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Old 26th October 2013, 04:57 AM   #41
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Join Date: Dec 2008
Quote:
Originally Posted by FairfaxStu View Post
Not to burst your buble, but the engineering that went into this thing is scary impressive. Tom Danley designed it and I must say he did an amazing job. Trying to replicate the actual ServODrive with bass module and cabinet will be quite challenging. From what I can tell, you would have to be both a master cabinet maker and a very skilled machinest.

-Stu
Thank you for the compliment, at least on the cabinetry. I worked for Tom at Intersonics, starting in late '86, for five years, then again for Servodrive for another eight. Inbetween I also had a year at R&R Cases, which has a speaker cabinet division and made most of the production cabinets.

That module in the photo for your Basstech 7 could be my handiwork, we made those in house during that era. At one point we also had a machine shop in house, and did much of the metalwork. The aluminum channels we had made at a sheet metal shop, but did the drilling on the CNC machine.

Someone mentioned steel cones-that is incorrect. Cones were a heavy paper pulp, and we treated them in an epoxy solution and baked them in a warming oven.

To Art-the belting was actually plain old polyester belting, no aramid fiber. I could supply the vendor if anyone is interested.

The motors will be pretty difficult to get anymore, they were originally used in large main frame disc drives. The Pacific Scientific motors are that shade of blue for a reason you know...:>)

It is a high speed, low inertia DC motor, with four brushes, in parallel wiring.

Technically, the "inductor" is an autotransformer, used to bump the impedance up to something safe enough for a pro audio amp. Later versions didn't require this, as we had Pac Sci wind the rotors to a higher DC resistance that raised the impedance naturally.

Best regards,

John
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Old 3rd December 2013, 01:55 PM   #42
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Location: Connecticut
My experience is they sound best (and the belts last longer) if you don't ask them to go above 60 hz. This means you need a system which is very capable in the 60 Hz - 120 Hz range, almost dictating the use of a mid bass module, and a 4 way setup.
There is also an art to changing and tensioning the belts. Check them occasionally, as the belts do stretch.
Also be sure to align the time delay at the crossover between the servos and the woofers in the next range. You can apply electronic time delay (preferred), or just move the cabinets around. The test requires a tone generator, and an spl meter. Play the tone gen at the crossover frequency with 1) subs only, 2) midbass only, and 3) both together without moving the meter or test mic. The sum of the two ranges should be +3db. Adjust time delay to maximize summation.
I have a working pair of Contrabass. I love them ! They are flat to 16 hz ! only 115 db max, though. Perfect for that tiny Rave party ! Very good on home theater, also - a bit better than the horn loaded BT-7. But for big shows, the Basstech 7 is still hard to beat.
Congrats on having a working model ! They get really amazing when you get 8 or more !
Hope you have a big garage...
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Old 3rd December 2013, 02:12 PM   #43
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Originally Posted by Zolof911 View Post
My experience is they sound best (and the belts last longer) if you don't ask them to go above 60 hz. This means you need a system which is very capable in the 60 Hz - 120 Hz range, almost dictating the use of a mid bass module, and a 4 way setup.
There is also an art to changing and tensioning the belts. Check them occasionally, as the belts do stretch.
Also be sure to align the time delay at the crossover between the servos and the woofers in the next range. You can apply electronic time delay (preferred), or just move the cabinets around. The test requires a tone generator, and an spl meter. Play the tone gen at the crossover frequency with 1) subs only, 2) midbass only, and 3) both together without moving the meter or test mic. The sum of the two ranges should be +3db. Adjust time delay to maximize summation.
I have a working pair of Contrabass. I love them ! They are flat to 16 hz ! only 115 db max, though. Perfect for that tiny Rave party ! Very good on home theater, also - a bit better than the horn loaded BT-7. But for big shows, the Basstech 7 is still hard to beat.
Congrats on having a working model ! They get really amazing when you get 8 or more !
Hope you have a big garage...
Personal taste. Certainly not unheard of, and the Contrabass is still operating over two octaves with a LPF at 60hz. It is quite capable of very good response and performance up into the typical 80-100hz range for crossover.

As for belt stretching, the material has less than a 2% stretch factor, so I'm not sure what you're experiencing. More often, belts and the drive shaft should be inspected and cleaned with alcohol or Acetone, and reinstalled. The tensioning nut on the center belt, should have a nylock nut preferably, if not, definitely a flat and splitlock washer under the regular nut.

I used my pair for many years as subs to my PA rig, and even in a 640 seat theater provided enough bass to at least sound very full range at reasonable levels. At small pub gigs, bartenders would have to watch anything on shelves. I also would high pass them at 25-30hz as well since I didn't have a lot of organ or synths on stage most times.

I still get them out for movie night at a friend's kid's school. Small gymnasium, the Contrabasses and SPL Runts(older version of Danley Sound Labs SH95). stacked either side of the screen. Works quite well.

Best regards,

John
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Old 4th December 2013, 12:44 PM   #44
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Location: Fairfax, VA
Thanks for information and tips John and Zolof. I am crossing it over at 80Hz and it sounds pretty good there. I bumped it down to 60Hz yesterday and noted a distinct difference as my mains do not cover that range very well.

8 of them huh? That sounds like the rig that a good friend used to have and used in stadium gigs for such bands as the Who and Pink Floyd when they toured the US. I just have the one and it sits in my living room. My PA setup sits along side my main audio setup. I only use the PA rig for music and it does a very good job of that.

-Stu
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Old 4th December 2013, 01:07 PM   #45
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The advice for the lower high frequency limit (60 hz or so instead of 80 - 90 hz ) came from Danley Labs while I was ordering a new set of belts. We did a DJ party on a 125 ft steel hull boat with two contrabass under a Nexo S2. Power was Chevin Research A3000 which gave 900 w / ch @4 ohm, and 1600 w / ch @ 2 ohm. We blew through a fresh set of belts in one show. Motors were undamaged, luckily. I was told that asking the reciprocating mass of the woofers and linkages to reverse direction more rapidly, as the crossover frequency was raised, could lead to increased heat, and ultimately, belt shear.
The funny part of the night was that for the first part of the show, we were not sure if the contrabass were working ok. Then, the DJ found a record (!) with drop bass tones, and the contrabass vibrated the entire hull of the boat ! The DJ got very excited, and began to select records he knew had the deepest bass. We heard them all night after that !
And 8 BT-7 is magic because you can make a giant Left and Right horn of 8 ft wide and 4 ft high using four on each side. They couple together nicely and throw very far. They seem much "punchier" in this configuration. This arrangement works with any bass horn, like the EAW BH-800 or the EM Quake.
Back in the day we had one sub that fired down, and we used it live as a stage thrust. Omni directional bass filled the room very smoothly from the center, and the lead guitar player rocked out on it. No worries only having one sub !
Brian.

Last edited by Zolof911; 4th December 2013 at 01:07 PM. Reason: name
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Old 4th December 2013, 02:43 PM   #46
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Thanks Brian. That makes perfect sense.

I bumped down the xover frequency to as low as my Rane AC23 will go which is somewhere south of 70Hz. I do not want to prematurely wear out the belts because it is a huge pain just to get the BT 7 module out of the ServoDrive - screw after screw after screw.

As for time delay, I just moved the cabinet around in my listening room until I found the sweet spot for my listening position. I do not have any electronic time delay capabilities. What crossover would do that?
-Stu
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Old 4th December 2013, 03:45 PM   #47
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Could be the crossover, or an equalizer, or digital mixing console. Common factor is that they would be digital, rather than analog. You might try something from XTA to replace your Rane when you are ready for an upgrade. A DP200 can be had for $200 used. It is more of an equalizer, but also has crossover and delay. With a sub as revealing as the BT-7, I believe you will hear a big difference. I had an AC23 years ago and found its deep bass potential a bit lacking.
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Old 4th December 2013, 05:47 PM   #48
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Quote:
Originally Posted by Zolof911 View Post
Could be the crossover, or an equalizer, or digital mixing console. Common factor is that they would be digital, rather than analog. You might try something from XTA to replace your Rane when you are ready for an upgrade. A DP200 can be had for $200 used. It is more of an equalizer, but also has crossover and delay. With a sub as revealing as the BT-7, I believe you will hear a big difference. I had an AC23 years ago and found its deep bass potential a bit lacking.
Hrrm, a DSP in the mix. I am very much an amature on this stuff [Pro Audio] but I am in general an audio fanatic that likes to collect toys. Is there a device available that includes a calibration microphone and does all of the setting for you - like my pricey receiver that drives my AV setup?

The DP200 sounds like a nice piece but also sounds like there is a huge learning curve to tweak it.
-Stu
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Old 6th December 2013, 02:26 PM   #49
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There have been attempts by manufacturers to provide this sort of device, but they never seem to work quite right. Used to be that an RTA and an auto EQ system was $10k or more. Now, you can use an inexpensive mic and an Real Time Analyzer app for an ipad for less than $1k .A RTA is useful to show you big peaks or dips in frequency, but it cannot distinguish whether the source of the problem is only frequency response, or is, in fact, time related comb filtering.
Best thing is to trust your ears. Listen to live acoustic instruments from time to time, then try to get your system to sound like that. The RTA is better used to confirm what you hear, rather than as a guide to be followed. Its a cool light show as well !
Actually, the DP200 is rather simple, if its right in front of you , and in the proper light. Located at the bottom of a rack in the bright sun, its very hard to see the display. Ah, such is most digital.
Brian.
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Old 11th December 2013, 09:54 PM   #50
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Would something like this fit the bill?

DriveRack PA+ | dbx Professional Audio
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