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Velodyne ULD-15 Subwoofer - Thumping/Refoam/Shim

P

Pete.Schmidt

New Member
Hi All - I'm new to the group and just got (for free) a Velodyne ULD-15 Subwoofer Series II that has no foam. It was posted (from the daughter of the original owner) a properly working when put into storage 4 years ago and other than the foam looks in mint condition (beautiful cabinet and amp has no rust or scratches). I checked the fuses & when properly hooked up and turned on (w/out any input signal) it starts to Thump Thump w/speaker moving in & out. I found this thread by Zundee

Velodyne ULD-15 subwoofer w/ matching amp https://audiokarma.org/forums/index.php?threads/velodyne-uld-15-subwoofer-w-matching-amp.792824/​

which seems to be the same condition. Blue72 responded and said, " If there is not a perfect air seal (for example, missing foam), the woofer cone will move back and forth by itself because the circuitry doesn't know what to make of the current condition and is trying to correct for something that it can't account for." I'm guessing/hoping mine is making the Thump Thump because the cabinet is not sealed when the foam is deteriorated/gone?

Has anyone else has the same Thump Thump speaker (moving all the way in & out) that was resolved after a Re Foam?
How important is it to remove dust cap and Re Shim when doing a Re Foam?
How do you safely remove the dust cap?
Can I use multiple sheets of paper for shims? I saw a guy on YouTube use paper and it seems that would work.
Are all Re Foam kits equal?
Are there some I should stay away from?
Any other helpful hints?
 
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Hmm, I wonder if the initial turn-on thump is causing the servo to cause this. At any rate I'm not an expert on this sub, but I'll try to answer your other questions:

  1. n/a
  2. Many people prefer to use a 30hz sine wave from a frequency generator or Youtube video (fed through a different amp), or the output of a AA battery, to keep the voice coil centered, rather than shimming. You definitely should use some method of centering, I wouldn't do it by feel as the risk of failure is high.
  3. Normally you'd remove the dust cap by cutting around the edge with an Xacto knife. However, having had a look at this woofer and its concave dust cap, I think it's a bad idea to remove it, as you run the risk of damaging the cone or the accelerometer. See previous response.
  4. Depends on the width of the voice coil cap. You can use cut up business cards, index cards, anything that will keep it centered.
  5. No. but it's unlikely that you'll find a surround made specifically for this woofer. I'd recommend contacting Rick Cobb (rcobb@tampabay.rr.com); his prices are reasonable and he can get almost any size.
 
Pete.Schmidt said:
Hi All - I'm new to the group and just got (for free) a Velodyne ULD-15 Subwoofer Series II that has no foam. It was posted (from the daughter of the original owner) a properly working when put into storage 4 years ago and other than the foam looks in mint condition (beautiful cabinet and amp has no rust or scratches). I checked the fuses & when properly hooked up and turned on (w/out any input signal) it starts to Thump Thump w/speaker moving in & out. I found this thread by Zundee

Velodyne ULD-15 subwoofer w/ matching amp https://audiokarma.org/forums/index.php?threads/velodyne-uld-15-subwoofer-w-matching-amp.792824/​

which seems to be the same condition. Blue72 responded and said, " If there is not a perfect air seal (for example, missing foam), the woofer cone will move back and forth by itself because the circuitry doesn't know what to make of the current condition and is trying to correct for something that it can't account for." I'm guessing/hoping mine is making the Thump Thump because the cabinet is not sealed when the foam is deteriorated/gone?

Has anyone else has the same Thump Thump speaker (moving all the way in & out) that was resolved after a Re Foam?
How important is it to remove dust cap and Re Shim when doing a Re Foam?
How do you safely remove the dust cap?
Can I use multiple sheets of paper for shims? I saw a guy on YouTube use paper and it seems that would work.
Are all Re Foam kits equal?
Are there some I should stay away from?
Any other helpful hints?
Click to expand...
Yes !
Both my B-I-L and myself both own those (him= (2), & me= (4) of them) that servo external amplifier series Velodyne ULD-15, and we both had the subwoofer wildly oscillate (thumping) when the foam surround started failing (deteriorating) some yrs. back !

After our local long time trusted speaker repair person replaced the the surrounds of the subwoofers, all the re-foamed 15" subwoofers preformed normally since.
 
Dear Pete Schmidt,

I've owned a Velodyne ULD-15 since the early 1990s, which transforms the sound of my (otherwise tube-based) stereo. The ULD-15 recently started making an oscillation sound. When I checked it, I found that the foam surround of the speaker cone had deteriorated, and half of it had fallen out. With no functional surround, the acoustic-suspension (sealed box) for the speaker is missing, and the Velodyne's accelerometer servo cannot function without it. I think once your speaker has been re-foamed, it should work properly again.

Please see my recent Audiokarma thread on this topic, at https://audiokarma.org/forums/index...-uld-15s4-re-foaming-recommendations.1078605/

Bill Nolting
 
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Pete,

I would recommend refoaming the driver while it remains in the cabinet. That process is shown in the YouTube video I link to in my post.

You should not open the speaker's cap, nor should you shim the cone to center it.

It should be possible to center the driver in the new foam surround by using the Velodyne's amplifier. A local speaker restoration expert will be trying this technique, and I'll provide an update soon after he's tried that.

Bill Nolting
 
Video by Springfield Speakers on how to center a woofer by using a 50zh sine wave. For a Velodyne, the tone could be fed into the Velodyne amp's RCA input.

Bill Nolting
 
ZenithFM said:
Pete,

I would recommend refoaming the driver while it remains in the cabinet. That process is shown in the YouTube video I link to in my post.

You should not open the speaker's cap, nor should you shim the cone to center it.

It should be possible to center the driver in the new foam surround by using the Velodyne's amplifier. A local speaker restoration expert will be trying this technique, and I'll provide an update soon after he's tried that.

Bill Nolting
Click to expand...
You cannot use the Velodyne's amp. Tried it and because of the accelerometer in the circuit it just oscillates violently (kinda freaked me out at the time until I realized what was happening). I used a 1.5v D cell. In phase the cone lifts up and makes it easy to glue the new surround to it. Once you disconnect the battery it settles down in exactly the right spot. I normally use a bunch of wooden clothespins and check by feel after every opposing pair and have always been happy with the result.
 
Chilibrother,

Many thanks for the great tip. I have forwarded it to the speaker expert who is restoring my ULD-15.

On my ULD-15, I could control the oscillation simply by gently putting my fingers on the driver cone.

The new foam surround should be glued to the cone first and allowed to dry. Then, the outer part of the new foam surround could be glued to the driver's frame. Before the glue sets, the driver could be centered using the Velodyne's amp with a 50hz sine wave. With the form surround attached to the frame, the box would be sealed, allowing the servo to work normally.

Bill Nolting
 
Pete.Schmidt said:
Hi All - I'm new to the group and just got (for free) a Velodyne ULD-15 Subwoofer Series II that has no foam. It was posted (from the daughter of the original owner) a properly working when put into storage 4 years ago and other than the foam looks in mint condition (beautiful cabinet and amp has no rust or scratches). I checked the fuses & when properly hooked up and turned on (w/out any input signal) it starts to Thump Thump w/speaker moving in & out. I found this thread by Zundee

Velodyne ULD-15 subwoofer w/ matching amp https://audiokarma.org/forums/index.php?threads/velodyne-uld-15-subwoofer-w-matching-amp.792824/​

which seems to be the same condition. Blue72 responded and said, " If there is not a perfect air seal (for example, missing foam), the woofer cone will move back and forth by itself because the circuitry doesn't know what to make of the current condition and is trying to correct for something that it can't account for." I'm guessing/hoping mine is making the Thump Thump because the cabinet is not sealed when the foam is deteriorated/gone?

Has anyone else has the same Thump Thump speaker (moving all the way in & out) that was resolved after a Re Foam?
How important is it to remove dust cap and Re Shim when doing a Re Foam?
How do you safely remove the dust cap?
Can I use multiple sheets of paper for shims? I saw a guy on YouTube use paper and it seems that would work.
Are all Re Foam kits equal?
Are there some I should stay away from?
Any other helpful hints?
Click to expand...
Pete, I can help you. I just finished Bill Nolting's ULD 15. You don't need shims but you sure do need to know what you are doing. Seal needs to be perfect.
 
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