method is to go to Lowes or Home Depot and get a big bag of the Safe n Sound insulation (like $70), make a couple temporary panels by wrapping them up in sheets held together with safety pins and just move them around the room to see how the sound changes. You can then use the same material to make your permanent panels, so you're not wasting anything. The panel pictured is 2" Corning 703 rigid fiberglass in the front and a 3" bat of Safe n Sound in back spanning the corner with an air gap behind. The Corning is more efficient per inch but hard to find locally.
     
  10. Kyhl

    Kyhl On break

    Location:
    Savage
    For what it is worth 703 means 3lbs of fiberglass per cubic foot. 705 is 5lbs per cubic foot. It is too dense to be effective with bass. 703 works better.

    703 is good to about 8" thick. I still wouldn't go that deep with it though. 2" of 703 with 5" of batting behind it would work better than the same depth of 703.

    Also, carpets, egg crates, blankets, pillows, and most drapes are not acoustic treatments. Neither are ceiling tiles or cube walls. They may make a difference but they are all narrow band absorbers that will do nothing to the bass. Bass and harmonics of bass is usually the root of most problems. It takes depth to effect long bass bass waves.
     
  11. DyersEve726

    DyersEve726 Schmo Diggy

    Location:
    Michigan, USA
    It's funny because when I built my panels, I didn't know this, but I had the Safe n Sound from testing and just threw it behind the 703 as a cost saving measure. Later found out this is somewhat standard practice. At only five inches thick in total, I find it insanely effective at taming my room. I just left open air behind the panels and feel no need to add more batting.
     
  12. chervokas

    chervokas Senior Member

    Egg cartons won't be diffusion. Diffusion evenly scatters all sound across an entire affected frequency range in both time and space. Egg cartons don't do that. Mostly they're absorptive, but only at the highest frequencies.
     
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  13. chervokas

    chervokas Senior Member

    Good advice. I'd add, go thick enough at first reflection points to have something actually effective to 125 Hz. If you're going rigid fiberglass, at least 4" thick and not too dense is probably the ticket. And yes to reading up about bass trapping. Porous absorption for bass is tough to be effective at truly low frequencies -- you need lots of thickness and the at those kinds of thicknesses you need less density.

    I'd add that ceiling as great places not only to damp first reflection but to go with something deep that can help with bass potentially, if you have sufficient ceiling height.

    I'd also add, flutter echo ain't your friend when it comes to imaging. Do what you can to break up parallel reflective surfaces
     
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  14. SandAndGlass

    SandAndGlass Twilight Forum Resident

    Your corner bass traps appear to be well designed and I would be effective for their intended use. But I think that you and I have a different definition of "furniture". :cool:
     
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  15. Claude Benshaul

    Claude Benshaul Forum Resident

    I have a lot of full bookcases. Listening to music is one of the reasons I didn't donate all my books and switched entirely to kindle.
     
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  16. Kyhl

    Kyhl On break

    Location:
    Savage
    The flutter echo came to light to me recently. I have been reworking my room, paint, furniture, and placement. I had it in my mind that corner busters were no longer necessary with all the other stuff that was going on in the room. Boy was I wrong. The imaging became a glob of goo. The front left corner was already covered floor to ceiling. Added a corner buster to the front right ceiling made a noticeable improvement.

    In all the reshuffling of stuff from one room to another and boxes everywhere, I managed to lose two corner busters. I have to decide where the second one will be most effective.
     
  17. DyersEve726

    DyersEve726 Schmo Diggy

    Location:
    Michigan, USA
    That's why I said "a little more like". I don't think there's any real way to make a giant slab of fiberglass insulation into some beautiful piece of furniture. Maybe I'm wrong :unhunh:
     
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  18. Hipper

    Hipper Forum Resident

    Location:
    Herts., England
    I suggest you do a lot of studying before investing money and/or time on the matter.

    The basic principle is that the speakers plus room gives you the sound you get at your ears. Even though you may get perfect sound leaving your speakers it will be interfered with by the room and its contents before it gets to your ears. To reduce this interference, and therefore get better sound, you need to do two, or even three things:

    1. Position your speakers and ears (listening chair) for best sound.

    2. Add room treatment, particularly bass traps

    3. Use an equaliser or DSP to complete the job.
     
    Kyhl likes this.
  19. timind

    timind phorum rezident

    I wish I had read your profile before answering this initial post. As you are a new member, it seems as if you're looking for advice. After reading your profile though, I'm sure you are not.

    This leads to my question, what's your point? Looking for discussion? Have advice to offer?

    Oh, and welcome to the forum.
     
    Last edited: Oct 17, 2018
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  20. DyersEve726

    DyersEve726 Schmo Diggy

    Location:
    Michigan, USA
    That's why I called for more info. Nobody can give accurate advice without knowing what he's actually trying to accomplish. All any of us can do is recommend solutions to the most common room problems, which I think we all agree on.
     
    timind likes this.
  21. hazyj

    hazyj Active Member Thread Starter

    Location:
    Berkeley
    @Kyhl to your statement "Also, carpets, egg crates, blankets, pillows, and most drapes are not acoustic treatments. "

    I've proven this statement wrong for 20 years now - no doubt many others have done the same for a much longer time. These are all *fantastic* acoustic treatments that both diffuse and absorb, regardless of which bandwidth is most efficiently diffused/absorbed by each listed. Effective absorption *need not* do its job over a broad bandwidth as you seem to imply - it need only be well placed.

    "They may make a difference but they are all narrow band absorbers that will do nothing to the bass."

    Another false statement easily disproven. Quick - everyone reading this remove the rug/carpeting just in front of your speakers at first reflection point. Did it "do nothing to the bass" as Kyhl implies? Rather, you'll likely find it prevents the large first reflection and therefore attenuates bass energy that may otherwise strengthen or even establish unwanted modes. And that's not all - it both diffuses and absorbs in quantities largely dependent upon density and thickness. All of this together results in one of the best and often cheapest means of acoustic treatments.

    Very similar arguments can be made for heavy drapes, pillows and blankets when well placed. The proof need not require calculation or even much logic - one needs only listen to a good setup in a room with only these items placed strategically throughout. For some of us this is by far the best way to find out how much absorption and diffusion is needed - that way when we drop $$ and time into projects that "clean up the look" we don't spend too much time and money.
     
  22. DyersEve726

    DyersEve726 Schmo Diggy

    Location:
    Michigan, USA
    You seem to believe you know more than everyone else on the topic so, again, what exactly was the purpose of starting this thread besides to argue?
     
  23. hazyj

    hazyj Active Member Thread Starter

    Location:
    Berkeley
    @Kyhl to your statement "Bass and harmonics of bass is usually the root of most problems."

    Define "usually". In my case what occurs most often is bass modes are the easiest to attenuate, even though they may be the biggest problem at first depending on room size/dimensions. Much more difficult can be the removal of other issues that are often in the lower midrange (i.e. above upper bass band). Sometimes well above this range even. As long as speakers are dispersing energy throughout the listening environment, unwanted reflections can occur throughout the midrange. Nodes/modes need not exist, only more energy at the ear than sounds right to the listener - this doesn't require resonance.

    You can be certain that when quality speakers are voiced correctly, a good amount of effort goes into ensuring the correct "blending" of energy from 40hz up through at least 10khz. Such voicing isn't possible unless done in a room that prevents extra & unwanted midrange-treble energy from arriving at the listening position.
     
  24. hazyj

    hazyj Active Member Thread Starter

    Location:
    Berkeley
    @Kyhl The topic is "When you decide to add absorptive material to your listening room, what do you use and where do you place it?"

    I ask this question because I don't know the answer - how can I??
     
  25. hazyj

    hazyj Active Member Thread Starter

    Location:
    Berkeley
    @chervokas "I'd add that ceiling as great places not only to damp first reflection but to go with something deep that can help with bass potentially, if you have sufficient ceiling height."

    I like this advice, though I'm guessing this may not have had the intended effect for others trying it (regardless of the aesthetics). It's the hardest place to put damping/diffusion, but IMO worth trying just to find out how the sound changes. In my case, I haven't gone far enough and have only hung fairly light & thin baffling (foam glued to cardboard) to block and diffuse first reflection at what was otherwise a problem high sloping ceiling. Seems like it made a big difference, but it looks like $#!t.
     
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