Glass walls
On Apr 8, 1:39=A0pm, Robert Peirce wrote:
I am contemplating buying a house with a screened in back porch I want
to close off for an office and music room. =A0My wife wants to replace th=
e
screens with windows. =A0That will leave me with mostly windows on three
sides and Hardiplank, a cement based exterior clapboard siding, on the
fourth.
What kind of problems am I going to have? =A0My current room is
double-layered 5/8" wall board on 12" studs. =A0It is pretty solid. =A0It=
is
also tapered to reduce any standing wave problems. =A0This room is all ne=
w
to me and I'm not sure what I am getting into.
My Goodness!
OK - a few basics of acoustics - and really these are basic!
Glass is a highly reflective material at all frequencies. With that in
mind, how it performs at very specific frequencies will be based on
how it is assembled. Large sheets of thick glass with no dimension
less than 24" (62cm) will resonate below most audible frequencies.
Dimensions less than that will resonate at higher frequencies. So, the
larger the dimension, the lower the resonant frequency. Unless the
glass resonates, it will reflect. This is true of any other hard
surface including GWB (gypsum wall board AKA Drywall), plaster, wood,
concrete, and similar.
Bass response (as perceived) is a combination of many things, salient
of which are woofer placement relative to the nearest flat, hard
surface, and the amount of air they move - directly related to the
size of the woofer, the signal fed into it, the power behind that
signal - the amount of headroom available. Placing the woofer centers
less than a diameter from a hard surface will (all other things being
equal) enhance bass response. Placing a woofer against a wall will
enhance bass response. Placing woofers on a long wall asymetrically
(as compared to a short wall) in a room will enhance bass response.
Placing woofers in corners will enhance bass response. Sometimes small
changes in placement can have huge effects.
I keep three essentially different types of speakers: Maggies (MG-
IIIs), AR3as and ARM5s. All others are variants on that theme. I have
listening rooms that are 17 x 28 x 10 feet (maggies), 17 x 14 x 10
feet (AR3a) and 14 x 12 x 9 (M5s). The maggies are fed from an HK
Citation 16. The 3as by an AR Model W receiver. The M5s by an AR
amplifier (US version). All of them are quite capable of getting to
near-ear-bleed volumes without strain. All of them are capable of
vibrating the floor quite nicely.
All of the rooms are very 'live' by any standard with hardwood floors,
lots of windows (the library (biggest room) has three full-glass
French doors to the exterior, and one French door to the inside. There
is a large brick fireplace, and the walls are 120 year old plaster.
The other rooms are smaller variations of the same elements. Lots of
glass, lots of hard surfaces.
I have had to struggle with speaker placement (and an extremely
tolerant wife) to get the speakers in the ideal position for sound-
stage, bass and so forth. Bless the woman who will decorate "around"
these needs. As to the AR3as, a difference of less than 6" (15mm) in
distance between/distance to corner was the difference between bone-
rattling bass and very even bass.
It can be done. Typically without equalizers, without 'sound tubes'
and without heroics or major costs - just experiment. Glass is no
worse than any other material once the essential nature of it is
understood. And, for the record, it is much better in so many ways
than soft surfaces.
And I have not even gone into resonances based on room shape. This is
why asymmetrical placement is often critical. There may be no standing
waves in the room itself, but the speakers may be cancelling each
other. Try it.
Back to lurking.
Peter Wieck
Melrose Park, PA
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