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Re: GSBN:Re: STC of Straw bales


I suppose you also read John Glassfords mail with ale in hand and decibel meter in other. Although his measuremnts seem crude he did very well by taking note of ambient sound levels. I expect a reasonably executed SB wall without acoustic defects like the ones described by Andre will perform in the region of 60dB and upwards.

The fact that SB walls are a poor sound insulator is a vicious rumor. I presume that Arnoud Cauwel is a promoter of pisee and other earth techniques. Heavy mass like a meter of concrete are necessary for very low frequencies ie <60 Hz above this most simple building structures, even quite light ones, can dampen sound quite effectively if executed properly. It is even possible to reach -60dB damping with a few not too thick panes of glass (like in sound studios).

Besides mass stiffness and de-coupling are very important for acoustic sound insulation. The relatively low stiffness of a SB wall with earthen plaster are ideal. The fact that the cavity between the two outer stucco shells is filled with straw is excellent acoustic damping. Beware to be careful and fill all cavities and voids with straw clay, avoid any direct mechanical contacts between inner and outer shells, these will seriously degrade sound damping performance. Contrary to what you would expect loosely packed bales will perform better then very tightly packed (rice is ideal). Pay a lot of attention to all openings and edges these are the weak points. An air leak of only a 1mm^2 will seriously degrade performance. Door openings and windows are literally acoustic holes in the wall these need special detailing and attention to even remotely approach the performance of the walls. Doors even double ones have a poor performance. The gaskets and seals in the doors should be double or even triple but even then there is the problem that over time the seals will degrade and leaks will occur. The type of doors you are aiming for is more like a steel watertight door in a ship then a house door with multiple closing bolts and tightening clamps.

In conclusion I would like to add due to the nature of a SB wall (homogenic continuous surface) the wall is not the problem but the connections between the wall and all other structures incorporated or surrounding it. I strongly suspect that most sound insulation tests executed on SB walls are measuring the defects of other structural components or mistakes in the test procedure (a non calibrated sound source, Background noise etc.)

Andre regarding room acoustics. Here are some simple rules of thumb depending on the type of acoustics you want ie very lively to very well damped. Soft acoustic instruments require a live room. Loud amplified sound a dead room. The single most important parameter is the reverberation time and level. The harder the surfaces the livelier the sound. A bathroom is lively hence your drive to sing even if you can't. The opposite is standing on top of snow bound hillock. The bigger and harder the room the longer the reverberation time ie a cathedral. Next the relative dimensions. An oblong box (like Concertgebouw Amsterdam) approaches the ideal. Preferably the dimensions relate to each other approximately in the following manner 2-3-5 (I don't have the exact figures at hand at the moment but this ratio will avoid predominant harmonic resonances and standing waves) the exact ratios depend on the size and acoustic reflectiveness. I personally prefer rooms without parallel surfaces thus avoiding standing waves. I think if you build a room with clay stucco and wooden flooring and a well pitched ceiling you will have quite acceptable acoustics for acoustic performances. If its too live you can always add some damping afterwards

At 10:47 AM 10/16/02, you wrote:

In France there is a vicous rumour going arround that SB walls are a poor
sound insulator. Arnaud Cauwel wrote a report for his school of architecture
in which he claimed that straw (because of its low mass) insulates poorly.
No numbers or test data is given.

Lars informed me on the Danish sound test some while ago, and specifficly
stated that I cannot quote him since the info is not official yet.
However I think it is safe to say that the result of the test was probably
greatly influenced by the post and beam structure and that the results were
not very impressive (for as far as I can understand them :-) 'cause the
universe of sound is complex thing. I feel that a beam (to carry the floor
for instance) that goes through the inside plaster and sits on the ring beam
would probably give a great transmission of sound to the outside plaster
just next to the ring beam, circumventing the 90% of the SB wall.

And than there is the question of indoor accoustics. Friends of us want to
build a SB Art & concert hall, so they are also concerned about how the
sound will be for the audience and what we can do to enhance that quality
with the shape and surface of the walls.  Any hints?


----- Original Message -----
From: Rene Dalmeijer rened@...
Cc: J.J.de.Groot@...; Rob Kaptein ramstrobouw@...
Sent: Tuesday, October 15, 2002 11:01 PM
Subject: Re: GSBN:Re: STC of Straw bales

> Bruce, Tom
> There is a chance that we will be doing a test here regarding the SB
> acoustic insulation value. The test if executed will be in a test
> at the Eindhoven University normally used to test window frames so I
> that the measured values will till how well the test facilty functions. I
> am sure that a properly executed SB wall has excellent sound insulation
> properties far exceeding normal brick walls. What are STC numbers? We
> use this qualification here. BTW the test will incorporate a spectral
> distribution.
> At 12:22 AM 10/15/02, you wrote:
> > > I recall there was some discussion of SB sound transmission on the
> > > list some time ago, including anecdotal evidence provided by the
> > > Straw Wolf's rock band or some such.  Anyone have any solid numbers
> > > for Katie?  Failing that, anyone have any good stories to tell? ;-)
> >
> >
> >To my knowledge, no formal tests have been done to provide STC numbers at
> >various sound frequency levels (such as building engineers sometimes
> >We all know they're mighty quiet, and that it's hard to shout through a
> >to someone on the other side, but don't have the exact geek numbers as
> >
> >Or, if someone does, I would very much appreciate learning of it, as the
> >culmination of the EBNet test program aims to be a compilation of ALL
> >testing of ALL sorts done to date - by EBNet or by others.
> Greetings,
> Rene Dalmeijer
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Rene Dalmeijer