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Re: GSBN: Bales and sound suppression

Very interesting information.  The main question we are dealing with at
this time is how effectively do sound walls constructed with bales of hay,
straw, alfalfa, etc. dampen noise generated during construction activities.
Will a hay bale wall reduce the noise 5 d(B)A, 10, 15.  The human ear has
trouble noticing a change of 3d(B)A.  We are looking for the noise
information to reduce construction noise on adjacent sensitive species
habitat.  the bales are natural products that can be reused after they
function as noise attenuators.

Thanks for the info.

John DiGregoria
Fish and Wildlife Biologist
Carlsbad Fish and Wildlife Office
6010 Hidden Valley Road
Carlsbad, California 92009
760 431-9440
fax  431-5902

                      builder.com              To:       bainbrid@...,  John_DiGregoria@...
                      08/04/03 01:43 PM        Subject:  Re: GSBN: Bales and sound suppression             

At 11:32 AM -0700 8/4/03, bainbridge wrote:
>Can anyone help?
>>Subject: Hay bales
>>To: bainbridge bainbrid@...
>>From: John_DiGregoria@...
>>During your work with hay bales as building structures, did you come
>>or conduct any research regarding how hay bale walls will attenuate
>>We often require project proponents to construct noise attentuation
>>structures to reduce noise impacts to sensitive wildlife and are looking
>>for some research regarding straw bales.
>>John DiGregoria
>>Fish and Wildlife Biologist

Below is a sampling of a thread on STC (sound transmission
coefficient) on the GSBN discussion list from around 10/02 (To see
the archives, go to http://groups.yahoo.com/group/GSBN-Greenbuilder/
and sign in as user = gsbn123 and password = bale123 .)

In 2001, Matts M yhrman (MattsMyhrman@aol.com)  helped Lars Keller
(lars.keller@mail.tele.dk) clean up an English-language version of a
summary of some testing to determine the "airsound insulation" of
straw-bale walls.  They concluded that the walls tested had an
airsound insulation value,"R'' w" (the w is actually a subscript), of
about 54 dB.  Lars should be able to tell us all how to access this

Rob Tom (rw_tom@hotmail.com) wrote:

I don't think that it would be unreasonable to suggest ... that the
STC rating would be in excess of STC 61;  the rating for which a 6"
CMU wall with batt-insulated/drywall-faced, 3.5" steel studs on *one*
face, is listed as being, for the purposes of the Ontario Building

Katie's suggestion wouldn't be unreasonable given that the faces of
the CMU consist of approx. the same thickness & material that
comprise the skins of a plastered SB wall, and 18 to 24 inches of
straw should provide at least the same acoustic isolation as 3.5" of
fiberglass insulation.

If a plastered SB wall were subjected to testing, I  wouldn't be at
all surprised if the actual STC rating were in excess of STC 70.

From: Rene Dalmeijer rened@...

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
Bill Christensen

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