At 3:09 PM -0500 1/14/07, Walter Knapp wrote:
>Posted by: "Rob Danielson"
>
>> Hi Klas--
>> A floating wooden or metal stud wall booth with an exterior made of 2
>> layers of 5/8" drywall and 8-12" of fiberglass batting on the inside
>> can drop the ambient level 40dB, maybe 45-46dB. I made the interior
>> walls by jamb-fitting homesote sound paneling. Two layers of carpet
>> on the floor. The biggest challenge/expense is the entrance door and
>> seal. I added another seal to an 2.5" solid door and it was almost as
>> quiet as the walls. Two 2" doors in one thick jamb would be better. I
>> floated the 800 lb structure on four rubber closet (toilet) washers.
>> Every joint and seam must be caulked. Ventilation is a bit of a pain,
>> but that can be done cheaply too. Rob D.
>
>Did you measure it's sound reduction abilities or was this a estimate?
>
>When I did hearing tests in the army, the one person soundproof chambers
>we had could do twice that drop at least. I never got any look at their
>internal wall construction but it was much thinner than your design. The
>doors were built kind of like walk in freezer doors. We were testing
>hearing down to -10dBA levels in multiple frequencies. At the time my
>hearing went down to those low levels easily, those chambers were
>absolutely silent when inside, even with lots of loud noise outside.
I obtained the attenuation range by recording inside (with my body
between the door and the mics) and outside by the door and comparing
the files.
The low frequencies are the rub. I could stand in the booth 150 yards
from a city blvd and hear nothing but a faint, very low (>50Hz)
presence coming from the direction of the street and from the floor.
A telling moment came when a bus passed and I found that not only
could I tell it was a bus, but that I could "point" to it as it
passed. (So much for low frequencies not playing a role in source
localization).
What kind of structure could absorb that much low Hz energy? I've
only built three projects with sound abatement priorities, but my
guess is that it should be almost free of ground transmission and
require a LOT of mass on all sides. If there's a way to do it without
mass/material, I'd love to know more about it. Of course, if the
chamber is constructed in a remote location away from local traffic
and one can work between commercial jet fly-overs, -40 from 40 =3D 0.
>
>As I've noted there is plenty of published stuff on building these
>things. The construction is not all that exotic and one does not have to
>reinvent how to do it.
Yes, and with commonly available materials except for extremely quiet
ventilation. Understandably, many of the web resources for designs
are produced by building industry manufacturers and well known tests.
Its worthwhile web research to do if not to observe how valued "quiet
living spaces" are becoming. I considered some new, promising
products/solutions like, "QuietRock" but it proved to be too costly
even for a one person booth. Rob D.
>
>Walt
>
--
Rob Danielson
Peck School of the Arts
University of Wisconsin-Milwaukee
http://www.uwm.edu/~type/audio-art-tech-gallery/
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