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
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...
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
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
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
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.
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.
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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
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
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
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.
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.
It would, but it has many features you would not need. The only one you might take advantage of is the subharmonic synthesizer. (even though its a bit of a gimmik, frowned on by purists)
I'd recommend something like this:
XTA Electronics DP200 Digital Equaliser with XLR Cable Manual 5 | eBay
XTA is the cream of the crop, and I'd take a used XTA over a new DBX, all else being equal. Plus the new driverack is more expensive than the used XTA.
I'd recommend something like this:
XTA Electronics DP200 Digital Equaliser with XLR Cable Manual 5 | eBay
XTA is the cream of the crop, and I'd take a used XTA over a new DBX, all else being equal. Plus the new driverack is more expensive than the used XTA.
The Driverack will auto EQ, but will not set crossover points or time delay. One problem with an auto eq is that it will try to correct problems in frequency response which are caused by phase errors (which can't be done). The box can't know what the best crossover frequency for a given driver is - this depends on power handling and displacement. This still requires a human...
So, even though the box will auto eq, a human is required to evaluate the result to see if it is reasonable.
So, even though the box will auto eq, a human is required to evaluate the result to see if it is reasonable.
Hmm. So I have a $1000 receiver that does EQ and Time Alignment and that is not available in the Pro Audio world? I find that hard to believe, but then again I am not a PA expert by any means.
Back when I was into hardcore car audio, I used an RTA and even TEF-20 for TDS on tuning cars I worked on. If you ask me, the real difficulty is in tuning a car system which is basically pure nearfield versus a PA setup. I say that without ever having to deal with echo in a large venue. Keep in mind that I am not dealing with a large venue here. This is a PA setup in my LR.
-Stu
Back when I was into hardcore car audio, I used an RTA and even TEF-20 for TDS on tuning cars I worked on. If you ask me, the real difficulty is in tuning a car system which is basically pure nearfield versus a PA setup. I say that without ever having to deal with echo in a large venue. Keep in mind that I am not dealing with a large venue here. This is a PA setup in my LR.
-Stu
What is the brand and model of your receiver? Does it do auto eq and auto time alignment using a mic? That'd be cool !
Any recollection of how much your RTA cost back in the day? Or the TEF system? Those were high cost boxes back then. Now we use PC based software, one of the most popular being called SMAART, to serve as our RTA, and delay finder. The problem being, the resolution of the system is less and less as the waveforms get longer , due to fewer and fewer points of reference on a low frequency wave. So, its hard to use on subs. The RTA is useful for giving a visual reassurance that your ears are telling you the right thing. Also good for dazzling newbies and getting chicks.
Any recollection of how much your RTA cost back in the day? Or the TEF system? Those were high cost boxes back then. Now we use PC based software, one of the most popular being called SMAART, to serve as our RTA, and delay finder. The problem being, the resolution of the system is less and less as the waveforms get longer , due to fewer and fewer points of reference on a low frequency wave. So, its hard to use on subs. The RTA is useful for giving a visual reassurance that your ears are telling you the right thing. Also good for dazzling newbies and getting chicks.
I have high end AV receiver from Onkyo that uses Audessey II technology:
Audyssey Laboratories - Wikipedia, the free encyclopedia
When I do the calibration, it knows exactly how far away from the listening position each speaker is. For instance, when I last calibrated, it knew that my mains were 17.6 feet away. Just for grins, I whipped out a measuring tape and sure enough, they are exactly that far away. Would be nice to see a pro audio piece that uses that technology.
As for the RTA and TEF-20, I am not entirely sure. As I recall the RTA was around $3K (not sure of the brand, something Acoustics???). The TEF-20 rig was expensive and required a big brain to use. The TEF-20 was about $6K, then you had to have a fast computer so add another $2K. Lastly you had to have a really nice flat microphone for probably another $2K. In a nutshell, the TEF-20 rig was about $10K.
-Stu
I am not sure what that means as I am not a pro audio guy. Can you please elaborate or provide some links?
-Stu
Minidsp is a very small and extremely versatile DSP circuit..
Welcome to the world of miniDSP | MiniDSP
REW (Room Equalization Wizard) is a measuring software that can analyze the environment and generate the reverse curve to import into the minidsp... Together they can neutralize the room sound. Then you can add stuff like the Linkwitz Transform(LT) to extend the bottom end...
REW is free, the minidsp is ~ $110 and the measurement mic is ~$70... So for less than $200 you have new, warrantied, equipment with factory support...
Welcome to the world of miniDSP | MiniDSP
REW (Room Equalization Wizard) is a measuring software that can analyze the environment and generate the reverse curve to import into the minidsp... Together they can neutralize the room sound. Then you can add stuff like the Linkwitz Transform(LT) to extend the bottom end...
REW is free, the minidsp is ~ $110 and the measurement mic is ~$70... So for less than $200 you have new, warrantied, equipment with factory support...
I have a $20 (used) Onkyo AV receiver that has Audyssey 2EQ built-in (don't have the mic); it was probably around $450 new back around 2007. I think most mid/high end AVRs did that; Pioneer called their version MCACC.
Behringer's DCX2496 Ultradrive Pro Digital Crossover System used to be the poor man's Driverack. No automatic stuff, but there's DSP crossovers, EQ, delay, compression/limiting and stuff. 3 channels in (one can be used for S/PDIF), 6 analog channels out. But it looks like the Driverack PA+ is almost as cheap, and more features?
Behringer's DCX2496 Ultradrive Pro Digital Crossover System used to be the poor man's Driverack. No automatic stuff, but there's DSP crossovers, EQ, delay, compression/limiting and stuff. 3 channels in (one can be used for S/PDIF), 6 analog channels out. But it looks like the Driverack PA+ is almost as cheap, and more features?
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