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Are my bass traps not working? Some changes in var smoothed frequency response, but not much in ERB smoothed one.

vroad

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Several months ago I built and installed 4 bass traps to my living room, each of them sizes W60cm x H72cm x D10cm.

I only used variable smoothing when I measured my speakers (ELAC DBR62) when I installed bass traps, and thought that they made some positive changes.
I posted FR graphs on reddit and at least some people thought the same.

But was var smoothed graph a good choice for this?
Later I learned that ERB (or Psychoacoustic) smoothing might be closer to what I hear with my ears.
With ERB smoothing, sharp dip at 100Hz disappears. Does this mean that var smoothing is too much detailed, and there was not much to fix in the room to start with? Or Is the ERB smoothing too much for this case?
With ERB anything below 30Hz disappears. Var and Psychoacoustic smoothing doesn't.

Aside from that, if I remember correctly my traps reduced peaks when I'm not in main listening position. I only tested this with my ears though.

I've found amir's post saying that velocity based bass traps can't fix room modes and few people have actually made effective changes in their room.
You may not need those in larger rooms, but what about small rooms like mine? My room is very small (W2.9m x D2.56m x H2.4m), and dips are at higher frequencies (80 - 100 Hz), which could be reduced with not so thick 10cm (= 4 inches) bass traps.
At lower frequencies velocity based traps might be impractical since they need to be super thick and visually intrusive.

As I bought a AVR with Audyssey MultEQ XT32 recently, I've also tested with/without Audyssey today. I didn't have a receiver with Audyssey when I built bass traps.
I used following settings.
Audyssey reduced the dip at 100Hz much further in the MLP, so Audyssey alone might have been good enough?

I've also attached mdat files in case if you want to see measurements in a different way.
RFrontERB.png
RFrontVar.png
RFrontAdyERB.png
RFrontAdyVar.png
 

Attachments

  • DBR62_R_Front_NoBT_BT.zip
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  • DBR62_R_Front_AdyOnOff.zip
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A 10cm thick panel isn't really a bass trap, and your panels are not very big in the other dimensions either. Admittedly you don't have a large room, so such panels might improve the overall room acoustics, but I would not expect significant changes in measured response.
 
10 cm depth doesn't even absorb well to 200 Hz. Not to mention the need for overall dimensions when dealing with lows.
This isn't a bass trap but an absorber that works for mids and highs.
A 10cm thick panel isn't really a bass trap, and your panels are not very big in the other dimensions either. Admittedly you don't have a large room, so such panels might improve the overall room acoustics, but I would not expect significant changes in measured response.
More coverage area is required for even better absorption, I agree with that, but is 10cm not enough even when straddled in corners?

If 10 cm is not enough, how much thickness would you think is enough? Also How much coverage, and which material? Do you have measurements that back it up?

GIK's 244 trap (full range version), which is similar to mine in thickness, is claimed to absorb highest at 125Hz.

I've seen gearspace posts saying that Glenn Kuras from GIK saying that 4 inches (10 cm) thickness works even for 60Hz or so. More coverage is probably required to absorb down to such low frequency, but is "10cm is not enough" statement is really correct? Even with more area covered, good insulation is used, and straddled?

He said that 6 inches thickness is indeed better but also said that 4 inches with more area is better than 6 inches with less area. Or is he simply wrong?
 
Foam is simply impractical for low bass, quarter wave of 50Hz is what six feet, far more effective to use resonators or membrane traps tuned to the specific frequency or just use EQ.
Keith
 
More coverage area is required for even better absorption, I agree with that, but is 10cm not enough even when straddled in corners?

If 10 cm is not enough, how much thickness would you think is enough? Also How much coverage, and which material? Do you have measurements that back it up?

GIK's 244 trap (full range version), which is similar to mine in thickness, is claimed to absorb highest at 125Hz.

I've seen gearspace posts saying that Glenn Kuras from GIK saying that 4 inches (10 cm) thickness works even for 60Hz or so. More coverage is probably required to absorb down to such low frequency, but is "10cm is not enough" statement is really correct? Even with more area covered, good insulation is used, and straddled?

He said that 6 inches thickness is indeed better but also said that 4 inches with more area is better than 6 inches with less area. Or is he simply wrong?

Realistically you will need to fix peaks with EQ/DSP, and live with the dips, or fix the dips via multiple subwoofers. To do it with absorbtion, you would need so much there wouldn't be much left of your room.
 
- absorbers way to thin for bass absorbing
- for measuring bass frequencies I would turn of smoothing or use only a little bit
- for the effect of basstraps / absorbers rather look at the waterfall / spectogramm than the spl graph. The latter one is easly EQed, but the decay/reverb not (which is the main purpose of bass traps and seen in waterfall/specto)
 
I don't really consider porous absorbers bass traps for home use, you can't really get them thick enough to do much. For bass I have good results with hanging mass loaded vinyl like materials in the corners (way more effective than porous stuff here), or my favorite bass treatment so far, more subs.
 
I'm not an expert and I don't have any acoustic treatment...

There are thin "resonant" or "membrane" bass traps. RealTraps is one seller. Ethan Winer (one of RealTraps founders) has article about how to build them.

The pictures on Ethan's website and on ReapTraps show LOTs of wall coverage and for best performance you MIGHT need to cover about half of your wall & ceiling area to get good results.
 
Foam is simply impractical for low bass, quarter wave of 50Hz is what six feet, far more effective to use resonators or membrane traps tuned to the specific frequency or just use EQ.
Keith
Who said that mine is foam?? But yeah I should have mentioned what material I used.

My bass traps uses cellulose insulation from Japanese company,
It's the insulatlon product that could be used for houses. GFR value is unknown though, the density is 90Kg/m3, which is close to GIK's commercial bass trap products.

Have you tried tuned traps or other treatments that works only at specific frequency actually? amir agrees in that thread that EQ works but do not recommend using tuned traps, it can work, but harder to use than EQ.

1/4 wavelength rule is for 100% absorption, for 85% absorption 1/10 wavelength thickness should work. Airgap between the panel and the walls also count as thickness.
 
I use three RPG Modex panels tuned to my rooms length mode, they work -5dB reduction but the peak ( ugly room) is 20+dB.
Adjusting speaker placement and listening position helps but ultimately EQ.

Keith
 
1/4 wavelength rule is for 100% absorption, for 85% absorption 1/10 wavelength thickness should work.

It just doesn't. Didn't you just prove that yourself with your tests and your measurements? You will get minimal effect under 100hz without massive treatments.
 
I also tried PSI’s active bass traps they work well too ,but you need a lot of them.
Built from scratch purpose built room if you limit yourself to passive absorption.
Keith
 
Try 600mm thickness and then we can talk. :)
preferably stacked into each corner of the room from the bottom to the top. That´s why is use so much subwoofers :D Tried also PSI AVAA and Bag End E Traps, which worked well - but multiple subs are much cheaper.
 
I agree with the other posters but even that said, your graphs are showing material improvements in the response? 3-5db of improvements would definitely be audible. You should check your decay time (waterfall) as well I'm sure there are gains to be seen there too.
 
Didn't you say you were going to attach an mdat file? I don't see it. Anyway, I did some calculations for you.

Your Schroder frequency is 2000 * sqrt (T30/V). I don't know what your T30 is (no MDAT) so i'm going to guess it's 0.3s. Room volume is 2.9 * 2.56 * 2.4 = 17.82m^2. Therefore your Schroder freq is 259.5Hz. This means your transition zone ends at 4Fs, or 1038Hz. The pressure zone will be half wavelength of the longest room dimension, in your case 2.9m. This corresponds to 59Hz.

This means: you will have no room modes below 59Hz since it will all be in the pressure zone (assuming the room is sealed). You will see modal behaviour between 59Hz to 259.5Hz. Your transition zone ends very high, at 1038Hz.

Therefore, if you want to use a velocity absorber, it only needs to absorb down to 59Hz. The thickness of the velocity absorber needs to be 1/8 the wavelength, or 72.5cm. You mention that you have 10cm thick absorbers. This will work down to 429Hz, so it will help in the transition zone, and provide a little bit of attenuation lower down than this.

To be honest, in a room that small you would be flooded with early reflections so a little bit of room treatment might help.
 
Didn't you say you were going to attach an mdat file? I don't see it. Anyway, I did some calculations for you.
Looks like I failed to upload it because of "file is too large error" and missed the error message. I re-uploaded zip files with only R speaker measurements to reduce file size.
Therefore, if you want to use a velocity absorber, it only needs to absorb down to 59Hz. The thickness of the velocity absorber needs to be 1/8 the wavelength, or 72.5cm. You mention that you have 10cm thick absorbers. This will work down to 429Hz, so it will help in the transition zone, and provide a little bit of attenuation lower down than this.
Doesn't air gap count as thickness? From what I've heard on other forums a panel absorber with airgap works mostly the same as triangular absorber. Filling the gap with insulation and making it triangle shaped only make it absorb a little more. As my trap is 60cm wide each and straddle mounted, there is 30cm air gap behind panel.
30cm airgap + 10cm thickness = 40cm
40cm * 8 = 3.2m (wave length for 107Hz sound wave)

Filling the corners will work fine and provide a little more absorption.

GIK's 244 trap (full range version) I mentioned earlier absorb the most at 125Hz, according to their graph. The thickness of the panel is 118mm (probably including timber frame).
 
@vroad We don't need to guess and speculate. You have the panels, and you have the ability to measure. Do measurements with no smoothing at all, with and without the traps. Then you can provide your findings here. :)
 
Realistically you will need to fix peaks with EQ/DSP, and live with the dips, or fix the dips via multiple subwoofers. To do it with absorbtion, you would need so much there wouldn't be much left of your room.
Or use tuned absorbers, e.g. membranes or helmholtz resonators. Those are specific problem solver tools for modal problems.

I've found amir's post saying that velocity based bass traps can't fix room modes and few people have actually made effective changes in their room.
This is true. Velocity absorbers can't deal with pressure zone problems.
 
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