velodyne dd plus? still considered best of the best?


are these subs still comparable to the top subs today for music and sound quality?  I was thinking about getting a used one, the resale value puts them around the same price for me as a new svs sealed 3000 series, new ryhmik , new  rel t7i, or used jl audio e series

audiocanada
Of the six Velodyne models I've owned over the years the only service issue I had was the remote receiver in one of my DD Plus which wasn't working at all.
I dropped it off at the Digital Drive location in the late afternoon and told them that the I purchased the unit new in a sealed box from an unauthorized New Jersey dealer and expected to pay for the repair.
 
It was repaired the next day at no charge so I bought a second unit right then and there. They're daisy chained master and slave using a custom length RS232 cable.  
I posted in another thread that Velodyne has sold its sub line to another company, so hopefully we’ll see some service available soon. I love my pair of DD10 plus, though the remote sensor seems to be less responsive lately. The nice thing is not only does it have high level speaker inputs like the REL, but you can also hook up the xlr or rca. I use high level for stereo and xlr for Home theater system, so subs work for both my systems.

The ddplus was designed for low bass in 20’s and below, and I like having ability to change crossover slope via remote.

They keep up well with my TAD’s which have wonderful bass, but roll off in low 30’s.   I like very tight bass with no overshoot, but the servo can be lowered for looser bass.

I’m using them in a 12,000 cubic foot space, and though I don’t like a lot of bass, they do satisfy my needs.  
Despite its age the DD Plus simply offers more than everything on your list. Its condition and how it was used could be an issue.  

The DD Plus is a sea change from HGS and a substantial improvement over the DD.
 
The JL Audio F series are as potent but their DSP is Auto only so your stuck with JL's choice of how a sub should sound. The version 2 added more frequency bands but it remains Auto only.
JL Audio now offers the CR-1 crossover for some manual settings of a single setup.

You would need to contact Audio Reference and ask about service support https://www.velodyneacoustics.com/
George Meyer AV in Los Angeles CA. was an authorized Velodyne service center https://www.georgemeyer-av.com

Reading the SVS Ultra manual it may be the closest to the Velodyne Auto/Manual concept. It offers three EQ presets and Q adjustability but not having any practical experience with it I can't comment.
They're not considered the best of the best but they're good enough.  Deep bass doesn't need to be perfect.  The room causes far more problems than the driver.  I've got a 14 year old DD18 that works fine and I'd never consider replacing it unless it stopped working and I couldn't get it fixed.  It's a great product.  The deepest bass without a hint of audible distortion.  Sealed box means no port noise.  There's auto eq and manual eq.  It's a thoroughly thought out product with several generations before it.  The question is just whether you want to risk buying an excellent older product that might have a part fail.  Can you get a replacement?  
The DD subs use to be cutting edge, but like others I would not purchase one now with the new ownership and questionable support.

One of the most musical subs I've heard is the Aerial Acoustics SW-12, however these are pricier than the others you mentioned.

I would go with the SVS sealed and not look back.

Good luck.
The DD and DD+ can be an incredible value in the used market considering their performance and features. Servo motor with manual control, auto as well as manual room correction, visualizing frequency response, low distortion, very well built, massive amp, sealed, remote, etc.
The DDs probably have the smallest cabinets in their respective woofer sizes of any premium sub. The DD+ versions have bigger cabinets but lovely aesthetics with the curved sides and esp the black glossy veneer. 
I almost went with a pair of the Rythmik 12" subs.  But decided to go with the REL S3's because of their high level connection.  They blend quite well because when connected that way they act like an additional woofer to help extend the bass without it sounding too boomy.  However, I really like the direct servo technology uses in their Rythmik subwoofers.  However, since they are sold direct it was difficult to buy them without hearing them first.  I have heard they are very musical.
+1 on paradigm defiance.  Absolutely tremendous subs for music and movies.  I sold my E112 stacked pair (poor mans / smart mans F212 pair) and I am running just a pair of X12 Defiance subs and they are unreal.  Just as tight as the JL, around the same output, yet they’re made in Canada and have the best room correction around (way better than the F113 v2 I had).  
The only caveat is that they are boring square boxes.  Although the woofer does look very cool.

See if you can find a local dealer that will let you take them home.  They will shock you.
I wouldn't buy a powered loudspeaker from a company that no longer services them or provides warranty service....stick to something with good warranty, and run some good room correction software and it will sound as good if not better than some old Velos.
Velodyne has not made a sub in a long time. they where good in their time, best in home theater. Good customer support, but not sure if they repair them any more. They have moved on from the sub business. I was at their factory 5-7  years ago and the sub was just a very small area of the plant and becoming smaller.  I had several of their subs with my last being HGS 18 for my home theater. Great sub. but i sold it a few years ago and have moved on to 2 channel only system. You should check if they are still servicing the subs before buying one.
Hardly relevant anymore...David Hall, incredibly smart guy, invented LIDAR and sold it to the US Military.  Velodyne is a shell of what it once was and is barely in business.  Because of LIDAR, David certainly doesn't need to live on subs anymore.

Please take a look at the Paradigm Defiance Series Subs.  Start at $400 and go to $1499. Starting at $549 they have Anthem Room Correction which can be run on an Apple or Windows PC or a Mobile Device,  Full App Control of the sub from a mobile device; which allows you to find all the rattles in your room at specific frequencies by doing a "Sweep" (from 20Hz - 120Hz that you can lock and adjust in 1Hz increments) so you can isolate those things rattling at every frequency and know what frequency it is.  It also allows you to hear where the dips are in the room at those frequencies.  And finally, all those have wireless capability as well if you can't get a physical wire run where you need the sub to be. 

X-Series made in Canada from $999 - $1499 and V-Series made in China from $399-$649.  X-Series woofers have two US Patents = 1) Increases output by +3dB, so double the output, and 2) Reduces the distortion by 50%, so cuts that in half...Musical and Dynamic for movies!

 https://www.paradigm.com/en/overview/series/defiance-series   
Ahh, the Muse 18.  I will better you, the Muse 16, which looked like a large, wood refrigerator on its side.  I heard one at Shelley's Stereo with Magnpan 3.3s in the mid 1990s.  Amazingly articulate, tuneful bass, until it bottomed.  

Going back to the OP's question.  I would pass on the DD for several reasons.  1)  Velodyne has all but abandon subwoofers and long term support is questionable.  2)  There are better alternatives now.  3)  The alternatives are better for the money.  

I used Velodynes for years, ULDs, F series, SPL, and HGS.  I have since moved onto Rythmik.  The Rythmiks offer a tighter, clearer, drier sound, while also having greater output capability.  In my office, I use an L12, which I say is slightly cleaner sounding than the HGS-12.  In my main system, a F15HP, which was a significant upgrade from the HGS it replaced in sound quality and output.  

For the same money as a used DD-15 (about $1400), you can get an F15HP, or enjoy the benefits of two subs (smoothing of room modes) with two F12-300s ($700 each on Rythmik's clearance page).  You will also get a warranty.  

Finally, for music, you may want to also look at the HSU ULS-15 MK2 dual drive (two subs) for $1499 a pair.  
Personally for music, the original 2W Vandersteen always sounded best, the setup provided a test box to match, and then order a finer component filter.......i think.
it had limited spl compared to the Velo for sure, the original Muse18 was spectacular with music too