Exactly.
One has to do with making low frequency vibrations using a clumsy motor but using feedback to control the motor somewhat; the other has to do with extending negative feedback (in this case, to the speaker), an historic theme of sound reproduction.
Ben
voice coil servo systems are pretty much useless for motional feedback and reducing distortion which is probably why Infinity ditched the idea after using it in their Servo Static speaker in 1968. After that they exclusively used accelerometers in their high end systems with the exception of one speaker which used a bridge arrangement in a feedback loop. Like voice coil feedback it extended the bandwidth but did nothing to reduce the distortion unlike a properly design motional feedback system using an accelerometer.
A voice coil servo will only be effective if the sensing voice coil is NOT wound around the driving coil sharing the same magnetic circuit. It needs to be mechanically coupled but have it's own separate magnetic circuit to be effective. Because of this a properly implemented system is not practical or economical !
Last edited:
Now THAT part of the post is exactly correct. While motional feedback is prolly not feasible for commercial implementation, it is quite a fun thing for the folks on this forum. There are a number of "loose cannons" (please excuse me for pluralizing a plural noun) rolling about in speaker feedback loops whether vc, accelerometer, or whatever and so it is hard to mass produce and sell to the uninitiated.
Are you recommending that people use accelerometers as sensors? That they use 50-cent gizmos to control their $250 woofers?
Whatever theoretical shortcomings there may be to voice coil feedback designs, the shortcomings are trivial compared to the benefits in making fabulously tight, clean, and extended bass.
Ben
what 50 cent gizmo are you talking about ? I don't know any 50 cent accelerometer that is suitable for the job.
There are plenty of short comings to voice coil servos that are not theoretical which is why any servo speaker design worth its salt never uses it.
Infinity, Genesis, Velodyne, Paradigm, Phillips all use accelerometer based motional feedback systems for good reason.
Trev
Do you have somthing to share with us ?
http://www.egr.msu.edu/~radcliff/LabWebPages/home/papers/SpeakerFB.pdf
Tha ACH-01 may not bee the way ? Audio Innovation - by Dan Marx www.danmarx.org
Speaker voltage driven...
Thanks for two interesting reports. In the first link, my original inspiration was the Werner paper cited in the references, 1958. I don't know of a better discussion of the main points of VC-in-a-bridge and general feedback issues.
Here's my take. Rice-Kellogg drivers have been debugged for nearly 100 years. That's a good foundation. It is tricky to "listen" to the output of a speaker using a mic or accelerometer because I don't think these match the mechanical goodness of a driver and the phase relationships may prohibit feedback use.
Anyone who doubts that enlarging the feedback loop has been the historic mission of hifi development should read more history. Speakers are the last frontier and speakers are, relative to electronics, a very weak link in the chain.
Ben
Here's my take. Rice-Kellogg drivers have been debugged for nearly 100 years. That's a good foundation. It is tricky to "listen" to the output of a speaker using a mic or accelerometer because I don't think these match the mechanical goodness of a driver and the phase relationships may prohibit feedback use.
Anyone who doubts that enlarging the feedback loop has been the historic mission of hifi development should read more history. Speakers are the last frontier and speakers are, relative to electronics, a very weak link in the chain.
Ben
Louis Erath was doing "something similar" to that back in the Sixties... LWE1's....
Last edited:
Alternate motion sensing
I work at a company that develops linear motors (actually linear alternator) technology.
In the mid 80' we got totally sick and tired of Linear Variable Displacement Transducers (LVDT'S), especially since we were placing them in a strong magnetic field.
And besides that their frequency response was dismal.
So, we invented a new transducer that had a moving Aluminum core and used the AC resistance of the coil in the transducer to calculate displacement.
The frequency response was good enough for less than 1 degree error at 120 Hz and was very immune to noise.
Of course we started a manufacturing company, but this was the mid 80's and the market was small.
We built transducers for Nascar vehicles to monitor the suspension travel, transducers to go inside hydraulic cylinders and transducers for people who were just sick of the limitations of LVDT's.
Of course like any start-up business there was hiccups and cash flow problems, and since we developed these transducers to instrument our own devices we decided to license them to another manufacturer.
Sunpower was the original inventor and manufacturer.
Sunpower Inc. - Welcome
They have since been licensed to among several company's, eventually to
http://www.sentechlvdt.com/pdf/Fastar.pdf
Fastar may not even be selling them anymore as the demand was so low that my company seemed to be the only costumer, we got sequential serial numbered products every 6 to 12 months.
These transducers measure actual displacement and are accurate to maybe 10 microns if mounted properly.
I think that anyone developing a Motion Feedback Sub woofer might want to take a look at this technology.
The technology is a very small market, hence the prices are quite high, but the actual cost of the transducers and transducer amplifiers would be quite low if used in quantity.
Dave Shade
I work at a company that develops linear motors (actually linear alternator) technology.
In the mid 80' we got totally sick and tired of Linear Variable Displacement Transducers (LVDT'S), especially since we were placing them in a strong magnetic field.
And besides that their frequency response was dismal.
So, we invented a new transducer that had a moving Aluminum core and used the AC resistance of the coil in the transducer to calculate displacement.
The frequency response was good enough for less than 1 degree error at 120 Hz and was very immune to noise.
Of course we started a manufacturing company, but this was the mid 80's and the market was small.
We built transducers for Nascar vehicles to monitor the suspension travel, transducers to go inside hydraulic cylinders and transducers for people who were just sick of the limitations of LVDT's.
Of course like any start-up business there was hiccups and cash flow problems, and since we developed these transducers to instrument our own devices we decided to license them to another manufacturer.
Sunpower was the original inventor and manufacturer.
Sunpower Inc. - Welcome
They have since been licensed to among several company's, eventually to
http://www.sentechlvdt.com/pdf/Fastar.pdf
Fastar may not even be selling them anymore as the demand was so low that my company seemed to be the only costumer, we got sequential serial numbered products every 6 to 12 months.
These transducers measure actual displacement and are accurate to maybe 10 microns if mounted properly.
I think that anyone developing a Motion Feedback Sub woofer might want to take a look at this technology.
The technology is a very small market, hence the prices are quite high, but the actual cost of the transducers and transducer amplifiers would be quite low if used in quantity.
Dave Shade
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.