SERVO Motor Drive

Anybody has tries or compared this to current largest low-frequency speakers?

Check this out then, this product is claimed to be only -4dB at 1Hz !!!

http://www.eminent-tech.com/RWbrochure.htm

Of course it's more for home cinema installation than PA, but even so....

Am just imaging the day when I go to a festival and see a large array of giant speaker fans in a row across the stage!

Edited by RosscoPico - 27 February 2013 at 6:10pm

RosscoPico wrote: I just looked up the patent no. and it's expired now. http://www.patentbuddy.com/Patent/4564727;jsessionid=4DA6EA374720F023500AB9EA639EE8AF Does this company even make these units any longer? The ServoDrive website has been down for years and the BassTech 7 is no longer manufactured (as far as I know).

The SDL is no longer made, and parts are difficult to come by, as the original uses for the motors have gone out of favor, driving replacement costs way up.
 The connection belts made from arimid fibers are very difficult to source.

I have replaced Servodrive units with conventional drivers, the horns still work fine.

For the late 1980's, the excursion was quite impressive, but modern conventional transducers can far exceed the servo-drive excursion and output.

Tom Danley, the designer of the SDL, and tapped horns, is  using  B&C drivers in most of DSL's sub designs.

Dear John, it is very nice to see you here.

May i ask you, How is the efficiency compared to current modern large linear drivers? 

Maybe the moving mass is larger due force transformation elements in the system,

but a good servo-motor probably gives better torque as well as higher conversion efficiency than linear coils.

Am I right?

Edited by Peter Papp [PKN] - 03 March 2013 at 11:07pm

I was fortunate enough to hear one of these servomotor subs and I thought they were fantastic.

For the size of cabinet they produced sub frequency output at much higher quality and volume than is achievable by any standard driver still to this day. I just don't think the concept was explored enough.

Doing it today, it would as noted be difficult to find servomotors of sufficient strength but that might not necessary at all. One could use several smaller motors sharing a shaft, and at least 2 for a symmetrically driven shaft. This would give the opportunity to scale it better.

I would also combine it with Tymphany's LAT concept as that's already (multi-)shaft driven, and gives an enormous surface area which is really the only thing limiting the performance. You can only get so much excursion out of a servomotor, not because the motor strength limits you but because of the difficulty of driving large enough cones with a belt drive mechanism. So a LAT/servomotor combo could potentially give a 15"x33" LAT array capable of producing the same output as 2x 21" drivers but at much higher sensitivity and output quality. And not least in a far smaller cabinet size.

I would even use symmetrically driven and push pulled shaft in such a set-up and aim to drive more cones at lower maximum excursions to improve quality even further. In such a set-up where the cones are driven by 3 shafts from each end (check the LAT to see the concept) and each shaft being symmetrically push-pulled by 4 servomotors for a total of 24 servomotors in total it's realistic that you could use standard small inexpensive 3.5" HDD servomotors.

I'd naturally also make them actively driven by digitally controlled servomotor drivers instead of an analogue amplifier output as that would give extremely high degree of control over the cone movement. 

Edited by Saturnus - 04 March 2013 at 12:08pm

Saturnus wrote: I was fortunate enough to hear one of these servomotor subs and I thought they were fantastic. For the size of cabinet they produced sub frequency output at much higher quality and volume than is achievable by any standard driver still to this day. I just don't think the concept was explored enough. Doing it today, it would as noted be difficult to find servomotors of sufficient strength but that might not necessary at all. One could use several smaller motors sharing a shaft, and at least 2 for a symmetrically driven shaft. This would give the opportunity to scale it better. I would also combine it with Tymphany's LAT concept as that's already (multi-)shaft driven, and gives an enormous surface area which is really the only thing limiting the performance. You can only get so much excursion out of a servomotor, not because the motor strength limits you but because of the difficulty of driving large enough cones with a belt drive mechanism. So a LAT/servomotor combo could potentially give a 15"x33" LAT array capable of producing the same output as 2x 21" drivers but at much higher sensitivity and output quality. And not least in a far smaller cabinet size. I would even use symmetrically driven and push pulled shaft in such a set-up and aim to drive more cones at lower maximum excursions to improve quality even further. In such a set-up where the cones are driven by 3 shafts from each end (check the LAT to see the concept) and each shaft being symmetrically push-pulled by 4 servomotors for a total of 24 servomotors in total it's realistic that you could use standard small inexpensive 3.5" HDD servomotors. I'd naturally also make them actively driven by digitally controlled servomotor drivers instead of an analogue amplifier output as that would give extremely high degree of control over the cone movement.

I'm afraid you're not correct.  It is quite easy to find very powerful motors.  Technically, the motors used originally are low inertia, high rpm DC motors using brushes/commutators.  They have approximately 2.5lbs. of Alnico V, and the windings are the rotational portion, using no frame to wind on-the windings were formed and shaped using special epoxies or something similar to hold the shape.

The limiting factor in excursion was due to cone construction.  At the time, the parts used were some of the highest excursion parts available.  The belt drive arms could've been made to accomodate any cone excursion capacity.  One of the great attributes of using a "traditional" motor is the linearity-the "voice coil" is always in the same magnetic field, so no matter where in the excursion path the cones might be, you weren't positioning the voice coil out of the magnetic gap.

Another great feature of the design was the Thiele Small parameters were such that much smaller system designs could be had and still produce incredible performance.   I still have a pair of the Contrabass model, which was the production version of a design originally developed at the request of Dr. Joyce Poole and Katherine Payne for a National Geographic funded project at the Amboseli Elephant Project in Kenya in 1988-90. 

The design for this project used the same motor, belt arm drive, and dual opposing 15" cones, housed in a 10 cu. ft. cabinet 37" tall(specific request to fit upright in the back of their Mitsubishi Trooper SUV.  The old speakers were considerably larger and rode on a roof rack rather precariously.  On all four sides at the bottom of the cabinet were 18" passive radiators, each with a moving mass of around 2500gm.

The design produced an F3 of 14hz, and acoustic output at that frequency in the range of 114-116db, measured with the speaker on the ground, and the mic 1m away.  It also did this with approximately 200watts of amplifier power.  Poole and Payne were quite happy and impressed with the design, as it had tons more output in that last octave where they needed it, and it was very clean, and fit into the truck.  I painted it elephant gray as well. ;>)

The commercial version, the Contrabass, was very similar, the only change was reducing the cabinet size to around 7.5 cu. ft., and losing one pair of passive radiators.  This yielded an F3 of 16hz, and left the other parameters the same.  I still use them occasionally for movie showings, and other notable folks have them installed in home theaters, including the Prince of Monaco, George Lucas, and a few others. 

As to the notion that full on servomotors and digital controller/amplifiers working better...I don't know that it is necessary, some things have been tried without much success(and cost/complexity being part of it).  The original Servodrive mechanism has one of the best impulse response measurements of any subwoofer we ever measured(and Tom used the TEF analyzer a lot looking at his designs and others). 

The double motor method was also the original design Tom implemented in the TP1 model.  A pair of smaller motors shared the drive shaft.  It was abondoned as it was more complicated and expensive to produce, and didn't outperform the final single motor version that Tom perfected after that.

Best regards,

John