Loudspeakers ServoDrive Speakers (Contra-Bass)

JD

JD

Well-Known Member
Nightmare of the Day!
We have a very nice pipe organ at Trinity, but the lowest stop is a 32 foot "speaker" stop. It appeared to contain four 15 inch speakers and four 18 inch passive radiators. The suspension on the 15's is shot. Went to take one out and Woooo! They are not "speakers" after all! The diaphragms are driven by a servo motor! So, they haven't been built since the 1980s and there are no replacement parts available! Just to make matters even more fun, each cabinet weighs 120 pounds and is 12 feet up inside the pipe chest with about 4 inches of clearance to work on them... This is going to be a fun project...
In any case, my options are limited. As far as I can tell, the manufacturer "ServoDrive" is long gone. (Contra-Bass is the model) The only option I can think of is to pull the servo guts and mount standard 15's in all 4 locations. It is going to be a real hit-or-miss in Passive radiator cabinets. My only thought is to find drivers with the lowest possible free air cone resonance. The JBL 2235 looked nice at 20Hz, but is discontinued. Foam surround on them as well, so used/old would be a bad idea. I figured before I headed into this one, I would try a post here on the off chance that one of the old-timers knew or had any experience on servo-drive speakers.
Any Thoughts?
 
I found this info at soundforums.net:
[FS] Servodrive Basstech 7 mod available
Of course, this is the basstech and not the ContraBass.
Ivan Beaver also states that DSL still gets calls from people asking about them.
You might also post your question at the prosoundweb.com subwoofer forum. The people there keep up with available speakers.
 
Thank you all for the input! I had already hit some of these sites, and as best quoted from another forum: "Even Danley has moved on from that technology."
The old time audio enthusiast in me wants to remove and rebuild these things. As you can see, there is great affection for ServoDrive out there. The realist in me realizes that I need to have this up and running in about 3 weeks for the Easter season. What trims that timeline even more is the fact that the cabinets are so inaccessible. If I could get them to a flat location, I would replace the surrounds. Done re-foams many many times, but never when the speaker is vertical, installed in the cabinet(s), and 12 feet up in a three story high chest of pipes that desperately look like they want to take core sections out of my butt! Audio repair work is one thing, it's the Indiana Jones part I don't like! It looks like the best option is changing them out to standard 15's. Those, I could take up with me and change them out without having to get the cabinets to a safe location which would require taking the chest apart and removing a rank or so of pipes. I have been on the phone with the engineers who first built the organ, and although they are very sympathetic to my plight, they also don't have any suggestions on how to proceed. Still, I figured having this thread may catch an idea that was beyond my my realm of thought! Sometimes in pursuit of a fix you get so set in your ways that you overlook some other way of achieving the result that would have been much easier.
 
FMEng said:
Explore the sources mentioned above first. After that, give Danley Sound Labs a call. Mike Danley was the genius behind the product. Even if he can't help you repair what you've got, he makes some outstanding subs that could retrofit what you have.
Danley Loudspeakers | Danley Sounds Labs | Danley Sound Labs, Inc.
Click to expand...
Actually, it was Tom Danley back in his Intersonics days, you probably mixed his name with the other founder of Danley Sound, Mike Hedden. Lots of interesting related stories as Intersonics was primarily involved in high tech R&D for NASA and the speaker business was a "in your spare time" effort that grew out of some of Tom's NASA work.

Tom, Mike, Ivan and others at Danley would probably be happy to talk to you about your ServoDrives.
 
I have an Email in to Tom Danley. I suspect he will have answers on what to do to repair the cabinets. I am confident that a repair could be made if I could get the cabinets down to ground level. That may be the stopper on this project.
 
Nothing to add, but it did remind me of this:
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Good luck with the repair!
 
No answer back from Tom. Just going to swap them out for Four Klipsch KI-115 subs for now. I think after the cabinets are pulled, I may try a "labor of love" rebuild with no time pressure. I'll post back if that happens. Should be fun. That belt assy will probably be the challenge.
 
Some closure to this thread for future reference. The Klipsch subs worked out great! If anyone else ends up with a Servodrive Contrabass and they really want to rebuild the belts and get it working, although no longer available, the belts are made from BIC200 belting material which is common in the aviation industry. (you have to cut and glue as needed.) Loctite Prism superglue is used in the manufacturing of finished belt sets.
 
Here's a picture of the Klipsch bins installed:
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Trashed belt in Contrabass:
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From inside the chest:
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Another shot inside the chest:
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Closeup of damaged belt unit:
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We changed file servers and in going over the log files, I was surprised at how many 404's there were for these pictures considering the age of the thread! So, I put them up on our new server:
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