Sure. As simple as that, at least in block form. But EQ is also needed to convert (differentiate) from a velocity feedback to an acceleration feedback (not that I actually know enough calculus to know what that means).
The bridge method provides feedback when the bridge is out of balance during a signal to the driver. In initial set-up, you balance the bridge for the voice coil resistance and any other static impedance you want, just as Werner says. So that sounds real precise with only "error" (AKA distortion and driver mechanical resonance movement) showing up across the bridge and then taken as the feedback signal.
But in practice, I suspect the simple resistor is just about as good as balancing the bridge. Both detect all the error although the bridge sort of subtracts the basic signal, which the resistor does not. Bridge is a good concept but I think Werner (RCA lab, Olson) were shooting for a patent.
Isn't it ridiculous for anybody today to have speakers without any kind of feedback. Sounds like the dark (or deaf) ages to me. (OK, sealed boxes are a kind of degenerative feedback.)
The bridge method provides feedback when the bridge is out of balance during a signal to the driver. In initial set-up, you balance the bridge for the voice coil resistance and any other static impedance you want, just as Werner says. So that sounds real precise with only "error" (AKA distortion and driver mechanical resonance movement) showing up across the bridge and then taken as the feedback signal.
But in practice, I suspect the simple resistor is just about as good as balancing the bridge. Both detect all the error although the bridge sort of subtracts the basic signal, which the resistor does not. Bridge is a good concept but I think Werner (RCA lab, Olson) were shooting for a patent.
Isn't it ridiculous for anybody today to have speakers without any kind of feedback. Sounds like the dark (or deaf) ages to me. (OK, sealed boxes are a kind of degenerative feedback.)
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Don’t put negative impedance and current drive under the same name. They are completely diferent. It is not the same. Negative impedance->zero impedance(voltage drive)->very high impedance(current drive)
@bentoronto
with reference to posts number 199 and 200 where you talk about feedback via a small resistor in series with the speaker.
have you compared with your ears and measurements a speaker with R-sense feedback and then the same speaker without this circuit? .in your experience with this system can a modest performance speaker match a high performance speaker?
with reference to posts number 199 and 200 where you talk about feedback via a small resistor in series with the speaker.
have you compared with your ears and measurements a speaker with R-sense feedback and then the same speaker without this circuit? .in your experience with this system can a modest performance speaker match a high performance speaker?
Philips had their famous motional feedback speaker using a cheap driver, a 10-cent sensor, and a poor small box and even to the present day, there seem to be big enthusiasts for it. Ditto for almost anybody who has reported their experience with DIY systems.
I did some testing at Bell Labs in 1968 of a Wheatstone Bridge amp using clicks and a multi-resonant Karlson box. The improvement was dramatic to the ear and on Polaroid pictures of the storage o'scope (of course Bell had all the very best test equipment, but sounds primitive today). Clicks audibly changed from almost "clunk" to almost "click".
For decades, I was using the bridge (but with minimal feedback) with a Klipsch bass horn. I'm not sure I could tell the difference and never did much comparison testing. Rather hard to improve a Klipsch bass horn in the transients that MFB helps since it is the best in those respects already and no MFB or EQ can do much for a horn low freq cut off.
Lots of trade-offs with bass speakers. While not of much interest here, low quality speakers can be greatly improved with electronic feedback. But for a medium sized box and good driver, I suspect the efforts are well worth the large benefit.
I did some testing at Bell Labs in 1968 of a Wheatstone Bridge amp using clicks and a multi-resonant Karlson box. The improvement was dramatic to the ear and on Polaroid pictures of the storage o'scope (of course Bell had all the very best test equipment, but sounds primitive today). Clicks audibly changed from almost "clunk" to almost "click".
For decades, I was using the bridge (but with minimal feedback) with a Klipsch bass horn. I'm not sure I could tell the difference and never did much comparison testing. Rather hard to improve a Klipsch bass horn in the transients that MFB helps since it is the best in those respects already and no MFB or EQ can do much for a horn low freq cut off.
Lots of trade-offs with bass speakers. While not of much interest here, low quality speakers can be greatly improved with electronic feedback. But for a medium sized box and good driver, I suspect the efforts are well worth the large benefit.
This principle works well if done right. The with /without comparison is dramatic with a closed box. The feedback does not only extend the drivers response, but stops the cone like a brick wall. What most will call a dry bass.
The last one I build used a 12" driver in a reasonable sized enclosure, driven by a very stable 350W amp and an active x-over. This gave impressive results.
I know this principle is often promoted to use very small enclosures and extend the bass response of small drivers. So you build a speaker wrong on purpose and then correct it electronicaly. I question this approach.
Pirate logic, the people that have evolved the Phillips MFB principle and sell reasonable priced, complete sensor systems, make the same mistake. They promote it to make small driver sound like large ones and irgnore the real strenght of the system: Improving the response of full size speaker or large sub woofer. Audiophiles don't want a speaker to be smaller, they want it to be better. Deeper, louder, faster.
The driver IMO has to be high excursion, very robust and with a not too strong magnet. Which is what you would take for a closed box subwoofer. The amp should have more power than the driver is made for, so you prevent it from clipping.
The last one I build used a 12" driver in a reasonable sized enclosure, driven by a very stable 350W amp and an active x-over. This gave impressive results.
I know this principle is often promoted to use very small enclosures and extend the bass response of small drivers. So you build a speaker wrong on purpose and then correct it electronicaly. I question this approach.
Pirate logic, the people that have evolved the Phillips MFB principle and sell reasonable priced, complete sensor systems, make the same mistake. They promote it to make small driver sound like large ones and irgnore the real strenght of the system: Improving the response of full size speaker or large sub woofer. Audiophiles don't want a speaker to be smaller, they want it to be better. Deeper, louder, faster.
The driver IMO has to be high excursion, very robust and with a not too strong magnet. Which is what you would take for a closed box subwoofer. The amp should have more power than the driver is made for, so you prevent it from clipping.
Very wise post, thanks.
But I've always said to use an amp with less power than the driver can handle to avoid very sad accidents during the R&D phase. DAMHIK.
Most females I know tend to detest large speakers and tell me they're a typical male thing
The real strenght of small drivers is that they don't suffer from cone breakup the way large ones do allowing you to extend feedback loop bandwidth to achieve better THD resdults. The larger a cone gets the harder it is to maintain pistonic motion and the smaller your usable correction bandwidth becomes. From an acoustic radiation impedance standpoint you want Sd to be as large as possible, from a servo standpoint you are better off combining Sd of smaller drivers then to use a single large driver. I actually tested this myself over last years xmas holiday using recycled Philips chassis comparing 4 x 8 inch with 2 x 15 inch and found the results both SPL & FR wise to be pretty much comparable.
4 x AD8066 series / parallel with 1 driver equipped with an accelerometer, AD7063 midrange and AD0160 tweeter. Xovers at 400 and 4Khz, 12dB servo loop between 30 and 300hz.
Mc Kenzie C200 15 inch bass, 7 inch audax midrange, JBL slit tweeter. Xovers at 400 and 6Khz, 12dB servo loop between 30 and 150hz.
Agree on your clipping & robustness statement but high Xmax only makes sense when there is enough BL available for the feedback loop to force it to follow the amplifier input.
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"high Xmax" is meant in contrast to many large speaker that have a smaller excursion, compared to smaller HIFI drivers. If you want the MFB to extend the low frequency response, you have to move the cone more out (and in) than in a passive configuration. Not very much to gain with an Xmax like +-5mm.
Of course the drive must be strong enough to control the cone on it's way. If the cone movement/ excursion get's too extreme you'l need a lot of power to stop it.
A large magnet, low excursion PA driver as used in a horn construction is not what makes MFB happy.
So you need a good compromise of a tough cone/ suspension, quite some excursion and a reasonable sized drive. The beating a subwoofer chassis has to take with MFB drive can not be compared to the "normal" use. For the same reason you need a very stable, strong amp that can not only accelerate the cone, but stop it as well. I have no measurements, but with MFB the power to the amp must be much higher than without it.
The cone break up thing is no problem if we talk about large subwoofer chassis that only need to work up to maybe 100-200Hz.
If you aim for a two way, that is something very different.
Quite interesting that you use 4 chassis with a single sensor. Are they critical to match?
Of course the drive must be strong enough to control the cone on it's way. If the cone movement/ excursion get's too extreme you'l need a lot of power to stop it.
A large magnet, low excursion PA driver as used in a horn construction is not what makes MFB happy.
So you need a good compromise of a tough cone/ suspension, quite some excursion and a reasonable sized drive. The beating a subwoofer chassis has to take with MFB drive can not be compared to the "normal" use. For the same reason you need a very stable, strong amp that can not only accelerate the cone, but stop it as well. I have no measurements, but with MFB the power to the amp must be much higher than without it.
The cone break up thing is no problem if we talk about large subwoofer chassis that only need to work up to maybe 100-200Hz.
If you aim for a two way, that is something very different.
Quite interesting that you use 4 chassis with a single sensor. Are they critical to match?