Velodyne HGS-12X - Manual (Page 7)

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Volume control
This control allows you to balance the output from the subwoofer to the
main speakers/amplifier in your system. This control should be set to
achieve similar output level from both the main speakers and subwoofer
when listening to music. A good starting point for the volume control is 4
or 5 dots from minimum.
Low-pass crossover - 40 to 120Hz
The line-level inputs sum the left and right channels together, with the
resulting signal passing through an adjustable low-pass crossover before
being amplified. The crossover control allows you to adjust the upper limit
of the subwoofer's frequency response from 40 to 120Hz. The subwoofer's
output will be reduced above the frequency you set this control to. You
should set the crossover frequency to obtain a smooth and seamless
transition from the subwoofer to the main speakers in your system. If your
main speakers are smaller units with limited low frequency output, you may
wish to choose a higher frequency (such as 100-120Hz) than you would
with larger speakers which have greater low frequency output. With larger
speakers, you might start with this control set lower, such as 80Hz.
A bypass switch is also provided if you wish to use an external crossover.
If you are not using an external crossover, we recommend that you
use the one provided within the unit for optimum performance!
Phase adjustment - 0°/180°
This control allows you the "reverse" the phase of the subwoofer's output signal
180° to correct for any possible mismatch and resulting cancellation between the
subwoofer and your main speakers/amplifier. To adjust, simply listen to the system
with music playing. Then move the switch from one position to the other and listen
for a change in low frequency output. The correct position will have a greater amount
of apparent low frequency output.
Subsonic - 20Hz/35Hz
This adjustment alters the low frequency limit of the subwoofer. In certain movie
theater installations which suggest that the extreme low bass be limited, move the
switch position to 35Hz and the response will be attenuated below this frequency.
The unit is protected against:
1) Overdriving the speaker or amplifier.
2) Overheating the amplifier.
3) Excessive drop in power line voltage.
The first type of protection circuitry which prevents overdriving of the
speaker or amplifier operates constantly without being audible under most
situations. In some extreme situations (sustained high output levels such as
pro sound usage), the unit may shut down momentarily. This indicates
operation of the thermal or undervoltage protection circuitry. If this should
happen, you should reduce the volume setting or shut the unit off until normal
operating conditions return. You may also want to plug the unit into a
different wall outlet, as dropping power line voltage will be most noticeable
under strenuous conditions.
Distortion in Loudspeakers
Nonlinear distortion is a problem which plagues all speakers. This particular
type of distortion is a common problem in subwoofers, which must move
large amounts of air to produce adequate levels of deep bass. Nonlinear
distortion is defined as any form of distortion that moves energy from one
portion of the audio frequency spectrum to another. When a single tone is
applied to a nonlinear system, the result is harmonic distortion. In which
some of the energy leaves the system at multiples of the original frequency.
When multiple tones are applied, intermodulation tones are produced,
usually as simple combinations of the input frequencies. Generally, 3%
distortion is considered a reasonable amount for speakers. This means that
3% of the total energy leaving the speaker is at frequencies other than the
intended input signal.
Most subwoofers on the market today however, produce much more than
3% distortion at common listening levels. Many models we have tested
produce greater than 20% distortion @ 20Hz when driven to 100dB. This
is a typical output level obtained in many systems, particularly home theater