[Angelo Campanella]

Tony wrote:
Angelo Campanella wrote:

1- The effectiveness in noise isolation strongly depends on the minimum
spacing rather than the maximum spacing in that wedged space. Hence, if
one wants maximum sound attenuation, one spaces the glass surfaces as
far apart as possible.


What's the theoretical basis for that Angelo?
I have always assumed it was
the average spacing that mattered.

Consider a window split down the middle or two windows side by side.
One half has a TL of 50 dB, the other half has a TL of 40 dB. What is
the resulting average TL? It would be 43 dB, closer to the 40 dB half
that to the 50 dB half. The definition of "Average" matters. If you
simply average numerals, you get 45 dB.

You might average sound power expressed in watts. Maybe one-half
picowatt goes through the 50 dB part, while 5 picowatts goes through the
40 dB part, the sum being 5.5 picowatts, nearer the 40 dB window part
than to the 50 dB window part.

I agree that tilting panes is not effective for improving isolation and is
often counter-productive for reducing light reflections, but it is sometimes
necessary in a low RT room for stopping a flutter echo.

I am only addressing sound transmission. Introducing flutter echoes is
a problem of a third kind. To effectively reduce flutter echoes, tilt
the whole wall. If that's not feasible (e.g. an existing room in an
existing building), then the choice becomes which side pane is more
readily tilted outward. Top? Bottom? Room lamp locations must be
considered. Think it out. That's what you are paid to do. Pane-tilting
on either the vertical or horizontal axis will suit for reducing flutter
echoes.

Of course, in
practice increasing the average spacing and increasing the minimum spacing
will often come to the same thing because one will optimise performance for
an overall window thickness by making the panes parallel. But on the
occasions when a tilted pane is required for whatever reason, your
philosophy will lead to a bigger spacing, or the need for thicker glass for
the same spacing, than mine.

The designer is obliged to pick a method and to defend that choice in
any way they please. I am only addressing accurately the sound isolation
feature of a window.

Ang. C.