http://www.acousticalsurfaces.com/acoustic_IOI/101_13.htm



According to this table, standard window glass has a high sound absorption coefficient for low frequencies with a downward slope in the mid to high frequency range. To me it seems like the ideal bass absorption panel would use a sheet of glass (window panel) covered by a diffusive material. This would diffuse the mid to hi range sounds but allow the low frequency sounds to pass through the diffuser and dissipate through the glass. However, I see nobody doing this. Is my logic flawed?

 

Absolutely. Where and how are you going to acquire a large pane of heavy plate glass? It would weigh a ton for starters.

And nobody in the industry does it. Why? It's inefficient.

And the frequency never goes below 125Hz. How is that an ideal bass absorption?

 

Not to mention - Drop or hit a standart industry bass trap made out of foam or rockwool etc.
Then do the same with window glass.

 

Sand, which is what glass is made of is an incredible sound absorption material. It weighs so much though, but if used in a sub floor will make it so your downstairs neighbors would not know of your existence even if you had a herd of buffalo doing their rendition of "Dancing With The Stars" in your studio.

Good idea about the glass as a backing material. It too is very dense as well as heavy in the size needed though. It is recyclable which is very cool.

 

Last edited by a moderator: Jan 3, 2017

I'm not sure how you're getting internet in your Amish community but in every city I've ever been in buildings have had glass windows. It seems as though it's quite easy to source.

Inefficient in terms of what? That statement means nothing without the actual metrics you are gauging its efficiency from specified.

What relevance does the fact "the frequency" (of what?) never goes below 125Hz in this conversation? I've clearly just posted a table that shows the frequency response from 125Hz upwards and didn't say a word about frequencies below 125Hz.

 

Last edited: Jan 3, 2017

Enlightening.

 

Thanks for your reply. I'm wondering what size you think would be needed and how you've calculated this. I figured that the fact that glass was denser than other materials would mean that less mass would be required in order to do the same job. I assume I'm oversimplifying the science. I don't believe that link I posted specifies the mass of each of the materials used, which makes the test a little less credible as really they should have kept one of the variables constant to make a valid comparison. However, they do mention that they used "ordinary window glass".

 

My thought was that the glass could be the backing for rock wool instead of the wall itself. It would also act as soundproofing. It would go by layer...rock wool, glass, air space and wall. It might prove hard to hang. Size, perhaps 100 x 80 cm. panels.

 

I don't want to start a new topic but the purpose of considering a material other than heat insulation is that I don't want to run the risk of breathing in fibers.

 

Hey lukeallison, of course the insulation, which by the way is used in most large corner traps and other panelled sound absorbers which are not yucky foam, are covered by material that lets the sound in and keeps the funk within in. No need for a new topic, it is used in top studios all around the world.

 

hello, audio love maker fellows ,

lukeallison, your logic is flawlessly excellent.

there exist solutions where plates of materials, creating mass, are used between layers of air, sandwiched between layers of fibrous material, where the surface of the mass plate makes it really hard for the waves in the air to make it through, thus converting the energy of the sound waves to heat the most inefficient way possible (luckily).

the plates should be attached to some rigid frame somewhat elastically, the used materials are usually heavy rubber plates, mixed or layered with some textile material, about three to seven millimeters thick, similar to the material used in x-ray rooms for the operators, without the lead content.

have not heard about glass plates yet, but why not?

they could be used in twin setup with some air between them, then the air layers outside of both, then the fibrous material, then one air layer against the wall.

wall or corner -> air layer -> fibrous stuff -> air layer -> glass or rubber -> air layer -> glass or rubber -> air layer -> fibrous material -> acoustically transparent textile covering.

me thinks there could be loads of loads of information to be searched up on the great webs of internet, books about acoustics might also be of some help.

all the best for all of us...

 

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Why am I interested in challenging the mainstream views on sound absorption?

1. Health concerns. Scientific literature shows that fibres from materials such as fibreglass can be breathed in and lodged into the lungs permanently where they cause inflammatory diseases such as lung cancer. To understand more I urge you to read about asbestosis and why most developed countries have banned this material from manufacturing. Meanwhile, some countries still use this material regardless of the proven consequence for those exposed to it. So factor that in when you argue that "companies have been making sound absorption panels for years using rock wool". It's not illegal to do it so why wouldn't they?

2. The frequency response of the absorption coefficients of these popular materials show an increasing effectiveness in the mid to upper frequency ranges while dropping substantially in the low frequency range. Seeing as the most common issue with room sound is bass reverberation it seems odd that the industry standard "bass trap" is made from this material. In order to remove bass reflections you are forced to eat up the mid and upper frequency content to an even larger extent. Wouldn't it be more appropriate to use a material that absorbs mostly low frequency energy?

In my studio my interest is mainly removing bass reverberation hence my interest in glass:

 

Last edited: Jan 4, 2017

People break glass for luck every day. Why should today be any different?

I think you have stumbled onto something mind blowing. If the glass were textured with other shaped pieces of colored glass, built upon thoughtfully to create beautiful art that would also make it act as a diffuser, well then, that would make it especially useful and additionally wonderful. It could also be lit from the rear to lend us another aspects of of it's intelligent, sensuous, formless beingness. We could watch the bass waves to be absorbed once again into the void, rediscover their state of lightness of being, bound within the rules of physical nature and their cyclic sonic karma. Glass dharma, it's a beautiful thing.

 

@lukeallison
I considered not answering this, to be true i didn't like your ironic response to magnaproxy. You asked something, you got an answer. It may not have been the most polite but it wasn't rude as well. I will let go of this though and focus on the matter at hand. A large pane of plate glass means a piece of glass that is at least 4-5 square mtrs big and about 3-4 cm thick. This alone should weigh about 50 kilos if not more. "Contraptions" this big, could theoretically serve as a bass trap in a huge theater (not in real life anyway) but i don't think it can do anything but bring trouble in a typical control room. First of all it doesn't just absorb bass, as the figure you posted shows its a semi-broadband absorbing material. Placing a piece of this size in the room should literally take up the space of half a wall depending on the size of your room of course. And then its the frequency response. How will you gain back the mids and highs lost when putting such a huge glass piece in your room? And even if you were able to cover this with some fabric, the glass is still there and will apply its character onto your room. And as correctly magnaproxy pointed out but didn't take the time to justify, there are 2+ whole octaves of bass under 125hz. Unless you are planning to monitor with the latest Logitech desktop of 30 euros worth or so, any decent pair of monitors will at least output about one more octave below 125hz, with a falling roll off curve of course depending how good the monitors are. Cheap KRK Rokit 6's go as low as about 40-38 hz. That is almost 1.5 octaves under 125hz. http://www.pagemac.com/_media/projects/speakers/krk-r6.png
So to sum it, plate glass is inefficient when used a bass trap because the material needed for the task, exhibits a broadband absorption character, its too heavy and big and still will not do the job efficiently as there are two octaves of bass it WON'T absorb.
Imho, do yourself a favor and built your own bass traps from wood (ecological alright) after some reading and based on designs like this for wall bass traps: http://www.dhaudioandhometheater.com/wp-content/uploads/2016/10/RearWallBehindLoveseat.jpg
And for corner bass traps read this guide http://arqen.com/bass-traps-101/placement-guide/
i hope it will prove helpful depending always you understand what you read

 

Just looking at the numbers they're not that good.

Here's my 3" Rockwool panel for comparison.

125 Hz = 0.52
250 Hz = 0.96
500 Hz = 1.18
1000 Hz = 1.07
2000 Hz = 1.05
4000 Hz = 1.05

And remember thats a 3" panel, not even a bass trap.

I can't remember exactly why (I think it has something to do with how the test is conducted) where coefficients can actually be greater than 1.

 

Thank you for your response, you essentially went into the detail that I would have expected from Magnaproxy given how strongly he opposed my ideas. I'll admit I am triggered when forum members shut down others ideas without any justification. It seems to kill discussions or lead them massively off topic. I really think he got the response his message warranted when you compare it to the constructive criticisms given from everyone else I've talked to on this topic.

Also, I think you misunderstood what was said in regards to absorbing sounds below 125Hz. I was arguing that I never anticipated ignoring this frequency band in response to Magnaproxy telling me that "the frequency never goes below 125Hz". Your opinion is the same as mine and opposes his. The fact that the particular test I posted didn't factor in sounds below 125Hz doesn't mean the material can't absorb sounds below this range. If you observe the increasing effectiveness towards the lower frequency you could safely assume that it is as effective or not more effective in the sub-125Hz range.

You mentioned that glass is a semi-broadband material. I agree but my original point was that the absorption coefficient drastically rolls off as the frequency increased. Compare this to rock wool/ mineral wool/ fibre glass, which all have a higher absorption coefficient as the frequency increases. With this in mind, why would glass absorb more mid-high frequency energy than these materials?

I see you've given dimensions for a glass panel. Obviously if you are correct this ends the debate. How have you calculated this size?

 

Thanks for weighing in on the discussion. You might not be doing a 1-1 comparison with the values you posted. The website I linked includes the absorption coefficients for rockwool so it would make more sense to use those figures for comparison. Notice how the absorption coefficient for rockwool increases as the frequency increases? Then notice how the opposite is true for glass. This is why I'm fascinated by the idea of using glass as a bass absorbing materia. It appears to be targeted at the lower range.

 

That was a spiritual journey! Thank you.

 

@lukeallison Let me just start with saying that proper bass traps are put in a (control) room not to absorb the bass per se but to stop it from reverberating. That's why depending on the case you typically go for either the corner bass traps or the asymmetric panels or a combination of both. For the corner traps its the elimination of the narrow corner vs the material used that does the job. But mainly it's the "loss" of the corner shape that does it. For the asymmetric panels its first the shape that does the job,and second the material it's made of. Anyway you look at it plywood has a property of 0.2 @125hz which is slightly better than plate glass and its also lighter. Add to this that constructing an asymmetric panel from plate glass ranges from adventurous to nearly crazy and you have your answer.
Just for info a 10cm fiberglass panel board has a property of 0.9, 0.99, 0.99 @125,500 & 4khz respectively.
When you have a soundproof room mainly all you need to do, is tame the static frequencies and the occasional bass reverberation. But to know which method to follow (even your plate glass theoretically) you have to first build a soundproof room, then do some accurate measuring which will reveal what kind of internal treatment the room needs. Even experienced architects make errors in designing rooms because they do not include in their design the calculations for the subjective hearing experience of loudness variation and the loss of intelligibility/ear annoyance caused by echo/reverberation. For example the Opera of Sydney, one of the most recognizable buildings in modern architecture has to be the worst building for live music ever. Although magnificent to the eye ,its shape is the worse possible for sound/music recreation.
Keep in mind that the various material acoustical absorption properties do not extend below 100 hz. Very few industry made materials can do this, and they 're made specifically for this which means are quite expensive. I was shown a material when i was designing my studio (its the 6th i make, the first fully designed by me) ,that looked like a cross between elastic and foam, it had a 0.85 property @ 20-20khz broadband at 1 cm thickness. The price was 170 euros per square meter. If i can find the brochure i will post it. This was 9 years ago. Needless to say i passed hehe.The cheapest material i can think of that can go as low as we hear is thick fiberglass but its nature and price present certain design difficulties plus the material has to be physically covered so its not harmful to health.
Oh how did i calculate the size of the theoretical plate glass? I did not really. I just looked at my living room huge round table which is covered with what is known as "a large pane of plate glass" . Cheers

 

"Ordinary window glass".