Specifications

Secrets Product Review
Velodyne SMS-1 Digital Drive Subwoofer Management System
Part IV
December, 2005
Roger Welch
Equalization
There are a number of different approaches to digital room correction in use these days.
Some of the more sophisticated techniques used in modern receivers and SSPs attempt
to reduce the extended decay times at the room’s modal frequencies by subtly modifying
the original signal (modal equalization). Other more traditional methods involve flattening
the magnitude of the frequency response using parametric EQ filters. The SMS-1 adopts
the latter approach.
I have seen some recent research suggesting that, below 100 Hz, the ear is so insensitive
to extended decay times, modal equalization is only worthwhile in really extreme cases.
Flattening the magnitude response below 100 Hz may actually be all that is required. This
is a contentious area with rival manufacturers making claims as to which approach is
best. There may even be some merit in using a combination of the SMS-1 to tame the
extreme low bass while letting your receiver or SSP's room correction deal with the
remainder of the frequency range.
The important thing to realize about equalization is that you can usually only achieve a
flat response within a relatively small listening area. Move even a small distance outside
that area and your nicely equalized system may actually produce even more lumpy bass
than you started with. Using two or more carefully placed subwoofers can sometimes help
in these cases. However, you may still have to compromise and put up with a slightly
bumpy response in order to achieve an acceptably wide listening area.
The SMS-1 incorporates an 8-band digital parametric equalizer. Each equalizer slider can
apply a cut of up to -13dB, or alternatively, a boost of up to +6 dB. The sliders move in
steps of 0.5dB at a time. When set to factory defaults, the sliders act at standard 1/3
octave frequencies (20, 25, 32, 40, 50, 63, 80 and 100 Hz).
It is most important to use the EQ boost capability cautiously. A +6 dB boost will require
the subwoofer amplifier to quadruple its power output at that frequency. This will limit
the overall headroom available and may be sufficient to cause amplifier clipping and/or
driver overload when played at very high levels.