Velodyne Acoustics Digital Drive Subwoofer - Manual (Page 30)

Velodyne Digital Drive User’s Manual Page 25
by dual spiders for even greater linearity. We designed this motor to produce over one-inch (1-1/4" to
be exact) of linear motion, with a maximum mechanical limit of 1-3/4" peak-to-peak. Also, with this
unique configuration, the distortion products are reduced by a factor of two over conventional single
coil structures with dramatically improved cone control. This driver alone would result in less distortion
than any other non-servo design. After optimizing every remaining part of the loudspeaker, we then
turned to the electronics.
As in our other servo products, we then incorporated closed-loop accelerometer based servo-control
of the loudspeaker. At the heart of this control system is a low mass digital accelerometer rigidly
attached to the voice coil. The accelerometer continuously monitors cone motions, providing a digital
feedback signal for the servo control circuitry. This high-gain system is designed to improve linearity
and reduce distortion approximately 30 times over conventional non-servo systems. While the input
signal is being sent to the amplifier which powers the driver, a continuous signal representing cone
motion is being sent to a computer. This computer constantly adjusts for any deviation between the
input signal and the subwoofer’s output. This self-regulation results in extreme control over cone
movement, and very accurate low distortion sound. All processing of the audio signal is done digitally.
To provide the power for driving this massive loudspeaker, we incorporated an extremely efficient
Class-D switching amplifier. This new amplifier features our patented energy recovery circuit design,
U.S. Patent #4,727,584 and 4,573,189 which drastically reduces wasted energy (heat) as compared
to traditional switching designs. One that is capable of running cool to the touch and providing 1250
watts RMS of power! At typical listening levels, Digital Drive subwoofers produce less than 1% harmonic
distortion with input signals extending to 20Hz. At higher levels the distortion barely exceeds 1%, far
better than any conventional design currently on the market. This combination provides you with the
best combination of clean, deep, accurate bass, without making any sacrifice to distortion.
Care of Your Digital Drive Subwoofer
Do not use any harsh detergents or chemicals to clean the cabinet. Abrasives, detergents, or cleaning
solutions may damage the finish on the cabinet. We recommend using a damp cloth to clean the
cabinet. During normal conditions, your new subwoofer may be left on continuously without any
problems. The unit is equipped with a signal-sensing turn on/off that will automatically turn on the unit
when a signal is present at the inputs and turn off the unit after several minutes when there is no longer
any signal at the inputs. If you plan to leave the subwoofer unused for an extended period of time, we
recommend that you unplug the unit.
Troubleshooting and Service
If you should experience a problem with the operation of your subwoofer, please check all of the follow-
ing before seeking service. Following is a simple troubleshooting guide to assist you.
1. Verify unit is plugged in and power outlet used is active.
2. Is the unit receiving an input signal from your source? A good way to test this is to connect the
EQ audio out to the LFE input (both on the subwoofer back panel), then enter setup mode (see
Step 6). The woofer should play the sweep tone used for room EQ.
3. Have all controls on subwoofer (volume, crossover, phase, etc.) been properly set?
4. If unit has been running at high levels for an extended period of time, one of the protection
circuits may be engaged.
• Has the built-in amplifier overheated?
• Is your power line voltage sagging under heavy use?