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expandable and responsive sound proofing?
Old 20th March 2008
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expandable and responsive sound proofing?

hello all - my first post on this forum

ive been looking around a bit into room acoustics and soundproofing as im an architecture student currently designing a music academy. the site is by a busy road and the building facade (the one facing the road - which will deal with the traffic noise) is currently projected to be responsive - that is, the facade alters according to the ambient acoustic environment as well as the internal sound generated. thats the fun part - the difficult bit is trying to get this to work.

so far - i've been thinking along the lines of an inflatable/expandable cell with some sort of translucent/clear sound barrier on either side. the facade would be a sandwich of MLV > Expandable Air Cavity> MLV again on the other side.

my question is whether this idea is a) completely ridiculous in terms of its effectiveness at absorbing traffic noise (i know low frequency rumble is a problem) but also whether increasing the air cavity by inflating the cell has any impact on sound proofing - ie. does a bigger air cavity equal a reduction in sound transmission?

ive also looked around for other types of "expandable" sound insulation - but havent really had much luck - im not sure if this concept will hold yet.

im willing to sketch/scan/upload basic facade sections if anyone's interested in seeing them.
Old 20th March 2008
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avare's Avatar

Im intrigued. Why responsive?

I am Curious,
Old 21st March 2008
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the idea is that the building acts as a sort of instrument - it projects the sound being generated inside the building via the facade - i.e. it translates the sound being generated inside into a visual language that motorists driving past can see/relate to

that is one aspect

then - the building/the facade, reacts to ambient noise generated by the busy road and "tunes" itself by increasing/decreasing the distance from the facade to the road (not huge distances - but nevertheless a visual and perceptible reconfiguration) depending on the demand from inside the building for quiet/studio space - and the conditions outside

so you see, the building becomes a tuning instrument relative to the community and visitors through the area, constantly adjusting due to changing circumstances and displaying this change overtly for all to see

ultimately i think the idea is that the facade should be able to dictate what happens inside the building - the "tuning instrument" seems a nice metaphor to carry this idea forward

i guess i am also interested in responsive architecture - architecture that can communicate to people on its exterior - but which can be controlled internally/ architecture as the expression of desire/intent on the part of the user and not the architect.

im only in third year of studying architecture so ive still got a way to go - but i hope this answers your query

do you think that a potentially responsive soundproof is a ridiculous idea?
Old 21st March 2008
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avare's Avatar

I understand now. Aesthetics, for lack of a better word.

Effective sound isolation requires mass. The cheapest way this is achieved in new structures is through the use of concrete. Poured, block, what ever. To have the sound isolation change with environment would be VERY expensive. I suggest using a permanent facade with the required sound transmission loos and then using electro-acoustics for the sound component.

What a great concept! Please keep us up to date on how it progresses. If you don't want to post here, could at provide a link to where you will provide updates?

Old 21st March 2008
Here for the gear

thanks for the encouragement (at least in the concept!)

by electro acoustic - do you mean some sort of active noise cancellation device

ive heard that active noise cancellation potentially works well for low frequencies in a 3dimensional environment (not so much for higher frequencies) but if a combination of inflatable sound proofing and active noise cancellation were employed - then this may provide basis for a more in depth analysis? or not...?

one idea bandied around is that the facade becomes the active noise canceller - the speaker - emitting reverse waves of whatever's coming at it

in effect the facade could be a metal sheet attached to a driver (something to make it oscillate) in response to the frequencies of the traffic

the idea here is that the low frequency rumble would hit the metal and be cancelled before it even got into the room your opinion is this even a feasible concept?

ideally i'd like to avoid a heavy concrete wall as much as possible

one element i did not mention however, is that the building will be raised off the ground by about 3 metres for visibility - currently there exists a heavy concrete wall (about 3 metres high) between the traffic and the site (the site is also about 1m lower than the road level)

i think this concrete wall is probably blocking out some of the noise coming to the site - but i also have the option of moving the building further away from the road if necessary since the site is rather large and i am only building on a tiny part of it right next to the road

the reason i have chosen to locate the building right next to the road (despite all the obvious issues regarding sound) is explained above - and id much rather work a way around the problem than just move the building back (although i do accept this may be ultimately necessary)

still - its all theoretical at the moment (not like it will ever get built)

i hope to build a website over the summer and display this project and some others - i'll provide the link for that once its done - but you can catch me posting on Dissensus (ive already put this question to some people there)

thanks for the feedback - its very encouraging and insightful to get other opinions - especially since i dont really know any sound engineers and im getting a rather sharp crash course in acoustics!
Old 22nd March 2008
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avare's Avatar

Great response and thanks for the link.

It is difficult to quote your response, so I will try and reply as best I can.

ideally i'd like to avoid a heavy concrete wall as much as possible
Understood. Unfortunately physics doesn't change. For effective sound isolation mass and space are used to achieve it. You need one or other or usually both. As economics work out, it is cheaper to have a heavy wall, as opposed to a thicker wall. The difference becomes quite apparent when doing life cycle analysis and the cost of empty air in walls and just the difference in taxes.

by electro acoustic - do you mean some sort of active noise cancellation device
No. I meant for reproducing outside what is desired to be heard outside.

Active noise cancellation is very expensive to implement effectively. It is used in aircraft where weight is a premium, etc.

I have not been to the linked site yet. Keep the communication going. It is an amazing concept!

Old 22nd March 2008
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ok - im getting the response from all angles that mass is what you need really to effectively block out sound

well - concrete is a fairly dense material - but is it used simply because of cost effectiveness - ie - could you get similar results from a different material which had a similar density - would a dense glass wall provide similar levels of sound attenuation to concrete?

concrete typically has a density of around 2300kg/metre cubed (Density of Concrete)

glass (at the higher end) has the potential to be very dense indeed - up to 8000kg/metre cubed (when lead is introduced)
(Density of Glass)

so am i right in thinking that there is a possibility of creating a glass wall which, because of its inherent density - would have similar, if not better, sound attenuation properties than a concrete wall?

though this line of thought isnt really getting me anywhere with the expandable idea...

i think my next physical step in this project will be to return to the site and actually measure the sound levels at different times of day and at varying distances from the road to see if the traffic noise is really that bad.
Old 22nd March 2008
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avare's Avatar

Yes you can use glass, or anything else that provides mass. I'm glad to read that you are thinking outside the box, so to speak.

The brainstorming is great.

Yes, sound survey is required.

Old 23rd March 2008
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ive been digging around an old acoustics book and i think ive come up with a workable solution (at least in theory)

traffic noise - in its low frequency form is mostly inaudible and is usually felt through vibrations. in this case - mass wont do anything to stop the rumbling and decoupling of the structure is what's needed.
outlne of impact sound transmission re traffic noise

proof that the mass law must be taken into account with coupled walls and slabs - or the results become innacurate

in that book it also goes on to say that the air cavity in a cavity wall should ideally be as large as possible in order to achieve maximum attenuation
so - my suggestion is to decouple the rooms requiring isolation from the supporting structure to reduce traffic impact sound transmission (either on fluid dampers as mentioned above, or on some sort of rubber or springs)
this then combined with the expandable sound isolation system (which should sort out higher and mid range frequencies by a mass loaded vinyl > expandable air cavity > mass loaded vinyl sandwich) would seem to deal with the vast majority of sound being generated.
just to clarify - this isnt a spec for a top notch recording facility, just a music production studio, and as such it doesnt need to completely sound tight.

ive also had an idea regarding an adjustable volume setting for the room. if the room was made to contract (the roof would descend powered by an inflatable air pocket) this would alter the acoustics of the room, making the sound generated inside seem louder and in effect cancelling some of the outside noise that still gets through whilst at the same time also increasing the sound proofing of the roof level.

the problems with this to me so far seem to be;
a) mass loaded vinyl (based on my crude calculations and best information on the internet) seems to be only available at about a sixth of the density of conrete. if concrete is 2300kg/metre cubed, mlv is only about 330kg/metre cubed - im not sure if its possible to get a denser vinyl system - currently this is what im counting on
b)air in the air cavity might not be the best sound attenuator - from this table here

fog and smoke both attenuate sound better than air - (with air's optimum humidity for attenuation being about 0.3-0.4%)
im wondering if there's denser gases (which are stable) that could be used to inflate the expandable system and so provide a better level of attenuation - any suggestions? (coloured gases could also be quite nice - aesthetically speaking)

this is more or less where im at - at the moment
i think the next step will be an actual sound survey of the site (deptford creek) so here's hoping i can blag a sound meter off uni - to see whether the traffic is actually that bad - i also have some scope of re-siting the building further away from the road.
thanks for all your suggestions so far
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