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.
Realizing that there are some customers who will not want to get into the
intricacies of the manual EQ set-up straight away, Velodyne equipped the SMS-1
with a couple of automated EQ set-up modes to minimize the effort required.
In order to use the simplest of these, the Self-EQ mode, you strictly only
need to hook up the microphone to the SMS-1 and the LFE output to the
subwoofer. However, I would always recommend connecting the video output to
your TV as well. That way, you can monitor the sweep level on-screen to ensure
it is not too low, or flat-lining along the top of the plot. You can then
adjust the subwoofer gain to compensate accordingly.
To engage the Self-EQ mode, all you do is press the sequence 3-2-1 on the
remote control while at the initial OSD display. The display will change to
the sweep screen as follows.
The EQ sliders are reset to the standard 1/3 octave frequencies, and the SMS-1
then perform 25 sweeps, moving individual sliders up or down to try and
achieve a flat response. Since the ear typically struggles to discern
variations smaller than ± 3 dB at these low frequencies, the SMS-1 stops
moving sliders when the response is within these limits. When it has finished,
it saves the settings and returns to the initial OSD page. Note that only the
subwoofer output is in play during Self-EQ. No EQ Output signal is sent to the
receiver/SSP, so the main speakers produce nothing.
My system response following Self-EQ appeared as follows.
That represents a further incremental improvement, and if I didn’t want to
venture any further into the set-up process, I could just decide to leave it at
that.
Click
Here to Go to Part V.
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