Introduction - PSB HD8 Owner's Manual

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 experience 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 subwoofer. First and foremost it
is important to us that a PSB subwoofer be musical. 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.
Achieving high performance in a compact subwoofer poses serious design
challenges. In theory increasing the woofer's moving mass, to counteract the
stiffness of the air within a small enclosure volume, along with upping the amplifier
power to counteract the attendant loss of sensitivity are all that are required to
achieve high performance in a compact subwoofer. In reality shrinking the system
makes every aspect of design much more difficult. A ported box design which gives
lowest distortion is virtually impossible as the vents need to be large in area and
considerably longer. They would quickly consume the precious volume of the box.
Passive radiators will achieve what ports achieve in a larger box, but high mass is
required and high excursion must be allowed for. The woofer also needs both
incredibly high mass and equally high motor strength to offset the acoustic
"stiffness" of the air within a compact enclosure volume. An amplifier with the highest
wattage of any PSB subwoofer amplifier ever assures that amplifier drive is not a
limiting factor. Since all of these components have to be more robust than with
conventional designs their cost and mass increase. In the end the PSB HD subs are
constructed with rugged and heavy components masterfully squeezed into a small
enclosure volume. For this reason we've chosen to name the new models our HD
Subs for "High Density". In the end the musicality our subwoofers are known for is
also preserved, so HD could also stand for "High Definition".
An ideal subwoofer should have the ability to maintain accuracy 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 soundtrack, they must 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 distorting on sustained tones.
We go to great lengths to reduce any mechanical noises our subwoofers may make.
For example our woofers are designed never to bottom harshly. Woofers and
passive radiators are designed to maintain high excursion without rubbing ticking or
creating air noises. Cabinets and amplifiers are designed so that no air leaks (which
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