Large speaker systems in diesel B-units
One of the best-sounding installation designs involves putting
speakers in a B‐unit. Here are two versions: one baffled and
one using an enclosure. Both have amazing sound. In both
cases, dual speakers were used. Check out my January 2014
column
for wiring methods. The connection to the
decoder in the A‐unit is through a 2‐pin connector.
First, let’s look at a design for a Stewart FT A‐B pair, shown in
[9] and [10]. The FT is a fine loco pair to do this with, as most
of them were drawbar-connected A‐B units.
The weight was milled or sanded flat between the trucks. The
weight and fuel tank plastic between the motor mount holes
was cut away [10]. If one had a mill, even more material could be
removed, but just cutting between the motor mounting holes is
enough. The fuel tank decoration was attached with caulk. Two
speakers were stuck down to a piece of styrene. Two vertical baffle
boards were fashioned out of thick (0.06 inch or thicker) styrene.
The baffle boards run wall-to-wall inside the shell and to the
ceiling on the sides. The gap created between the top of the
(straight) plastic and the (curved) ceiling allows back pressure to
find its way out through the truck openings.
A Westside Alco PB unit was similar. However, the design didn’t
lend itself to baffling, so I created an enclosure with styrene
vertical bulkheads attached with caulk. I made sure that the
area between the bulkheads [11] was sealed on both the shell
and the floor.
There you have my most frequent methods of installing speakers
in HO‐scale diesels. For more food for thought, including exam-
ples in other scales, check out my website,
In my August column I’ll show you some quick methods for cut-
ting and fitting these baffles and enclosures.
9. Stewart FT B with two baffled 28 x 35 mm speakers.
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10. Stewart FT B fuel tank opening to allow the sound out.
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DCC Impulses Column - 9
MRH-Jul 2014
