I am trying to find a schematic of a direct servo subwoofer amp so I can try to understand it's design better.
I guess the idea is there is another coil in the sub driver that senses something and sends a feedback signal to the amp so it corrects differences between the original signal and what the driver is doing.
Sounds kind of like negative feedback to me. I don't really know because I can't find any design schematics of this so it seems like just a bunch of hype to me. I know the patent is from the early 70's at least so if it was worth doing I don't see why it wouldn't have caught on.
I recently saw pics of the internals of a plate amp with this technology and there didn't seem to be much to it. I also can't find any measurements of subs with the circuit out vs in.
I guess the idea is there is another coil in the sub driver that senses something and sends a feedback signal to the amp so it corrects differences between the original signal and what the driver is doing.
Sounds kind of like negative feedback to me. I don't really know because I can't find any design schematics of this so it seems like just a bunch of hype to me. I know the patent is from the early 70's at least so if it was worth doing I don't see why it wouldn't have caught on.
I recently saw pics of the internals of a plate amp with this technology and there didn't seem to be much to it. I also can't find any measurements of subs with the circuit out vs in.
Hi,
There are various ways of doing it from cone accelerometers
to a simple pressure sensing device in sealed sunwoofers.
Yes it is a feedback loop, and its main problem is harsh
clipping rather than gradual overdrive. The loop would
make it flat to DC, so you have to add an active roll-off.
It doesn't suit anything other than sealed subs.
It doesn't really do anything in sealed subs that
can't be done well another way.
Still it can be made to work well with low distortion,
but with a lot of details tagged onto the basics.
It can also work well with wacky bass drivers
with odd drive systems that distort a lot,
like DC motors and drive belts and the like.
rgds, sreten.
There are various ways of doing it from cone accelerometers
to a simple pressure sensing device in sealed sunwoofers.
Yes it is a feedback loop, and its main problem is harsh
clipping rather than gradual overdrive. The loop would
make it flat to DC, so you have to add an active roll-off.
It doesn't suit anything other than sealed subs.
It doesn't really do anything in sealed subs that
can't be done well another way.
Still it can be made to work well with low distortion,
but with a lot of details tagged onto the basics.
It can also work well with wacky bass drivers
with odd drive systems that distort a lot,
like DC motors and drive belts and the like.
rgds, sreten.
The velocity signal fedback by the sensing voice coil lowers the Q of the system (amp + driver + box) so its slope looks like as 6 dB/o in the resonance region.
Adding a 6 dB/o bass boost extends the overall response in the bass region.
You refer to the Rythmik Audio direct servo subwoofer.
The amp is certainly conventional. What is interesting is the driver with its velocity sensor. The concept, known since long, is the most simple of all servo drivers technologies.
Adding a 6 dB/o bass boost extends the overall response in the bass region.
You refer to the Rythmik Audio direct servo subwoofer.
The amp is certainly conventional. What is interesting is the driver with its velocity sensor. The concept, known since long, is the most simple of all servo drivers technologies.
Measure the Induced Voltage across the voice coil. That is the Velocity, basic electro-magnetics.
Since this is also the drive coil, you need bridge techniques to null the drive voltage and parasitics.
And why? Accelerometers used to be BIG BUCKS, today they are sub-Buck (most cellphones have several).
Since this is also the drive coil, you need bridge techniques to null the drive voltage and parasitics.
And why? Accelerometers used to be BIG BUCKS, today they are sub-Buck (most cellphones have several).
The answer is in the post before. Bridge technique.
In 1967, I saw it, in a thesis at my engineering school. They were using a second driver that they sacrificed jamming the coil with glue.
The difference signal between the working coil and the dead coil gives accurately the speed of the moving coil.
This speed signal is then applied as negative feedback at the power amplifier.
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All I remember was an equation about the driver where the difference between the moving coil and the same not moving was exactly the speed of the coil.
Using this difference as a feed back is a servo about speed....or was that integrated to do a servo about position ?
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This is what they were doing. They used a second driver ( destroyed ) with its moving coil jammed with glue.
I understand that was to have two identical drivers, one of them with its coil not moving, so the difference signal would exactly represent the motion of the moving coil.
I understand that was to have two identical drivers, one of them with its coil not moving, so the difference signal would exactly represent the motion of the moving coil.
where its jammed? Is it an additional coil which is placed away from the driver? I mean outside the motor?
I saw this in 1968 in a thesis at École Nationale Superieure des Arts et Métiers ( ENSAM Paris ).
I only saw text and figures and do not remember all details.
I remember, at the second driver, they just loaded the space between the moving coil and magnet with epoxy glue.
I only saw text and figures and do not remember all details.
I remember, at the second driver, they just loaded the space between the moving coil and magnet with epoxy glue.
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