Ben,
The commercially available (to original equipment manufacturers) B&C/Powersoft IPAL system discussed in posts 27, 31 and 33 does not "go nuts when naive customers push them outside their working range".
The system limiters make it impossible for end users to cause any damage to the system if it was properly set up by the OEM.
Since a manufacturer's warranty covers failures, it makes no sense for an OEM manufacturer to set limit parameters even 1/4 dB higher than safe levels.
After the original failures associated with finding what the real world of DJ abuse could dish out, the systems have been quite "foolproof", and offer the highest clean, near transient perfect output potential in a small package presently available.
That said, few are willing to pay the rather large cost difference for improvements that are (arguably) masked by room modes and reflections or compromised by addition of multiple arrival times due to the large number of open microphones on any concert stage.
Having proved to my own satisfaction that the differences in phase response a MF system can provide is inaudible to my (59 year old, NIHL) ears, I am satisfied with using other (very) good speaker products from B&C.
In the (relatively, compared to this three year old zombie post) near future I will be building a half dozen Keystone "stretch" (taller, lower LF cutoff) subs, and will compare the pair of B&C driver loaded units to the other four loaded with cheaper drivers that I purchased previously, thinking I wouldn't hear the difference in quality.
I have a premonition that four inexpensive drivers will be up for sale once their rental income pays for the cost difference between them and more B&C drivers to replace them ;^).
Art
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Hi,
Years ago I bought a small ported Sony subwoofer for my brother
to go with the Pro LX5 speakers I had previously bought him.
It really was rather good for the £100* I paid for it, and worked
just fine with his speakers, completely did a very good job.
Long term it didn't add much to speakers with much better
bass, but it was just fine adding bass to no bass speakers.
It certainly was not boomy mass market junk.
rgds, sreten.
* I think it was half price, (Richer Sounds), and certainly
£200 was a lot then for a 6.5" small ported subwoofer.
Yes, but....
Recently in the ESL and planners forum, there was discussion of the Sony SA-EX100. (It has ESL tweeters.)
That unit has a trick double coil woofer driver. The feedback coil is custom designed for its purpose (unlike ordinary DVC drivers). That means the coils are not acting like a transformer that inductively sends input electrical signals to the feedback coil from the drive voice coil. Way to go!
Pity the size and other aspects aren't HiFi-worthy. Alas, it is a historic truth that manufacturers (like Sony and Philips) want to use MF to get superior sound out of modest speakers. But DIYers like us aim to take quality systems and make them better.
BTW, BR boxes are not suitable for MF. The sound output does not mimic the cone motion across the range you care about the most. Might have some benefit anyway, maybe.
Ben
Recently in the ESL and planners forum, there was discussion of the Sony SA-EX100. (It has ESL tweeters.)
That unit has a trick double coil woofer driver. The feedback coil is custom designed for its purpose (unlike ordinary DVC drivers). That means the coils are not acting like a transformer that inductively sends input electrical signals to the feedback coil from the drive voice coil. Way to go!
Pity the size and other aspects aren't HiFi-worthy. Alas, it is a historic truth that manufacturers (like Sony and Philips) want to use MF to get superior sound out of modest speakers. But DIYers like us aim to take quality systems and make them better.
BTW, BR boxes are not suitable for MF. The sound output does not mimic the cone motion across the range you care about the most. Might have some benefit anyway, maybe.
Ben
The SA-100EX is ported too.
The MF part of it is hardly a feature as far as I'm concerned, I'd much rather spend my money on a larger woofer (or more woofers) than on MF capability.
Ben,
As the photos clearly show, the sound output of the IPAL bass reflex MF system does accurately "mimic" the transient response of the low frequency input signal.
That said, the mid-range decade from 400 to 4kHz is the range I care about the most.
Curious, what made you decide to resurrect this three year old thread?
Art
In searching for applications of Raspberry Pi (or Arduino) for MF*, came across a post that I felt needed comment. I view DIYaudio as an enduring archive of comments, not as a Twitter message board.
B.
*Anybody have any ideas?
Yes, but apropos subs and MF, the region around system resonance calls out for remediation. Dumb engineering to run a system that goes off the rails with a resonance in the middle of the range.
B.
I just don't believe it.
IPAL are attempting a design which any totally naive DIYer would immediately think of first: hey, just measure the output with a mic in front of the speaker and feedback with enough corrective force to make it flat.
Anybody with any knowledge of feedback theory would just laugh at the naive confusion of phase, distance, frequency, etc that runs riot in that kind of model where you might stick a mic (or in this case, what IPAL calls a pressure transducer of some kind) in front of a driver.
However, IPAL have an interesting variation in that they are comparing interior box sound to outside sound. Beyond my technical grasp to decipher what that means for a BR box, even if it does mean that feedback of this type really does mirror total system output (driver plus vent).... just as a mic might do with a sealed box.
Can a bee fly? Can this system avoid self-destruction? Maybe it can work somewhat provided the feedback is small, feedback is highly shaped by DSP (Raspberry Pi?), band of operation is restricted to small band, or etc.
Ben
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Esgigt,
Believe it or not, (and I do not care whether you do) there are many nightclubs and concert sound systems using the most demanding live and recorded music sources utilizing IPAL systems that prove their reliability on a daily basis.
For what they cost, and in the "mission critical" applications they are used, they must be reliable, or they simply would not be used.
Art
Art - you must have missed my caveats in post 48, esp the one unambiguously identified as "etc"
A lot the commercially viable MF systems seem to use just small feedback fractions (for safety) as revealed by their modest distortion reduction stats. Might be enough sound improvement to justify the added complexity burden or maybe just to justify the marketing efforts.
More feedback fraction, as per this discussion, can lead to blown up expensive drivers (DAMHIK).
B.
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Art, do the math....
EDIT: besides... I've talked to the "inventers" over here of the MFB system and all of them rejected the idea of an open system. Some of them are still (even at high age) busy developing the system further with great results.
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The literature discusses this
The literature also discusses how it incorporates impedance feedback from the woofer into the model, which presumably helps to keep the feedback stable and reduce error.
It seems a strange argument to make: that feedback loops carry an inherent risk of system instability, so a commercial product that uses it both effectively and reliably shouldn't exist.
I'm sure Powersoft's engineers have spent quite a bit of time minimizing the risk of blown drivers. There's quite a lot of computational horsepower in this hardware. I have no doubt there's code in there somewhere to recognize the signs of system instability and limit the possibility of damage.
You keep saying this but please inform me of the dangers in resonances (either driver or cab resonances) within the passband.
ALL of the subs you have used and have been very satisfied with have resonances (either driver or cab resonances OR BOTH in many cases) within the passband.
For example, your sealed sub has an enclosure resonance right in the middle of it's passband. your Klipschhorn has BOTH a driver resonance AND SEVERAL enclosure resonances inside the passband. In all likelihood your big OB hybrid (with close wall placement) also has both driver and "enclosure" resonances in the passband.
Where's the remediation, Ben? All the subs you own and have owned all have the problems you constantly complain about but you've been very satisfied with them. This necessarily points to the fact that you don't understand the issues at play and their importance.
AKA "proportional gain"
All practical systems become unstable at some level of gain.
So which are the systems that use "too-low" (your definition) gain and how do you know this?
What is acceptable (to you) distortion reduction?
Ron E -
Thanks for advancing the discussion intelligently.
First of all, anybody who has worked with op amps (which would immediately self-destruct without proper feedback) or tweeking audio amps (all of which must have feedback to have tolerably low distortion), knows that proper steps need to be taken to ensure stability, as Ron correctly points out.
But I can see that some posters are poorly informed about the vicissitudes of phase in woofers. Perhaps they have been too immersed in endless playing with their sims and not spending enough time with electronic lab tools exploring the behaviour of Rice-Kellogg drivers. And, in reply to weltersys, some are also poorly informed about what happens to feedback when some drunk patron of a dance club innocently pokes their cocktail straw into a driver. Or the everyday wonky behaviour during turn-on of amps, etc.*
My point is that almost everybody knows about Nyqvist analysis of feedback and what happens when phases go wrong. But it must be recognized that driver phases and feedback - esp if you are doing the naive pressure method - are all over the place and make a big mess of the Nyqvist analysis.
So if you are intent on controlling your driver through the resonance range (which as discussed earlier is the real core purpose of MF), you can't be careful enough as the phase hops around something terrible.
Ben
*now that's a good reason to work with an oscilloscope, eh
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I'm not sure why your endless tirade against simulators and people that use them equate these people with functional idiots. Anyone that has used a simulator proficiently is quite intimately familiar with phase and how moving coil drivers work.
Furthermore anyone that has used a passive crossover simulator has had to integrate the phase of 2 (or more) drivers into a smooth phase response to avoid problems in the crossover bandwidth. This is all par for the course and old news to sim users.
It's also implied in your post that sim users have little or no practical experience while in fact everyone that has posted in this thread has built and measured quite a few projects. Except for you. (Cutting a hole in a sheet of wood and sticking an antique driver with 2 mm xmax in it and using it as a subwoofer doesn't count.)
Ben,
I started my 41 adult years in sound reinforcement mixing bands in bars, some of the lightweight mid cones we used back then might not withstand a plastic straw, so we used grill cloth over them to avoid that problem
.The BC 21IPAL can handle 2500 watts (that's 3.3 horsepower to us old-timers) and has moving parts weighing in at 487 grams. Put a drinking straw in front of it while it moves through it's linear stroke of +/- 22 mm (about 1 5/8 inch travel, it can do 80mm peak to peak without damage) and you will have a smashed drinking straw, and perhaps a bruised hand. You can throw baseballs a surprising distance with these drivers, and they sound fine while doing it.
Unlike the crap I started out with 45 years ago, IPAL amps have no wonky turn on transients. Since I started using decent amps, I never have felt the need for an oscilloscope, eh
.Art
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@ bentoronto
No thanks for Not advancing the discussion intelligently
If you had bothered to read the widely available tech etc info on IPAL & Powersoft, you would soon discover that, proper steps Have indeed been taken to ensure stability. If they hadn't, the drivers & amps would be in serious trouble, & 100's of thousands of angry customers $ would have been wasted. Plus their reputation, & the manufactures would be in tatters by now !
It seems like you have NOT been, immersed in endless playing with sims, and spending enough time with electronic lab tools exploring the behaviour of Modern Rice-Kellogg drivers. If you had you wouldn't keep posting such drivel. The way you write, is as if RKD's havn't improved Massively in All sorts of ways, since they were invented.
I've Never experienced or known of even 1 person in Any dance club etc, that has poked a cocktail stick etc into a driver. When was the last time you were in a dance club etc ?
Everyday wonky behaviour during turn-on of amps is a thing of the past for Pro amps. They self mute and safely disconnect their outputs on turn-on/off. But you obviously are Not aware of such developments, which have been standard for Decades !
It's Nyquist, not Nyqvist ! Maybe you should contact Powersoft etc, & inform them of your concerns. I'm sure they having nothing better to do than have their time wasted
Look, there is nothing wrong being an older geezer, with or without a university degree etc etc but, continually talking down to people who have had Many more years with not just theoretical/simming experience, but also Practical experience, doesn't do you any good, or help Anybody, least youself !
Time for you to read up, & catch up
No thanks for Not advancing the discussion intelligently
If you had bothered to read the widely available tech etc info on IPAL & Powersoft, you would soon discover that, proper steps Have indeed been taken to ensure stability. If they hadn't, the drivers & amps would be in serious trouble, & 100's of thousands of angry customers $ would have been wasted. Plus their reputation, & the manufactures would be in tatters by now !
It seems like you have NOT been, immersed in endless playing with sims, and spending enough time with electronic lab tools exploring the behaviour of Modern Rice-Kellogg drivers. If you had you wouldn't keep posting such drivel. The way you write, is as if RKD's havn't improved Massively in All sorts of ways, since they were invented.
I've Never experienced or known of even 1 person in Any dance club etc, that has poked a cocktail stick etc into a driver. When was the last time you were in a dance club etc ?
Everyday wonky behaviour during turn-on of amps is a thing of the past for Pro amps. They self mute and safely disconnect their outputs on turn-on/off. But you obviously are Not aware of such developments, which have been standard for Decades !
It's Nyquist, not Nyqvist ! Maybe you should contact Powersoft etc, & inform them of your concerns. I'm sure they having nothing better to do than have their time wasted
Look, there is nothing wrong being an older geezer, with or without a university degree etc etc but, continually talking down to people who have had Many more years with not just theoretical/simming experience, but also Practical experience, doesn't do you any good, or help Anybody, least youself !
Time for you to read up, & catch up