SoundTraxx DSD-150/DSX Owners Manual - Manual (Page 7)

Digital Sound Decoder Owner's Manual 7
oped by the front of the speaker is canceled by an opposite pressure behind the speaker. The enclosure isolates the
front and back surfaces of the speaker, thereby increasing the sound pressure and hence, the volume.
Additionally, the enclosure must be sized proportionally to the speaker such that the volume of air enclosed is several
times larger than the speaker diameter. If an enclosure is too small, it will interfere with the speaker operation and
although it cannot be made too large, there is a point of diminishing return. As a rule of thumb, for small speakers, the
minimum for the length, width and height should be equal to the speaker diameter. Thus the smallest enclosure for a
1" speaker would be 1" X 1" X 1", while 2" X 2" X 2" would be the smallest size enclosure for a 2" speaker. As this is
only a general guideline, exceptions can and must be made in many circumstances.
HOWEVER, the use of a proper speaker enclosure cannot be over emphasized and failure to use one
is almost always the cause for poor sound quality.
Fortunately, most steam engines have a tender and with a little work, the tender itself becomes a great speaker
enclosure. The speaker can face up through the coal bunker or down through the floor. Either way will produce
equally good sound.
You will also want to use the largest speaker possible to get the best bass response. Larger diameter speakers can
be trimmed down in width so they will fit within the tender shell. By building an internal baffle, they can also be
mounted at an angle although this will compromise the available space for the DSD module in all but the largest of
tenders.
In small tenders, the speaker should be mounted forward in the coal bunker area, where higher walls are available to
cover the speaker magnet.
For other locomotives, the speaker enclosure need not be fancy and can be fabricated from sheet styrene, bass
wood, and even cardboard in a pinch! A 35mm film canister usually produces excellent results, as does the card-
board tube center of a roll of paper towels.
The Digital Sound Decoder is best suited for installation in the tender, although it will fit in the boiler of larger
locomotives. Boiler installation has the advantage of requiring considerably less wires that have to be routed between
the engine and tender. It will usually come at the expense of some boiler weight and possible reduction in traction.
It is normal for the DSD to get warm after periods of extended operation and its built-in thermal overload protection
will automatically shut down the throttle and audio amplifier if it gets too warm. Therefore, it is important to install the
DSD in a location where it can dissipate the most heat. Avoid placing the DSD near heat sources such as the motor
or lights.
You will also need to decide how you will synchronize the exhaust chuff. The DSD provides two means for synchro-
nization. The first method is to use the mechanical cam which works by opening and closing a switch contact with the
locomotive wheels or axle.
The exhaust cam switch is best mounted so it contacts the inside face of a driver wheel. This will give the most
precise synchronization and even produce a wheel slip effect if the locomotive is accelerated too quickly! In a pinch,
the exhaust cam can be used with a tender axle, although the synchronization effect will not be exact unless the
tender wheel diameter is an exact multiple of the locomotive driver diameter.
The other method of exhaust synchronization is the DSD’s Auto-Exhaust feature which produces chuffs in proportion
to the throttle setting. This method is recommended for those locomotives where a mechanical cam would be difficult
to install such as N scale and smaller HO locomotives. When used in conjunction with the programmable speed
curves, it is difficult to tell the difference between the Auto Exhaust and the exhaust cam at all but the slowest
speeds.
Next, you will need to consider which lighting effects you will use. The DSD provides four auxiliary function outputs
which can be used for controlling miniature lamps or LEDs. Two of the outputs will usually be used for the headlight