Velodyne ULD-18 or Audio PHysic Rhea sub....

The Velodyne HGS series have the lowest distortion and flattest frequency response of any subwoofer. With the servo feedback system they react and decay immediately. It is the most accurate subwoofer for music or theater. Whether one likes accurate sound or not is another issue. The Velodyne Servos play the signal they receive more accurately than any other subwoofer. You certainly should audition the various HGS models and decide for yourself. In regard to the older ULD-18, the new HGS-18 has more output, deeper extension and less distortion. It is my reference.
Take Care,
Curt

Curt,

Please, no offense intended but stating that ANY Velodyne sub has the lowest distortion and flattest response of any sub is laughable! Of course, if all I had ever heard was Velodyne, I also would say it was impressive. But, have you ever heard a Talon or REL sub before? If yes and you still feel the way you do, then I am at a loss. If not, you should (after which I don't think Velodyne would be your reference anymore). Servo-sub designs are simply an excuse for lazy design work! Ok, I have said my peace ;-)

Best Regards...Mike - Father & Son Audio

Mike,
I've been in Audio over fifty years and have owned or listened to just about every sub out there. I've heard all the Rel's and yes the Talon and the Aerial. I wish you'd try to design a servo feedback speaker and see the difficulties involved. Very few of the top audio engineers have been successful. That's why many subwoofer designers use Velodyne as their reference in designing their own product. We can all chose what we like or don't like but facts are facts. I suggested Mythtrip audition for himself and then decide. I stand by that.
BTW I stated the Velodyne HGS series (not any Velodyne) had the lowest distortion and that's a fact.
Regards,
Curt

I have a ULD Series II 18, which crosses over to my Budge
Khorus speakers at 60 hz. It does not sound slow or on-musical.

The standard crossover point of 100 hz is too high for hiend
speakers, and may account for Uncle Mike's poor impression.

A variable crossover is essential when working with hiend speakers.

And, yes I'd love have the new Talon Roc, but I'll have to
live with my old ULD 18 SII until the dock strike is over.

Aloha.

"The Velodyne HGS series have the lowest distortion and flattest frequency response of any subwoofer"

There's a Swedish engineer with a subwoofer claiming 140db dynamic range--they say its "the best in the world." I'm sure it could hold its own with Velodyne. There weren't many specifics in the article since its focused on the new digital formats. But, I'm sure its distortion is quite low, especially when brought to a 'meager' 110db or 120db. The Velodynes aren't bad, but there is better. And I still wonder what the performance of the Kharma Acoustics Grand Enigma really was.

"I have a ULD Series II 18, which crosses over to my Budge
Khorus speakers at 60 hz. It does not sound slow or on-musical."

I would just like to point out with subs that there is a distinction between the actual speed and perceived speed (subjective, "it sounds fast"). I'm not qualified to comment too heavily on the difference, but in reality, cabinet colorations and internal standing waves, a non well damped cabinet can muddy the sound regardless of what the driver is physically doing: whether or not it is servo controlled, etc. Not to mention dreaded room acoustics coloring things up.

[The crux of servo control from what I gather, is that since it is a measuring device there is technically a time-delay between sensing the drivers motion and then sending the appropriate command to the circuitry to correct the motion--this is why some bash on it. It may not be significant given the human ears perception down low isn't as sensitive as the midband region, hence the benefits to the design outweighing the possible negatives (however, the switching distortion in a Class B circuit is still far shorter and the Class A buffs complain of that)]

Audition them both (all) if you can, but be careful of room room placement and nodes. Do your best to level the playing field. Velodyne are nice subs though and not a "home theater" sub (at least not the better ones). Ideally a sub would do it all, but when you have to compromise the design, the differences for a HT sub would come when the designer opts for a higher system Q, higher output, which in turn usually means greater efficiency going the bass reflex route and less extension. A comparably priced "Music" sub would possibly have a lower Q and less output (maybe sealed), with a bit better extension. (Note: I am not encouraging the "Bass Reflex=HT and Acoustic suspension=music" stereotype. I'm just using an example. There are very nice ported systems, along with many other possible designs: TL, etc.)