[Strawbale] Sound insulation with regards to a recording studio

[paul sheraton]

Hi Walter

I can only offer you my perspective as I understand it. Im currently 
designing a straw bale sound recording studio/center though it differs from 
your project in that it is new build and will be in the countryside.

My apologies in advance if I am saying anything you already know, these are 
just my thoughts on the matter.

>From what I can see, depending on the complexity of the project and what is 
trying to be achieved, straw bales can go a long way to treating certain 
aspects of accoustic design. However accoustic treatment is very complex and 
for the level of sound control required for recording studios I feel that  
straw bales by themselves might not be enough. 55 bd is good but not a huge 
amount.

Bass sounds are the most difficult frequencies to control, the ususal 
approach being high density materials along side techniques to isolate 
structural elements so as to reduce resonances and transfer of vibrations 
through the building. Plasterboad doubled or tripled up is considered a good 
material for reducing low frequency noise transmittence, or a thin lead 
sheet like material sandwiched between two sheets of plasterboard. Behind or 
on top  this would normaly go some kind of foam material to help absorb and 
disperse higher frequency sounds, bearing in mind that most materials absorb 
HF noise anyway.

While bales are a good material for absorbing mid to high frequency sounds, 
I feel they dont have the density to cover the lower frequencies. Prehaps if 
larger sized jumbo bales were used to increase mass but this isnt really an 
option for refurbishments.

Maybe the bales can be coated with a thick dense plaster to absorb the bass 
sounds, but care needs to be made that the plaster and bales are isolated 
from the structure, including roof and floor etc.

The angles of the walls is also very important, you dont want to have 
parallel walls setting up standing waves,  and  avoiding wall sizes which 
are multiples of themselves is also important. (you probably already know 
this but I include it for anyone interested)

The approach that I am taking is to build a timber framed straw bale 
structure and then create suspended floors, walls and ceilings inside. Wood 
as a covering for walls,floor and ceiling gives good colouration to the 
performing and recording enviroment though again it depends on what type of 
sound you are trying to create.

Just an idea but If you are thinking about building bale walls inside an 
existing structure Im wondering if it might be possible to create a "bass 
trap" by leaving a cavity between the existing and new structure. the bass 
sound would pass through the bales into the void and if that side of the 
bales were left unplastered the bass noise would bounce off of the existing 
structure and back onto the bale to be absorbed. To stop the bass noise 
passing out through the existing structure it might be necissary to line it 
with plywood on battens so that it is the ply that resonates and bounces the 
bass back and not the existing wall. Lifting the straw bales walls of off 
the floor would be a great help along with a  suspended floor inside the  
studio isolated from the walls and probably a suspended ceiling.


Good luck, keep the forum upto date with how it goes.

Paul Sheraton



>From: "Walter Faas" <w.faas at student....nl>
>Reply-To: European strawbale building discussions 
><strawbale at amper....muni.cz>
>To: strawbale at amper....muni.cz
>Subject: [Strawbale] Sound insulation with regards to a recording studio
>Date: Thu, 23 Mar 2006 12:47:23 +0100
>
>Dear balers,
>
>It has been quite a long time since I last posted something
>on this mailinglist. I have been working hard on my study
>and didn't manage to keep up with recent developments
>(which are undoubtly taking place even while writing
>this!).
>
>Currently I'm working at an architect agency. In one of our
>projects we have to design a recording studio in an
>existing building (1920's). Given the fact that the
>  recording can produce up to 100 decibel and there will be
>a school nearby, we need to focus heavily on sound
>insulation. At the moment I'm doing some research on
>suitable materials and I just cannot resist seriously
>looking into strawbales.
>
>While travelling through time I found myself reading some
>posts from june 2004 which contained information about the
>soundinsulation of strawbales. I found that the typical
>Rw-value of a strawbale construction according to ISO 140-3
>was about 55 dB(A). This was a normal 2-string bale with
>35/25mm plaster applied. To pass for a building permit we
>must get a Rw-value of about <57 dB(A). This minimum
>standard probably won't be sufficient to achieve a
>comfortable area around the studio. We're striving for
>about 65 dB(A) at the moment.
>
>Does anybody have data about soundinsulation and/or has
>pointers about the true limit of pure strawbale building
>(just straw and plaster, that is. No fancy and expensive
>acoustic materials applied) ? I'm looking for insulation of
>the low-range frequencies since these are hardest to
>insulate. I know of the soundstudio in Germany. Is there
>any information about that project somewhere (I can't seem
>to find more than pretty pictures)?
>
>Kind regards,
>
>
>
>Walter Faas
>
>
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