For example, I was asked to install sound into an O-scale F3A.
The top of the shell had a lot of fan grille openings, but the
space below them was a long rectangle. To maximize the
sound, I used the array shown in (4). A total of 4 (27 mm diam-
eter round high-bass) speakers were assembled onto a sheet of
thick (0.08 to 0.10" thick) black plastic. This was sealed to the
roof of the locomotive so that the sound would be forced out
the top of the loco and the negative pressure (see my August
2012 column
if you
don’t understand the term) gets routed through the loco and
out the openings for the trucks.
Similarly, I had room for two 16 x 35 mm rectangular speakers in
an Athearn Genesis SD75M HO-scale locomotive, as shown in (5).
Okay, once you decide on what sort of acoustic baffling you are
going to use and what size speakers will fit, it is time for the
electronic side of the design.
DCC Impulses Column - 4
shrink tubing inside the decoder wrap. That makes one side of
the decoder flat. This flat side (right side in 3) is held down to
the brass plate (2) with thermally conductive epoxy. The heat is
conducted from the decoder into the brass plate and into the
frame of the locomotive. The heat that is conducted away in
this fashion will help keep the decoder cool.
With that technical stuff aside, let’s get started planning an
installation.
What will physically fit?
Sometimes things just work out. When you open up a loco to
put sound into it, you find a pre-made opening for a standard
size speaker (or two) and you are good to go. But that's not
always the way.
When converting older locomotives, frequently the installer is
left with the task of designing the acoustics as well as the nor-
mal issues of an installation.
5: Two 16 x 35 mm speakers in an HO scale Athearn Gen-
esis SD75M.
5
MRH-Jan 2014
