New driver servo system

[tomp]

I participated in a Boston Audio Society Zoom meeting Sunday where one of the topics was a new driver servo system. I'm trying to find out if any driver or speaker manufactures will be using it. Here is a link:

https://www.subvo.com/klara-t

[SoundMods]

I participated in a Boston Audio Society Zoom meeting Sunday where one of the topics was a new driver servo system. I'm trying to find out if any driver or speaker manufactures will be using it. Here is a link:

https://www.subvo.com/klara-t

Not sure about that, but the most famous (not necessarly the best) was Velodyne servo-controlled sub-woofers. They had direct speaker-mounted sensor feedback incorporated into the built-in amplifier.

It looks like these Klara-T guys may be "reinventing the wheel."

[HAL]

Interesting sensor tech. Very low mass for the sensor from the description is good. DSP based correction software is interesting.

The Rythmik Audio sense coil style servo drivers have worked well in my subs and sounds very good to me.

Velodyne and early Infinity used accelerometers on the cone for servo sensing. Genesis was doing servo feedback coils in subs like their 12M.

Fun stuff.

[tomp]

I spoke with my editor Joao Martins of audioXpress who said that Mike Klasco (Menlo Scientific) who writes for the sister publication Voice Coil is in touch with the manufacturer and will be handling licensing for them. We should see an article on the system in Voice Coil in the near future.

[tomp]

I participated in a Boston Audio Society Zoom meeting Sunday where one of the topics was a new driver servo system. I'm trying to find out if any driver or speaker manufactures will be using it. Here is a link:

https://www.subvo.com/klara-t

Not sure about that, but the most famous (not necessarly the best) was Velodyne servo-controlled sub-woofers. They had direct speaker-mounted sensor feedback incorporated into the built-in amplifier.

It looks like these Klara-T guys may be "reinventing the wheel."

No doubt that Velodyne has been a leader in sub servo systems but according to the info on this system it should be able to work at much higher frequencies, even up to 20KHz. Not sure how and how well that will work but we shall see.

[Pelliott321]

I understand that whatever the system that is used that is keeping track of what the speaker cone is doing, it sends that info to the amplifier. What I do not understand is what is it in the servo amp that is making the correction. Is it some feedback system

[SoundMods]

I understand that whatever the system that is used that is keeping track of what the speaker cone is doing, it sends that info to the amplifier. What I do not understand is what is it in the servo amp that is making the correction. Is it some feedback system

Yes! They call it motional feedback.

[tomp]

Essentially the amplifier used in the servo system looks at the input signal and compares it to the positional feedback from the sensor and if there is a difference between the input and what the sensor should feed back it does a correction. It can do so as an additional drive level if the driver is lagging behind or a decreased or even opposite polarity signal if the driver is overshooting the signal. The key is that the "correction" circuit must have two things:

First, there has to be enough gain/bandwidth product so that the correction can be applied in the right amount at the right time. If not, the correction circuit, if it lags, can actually introduce more distortion than it fixes. That is why up to now these servos have been used mainly on subs. The problem has not been so much the speed of the amplifiers as the delays caused by slow feedback sensors.

Second, the design of the circuit has to be smart enough to realize when the motor structure has run out of steam and any magnitude applied correction signal can no longer make the necessary correction. Otherwise the correction circuit can potentially send a large enough signal out that it can destroy the driver because the feedback sensor says there is not enough correction. That is one of the many hurdles that Velodyne had to deal with in the early days.

BTW, you have to remember with any feedback circuit, whether in amplifiers or speakers, an error has to occur before a correction can be made. The more competent the feedback circuit, the smaller the error and therefore lower the distortion can be. That is why it is always best to make the system as linear as it can be before applying feedback. If you start with an essentially non-linear system the feedback circuit has a very difficult time to try to make it linear.

[Stuart Polansky]

BTW, you have to remember with any feedback circuit, whether in amplifiers or speakers, an error has to occur before a correction can be made. The more competent the feedback circuit, the smaller the error and therefore lower the distortion can be. That is why it is always best to make the system as linear as it can be before applying feedback. If you start with an essentially non-linear system the feedback circuit has a very difficult time to try to make it linear.

Enter the 12B4 (and others)

[SoundMods]

Essentially the amplifier used in the servo system looks at the input signal and compares it to the positional feedback from the sensor and if there is a difference between the input and what the sensor should feed back it does a correction. It can do so as an additional drive level if the driver is lagging behind or a decreased or even opposite polarity signal if the driver is overshooting the signal. The key is that the "correction" circuit must have two things:

First, there has to be enough gain/bandwidth product so that the correction can be applied in the right amount at the right time. If not, the correction circuit, if it lags, can actually introduce more distortion than it fixes. That is why up to now these servos have been used mainly on subs. The problem has not been so much the speed of the amplifiers as the delays caused by slow feedback sensors.

Second, the design of the circuit has to be smart enough to realize when the motor structure has run out of steam and any magnitude applied correction signal can no longer make the necessary correction. Otherwise the correction circuit can potentially send a large enough signal out that it can destroy the driver because the feedback sensor says there is not enough correction. That is one of the many hurdles that Velodyne had to deal with in the early days.

BTW, you have to remember with any feedback circuit, whether in amplifiers or speakers, an error has to occur before a correction can be made. The more competent the feedback circuit, the smaller the error and therefore lower the distortion can be. That is why it is always best to make the system as linear as it can be before applying feedback. If you start with an essentially non-linear system the feedback circuit has a very difficult time to try to make it linear.

Then of course there is the delay within the feedback network and the response time of the sensor at the woofer, which typically may be an accelerometer, an additional voice coil winding, the combined woofers back EMF read off two parallel 0.1 ohm resistors, or a strain gauge, that adds to the errors. I am not sure any of those schemes can replace a really well designed driver and enclosure method.