Secrets Product Review

Velodyne SMS-1 Digital Drive Subwoofer Management System

Part II

December, 2005

Roger Welch



The SMS-1 can be connected to an existing system in several different ways. I chose to evaluate it for this review in the configuration that I believe will be most commonly used. That is to control a single subwoofer in an A/V system, driven at line-level from the sub-output jack of the SSP/receiver which performs all the bass management.
The manual provides step by step instructions that lead you through the set-up process, although a certain amount of practice is needed to fully master some of the functions.

The balanced measurement microphone (supplied) is connected to the XLR microphone jack on the front (or rear) panel, and placed on the back of your chair close to where your head would be when listening to music or watching movies.

Next, either a coaxial RCA composite cable (supplied) or S-Video cable is connected to the video output jack on the rear panel, and the other end to the TV or other display device. A stereo coaxial cable (supplied) is also connected to the EQ output jack on the rear panel, and from there to a spare analog input on the receiver/SSP. This is used by the SMS-1 to generate the test sweeps used to measure the system response.
Finally, the sub pre-out from the receiver/SSP is connected to the input of the SMS-1, and one of the LFE outputs is connected to the subwoofer.

Since the SMS-1 performs the functions so much better in the digital domain, it is advisable to disable any functions on the subwoofer that modify the signal. For example, the phase control should be set to 0 and any low-pass crossover disabled or set to the maximum available frequency position.

You then turn on the receiver/SSP, the SMS-1, the subwoofer, the TV, and settle down with the remote control.

For this review, the partnering equipment was my Theta David II DVD player, Theta Casablanca III SSP, Krell power amps, and Martin Logan speakers. The subwoofer I used was an early SVS 20-39 PC Plus in its native 20 Hz tune. I used an XLR balanced connection from the SSP to the SMS-1, and a single RCA cable from the SMS-1 to the sub. I connected the EQ Output from the SMS-1 to a spare analog input on the SSP which I configured for stereo use with bass management. I kept the 63 Hz, 24 dB/octave crossover and slope settings that I normally use in the SSP with my floor-standing main speakers.

The initial screen of the OSD is shown below. It tells you the current subwoofer volume setting (00-99) and which preset (there are six to choose from) is currently selected.

Pressing Menu and/or 1-2-3-4-5 on the remote control (shown below) brings up the sweep test screen OSD.

With the sweep test screen displayed, the SMS-1 generates a continuous series of sine wave sweeps from 15 Hz to 200 Hz, repeating every 3 seconds or so. The measurement microphone then listens to the response at the listening position and plots the overall in-room response of the system on the screen. It may be necessary to adjust the receiver/SSP volume control and/or the gain control on the subwoofer to obtain a trace around the required 80 dB level and correctly balanced between what the subwoofer and main speakers are producing.

Click Here to Go to Part III.

Copyright 2005 Secrets of Home Theater & High Fidelity

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