TIPS & TECHNIQUES

Sound System Speakers


    In response to all the e-mails I have received,  I am addressing a
short topic on speakers for model railroad sound systems.
    Most people will agree that sound brings large scale trains to
life.  Without it, the illusion of a real railroad in miniature is hard
to maintain.  High quality sound systems are expensive, in fact a
quality system can cost as much or more than the locomotive.
    Your choice of a speaker can determine whether your sound system
sounds realistic or not.  I have found that the higher cost sound
systems require a really good speaker and a good installation to bring
out quality sound.
    Phoenix and Sierra diesel sound systems are both excellent, because
they have a lot of bass in them which enhances their overall effect.  To
take advantage of this, you need to look for a speaker with a large
magnet on the back.  Most large scale locomotive installations use a
2.5" or 3" speaker, so the larger the magnet, the better the sound at
the low end.  I have ordered good speakers from electronics firms, but
my speakers of choice are the ones offered by Phoenix.  These speakers
were chosen by the engineers to match the response level necessary for
scale sound systems, and sizes are available for almost any
installation.  The part numbers that I use in most of my installations,
are:  SP2.5V (2.5  inch oval), SP2.5SQ (2.5 inch round), SP3F (3 inch
round).
    A proper enclosure is mandatory for a speaker to perform at its best
level..  When a speaker generates sound, it actually produces it from
both front and rear.  If the speaker is not properly enclosed, the
sound  waves moving to the rear will cancel out the sound waves from the
front.  Thus by using an enclosure, you actually trap and dump the sound
from the back of the speaker to the front.  The sound engineering rule
of thumb is that speaker enclosures should be at least the same depth as
the diameter of the speaker.  i.e.: a  2.5 inch speaker should have at
least a 2.5"x2.5"x2.5" enclosure.   Most steam locomotive tenders
therefore do an excellent job acting as an enclosure, since they are
large and can be made air-tight.  Any speaker should be sealed to the
opening with clear silicone, and all holes such as those for wires
should also be sealed.  Many diesels have speakers mounted in fuel tanks
or battery boxes, and these do a good job of trapping and radiating
sound.  If you are opting for an enclosure within a diesel body shell,
I would recommend using heavy clear acrylic for your speaker enclosure.
Styrene will work, but may vibrate and buzz unless it is of substantial
thickness. (at least 0.062")
       For the best sound reproduction, a trail car is the ultimate
choice for a speaker enclosure.  A 5x7 car stereo speaker can be fit at
an angle within a boxcar or stock car.  A triangular shaped housing can
be made from 0.062" or thicker styrene or acrylic to enclose the speaker
so it can project it's sound out an open door,  through the slats of a
stock car, or through holes drilled in the floor.  Make sure you always
use an 8 ohm speaker for any of these installations.  This type of
installation has two advantages:  (1)You get excellent sound
reproduction, especially the bass needed for diesel sound. (2) You do
not have to buy a sound system for each locomotive that you own.
    You can connect more than one speaker to many sound systems.  (Check
with the manufacturer first)   This is usually done when there are
multiple lash ups of diesels, so that the sound can come out of more
than one unit, such as in an A-B-A set.   These speakers must always be
connected in series in order to work. When running the single unit with
the sound system, a plug can be inserted in the leads to shunt the
circuit,  otherwise the speaker in this unit will not work.  The catch
to this system is that by connecting two 8 ohm speakers in series you
will actually have less volume than using one speaker.  Putting two 8
ohm speakers together results in a 16 ohm load, which will draw half the
output current resulting in half the total output power. Only sound
systems that have two power amplifiers or a booster amp lend themselves
to running two speakers, otherwise you may run the risk of burning up
the sound system from the overload..
    When running your sound equipped locomotives, always keep in mind
the sound level should be in proportion to the scale of your trains.  If
you turn the sound level up too high, you run the risk of distorting the
sound and eventually ruining your speaker.  You will definitely destroy
the illusion you are trying to create,  plus will turn off many of your
guests.  Remember,  prototype railroads issue hearing protectors to
their employees to save their hearing when they work in yards or engine
terminals.