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

[kemmler3D]

I would also kinda dispute the idea that the treatments didn't work. The measurements show >3dB improvement in many areas. Sure, the problems are bigger than that, but it's not a trivial change and I'd call it a good start. I've seen people's before/after measurements that had a lot less movement than this...

I would agree with most of the advice in this thread, bass traps are really hard, dialing in your room EQ more might be easier.

On topic but not about OP's specific issue, I have recently read some claims (not just in one place) that putting a binary amplitude diffuser panel on the front of an absorber somehow increases its absorption at lower frequencies. I think on one of the brand's pages it suggested that it was acting like a resonator, or membrane, or something. It was that confusing mix of marketing and scientific jargon that makes things hard to parse.

Anyway, does anyone know if there's any merit to that in real life? A BAD panel would be easy to 3D print and I'm thinking a nice thick 8" absorber cloud with BAD facing might be my next acoustic upgrade in my office.

 

[Sigberg Audio]

Or use tuned absorbers, e.g. membranes or helmholtz resonators. Those are specific problem solver tools for modal problems.

Yes, but not very practical (imo).

 

[kemmler3D]

Yes, but not very practical (imo).

I don't think membranes are any worse than normal absorbers once you get them installed, but AFAIK they are expensive and/or tricky to build. Helmholtz resonators are only for those with giant rooms and nothing but a listening setup in them.

It is worth emphasizing that tuned absorbers can be much better for bass. If you look at OP's results they got maybe 3dB improvement over a fairly wide band. But what you actually want is for peaks and dips to go away - which would require 10+ dB absorption at specific frequencies, not the whole range. It looks like nothing happened because the whole curve shifts down, but with the peak intact. Steep slopes sort of visually mask small changes, but if you count the gridlines it's there. It's just not solving the problem.

 

[dfuller]

Yes, but not very practical (imo).

Eh, they can be, not in a domestic environment though.

 

[dasdoing]

there is visible improvement.
Anyway, focus on the time factor with the traps. let Ady do the FR correction.
for example here on the Ady corrected graph, I circled your main problem zone:

this is probably a combination of width and height modes?
experiment with the traps to bring this down.
put more material into the width axis, and remove from the length that doesn't seem to be a big problem.
you have a sub? test by moving it from the floor to see what it does to the height modes.

would be easier to make suggestions with pictures of the setup

 

[theREALdotnet]

More coverage area is required for even better absorption, I agree with that, but is 10cm not enough even when straddled in corners?

Air gapping or corner straddling is more important than thickness. Also, make sure you enclose the air gap, or make the corner absorbers floor-to-ceiling.

Your absorbers seem to have had some positive effect on the 85-90Hz mode, so that’s not too bad.

The ~105Hz suck-out is not a room mode, that’s extinction due to SBIR. Measure from the centre of the woofer to the floor, side wall or front wall and plug this distance D into this equation: f=343/4/D. I bet with one of the distances you will get the frequency of that null. There is not much you can do about it, other than changing the frequency by changing the distance. This won’t work too well if it’s the distance to the floor, of course. But if it’s side or front wall SBIR you can try to make the null coincide with the 85-90Hz room mode (i.e. change the distance from ~80cm to ~100cm).

 

[Keith_W]

Doesn't air gap count as thickness?

A 10cm velocity absorber with a 20cm air gap is not the same as a 30cm thick absorber. It will have the same effective frequency but provide much less attenuation.

Also, I realized I forgot to answer your question about ERB smoothing. ERB refers to the ear's ability to discriminate between two tones which are close to each other in frequency - if the second tone is too close to the first and below a certain volume threshold, the first tone will mask the second. It is conceptually similar to the "two point discrimination test" performed by doctors, where two sharp points are applied to the skin with calipers, and the distance increased until two sharp points are perceived instead of one.

Pay attention to the ERB curve. Note that at 100Hz, the ERB bandwidth is about 25Hz. Now imagine you have a notch at 100Hz which is 25Hz wide. ERB smoothing will remove it.

This does not mean that the notch is not there. You can easily see it in "normal" 1/6 or 1/12 smoothing. And you will easily hear it if you played a 100Hz pure sine wave tone. What it means is that if a masking tone is present, e.g. in complex signal like music, you are less likely to hear it.

I think ERB smoothing should be for interest only. I would look at it and think "that's nice, I am less likely to hear it" and then take steps to correct the variable smoothed curve anyway.

 

[dasdoing]

Roughly, the critical band is the band of audio frequencies within which a second tone will interfere with the perception of the first tone by auditory masking.

which basically means it only applies to broadband noises.
the denser the music, the more it will approach noise,
but with a single instrument you probably best look at the unsmoothed graph

 

[dasdoing]

about the air gap. to absorb a given frequency the most efficiently (for porous absorbers) you need material at 1/4 wavelength distance from the wall:

source: https://www.ekustik.eu/tips-and-tricks-blog/low-frequency-absorption


in the corner, you will have varying distances to hit many frequencies, and you also act on the length and the width.
but with this 1/4 rule, you can target frequencies and don't necessarily have to focus on the corners.

 

[Justdafactsmaam]

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.

FlexRange® Bass Trap Panels

FlexRange® Bass Trap Panel—the evolution of GIK’s 244 and Monster panels—now for even deeper low-end control. Choose Full Range or Range Limiter tuning, add optional diffusion, and treat corners, walls, or ceilings with patented, air-gap design.

www.gikacoustics.com

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?

https://gearspace.com/board/showthread.php?p=5040734

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?

If that is your limit for size you need to make tuned diaphragmatic bass traps. It’s more involved but is still something a DIYer can do

 

[Justdafactsmaam]

Yes, but not very practical (imo).

How are diaphragmatic bass traps impractical?

 

[Sigberg Audio]

How are diaphragmatic bass traps impractical?

Depends on the context and what we mean by impractical I guess. But you are likely to need several both for effect and because each only cover a narrow frequency range. And they may need to be placed somewhere it's not suitable to have them at least in a non-dedicated room. If you find them practical, I am not going to argue with that of course. Personally I do not.

 

[Justdafactsmaam]

Depends on the context and what we mean by impractical I guess. But you are likely to need several both for effect and because each only cover a narrow frequency range. And they may need to be placed somewhere it's not suitable to have them at least in a non-dedicated room. If you find them practical, I am not going to argue with that of course. Personally I do not.

In the OP’s case they should be relatively practical since we know he has wall space. And that is where they need to go, against the walls

 

[Bjorn]

How are diaphragmatic bass traps impractical?

It's impractical for those who sell subwoofers and advocate multiple subwoofer approach. Which does nothing with the important upper and mid bass and low midrange. And also in most cases costs far more.

 

[Sigberg Audio]

It's impractical for those who sell subwoofers and advocate multiple subwoofer approach. Which does nothing with the important upper and mid bass and low midrange. And also in most cases costs far more.

Could you help explain the conceptual difference between someone selling subwoofers arguing for subwoofers, and someone selling acoustic treatment arguing for acoustic treatment?

 

[kemmler3D]

Could you help explain the conceptual difference between someone selling subwoofers arguing for subwoofers, and someone selling acoustic treatment arguing for acoustic treatment?

 

[Bjorn]

Could you help explain the conceptual difference between someone selling subwoofers arguing for subwoofers, and someone selling acoustic treatment arguing for acoustic treatment?

First of all, people can decide for themselves whether it's impractical or not. And not sure why it should be less practical then multiple subwoofers in many cases.

Secondly, I have several subwoofer designs I plan to release. Will I speak differently when I do? No, because to me it's about recommending the better approach and just not selling products. And you simply don't deal with many of the important issues with only subwoofers or EQ for that matter.

Acoustic products to home market generally doesn't generate much income. And I often recommend people to build their own products.

 

[Justdafactsmaam]

Could you help explain the conceptual difference between someone selling subwoofers arguing for subwoofers, and someone selling acoustic treatment arguing for acoustic treatment?

Imagine you have a room full of junk piled up unevenly in a room. The treatments remove some of the junk. The subwoofers organize it in a more sightly fashion.

Bass traps reduce bass reverb. Subwoofers help you maneuver bass reverb

 

[Duke]

Matthew Poes, acoustician, on multiple subs versus bass traps (from a video recorded years before he became a dealer for Perlisten):

"I've installed a lot of bass traps in people's rooms, I've filled every corner, the ceiling, you name it, and it didn't make anywhere near as big a difference as four subs did."

Here's the video, cued up to that part. He gets his point across within about 30 seconds:

Of course multiple subs, bass trapping, and EQ are NOT mutually exclusive! They can be used in combination, and imo that would be ideal.

 

[Bjorn]

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.

FlexRange® Bass Trap Panels

FlexRange® Bass Trap Panel—the evolution of GIK’s 244 and Monster panels—now for even deeper low-end control. Choose Full Range or Range Limiter tuning, add optional diffusion, and treat corners, walls, or ceilings with patented, air-gap design.

www.gikacoustics.com

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?

https://gearspace.com/board/showthread.php?p=5040734

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?

You're asking a lot of questions here and this is waste topic. We can only scratch the surface here.

First of all posted data/measurements of acoustic products are not necessarily to be trusted. There are several reasons for that but one is that the measurement method for lowest frequencies isn't always trustworthy. Secondly, they can be based on reverberation, and which means it isn't something you can automatically transfer to small rooms. Said in other words, the unit will not absorb as well in a small room.

Thirdly, when someone says it works down to a specific frequency, this doesn't mean it's very efficient to that frequency. It may be that it only absorbs 30 %, 20 % or 10% there. And we need a lot more for a good result.

There are new measurements out there today that suggest that a 10 cm panel can be very effective to about 80 Hz. But it's only a certain material. Or a product that uses multiple cores like the Broadsorbor from RPG. I have seen great effect to 110 Hz with only a few such panels and to 80 Hz with more panels.

As for air gap, too much of that with openings and the effect will actually become worse.

While pressure based traps can be far more effective at the lowest frequencies, they generally tend to be band limited and not addressing the most sensitive area great. So often a combination is the better approach.