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SYSTEM PLANNING
The largest possible impact on any audio
system (home or car) is the quality of
loudspeakers used and their placement.
EFFICIENCY defines how loud a speaker
will play for a given input power and is
often quoted at 1 watt input and meas
at a 1 meter distance. When designing a
system you want to keep the component
efficiencies as close as possible. Always
match components for efficiency and
complementing frequency response to
ensure smooth transition from IOW
frequencies to higher ones for accurate
performance. Remember that for every 3
the amplifier has doubled it's power output.
SPEAKER CONFIGURATIONS can become a problem in autosound installations. We would
like to achieve a sound field in front of us (like a live concert) as compared to sound partly
from the front and partly behind us. This virtually dictates good midrange and tweeter
speakers in front, usually mounted in the doors for good left/right balance, with high-pass
crossovers set greater than 80-100 Hz. For deep bass a subwoofer is required but is nearly
always located behind us in a rear trunk or hatch area. If the subwoofer crossover is too
high in frequency male voices can be heard "gurgling" out of the subwoofer speaker and
therefore pulls the sound-stage to the rear of the car, which is undesirable.
AMPLIFIER POWER is important but should be of lesser importance compared to speaker
choice and placement. Matching the rms (continuous) power levels to that of the speaker
is important but it should be noted that under-powering a system can often cause more
damage than slightly overpowering it. If the speakers are rated for 50 watts rms, you can
often drive them with a 100 watt power amp without concern. IMPEDANCE is the electrical
resistance to AC current flow and is typically 4 ohms for most car speakers. Impedance
loads for a speaker configuration shouldn't fall below 2-4 ohms for most installations to
avoid amplifier overheating, regardless of manufacturer (Impedance = D.C. resistance of
the voice coil wire + A.C. resistance due to the coil of wire formed).
At some point, the subwoofer speaker must be electrically connected to an audro amplifier,
be it a stand-alone unit of some kind or the amplifier built inside the radio. The highest level
of performance will be from the outboard unit in most cases due to its power. To avoid
disapppointing performance we recommend power amplifier levels above 40-50 watts. This
is NOT a minimum value; it is simply a nice power point where you begin to really u the
substantial improvements in sound offered by a good subwoofer.
In addition to the amplifier, there needs to be an electrical "crossover" which limits the
frequencies sent on to the subwoofer speaker to only bass type signals. There are two
types of electrical crossovers; ACTIVE and PASSIVE. The Active crossover requires an
interface box (the Active crossover) and connects between the radio and amplifier thus
limiting the frequency range of signal (e.g., below 100 Hz) before it's sent on to the
amplifier.
The Passive crossover allows the amplifer to reproduce all frequencies (20-20
before being passed on to the woofer. The Active crossover offers the highest performance
but is more expensive and has increased installation complexity compared to the Passive
design.
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FREQUENCY [Hz1
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