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Acoustic treatment with slats - before-and-after measurements

Can you elaborate on this, or point me towards some reading that explains the small room aspect?
There's some write up here below. That's a summary, going into depth would require a lot of writing.

But in short you don't have requirements needed in a small room for reverberation. An acoustic called Theodore Schultz proved that mathetically several decades ago, but knowledge and info doesn't always reach the majority. There's no stochastic sound field or critical distance in a small room, something that's absolutely required for there to be a true reverberation time. Most acousticians are trained in large room acoustics and simply apply the same method to small rooms. But small room acoustics is a very different field that not many are trained in or understand well.

I have been involved in several rooms that were treated in regards to RTx measurements. Sounded very bad despite the RTx looked good and needed to be totally changed. RTx are very misleading when used in a small room, despite that the numbers go down with absorption added. It's like using a wrong mathematical equation. It will change with the numbers you add into the equation, but the result is still wrong.
We can also easily see that when for example using a cumulative spectral decay or if appplying a filtered ETC/impulse. This is also the reason we use two different measuring methods for acoustic products. One is applicable to large venues and one is applicaple to small rooms. Very often, only the first is shown because it looks better, though it's not valid for a small room.
 
I disagree with this. In my case, working within contraints (aestethics and space), and trying to fix an explicit problem (flutter echo), I think slats should be considered a «serious acoustic treatment». The measurements I showed in the first post are exactly the kind of information I would have wanted to see, if I had started again from the beginning.

Out of curiosity, what would it take for you to consider an acoustical treatment effective? Could you please quantify this? What kind of measurements, and what *numbers* would you require to declare a successful reduction of flutter echo?

Regarding RT60, that terminology comes from REW. In my graphs, the plotted quantity is Topt (which is REW specific and defined here). I could have used others, like T20 or T30, but does it really matter? They are all quantifying decay times.
Effective treatment would do the following:
- Improve the frequency response
- Improve the time domain behaviour in both lows and mids/highs. Generally seen by spectral decay/waterfall of the lows and filtered ETCs for the frequency area above the Schroeder frequency.

With diffusion, the energy would be packed tighter together with less sparse reflections and also attenuated gradually. Not quite unlike what you see in the illustration below. Though there are those that diffuse early arriving reflections too, accuracy would imply that those are strongly attenuated in a reflection free zone. Preferably below -25 ms.
ETC before and after treatment.jpg
 
Due to space, budget, and/or aesthetic constraints highly engineered rooms matching figure 2.10 above is not really feasible for many.

People often adapt and get used to their room acoustics environment over time, and so this is probably why many simply don't critically obsess over their rooms the way some of us in audio forums do...

Hmmmn, a way to get around the lack of "envelopment" in overly dry rooms -- say, in the first image example I gave -- due to too much absorption (usually a "problem" in the mids and highs and not so much the bass) is by employing multichannel sound reproduction and/or upmixing DSP for stereo only content. That is basically what I myself do to compensate for this "deficiency". JRiver media center, for example, will delay the toned-down, decorrelated upmixed surround channels between 20 and 30ms... Besides manually adjusting channel levels and other PEQs, one also could apply additional reverb/envelopment convolution VST effects globally or to select channels to improve the overall feel of the mix to suit the type media or one's personal taste or mood for the day.
 
Some people here at ASR are quite particular with how data is presented. To make your original post more "complete", I suggest attaching a zipped (or compressed) before and after mdat file to let others do their own "in-depth" analysis and breakdown of the provided information however they will.
Good suggestion. Unfortunately, I'm not able to edit the original post. I tried to uplad a zipped mdat file here, but it says the file is too big. It's 8 MB, just six measurments. Is there a maximum filesize for uploads? Or am I too new here on ASR to be allowed to do this?
 
It's 8 MB, just six measurments. Is there a maximum filesize for uploads?

I believe somewhere between 4 or 5MB is the limit.... You could split the before and after into two separate zipped mdat files.
 
These look great, and thanks so much for sharing your before and after measurements and listening impressions!
Thanks!

Sorry if I'm being daft, but don't the MDF slats primarily serve as diffusers rather than absorbers? And if so, doesn't their standardized/non-random orientation and depth make them rather poor diffusers? Not trying to criticize the OP, just asking.
Regarding the slats themselves, I believe these are diffusers. However, they are mounted on a felt mat, which is absorbing. The manufacturer Fibrotech has a webpage with datasheets containing measurements of the absorption coefficients - see the pdf for the BASIC acoustic panel here. There are no details about these measurements, but I would give them credit for publishing it.
 
I believe somewhere between 4 or 5MB is the limit.... You could split the before and after into two separate zipped mdat files.
Excellent - thanks! Uploaded before and after in two separate zip files.

Two comments on the measurents:
  1. I discovered an error in the L and R after measurements, so I just redid those today. This doesn't make any difference for the TR60/Topt, but maybe to the ETC.
  2. The NAD M33 doesn't allow me to play each speaker separately without the subs when Dirac Live is turned on. This is a strange restriction on how Dirac works on the M33. The workaround is the turn the crossover all the way down to the minimum 40 Hz, and turn down the volume on the subs (to -60 db). This shouldn't be relevant for the frequencies I'm interested in well above the Schroeder frequency.
  3. In the "All, after" measurements, there *may* be some noise around 130-150 Hz due to my refrigerator, or something like that. Sorry! I haven't mad an effort to investigate that further, because - again - I'm interested in higher frequencies.
I'm happy if people would find it interesting to play around with these measurements. In fact, I'm happy that this subject has generated a lot of discussion!
 

Attachments

  • 2023-03-05-before-panels.mdat.zip
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  • 2023-03-05-after-panels.mdat.zip
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Due to space, budget, and/or aesthetic constraints highly engineered rooms matching figure 2.10 above is not really feasible for many.

People often adapt and get used to their room acoustics environment over time, and so this is probably why many simply don't critically obsess over their rooms the way some of us in audio forums do...

Hmmmn, a way to get around the lack of "envelopment" in overly dry rooms -- say, in the first image example I gave -- due to too much absorption (usually a "problem" in the mids and highs and not so much the bass) is by employing multichannel sound reproduction and/or upmixing DSP for stereo only content. That is basically what I myself do to compensate for this "deficiency". JRiver media center, for example, will delay the toned-down, decorrelated upmixed surround channels between 20 and 30ms... Besides manually adjusting channel levels and other PEQs, one also could apply additional reverb/envelopment convolution VST effects globally or to select channels to improve the overall feel of the mix to suit the type media or one's personal taste or mood for the day.
I hope you are aware you won't get room without refractions and out of echo no matter how much you try. At best with minimal furniture and properly fully treated one will have some from ceiling and wall behind. As we don't live in bunkers without windows it's favorable that listening position is towards wall with windows and with thich curtains of course.
Not the easiest to back track but useful read.
 
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One treatment I always recommend is ceiling treatment.

The ceiling is a large empty surface and treating it is highly effective for reducing decay times and it is visually unobtrusive.

Foam like basotect is really easy to install with glue on hooks or directly glued to the ceiling.
 
Thanks!


Regarding the slats themselves, I believe these are diffusers. However, they are mounted on a felt mat, which is absorbing. The manufacturer Fibrotech has a webpage with datasheets containing measurements of the absorption coefficients - see the pdf for the BASIC acoustic panel here. There are no details about these measurements, but I would give them credit for publishing it.

Thanks for your reply! I am not an engineer, but I think the professional experts on the forum here will likely agree with me when I say that 9mm thick felt is simply incapable of absorbing the longer-wavelength lower frequencies like the ones you are looking to get better control of - which, if I read your measurements correctly, is why the room response at those lower frequencies appears to have changed in your before and after, but not necessarily improved. I would guess that most of the differences you've measured below about 2kHz would be more impacted by the diffraction of the slats than the absorption of the felt.

Again, I don't say this to sound like a know-it-all or to criticize your choice or measurements in any way. As for the manufacturer's data, all I can say is that virtually every manufacturer of acoustic absorbers that publishes data, shows absorption coefficients that appear to be much greater than we tend to achieve in real-world situations. I believe some of that comes from the types of chambers the manufacturers use to measure the absorption, but again, I am not an expert so I could be wrong about that.

Regardless, your installation looks awesome and clearly has given you some real improvement, so that's what matters!
 
Excellent - thanks! Uploaded before and after in two separate zip files.

Two comments on the measurents:
  1. I discovered an error in the L and R after measurements, so I just redid those today. This doesn't make any difference for the TR60/Topt, but maybe to the ETC.
  2. The NAD M33 doesn't allow me to play each speaker separately without the subs when Dirac Live is turned on. This is a strange restriction on how Dirac works on the M33. The workaround is the turn the crossover all the way down to the minimum 40 Hz, and turn down the volume on the subs (to -60 db). This shouldn't be relevant for the frequencies I'm interested in well above the Schroeder frequency.
  3. In the "All, after" measurements, there *may* be some noise around 130-150 Hz due to my refrigerator, or something like that. Sorry! I haven't mad an effort to investigate that further, because - again - I'm interested in higher frequencies.
I'm happy if people would find it interesting to play around with these measurements. In fact, I'm happy that this subject has generated a lot of discussion!

Seems like there's something weird going on in your L+R measurement -- could be operator error. The bass appears abnormally high as opposed to what one gets with a simple vector average or "aligned sum" between left and right.

1678040380855.png


1678040385464.png



*Generally, decay in the bass (when it is not elevated up so much) is actually okay; and, I do see indeed a marked improvement in the clarity above 500Hz after treatment. Still not perfect -- and a little uneven -- but better than before.

1678040561030.png
 
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Thanks!


Regarding the slats themselves, I believe these are diffusers. However, they are mounted on a felt mat, which is absorbing. The manufacturer Fibrotech has a webpage with datasheets containing measurements of the absorption coefficients - see the pdf for the BASIC acoustic panel here. There are no details about these measurements, but I would give them credit for publishing it.
There are no acoustics test data on their site that I can find, maybe I’m missing something?

I’m going to put similar/identical slats in y living room. They offer a nice look. However, they offer very limited absorption, and only in the higher frequencies. A half inch of felt backing will only do so much…

In my case I’m going to use 2” PET behind the slat+felt, to provide absorption for lower frequencies. Bass trapping will be entirely separate.

I think these slat walls are great, but the vendors don’t make it clear at all that they will be even somewhat effective only in a limited frequency range.
 
One treatment I always recommend is ceiling treatment.

The ceiling is a large empty surface and treating it is highly effective for reducing decay times and it is visually unobtrusive.

Foam like basotect is really easy to install with glue on hooks or directly glued to the ceiling.
Regular foam won't absorb much and rock wool is relatively heavy and hard to mount on ceilings.
Some time ago I run on to this:
 
Regular foam won't absorb much and rock wool is relatively heavy and hard to mount on ceilings.
Some time ago I run on to this:
It certainly won't absorb any bass but is really good for mids and highs. Ceiling treatments will be in the range of 5 to maybe 15cm of thickness and foam will be more effective than Rockwool or glasswool at this depth.

This is basotect (12300 Pa*s/m2, blue) versus Rockwool (6000 Pa*s/m2).
For first reflections and lowering RT60 in mids and highs, Basotect (melamine foam) or any other good acoustic foam is a better choice than Rock or glasswool which works best at 30cm depth and higher.

1678038427322.png
 
I hope you are aware you won't get room without refractions and out of echo no matter how much you try. At best with minimal furniture and properly fully treated one will have some from celling and wall behind. As we don't live in bunkers without windows it's favorable that listening position is towards wall with windows and with thich curtains of course.
Not the easiest to back track but useful read.

Sorry, but I do not know what this research is all about and how it relates directly or is of significant benefit to what I only briefly described my method of DSP compensation. I do not live in an anechoic room -- the room is heavily, acoustically dampened on top of having normal household furnishings, yes. Do I hear an echo with me clapping? Yep, there's some of that as it's not totally 100% "dead" anyways.
 
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Sorry, but I do not know what this research is all about and how it relates directly or is of significant benefit to what I only briefly described my method of DSP compensation. I do not live in an anechoic room -- the room is heavily, acoustically damped on top of having normal household furnishings, yes. Do I hear an echo with me clapping? Yep, there's some of that as it's not totally 100% "dead" anyways.
It's about DSP compensation but that is less important, what's important is gathered data in the different dumping room conditions as they used rather special room with flip side absorber/diffuser panels...
 
It's about DSP compensation but that is less important, what's important is gathered data in the different dumping room conditions as they used rather special room with flip side absorber/diffuser panels...

The convolution reverb room effect is only secondary/tertiary to the basic upmixing method used (which is often more than adequate for me), and, I only occasionally add it in anyways. I would not obsess over how it's created, and it's enough for me to do listening tests to see if I like whatever additional effects there is available for me to apply or not.
 
Due to space, budget, and/or aesthetic constraints highly engineered rooms matching figure 2.10 above is not really feasible for many.

People often adapt and get used to their room acoustics environment over time, and so this is probably why many simply don't critically obsess over their rooms the way some of us in audio forums do...
Sure, but the point was to describe what happens with quality treatment to answer the question posted. Proper diffusion will create less sparse reflections and pack them closer together. Both diffusers and absorbers attenuate reflections. Slats neither diffuse or absorb well. The periodicity with slats is also an issue.

Hmmmn, a way to get around the lack of "envelopment" in overly dry rooms -- say, in the first image example I gave -- due to too much absorption (usually a "problem" in the mids and highs and not so much the bass) is by employing multichannel sound reproduction and/or upmixing DSP for stereo only content. That is basically what I myself do to compensate for this "deficiency". JRiver media center, for example, will delay the toned-down, decorrelated upmixed surround channels between 20 and 30ms... Besides manually adjusting channel levels and other PEQs, one also could apply additional reverb/envelopment convolution VST effects globally or to select channels to improve the overall feel of the mix to suit the type media or one's personal taste or mood for the day.
Good treatment doesn't add more absorption than necessary. Better to get it right from the beginning. Multichannels will create it own issues with lobing and combing.
 
Are there any calculators that output a the best spacing for wood slats with a given width?

Random distance between slats is better than having the same distance but there probably is an even better setup from an acoustic's standpoint.
 
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