Page 4 © Copyright 2002 Rives Audio, Inc.
Operator’s Manual
Basic Function
The basic function of the PARC is to minimize bass anomalies in the room. The most prominent bass
anomalies occur when two parallel walls (or floor and ceiling) excite a particular frequency. 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, over damping 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 16 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, or “quality”
factor. The Q factor is expressed as:
Center Frequency (Hz) / the Width (Hz) at 3dB below the peak frequency.
Thus the higher the Q the narrower the band of attenuation.
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 more
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. This is much broader than we ever anticipate using.
The narrowest Q factor is 10. For more information on Q factors see appendix B.
