Velodyne ULD-18 & ULD-15 subwoofers Page 3

Just the act of adding one more huge box to a room already crowded with two large planar speakers can precipitate a decorating crisis and serious domestic friction. Like it or not, the ULD-18's WAF (Wife Acceptance Factor) may be lower than its sonics deserve. After all, the ULD-18 is as big as a small freezer!

Actually, the ULD-18's 5.7-cubic-foot enclosure would have been larger, but the technology involved has kept the size down. Its legs have rollers that allow a normal mortal to move it around without scratching the floor. There are the single pair of 5-way binding posts and a single RCA jack for the servo line on the unit's bottom. A flashlight helps while plugging in the speaker cable, because it is critical to keep the red terminal of the Velodyne amplifier connected to the red terminal of the subwoofer box (if the cables are reversed, deafening low-frequency feedback occurs in massive amounts, and can damage the speaker if continued for more than a few seconds). Aficionados can replace the rollers with Tiptoes for ultimate stability.

The remote is a black, finned box, with a power switch and level control on the front panel and RCA jacks, a pair of 5-way binding posts for a single speaker cable, and a single RCA jack for the servo line on the back panel. No tape-monitor output is provided on the Velodyne remote, so an external box would be required if you are using an integrated amp or receiver, rather than a preamp. Inside the unit, a single power supply drives all the electronics, including the bridged power amplifier. This "remote" unit is best placed next to the main system's preamplifier, as it divides the signal to all the power amplifiers. A 24' RCA cable is supplied with the system, and serves as the line for the servo signal.

The servo works soon after the unit turns on. One can tap the woofer cone with the servo off and on, and the resulting sound is very different. The servo-activated cone is stiffer and does not make the hollow "thunk" it does when outside the servo loop. Each time the Velodyne system is turned on, it makes a noticeable "pop" as the servo trims in the system. Years ago, this sound meant I had an amplifier with a turn-on or turn-off transient, typical of a prototype unit a manufacturer hadn't put the finishing design touches on. With the Velodyne system, this sound means you're in business.

The crossover and phase adjustments for the Velodyne amplifier are controlled by a series of seven soldered-in resistors on a carrier, which plugs into a socket on the back inside panel. An optional Velodyne data sheet explains the method of changing the crossover high- and low-pass frequencies, the slope of the high-pass filter, and the phase of the system. I found that having additional sets of resistor carriers (available from the dealer) for different frequencies and phase helped with the review; it could also help an owner who buys new full-range speakers. Once set up, plugging carriers in is easy and safe (with the unit turned off, of course). Soldering on the small card is tricky, for the plastic may melt at the same time the solder does.

The Velodyne system is sold as a single woofer system, and the remote unit sums a signal to go to the single subwoofer. Using two woofers requires two remote boxes, with right and left interconnects from your preamp going to the right channel of each Velodyne remote.

I had auditioned subwoofers before, and had always come back for more subwoofing, despite the following drawbacks. I did not enjoy: the need for an extra amplifier; the sense that bass information came from a different location than the rest of the music; the added colorations in the midrange; or the added clutter in my living room. Despite wood floors, different amps, and using two different electronic crossovers, I could never get the bass to play loud enough without producing all the ills of poorly controlled subwoofing—room overhang, echo, muddied midrange, and loss of imaging.

Moving the 105 lb cabinet around my newly-finished floors was best handled by two people to avoid scratches. The ULD-18 was rolled to two locations. First, keeping in mind the WAF, I "hid" the speaker enclosure behind the sofa, off to the right and behind the listening position. Signal-generator sweeps revealed that location to produce low levels of 20–30Hz bass. Also, it was 15' from the Quad ESL-63s, and the phase and timing differences muddied up the midrange and weakened the power and definition of the bass. Moved to a central spot between and one foot behind the Quads, the subwoofer "disappeared" sonically from the midrange, introducing no colorations from the crossover. I was surprised, because this location meant that the subwoofer was placed next to the back wall, which could have produced heaviness and unwanted bass reinforcement. The ULD-18 remained unobtrusive, only coming to life when deep bass information was present. I also discovered that the floor was not level, which meant that the ULD-18's wooden roller-wheels rattled during loud bass passages (the Dafos drum crash). Wadding paper under the loose wheels quickly stopped this annoyance.

Once the crossover slopes and frequencies had been chosen by plugging in the appropriate carrier jig, the level control on the outside of the remote was adjusted. I had chosen the nominal 85Hz, 12dB/octave setting shipped with each ULD-18 for use with the Quad ESL-63s. (I also tried a 60Hz crossover point carrier, but this muddied up the upper bass and low midrange.) I listened to male announcers on FM radio for starters, and found that a natural bass tone was achieved by setting the Velodyne's level control to about 8:30 (using the settings like a clock face). Further listening to double-bass recordings confirmed that was the most natural setting. Cranking the control higher added unwanted upper-bass colorations.

Listening tests
Listening to the Velodyne for the first time was dramatic. The ULD-18 system came on with a "pop" from the subwoofer indicating that the servo had set itself. I put on David Wilson's new CD, Winds of War and Peace, which begins with the "Liberty Fanfare." The Velodyne remained silent for the first 55 seconds of the CD, but then burst into life as a bass drum joined the orchestra. As I heard the solid, gut-punching bass note, I felt the wood floor flex under my feet! The impact of the floor shock reminded me of the shift caused by a Richter 4.5 earthquake that had hit the New York area 22 months before. Yet there were no unnecessary overtones, no overhang, no disturbance of the midrange or treble sounds, just that big bass note with its clean, well-defined leading edge. All the overtones of the bass drum were there, as I had not heard them before, although I was surprised that the drum could be so closely miked.

Velodyne Acoustics, Inc.
345 Digital Drive
Morgan Hill, CA 95037
(408) 465-2800

Staxguy's picture

What a great, great article!

Well, and informatively written.

Thank you, editor, for re-publishing!