basic function of the PARC is to equalize bass anomalies in the
room, commonly referred to as room modes. The most prominent bass
anomalies occur when two parallel walls (or floor and ceiling) excite
a particular frequency (an axial mode). The distance between the
two walls determines which frequency is excited. The most problematic,
or highest amplitude, is generally ½ of a wavelength between
two walls. The way to calculate the distance is:
½ * speed of sound / distance between walls = Frequency
The speed of sound is 1130 feet per second. Thus a room with 17
foot spaced walls would have a frequency bump at:
565 / 17 = 33.2 Hz.
This is considered the first mode between those two walls. The second
mode is for a full wavelength, which would be at 66.4 Hz. The third
mode would be at 3/2 wavelengths, or 99.6 Hz. Each mode has lower
amplitude than the previous mode. However, imagine a room where the
length is 2 times the width. In this example 34 feet long. The first
mode for that room is at the same frequency of the second mode of
the width, or 66.4 Hz. When modes combine like this the problem is
compounded, and the bass can become very bloated and distorted.
Even at Rives Audio we recommend reducing any bass anomalies as
much as possible before employing the PARC; the less electrical equalization
the better. However, overdamping a room, or filling it with bass
traps can be impractical, expensive, and may not lead to the best
sounding environment. The PARC employs the highest grade components
and shortest signal paths possible. The goal is to make these alterations
to compensate for bass problems with as little effect as possible
on anything else in the audio chain.
The PARC operates between 18 and 350 Hz. It attenuates ONLY, there
is no gain in the PARC. The purpose is to reduce the frequencies
caused by room excitation.There are three bands per channel. These
three bands were originally designed to compensate for the 3 parallel
surfaces in most rectangular rooms (side to side, front to back,
and floor to ceiling). However, they can be cascaded or used in a
variety of settings to best suit the room.
For each band there are 3 settings: frequency, width, and attenuation.
Frequency is the center frequency that will be attenuated. It is
represented in Hz. Attenuation is the dB in attenuation. The number
is positive, but the function is reducing the amplitude at that frequency
by the dB shown on the display. The range is from 0 to 18 dB. If
it is set to zero, then no attenuation is employed. Width is expressed
by a Q factor. The Q factor is expressed as:
Center Frequency (Hz) / Width of Frequency (Hz)
Thus the higher the Q the more narrow the band of attenuation. The
width is expressed at 3 db below maximum peak.
As an example a Center Frequency at 100 Hz, with a width of 25 Hz,
would have a Q of 4. Also, Q can be expressed in terms of Octaves.
One Octave doubles the frequency. Keep in mind that Frequency is
a log function of Octaves, so a center frequency of 100 Hz with a
width of one octave is not exactly 100Hz, it's slightly less than
100Hz. In our example of 100 Hz center frequency and a width of 25Hz,
the relative octave width is approximately ¼. The Q factor
is inversely proportional to the octave width. This is not important,
unless you are a musician and more comfortable with octaves. All
instructions for set-up will be relative to Hertz, and the Q factor.
The width will change depending on what types of walls, floor, or
ceiling you have. In general hard, rigid surfaces, such as concrete,
will exhibit a high Q factor, whereas sheetrock on wood studs will
exhibit a low Q factor. The lowest Q factor the PARC can produce
is 1, which is slightly more than one full octave. This is much broader
than we ever anticipate using. The narrowest Q factor is 10, which
also corresponds to approximately 1/10 octaves. This entire method
is far more comprehensive, accurate, and well suited than the traditional
graphic equalizer. Only a parametric can compensate naturally and
bring the frequency response, including phase back into balance.
Once the PARC is set up and calibrated the bass response will be
near flat. The result will be better bass definition, but also a
perceived increase in clarity throughout the midrange and even high
Adding the PARC can bring back the clarity and reference quality
sound your system deserves.