Glass vs Drywall : Similar absorption coefficient !?

[AVUser001]

Wow.. Glass vs drywall sound absorption

I was thinking I need to do something about my glass doors , besides the curtain..and was looking around , when I stumbled into this.

Jesco from Acoustics Insider seems knowlegable..

What do you guys think ?

 

[slipperybidness]

Wow.. Glass vs drywall sound absorption
View attachment 33103


I was thinking I need to do something about my glass doors , besides the curtain..and was looking around , when I stumbled into this.

Jesco from Acoustics Insider seems knowlegable..

What do you guys think ?

Seems reasonable, I guess, and I'm not knowledgeable enough to argue against the data set.

But, I think your title "
Glass vs Drywall : Same absorption coefficient !?
"
Is misleading. I certainly don't draw that conclusion from anything in that chart that you posted. If you siad "same coefficient @~1500Hz", I would agree.

 

[AVUser001]

But, I think your title "
Glass vs Drywall : Same absorption coefficient !?
"
Is misleading. I certainly don't draw that conclusion from anything in that chart that you posted. If you siad "same coefficient @~1500Hz", I would agree.

Maybe I should change the title to replace "same" with "similar" , which is actually the bigger point, the author is trying to highlight here.

If you watch the video , at the start , he posts the absorption coefficient of Single pane of glass & Single layer plasterboard , both at 0.3 at 125Hz and infact drywall's going below glass to 0.1 upto ~4Khz.

Again , at 2.25 of video, he posts the coefficient of double pane of glass and double layer of plasterboard at just above ~0.1 in the same range.

Did you see that ?

the bigger point here is they behave similarly , in this frequency range..,which is contrary to what I thought they'd be..

 

[Swerd]

I watched the video. It seems reasonable to me. The basic info that glass windows or standard drywall are similar is useful to know.

But sometimes he spoke of sound absorption vs. sound passing through walls or windows, and other times he spoke of absorption vs. reflection. It wasn't clear to me if it makes a difference or not.

 

[slipperybidness]

Maybe I should change the title to replace "same" with "similar" , which is actually the bigger point, the author is trying to highlight here.

If you watch the video , at the start , he posts the absorption coefficient of Single pane of glass & Single layer plasterboard , both at 0.3 at 125Hz and infact drywall's going below glass to 0.1 upto ~4Khz.

Again , at 2.25 of video, he posts the coefficient of double pane of glass and double layer of plasterboard at just above ~0.1 in the same range.

Did you see that ?

View attachment 33104

the bigger point here is they behave similarly , in this frequency range..,which is contrary to what I thought they'd be..

I didn't have a chance to watch the video, I was just inspecting the chart that was posted. I'll give it a watch when I have a minute.

 

[KEW]

I have two problems with the charted data:
1) The chart is scaled to include the absorptive "Heavy Folded Curtain" which compresses the range of all of the remaining materials (which happen to be pretty reflective! Visually that puts everything else at the bottom of the graph and you tend not to notice that the differences are actually 2 to 4 fold (see below)!
2) The data stops at 4000Hz, well before our hearing goes south! If you look at the chart, at 4000Hz, double sheets of plasterboard are twice as absorptive as glass and a single sheet is 3.5 to 4 times as absorptive! That is a big difference and I bet if the data had continued to 8000 and 16000Hz coefficient for glass would continue near zero while plasterboard continued to climb!

As a point of reference, the 6kHz-8kHz range is associated with "sibilance" and 8kHz to 16kHz is associated with "brittleness"!

 

[AVUser001]

I have two problems with the charted data:
1) The chart is scaled to include the absorptive "Heavy Folded Curtain" which compresses the range of all of the remaining materials (which happen to be pretty reflective! Visually that puts everything else at the bottom of the graph and you tend not to notice that the differences are actually 2 to 4 fold (see below)!
2) The data stops at 4000Hz, well before our hearing goes south! If you look at the chart, at 4000Hz, double sheets of plasterboard are twice as absorptive as glass and a single sheet is 3.5 to 4 times as absorptive! That is a big difference and I bet if the data had continued to 8000 and 16000Hz coefficient for glass would continue near zero while plasterboard continued to climb!

As a point of reference, the 6kHz-8kHz range is associated with "sibilance" and 8kHz to 16kHz is associated with "brittleness"!

Actually I dont see the remarkable difference you're seeing in that chart...they're all in the same vicinity ( ~0 -0.1) , with the drywall at 4Khz , only a bit better .

In any case, I thought I'd double check this data, with couple of other sources and it does surprise me there's not a remarkable difference I expected between drywall/plasterboard vs Glass.

Commercial acoustics

Soundproofyourhome

You need to look at the absolute values, compared to different materials that have drastically different sound absorptions..for eg this drapery rating. , to appreciate what they're trying to highlight..

or look at Fiberglass

thats night & day difference .... Looks like drywall is only marginally better than glass.., not the night&day difference , you get with 18oz drapery or Carpet , for eg..

for some reason many of these sources go only upto 4Khz.

and another source.., shows the same ballpark readings for glass vs drywall . Not all of them will be wrong, I suppose..
Its clear to me..,for what I was looking into room treatment for my office with glass windows , as well as my HT, I know where to & where not to invest

engineeringtoolbox

 

[KEW]

It is a matter of perspective.
Looking at your original chart at 4kHz, I would read the following estimates of the values:
Glass (single or double) E=~0.01
Plasterboard (double) E=~0.04
Plasterboard (single) E=~0.09
So that would actually indicate plasterboard is around 9 times as absorptive as glass at 4kHz.
That was the perspective behind my statements.
But yes, you are right, in the overall scheme of things, both are reflective materials!
Is there a theoretical optimum value for the absorption coefficient for a listening room?
I believe actual objective is generally to reduce reverb time.
You may be well ahead of me, but here is a link I found:

Reverberation Time - an overview | ScienceDirect Topics

www.sciencedirect.com

If you scan down the left side you will see "(13.10)" which gives the basic function for calculating the reverb time and that "alpha" (the absorption coefficient) is on the bottom, so the reverberation time is inversely proportional to the sound absorption coefficient, and (in the same room) a coefficient of 0.01 would have a reverb time that is 9 times longer than 0.09 (single plasterboard) and 70 times longer for 0.70 (heavy curtain at 4kHz).
We can also see that the reverb time for single plasterboard (at 0.09) is around 8 times longer than curtains (at 0.70) which means (in the context of reverb time) the difference between glass and single plasterboard (9X) is equal (or slightly greater) than the difference between single plasterboard and heavy curtains (8X).

Of course my estimates of the values in the chart may not be exact, but they are close and I believe the relationship/conclusions are valid!