Good morning everyone.
Metalsculptor your comment that that the feedback will “eliminate power compression” is not entirely accurate as it will not reduce the disastrous thermal effects on the VC. The negative feedback loop will minimize the acoustic DB drop from the driver for a while; until the control loop can no-longer correct for the increased VC impedance. In the effort to maintain the output level, the correction loop will continue inject still more power to the VC. Unfortunately, as the VC heats further, a thermal run-a-way affect will ensue until the amplifier either runs out of power, or more often the case results in a burnt out VC. Of course this effect would be limited by the open loop gain of the feedback network, and for this reason the open loop gain should always be minimized especially if there will be a strong possibility of encountering power compression, 10db may be way too much unless some sort of thermal protection (a power limiter) system is also used.
Cheers
Philip
Metalsculptor your comment that that the feedback will “eliminate power compression” is not entirely accurate as it will not reduce the disastrous thermal effects on the VC. The negative feedback loop will minimize the acoustic DB drop from the driver for a while; until the control loop can no-longer correct for the increased VC impedance. In the effort to maintain the output level, the correction loop will continue inject still more power to the VC. Unfortunately, as the VC heats further, a thermal run-a-way affect will ensue until the amplifier either runs out of power, or more often the case results in a burnt out VC. Of course this effect would be limited by the open loop gain of the feedback network, and for this reason the open loop gain should always be minimized especially if there will be a strong possibility of encountering power compression, 10db may be way too much unless some sort of thermal protection (a power limiter) system is also used.
Cheers
Philip
Some thoughts:
1. if your application has thermal run-away concerns, it isn't likely to be a candidate for the fine distortion reduction of feedback (at least as conceived heretofore). Not to deny that it wouldn't make some kind of non-hifi practical sense. If you simulate the thermal run-away in the amp feedback circuit, you can get around that problem.
2. yes, many kinds of sensors have been proposed over the years BUT they must be more precise than the distortion they aim to curb; in earlier years, there was talk of taking cheap woofers in small boxes and using cheap accelerometers to improve them. For sure, better sensors are created all the time and at some point they will be (or already are economically feasibly) better than a voice-coil back-EMF concept.
1. if your application has thermal run-away concerns, it isn't likely to be a candidate for the fine distortion reduction of feedback (at least as conceived heretofore). Not to deny that it wouldn't make some kind of non-hifi practical sense. If you simulate the thermal run-away in the amp feedback circuit, you can get around that problem.
2. yes, many kinds of sensors have been proposed over the years BUT they must be more precise than the distortion they aim to curb; in earlier years, there was talk of taking cheap woofers in small boxes and using cheap accelerometers to improve them. For sure, better sensors are created all the time and at some point they will be (or already are economically feasibly) better than a voice-coil back-EMF concept.
Yes, seemingly, that to me you will understand very difficultly for google transfer doesn't allow to catch an essence you told.
If you want to tell that for measurement of the big course speaker cone the coil of the gage of bigger sizes, it not so is required also. For this purpose to be necessary to increase only the sizes metallic plates strengthened on the speaker cone.
Thanks
If you want to tell that for measurement of the big course speaker cone the coil of the gage of bigger sizes, it not so is required also. For this purpose to be necessary to increase only the sizes metallic plates strengthened on the speaker cone.
Thanks
For bentoronto,
1. The thermal problems mentioned by you at application motional feedback will always arise. They can be solved applying more power speaker or limiting submitted on it power.
2. Nonlinearity of my gage under the form reminds the entrance characteristic of the transistor and on it it is possible to find though also small, but a linear site. Anyway, distortions of my gage, are incommensurably small with distortions which brings speaker.
Thanks
1. The thermal problems mentioned by you at application motional feedback will always arise. They can be solved applying more power speaker or limiting submitted on it power.
2. Nonlinearity of my gage under the form reminds the entrance characteristic of the transistor and on it it is possible to find though also small, but a linear site. Anyway, distortions of my gage, are incommensurably small with distortions which brings speaker.
Thanks
Hi grandfank,
Have you measured distortion before and after applying your circuit?
FYI, A picture showing ACE-Bass distortion figures to compare with:
b
Attachments
Not quite a voice coil in a magnetic field is purely a current to force converter the DC resistance of the voice coil is irrelevant in a current driven application except for heat production. Meaning the feedback loop is not correcting for power compression because there is none with current drive. naturally if the thermal limits of the voice coil or the voltage limits of the amplifier are reached that goes out the window.
FWIW one of the primary force standards used to be a coil in a magnetic field with current drive, I have a set of sub milligram scales which work on the same principle. The application I used to use current drive for was current variable pressure regulators. Damping factor is non existent with current drive but the feedback loop takes care of that just like the head positioning system in a hard drive which achieves sub micron positioning at around 50 Hz
That is what I meant to say Using a larger plate instead of a larger coil for large excursion sub woofers should work.
I understand the problems with google translate I use it to read Chinese
Hay, bjorno!
I talked about the distortions introduced by my sensor and it generates a perfect sine curve, which is the approximation to an iron bar only changes in amplitude without distorting the shape of the curve. He has simmetrical (as multivibrator) generator. But, as I have said, he has no linear characteristic, ie its sensitivity to positive and negative half-waves are not much different. In this respect, the same linearity has not, in my opinion, and capacitive sensors, but they are susceptible to external factors such as humidity and temperature is probably yes.
Actually nor any measure, I did not hold. I just wanted to show you all your sensor and propose to use it because of motional feedback did not see a problem why he is in this case would not help.
Your graphics are very dull and hard to parse that either.
Thank you.
I talked about the distortions introduced by my sensor and it generates a perfect sine curve, which is the approximation to an iron bar only changes in amplitude without distorting the shape of the curve. He has simmetrical (as multivibrator) generator. But, as I have said, he has no linear characteristic, ie its sensitivity to positive and negative half-waves are not much different. In this respect, the same linearity has not, in my opinion, and capacitive sensors, but they are susceptible to external factors such as humidity and temperature is probably yes.
Actually nor any measure, I did not hold. I just wanted to show you all your sensor and propose to use it because of motional feedback did not see a problem why he is in this case would not help.
Your graphics are very dull and hard to parse that either.
Thank you.
Hi Acoustic1,
You mention building the motional feedback subwoofer designed by Russel Breden in electronics world magazine, feb 97 and that it didn't work.
I have build it many years ago and it works perfect.
However, initially I had some problems related to the post 12 of Forr, that could be corrected after emailing with Russel. Back then, it was kind of weird to experience a subwoofer oscillating at high frequency. I used 2 x Visaton GF250, and feel no need to update or upgrade. The closed box, which is rare in subwooferland, is very fast and really matched well with the Martin Logan Arius electrostatics.
The only alternative I read about recently that I would be willing to try was published by the German magazine Hobby-Hifi of 5/2010, that uses two Mivoc XAW 310 HC in a special way. This also closed box design seems a real winner that also is able for 16 Hz as is the Russel design.
Arjen.
You mention building the motional feedback subwoofer designed by Russel Breden in electronics world magazine, feb 97 and that it didn't work.
I have build it many years ago and it works perfect.
However, initially I had some problems related to the post 12 of Forr, that could be corrected after emailing with Russel. Back then, it was kind of weird to experience a subwoofer oscillating at high frequency. I used 2 x Visaton GF250, and feel no need to update or upgrade. The closed box, which is rare in subwooferland, is very fast and really matched well with the Martin Logan Arius electrostatics.
The only alternative I read about recently that I would be willing to try was published by the German magazine Hobby-Hifi of 5/2010, that uses two Mivoc XAW 310 HC in a special way. This also closed box design seems a real winner that also is able for 16 Hz as is the Russel design.
Arjen.
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Yes, I'm with av-trouvaille! Can't be beat for solid, extended bass. I think it is one of those designs that most everybody who tries is gets impressed. CAUTION: you can blow an expensive driver, DAMHIK.
MF is natural to sealed boxes and OBs (both need EQ after, of course). My experience is it good with true horns with a sealed box behind the driver like the Klipschorn. Screwy if used with a Helmholtz box, but I'd say that about such a device without MF too. I'd be immediately tossed from this forum if I candidly expressed my views of tapped horns.
Can anybody provide links or copies of the Breden article? Bjorno, I'd like to be able to read, understand, and otherwise learn more about your attachment, please (I can't even print it out nicely).
MF is natural to sealed boxes and OBs (both need EQ after, of course). My experience is it good with true horns with a sealed box behind the driver like the Klipschorn. Screwy if used with a Helmholtz box, but I'd say that about such a device without MF too. I'd be immediately tossed from this forum if I candidly expressed my views of tapped horns.
Can anybody provide links or copies of the Breden article? Bjorno, I'd like to be able to read, understand, and otherwise learn more about your attachment, please (I can't even print it out nicely).
Hi bentoronto,
Just click at the thumbnail and the picture will be magnified but then you must also click at the lower left corner for further expansion..
b
Hi grandfank,
I guess you have similar problems to magnify the picture as bentoronto hereabove?
b
You can find quite a lot of documentation about speaker servos I compiled some time ago here
Index of /electroac/lectures_utiles/asservissement
Index of /electroac/lectures_utiles/asservissement
Servo latest thinking
Hi all,
I thought you might be intereted in this link to a Patent App for a servo woofer system. Download pdf available from documents tab. The completed idea is used in the Martin Audio ASX and also their latest MLA sub. OK these products are not applicable to a home hi fi. But it gives an idea of what is achievable using this, or similar technology.
Iain.
Hi all,
I thought you might be intereted in this link to a Patent App for a servo woofer system. Download pdf available from documents tab. The completed idea is used in the Martin Audio ASX and also their latest MLA sub. OK these products are not applicable to a home hi fi. But it gives an idea of what is achievable using this, or similar technology.
Iain.
I have nothing against hybrids per se, but that ASX looks like Frankenstein conceptually.
Haven't looked closely, but I think Tymphany Corp has a patent that captures the whole MF picture pretty well.
Rod Elliot (ESP) lays out the amp issues in negative output impedance beautifully - as he always does. Oddly, he doesn't mention a word about motional feedback. But he does complain about the Tymphany patent. Good place to read because he is clear how tricky it is to use positive current feedback to produce negative output impedance (you read that correctly). Also another of his articles goes into some depth about it:
Effects Of Source Impedance on Loudspeakers
Try this on paper. If your cone driver is 6 ohms at 100 Hz and 30 ohms at resonance, and has a great big boom at resonance.... what would a negative output impedance amp be feeding your driver at those two frequencies? (A low output impedance amp would, of course, be feeding almost exactly the same voltage at both.)
Haven't looked closely, but I think Tymphany Corp has a patent that captures the whole MF picture pretty well.
Rod Elliot (ESP) lays out the amp issues in negative output impedance beautifully - as he always does. Oddly, he doesn't mention a word about motional feedback. But he does complain about the Tymphany patent. Good place to read because he is clear how tricky it is to use positive current feedback to produce negative output impedance (you read that correctly). Also another of his articles goes into some depth about it:
Effects Of Source Impedance on Loudspeakers
Try this on paper. If your cone driver is 6 ohms at 100 Hz and 30 ohms at resonance, and has a great big boom at resonance.... what would a negative output impedance amp be feeding your driver at those two frequencies? (A low output impedance amp would, of course, be feeding almost exactly the same voltage at both.)
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