II.
INTRODUCTION
PSB subwoofers are designed to provide the flattest possible frequency
response, full bass extension, low distortion and high output. Frankly, these are
characteristics that most manufacturers would strive for. Our years of experi-
ence and our sophisticated design and measurement tools allow us to achieve
ideal subwoofer performance. Beyond these characteristics there are a few other
parameters that we uniquely feel are very important in the design of a sub-
woofer. First and foremost it is important to us that a PSB subwoofer be
musi-
cal. In this era of home theater this might at first seem out of step, but we
believe that a musical subwoofer will also sound the most natural when playing
movie soundtracks. Furthermore, an ideal subwoofer should have the ability to
play musically even under conditions of overload or stress. No subwoofer is so
large with its limits so great that it can never be overloaded, especially with
modern movie soundtracks. For this reason PSB subwoofers incorporate very
intelligently applied proprietary limiting circuitry to prevent audible overload.
The limiting circuitry of all PSB subwoofers is a combination of peak limiting
circuits that hold amplifier signal swing to the point just short of the amplifiers
clipping, and compression circuitry that will come in under conditions of long
term overload and reduce the amplifiers gain. The trick is to apply these circuits
in such a way that they don’t squeeze the life out of the music or movie sound-
track, to allow the dynamics to get through while preventing gross distortion.
We do this by being mindful of the dynamics of music and carefully tailoring the
time constants of the circuits to that of music. For example, it is known that
most music is performed with a beat of 80 to 140 beats per minute. Our test
signals are configured to follow this timing and allow maximum transient effect
without distortion on sustained tones.
We go to great lengths to reduce any mechanical noises our subwoofers may
make. Woofers are designed never to bottom harshly. Ports have large radius
end flares to reduce noise from turbulence. Cabinets and amplifiers are designed
so that no air leaks (which can contribute minute amounts of noise) are possi-
ble. All of our designs are exhaustively tested. A subwoofers design isn’t com-
plete until the sub’s amp and woofer can survive a 15 hour test of being driven
continuously to maximum output.
SubZero
i
The SubZero
i
has a few unique features worth mentioning. We have mounted
Volume and Crossover controls on the front of the cabinet. Most subwoofers are
tucked away in a dark corner and once in place it can be very inconvenient to
access the controls. Placing volume and crossover knobs on the front of the
cabinet will allow you to adjust these most important functions more conve-
niently. Despite its modest price the SubZero
i
contains a simplified version of
our two part limiting circuit and a 100 watt class AB amplifier.
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