Should I worry about overdoing it?

Discussion in 'Room Acoustics and Treatments' started by Eric SVL, Jul 31, 2018.

  1. Eric SVL

    Eric SVL Active Member
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    I'm considering thick bass traps in the corners. Specifically the GIK Soffit traps, which I was put onto by Matthew's recent posts, and others, on the topic.

    Backing up a little, I use dual subs to actively correct my frequency response from 0-100Hz. It's the 100-300Hz range that my room could use some help with, as well as overall decay times. I do use EQ, but wouldn't these traps help further smooth out the response? It's my understanding that the corners build up bass energy and that's where you should use thick absorption to help with modes and reduce decay times. Room is a rectangular bedroom of dimensions 17L x 10.5W x 8H.

    I've already cleaned up the source signal significantly by using servo-controlled subs set to high damping. So, there is already low ringing from the source. There is a lot of tactility in the bass and it is not boomy at all. Is it possible that by adding bass traps I could end up overdamped and unhappy with the sound? Or would the mic hear the difference and just apply a little less EQ? I know at this point some would ask for waterfall graphs, etc, but what are your general thoughts? I can do some measurements if requested.
     
  2. ddude003

    ddude003 Active Member

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    Since we are talking in general terms and there is no indication of how many of these Soffit traps are being installed in the small room, it is possible to overdo it... And my thinking is that several of these devices placed in the corners will only help to tame the energy lighting up the room...

    If you are worried that you will be unhappy with the sound add two at a time... If you think it made a positive impact on your room/system... Then add two more... Rinse and repeat...

    My own philosophy is to tune the room (absorption and diffusion) then the system (eq)...
     
  3. Eric SVL

    Eric SVL Active Member
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    Thanks.

    In general, if you have a room with 4 corners, and you have 4 bass traps, will the effect be similar whether you place 1 in each corner vs all 4 in one corner, floor-to-ceiling? Sorry for the newbie questions. This is something I want to get into.
     
  4. ddude003

    ddude003 Active Member

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    Generally speaking, if your room is symmetrical and your speakers are aligned to a "front" wall, you would be better served with traps in the corners of that "front" wall floor to ceiling... Next choice would be in all four corners... You can measure the energy in each corner and other areas of the room to determine where the "hot spots" are and place the traps there if the room is asymmetrical or have other factors to consider...

    For you consideration: http://arqen.com/bass-traps-101/placement-guide gives a good treatment of the subject... And I have no relation to/with the company or its products...
     
    #4 ddude003, Aug 2, 2018
    Last edited: Aug 2, 2018
  5. Eric SVL

    Eric SVL Active Member
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    That makes sense, as the waves reaching the back of the room having reduced in level by the square of the distance. I'll take a look at the link, thanks.
     
  6. Eric SVL

    Eric SVL Active Member
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    Thinking logically, I think what I'll do is start with a new set of measurements and find where my decay times are the worst. Then, I'll focus my attention on bass traps that have the appropriate "profile". By that, I mean I can judge whether I need serious trapping at the lowest frequencies, or a more even absorption to bring things in line. If the idea is to achieve decay times that are similar across all frequencies, decay measurements combined with graphs like these would be very informative in guiding you to ensure you are not under-or-over-doing it.

    abs-megatrap.gif
    RAL-Sound-Absorption-Report-Soffit.jpg
    abs-comp.gif
     
  7. Mark Seaton

    Mark Seaton New Member

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    Jumping into this late, but in the vast majority of closed rooms you will never have too much absorption below ~300Hz. The concern comes more from ending up with an imbalance of high frequency absorption in the process of attacking the rest of the range. By and large, the front and rear of the room is where thick treatments are of great benefit. It is much more practical to combat width modes through multiple subwoofer placement, while your LCR speakers and front subwoofers are all subject to the similar front-to-back interactions.
     
  8. Eric SVL

    Eric SVL Active Member
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    Thanks, Mark. I'm going to start with thick traps in the front corners and move to the back once those are filled. I'm covered up to 100Hz with my 2 subs but around the crossover region I start having issues.
     
  9. Matthew J Poes

    Matthew J Poes Staff Writer
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    Hi Eric, So I totally missed this exchange, but I think you got great advice from Mark. What he says is right on, the general view is that in small spaces (acoustically all domestic spaces are typically small), we can never have enough LF absorption. You want some reflections in the mids and highs, but if you had a nearly anechoic space at LF's, that wouldn't be so bad. I won't go into this much, it's better for another topic, but....there is a reason to keep certain specific LF reflections between 80hz and 500hz in place, as they impact our perception of spaciousness.

    My suggestion around bass traps is to use as many as possible of the biggest ones you can, but not to use a lot of broadband absorption. I tend to speak out of both sides of my mouth on this topic, which get's confusing, but I use RT60 measurements, even though I think they are theoretically wrong, as a means of judging how I handle a rooms broadband treatment. One one hand, they aren't very accurate, especially when you have noise mics, noisy rooms, and they are physically small. This leads to inaccurate estimates. On the other hand, if you can address those problems and know what to look for, use something like EDT and TOPT, you can get a good enough approximation of the decay of a room. What I look for is a balance, and I target decay rates in the neighborhood of .5 seconds for music only rooms and .3-.5 seconds for movie rooms. I vary those targets by the size of the room, the larger the room, the higher the number we want/accept. That means that sometimes (though rarely) I might use a broadband absorber bass trap if I generally need to bring down the RT60. I also might use a faced panel with an MLS or other pattern to try to target a peak of absorption both down low and in some midrange area, but keep HF absorption low.

    GIK's panels are available in a LF restricted version, so that is why I promote them. I like their bass traps for that reason.

    How are things going so far?
     
  10. Eric SVL

    Eric SVL Active Member
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    Well Matthew, I planned on doing the GIK Soffit Traps in the corners to start based on the prior advice that I can't have too much absorption, but I'm hesitant given your statements here. Should we start with measurements?
     
  11. Matthew J Poes

    Matthew J Poes Staff Writer
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    Taking measurements first is always a good idea. If nothing else it gives you a baseline.

    However I didn’t mean to scare you off from this.

    The Soffit traps are a great option. Just get the range limiter if you like. It’s something you cant go wrong with. Measurements are still good though. Sorry if I added confusion.
     
  12. Eric SVL

    Eric SVL Active Member
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    How does one choose the range? Simply by determining where you need absorption most? I guess that would make sense.

    I think the reason I paused at your comment was because earlier sentiment had me feeling pretty confident that I couldn't over-do it - but you suggest a more targeted approach than by stacking the corners with broadband traps.

    Because we don't yet have a normalization feature for the waterfall and spectrogram in REW, I need to get frequency response flat before I can compare decay times. Am I thinking correctly about this?
     
  13. Matthew J Poes

    Matthew J Poes Staff Writer
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    Flatness isn’t important for decay, just don’t use waterfall. Use actual measures of decay and Wavelet spectrograms. Both display the energy decay over time more usefully. Personally I think Wavelets are the best option. I’ve been really into them lately.

    Also consider looking at filtered impulse responses. I find these helpful for hunting down issues. For example, I noticed a lot of rooms had a similar double impulse shape at around 200-300hz. I could see it in every impulse response I looked at. Didn’t take long to realize that matched a ceiling reflection. Most rooms have similar heights and similar construction. Hence why it always showed up. I confirmed it was treatable when I noticed it was weaker in a room with an acoustic false ceiling (and made it disapear after treating that ceiling). If you watch my videos you can see reference to this.
     
  14. AudiocRaver

    AudiocRaver Senior Admin
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    My approach has always been similar to what Matt and Mark have suggested, you can't have too much LF absorption. starting with front wall and corners....
     
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  15. Negatron

    Negatron Senior Member
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    In my last house we made bass traps in all 4 corner floor to ceiling, and also 9" (I think it was 9 but it could have been 12) of Roxul for the entire rear wall. Definitely helped the bass!
     

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