Jeff Liebermann wrote on 11/17/2017 1:47 PM:
On Thu, 16 Nov 2017 04:29:12 -0800 (PST), Phil Allison
wrote:

** By all accounts, bouncing a IR laser off a widow is not
practical. The beam has to be precisely aligned *square on*
to the window and the resulting sound quality is abysmal.

This might help:
"Laser Bounce Listening Device"
http://gbppr.dyndns.org/~gbpprorg/mil/laserl/index.html
See Fig 9 and associated text, which discusses the angles of incidence
and reflection.

In my never humble opinion, there are several reasons why it is better
to use a laser source and detector at the same location.
1. Any common mode vibration of the laser and detector mounting would
cancel if they are mounted on a common surface.

I believe you have that wrong. If the laser and detector vibrate the same
in the direction toward/away from the reflector, the vibrations add, not
subtract.

--

Rick C

Viewed the eclipse at Wintercrest Farms,
on the centerline of totality since 1998