Constant Power
- Thread starter mep
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I had previously written:
"...we can bend Hoffman's Iron Law to our advantage if we do it right by choosing an amplifier that delivers increased power into a duly optimized speaker's bass impedance peaks (like in my example above). Better performance at the expense of near-universal compatibility might not interest you, but I bet it would interest some people."
To which andy_c replied:
What I meant was, if you want the improved low end extension ("better performance") that you get with an OTL amp and optimized speakers, you lose the near-universal compatibility that you'd otherwise enjoy with voltage paradigm amps & speakers. That's what I meant by the phrase "at the expense of near-universal compatibility". But I can see how that phrase could be interpreted either way.
I'm not mathematician enough to show you the derivation, sorry. I have to resort to posting examples, and did so in post number 101 (using the methodology described in post number 87), which you are more than welcome to critique or refute with a counter-example.
"...we can bend Hoffman's Iron Law to our advantage if we do it right by choosing an amplifier that delivers increased power into a duly optimized speaker's bass impedance peaks (like in my example above). Better performance at the expense of near-universal compatibility might not interest you, but I bet it would interest some people."
To which andy_c replied:
What I meant was, if you want the improved low end extension ("better performance") that you get with an OTL amp and optimized speakers, you lose the near-universal compatibility that you'd otherwise enjoy with voltage paradigm amps & speakers. That's what I meant by the phrase "at the expense of near-universal compatibility". But I can see how that phrase could be interpreted either way.
I'm not mathematician enough to show you the derivation, sorry. I have to resort to posting examples, and did so in post number 101 (using the methodology described in post number 87), which you are more than welcome to critique or refute with a counter-example.
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Yes. Global feedback has a problem because the propagation delays of several stages compound. That is not a necessary condition for feedback, however. There can be local feedback to each stage, hence no accumulation of delay around the whole amp. This is not a new concept.
And to whatever extent global feedback may raise odd-ordered harmonic distortion, it only matters if the level is high enough to hear. Same is true for any tube amp including OTL, which also have odd-ordered harmonic distortion. The question is how much, and how is it distributed spectrally.
Could you describe the essential characteristics of distortion criteria (even and odd) that correlate with good sound?
If you could have an amplifier with 0.1 ohm output impedance, and exactly the same distortion characteristics of your OTL amps, would you want it?
I think you are talking about perceived loudness?
I like to second this. Agree or disagree, let's show them respect so that they continue to share with us their real-life experience.
I had previously written:
"It depends on whether your top priority is sound quality or virtually carefree system matching. If the latter, then solid state amps with large amounts of global negative feedback offer all you could ever ask for."
To which Roger Dressler replied:
Your critique of my statement as being prejudicial is justified. I committed the fallacy of assuming facts not in evidence, at least not in evidence to your satisfaction and that of many others in this thread. I have posted a retraction in my original post, and now if you'll excuse me, I'll go back to eating this delicious plate of crow followed by a generous serving of humble pie.
"It depends on whether your top priority is sound quality or virtually carefree system matching. If the latter, then solid state amps with large amounts of global negative feedback offer all you could ever ask for."
To which Roger Dressler replied:
Your critique of my statement as being prejudicial is justified. I committed the fallacy of assuming facts not in evidence, at least not in evidence to your satisfaction and that of many others in this thread. I have posted a retraction in my original post, and now if you'll excuse me, I'll go back to eating this delicious plate of crow followed by a generous serving of humble pie.
I very much appreciate your good-natured reply. Be comforted that while the issue was based on your post, it gave me the opportunity to highlight a fallacy harbored by many in these here parts. I hope there's some leftovers to share.
I very much appreciate your good-natured reply. Be comforted that while the issue was based on your post, it gave me the opportunity to highlight a fallacy harbored by many in these here parts. I hope there's some leftovers to share.
Thank you very much, Roger. When I've attained Infallibility, I'll be sure to let you and everyone else know.
What's that? Another serving?? Oh but I couldn't....
Your amp is in the power paradigm forest, but not in the deepest darkest part. It will work well with many voltage paradigm speakers as long as their impedance curves are reasonably well behaved, and will work well with all but a few power paradigm speakers (both within whatever constraints its power limits impose). You have lots of options. The audio gods smile upon you in appreciation of your many expensive sacrifices at the altar of your local dealer.
edit: Ah, I see that you are a dealer! That means you make your sacrifices directly to the Manufacturer, kind of like a high priest, you know...
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Yes, I read your posts, even #101. How is the modeling that you provided not an example? Really? You need an answer to that beyond the fact that it is a model, and is not an example? Pick a passive sub. Pick an OTL amp. Measure the extension and the frequency response. That is an example. A model is a model. In all of this designing of speakers and selling of OTL amps and matching of the two and discovering of synergies between them you don't have one real world example? You didn't take, or even find, one real world measurement to support your hypothesis? When you found a particularly good synergistic match, when your ears told you that the conventional wisdom had been trumped, you didn't take it into your testing room and see exactly what you had?
I do understand this, but when were we talking about apples to apples? I thought you were talking about optimizing technologies? Does your model optimize the match between OTL and speaker and then force the SS example into the OTL's ideal? Do you imagine that a speaker of the same size and efficiency is going to the optimal match to both a 30 watt OTL amp and a 1000 watt class D sub amp?
I'm not arguing with you Duke; I'm still trying to get to something substantive enough to argue with.
Tim
I do not know how Ralph measures the output impedance of his amplifiers, but having designed numerous speakers for them, I can tell you that they behave as if their output impedances are what he claims.
I have no reason to doubt the accuracy of those output impedance measurements either. In fact, the larger the output impedance, the easier it is to measure. What's hard is measuring very low output impedances, such as the Parasound JC-1, at 0.045 to 0.06 Ohm as measured by Stereophile.
The point I was trying to make is that there is no mystery to the process of measuring the output impedance.
First off, sorry I was so crotchety in my last post to you. You resisted the temptation to reply in kind, and I tip my virtual hat to you for that. I bet if we met in person, we'd get along great, and our difference of opinion over this stuff wouldn't amount to a hill of beans.
Yes, really!
Let me explain, and I hope you find the reason for our disconnect amusing, because I do:
My kind (speaker designers) use modelling programs all the time to analyze and compare the low-frequency performance of speaker systems. It is much faster and more reliable for making comparisons than running actual measurements, into which inconsistencies and human error can and do intrude. So it simply never occurred to me that you might consider computer modelling to be invalid. In that case, I will not be able to offer any evidence that you accept. So... I guess you can stop reading now, if you want to!
You have lots of people on your side who have a strong technical background. Maybe you could ask one of them if computer modelling of loudspeaker low-frequency performance is valid for making comparisons? Obviously there's limited incentive for you to do so, because their response might give my analysis a toe-hold of credibility.
If you provide the passive sub and OTL amp, and pay for shipping both ways, I will gladly do the measurements for you. Otherwise, what you are asking me to do for the sake of an obscure argument on a high end audio forum just isn't reasonable.
I don't have any real-world examples that meet the requirements you have laid out (measurements done on subwoofers driven by OTL amps). I work with loudspeaker design every day, always taking amplifier output impedance into account, so I don't need to keep proving this stuff to myself over and over.
None that meet your criteria. I've never driven a subwoofer with an OTL amp, much less measured one.
I did exhaustive measurements of OTL amps and full-range speaker systems over the course of about six months, back in 2006. That established to my satisfaction the validity of taking amplifier output impedance into account in crossover design and in box design and tuning. Those measurements were lost in a hard drive crash a couple of years ago, so I no longer have them. I no longer need them, so it's not worth the time and effort for me to replicate them, even if doing so might just might score me a point in an internet squabble.
It was the other way around. I already knew exactly what I had. I found it by following the science, then took it into my living room to listen to it.
I have been describing an apples-to-apples comparison to you since post 87.
No. Each speaker system is optimized for best possible response with its respective amplifier. We keep the box size and efficiency the same ("apples to apples"), but each speaker system can use whatever woofer and box tuning works best with its respective amplifier. Then we compare the bass response primarily for low-end extension (-3 dB point), but also for smoothness.
Yes... but let me explain:
If we have two speaker systems of the same size and efficiency, one optimized for best response on the 30 watt OTL amp and the other for best response on the 1000 watt Class D amp, and we drive them both at the same power level, assuming neither one is driven into non-linearity (either thermal or mechanical), my claim is that the one on the OTL amp will have deeper bass extension. (I can even model that for you, if you'd like!! Sorry, couldn't resist.)
The amplifier power doesn't come into play in my claim. It does not enter into Hoffman's Iron Law, which is what my claim is focused on. The Iron Law is only about box size, bass extension, and efficiency.
* * * *
As long as you refuse to accept computer modelling, I can't even offer any evidence that meets your approval, much less proof. Stick to that, and by internet standards, you are guaranteed to win.
Which is fine with me, my skeptical friend. My audience is the people who are open to things that challenge conventional wisdom. And obviously I think it helps my cause if they have reasonable trust in the work of Neville Theile and Richard Small (so I'm selectively accepting of conventional wisdom!), and accept that the engineers at companies like LinearX and Harris Technologies were faithful to the work of Thiele and Small when they wrote their loudspeaker modelling software.
Yes, really!
Let me explain, and I hope you find the reason for our disconnect amusing, because I do:
My kind (speaker designers) use modelling programs all the time to analyze and compare the low-frequency performance of speaker systems. It is much faster and more reliable for making comparisons than running actual measurements, into which inconsistencies and human error can and do intrude. So it simply never occurred to me that you might consider computer modelling to be invalid. In that case, I will not be able to offer any evidence that you accept. So... I guess you can stop reading now, if you want to!
You have lots of people on your side who have a strong technical background. Maybe you could ask one of them if computer modelling of loudspeaker low-frequency performance is valid for making comparisons? Obviously there's limited incentive for you to do so, because their response might give my analysis a toe-hold of credibility.
If you provide the passive sub and OTL amp, and pay for shipping both ways, I will gladly do the measurements for you. Otherwise, what you are asking me to do for the sake of an obscure argument on a high end audio forum just isn't reasonable.
I don't have any real-world examples that meet the requirements you have laid out (measurements done on subwoofers driven by OTL amps). I work with loudspeaker design every day, always taking amplifier output impedance into account, so I don't need to keep proving this stuff to myself over and over.
None that meet your criteria. I've never driven a subwoofer with an OTL amp, much less measured one.
I did exhaustive measurements of OTL amps and full-range speaker systems over the course of about six months, back in 2006. That established to my satisfaction the validity of taking amplifier output impedance into account in crossover design and in box design and tuning. Those measurements were lost in a hard drive crash a couple of years ago, so I no longer have them. I no longer need them, so it's not worth the time and effort for me to replicate them, even if doing so might just might score me a point in an internet squabble.
It was the other way around. I already knew exactly what I had. I found it by following the science, then took it into my living room to listen to it.
I have been describing an apples-to-apples comparison to you since post 87.
No. Each speaker system is optimized for best possible response with its respective amplifier. We keep the box size and efficiency the same ("apples to apples"), but each speaker system can use whatever woofer and box tuning works best with its respective amplifier. Then we compare the bass response primarily for low-end extension (-3 dB point), but also for smoothness.
Yes... but let me explain:
If we have two speaker systems of the same size and efficiency, one optimized for best response on the 30 watt OTL amp and the other for best response on the 1000 watt Class D amp, and we drive them both at the same power level, assuming neither one is driven into non-linearity (either thermal or mechanical), my claim is that the one on the OTL amp will have deeper bass extension. (I can even model that for you, if you'd like!! Sorry, couldn't resist.)
The amplifier power doesn't come into play in my claim. It does not enter into Hoffman's Iron Law, which is what my claim is focused on. The Iron Law is only about box size, bass extension, and efficiency.
* * * *
As long as you refuse to accept computer modelling, I can't even offer any evidence that meets your approval, much less proof. Stick to that, and by internet standards, you are guaranteed to win.
Which is fine with me, my skeptical friend. My audience is the people who are open to things that challenge conventional wisdom. And obviously I think it helps my cause if they have reasonable trust in the work of Neville Theile and Richard Small (so I'm selectively accepting of conventional wisdom!), and accept that the engineers at companies like LinearX and Harris Technologies were faithful to the work of Thiele and Small when they wrote their loudspeaker modelling software.
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I certainly accept computer modeling as a proof point for such discussions. I also hope though that the people in the industry do provide in-situ measurements to complement them to show that the theory holds in practice. I realize that winning the argument isn't worth the effort for many. But it often is for me to go and run such tests
.
Good answer.
I don't consider modeling invalid, but I consider it a development tool, not proof of actual performance. I doubt that I'm alone in that POV, even among those who are open to things they hadn't previously considered (Mine is a pre-amp free, all-digital front end, fully active system, by the way. I'm all over stuff most audiophiles still won't consider). Where you lose me, and you may simply be over my head, is in your attempt at "apples to apples vs. your attempt to optimize performance. In my admittedly limited experience, SS, particularly when driving bass, is usually optimal in a place where headroom is massive, efficiency is fairly low and output impedance is deep below the subbasement. It's a place where most OTL amps need not apply. I don't know how you can optimize both technologies and even approach apples to apples; though perhaps you can model it. In any case, I am in over my technical head at this point and would require real-world examples, and to be free of "apples to apples" to proceed. But with that said, while I'm sure you can model the performance of speakers of the same size and efficiency going deeper, smoother, with OTL power, I remain confident that, given the real world OTL/speaker example that resulted from that model, I could find a real world SS/speaker one that, taking full advantage of the strengths of that technology instead forcing an apples to apples comparison with a technology that has very different requirements, could go deeper and smoother still, with an even smaller cabinet.
It was fun fencing with you, Duke. A great workout.
Tim
I certainly accept computer modeling as a proof point for such discussions. I also hope though that the people in the industry do provide in-situ measurements to complement them to show that the theory holds in practice. I realize that winning the argument isn't worth the effort for many. But it often is for me to go and run such tests
If you would be willing to thoroughly design and optimize, buy the parts for, and build two subwoofers, and then supply two different amplifier types, and take them all to an independent third party to have them carefully measured (probably at additional expense; the third party measurement was asked for by Phelonious in post 93) in order to meet the criteria laid down by your sparring partner in an internet forum debate, then you are a far better man than I am!!
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Good answer.
I don't consider modeling invalid, but I consider it a development tool, not proof of actual performance. I doubt that I'm alone in that POV, even among those who are open to things they hadn't previously considered (Mine is a pre-amp free, all-digital front end, fully active system, by the way. I'm all over stuff most audiophiles still won't consider). Where you lose me, and you may simply be over my head, is in your attempt at "apples to apples vs. your attempt to optimize performance. In my admittedly limited experience, SS, particularly when driving bass, is usually optimal in a place where headroom is massive, efficiency is fairly low and output impedance is deep below the subbasement. It's a place where most OTL amps need not apply. I don't know how you can optimize both technologies and even approach apples to apples; though perhaps you can model it. In any case, I am in over my technical head at this point and would require real-world examples, and to be free of "apples to apples" to proceed. But with that said, while I'm sure you can model the performance of speakers of the same size and efficiency going deeper, smoother, with OTL power, I remain confident that, given the real world OTL/speaker example that resulted from that model, I could find a real world SS/speaker one that, taking full advantage of the strengths of that technology instead forcing an apples to apples comparison with a technology that has very different requirements, could go deeper and smoother still, with an even smaller cabinet.
It was fun fencing with you, Duke. A great workout.
Tim
Thank you, Tim. It's a pleasure to get to know you a bit, even though we met under less than ideal circumstances!
If the challenge is to see which can deliver the deepest loudest bass in the smallest box, using real-world available amps, then I'd have to switch sides. I was claiming something else entirely. I think I was saying "it's not po-TAY-toe, it's po-TAH-toe", while you were talking about tomatoes all along.
Duke
wait a sec... preamp-free, all digital, fully active? Blasphemy! Where's my torch and my pitchfork??
(and in the meantime... what digital front end, what speakers, how does it sound? I used to be an ATC dealer, still think very highly of the line.)
I don't think he asked for that much. I am sure he would accept measurements from you on two versions of reality here. I assume one of those paradigms is already what you have built so only one other would need to be built.
But yes, I have gone nearly that far for the sake of getting concrete data
. I am testing some new technology on my boat. I spent some 6 hours on the water last weekend just to get proper, objective data as to whether the technology really works. On paper, the new system should run circles around the old. That is what the theory and "simulation" said. Then I tested it in one condition and the new tech was actually worse! Major dismay as I spent some $3,500 on it. The second 6-hour test did show some benefit but nowhere near what the theory proved. What is remarkable is that despite multiple companies producing these systems, no one, including the press, has ever tested them objectively! So while I am out thousands of dollars and continue to spend a lot of money and time on researching it, I think it is a worthwhile contribution to the community. I learn a lot from others and try to reciprorcate when I can .
It's not quite that simple.
I've learned the hard way not to commit to a project before I can make a reasonably comprehensive estimate of how much time and money it's going to take (and I'm usually overly optimistic - for example, writing this post took far longer than I expected when I made the decision to do so!).
The research alone could easily take a day. If we're going to hold the efficiency constant, that means I have to find two (or more) woofers with the same efficiency (calculated from the T/S parameters, and that's not what manufacturers publish as efficiency so I have to calculate it myself, for a lot of different woofers). That's easy. Next I have to find many such sets of woofers, because here comes the hard part: Out all the sets of woofers I find that are the same efficiency, I have to find a set that includes one woofer that is optimal for the OTL amp in question, and another that is optimal for the solid state amp, with BOTH delivering their optimal performance in the SAME SIZED box, so that we can hold the box size constant without either of the woofers being cheated. If we find two such woofers (and we may not!), we can proceed to build the boxes and make an apples-to-apples comparison.
Doing it half-way is not an option. Bad data is worse than no data.
I hope they aren't uber-expensive woofers, because this is not something I want to spend a lot of money on.
If I don't screw up, maybe I can build both boxes in one day, not counting the half-day trip to buy the plywood. I hope those aren't big woofers, because big boxes could take me a day each. I'm not a professional woodworker by any stretch.
If released from the independent third party measurement requirement, that probably saves me a day.
More than likely someone is going to find fault with my woofer choices and/or box optimizations and/or measurement technique. How much additional time to satisfy them? Another round of boxes? With different woofers?
On the other hand, I can do the same thing on my computer in about fifteen minutes because I can adjust the T/S parameters to match the efficiencies and to optimize the woofers for their respective amps and boxes at the same time (which is admittedly more than I did in post 101, but I got closer to optimum for the three woofers on the solid state amp than I did for the one woofer on the OTL amp). In fact, making comparisons such as this is pretty much what loudspeaker modelling software was invented for! I have to be sure that my T/S parameter adjustments are realistic, so that I'm not modelling an impossibly optimistic woofer, but that can be done without too much trouble. And if someone finds fault with my simulations, I can probably address that in ten or fifteen minutes.
Trying to accommodate everyone who asks you for data that meets their standards can eat up a lot of your time, so I pick and choose. And in this case I choose not to analyze the available woofers, optimize, buy the woofers and wood, and build the boxes.
And now that my erstwhile nemesis and I seem to be on the verge of buy-you-a-beer good terms, it turns out that our respective dogs were in totally separate fights all along. So any measurements that I might have generated would have been irrelevant to what he was talking about. Glad I didn't start on that project after all!
On a different subject, I am totally digging your article on the Perceptual Effects of Room Reflections and the ensuing thread. Your article's and posts' Toole-per-unit-volume ratio is only rivaled by Toole himself. Will finish reading the thread tomorrow.
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Both of you gentlemen are giving me far more credit than I deserve. I'm a simple man; I was just looking for some real-world examples. I hoped Duke had tried this theory on some existing OTL amp/speaker combos and had some results he could point to that we could use as a point of reference. With money as no object, I figured I could pretty easily find a modern SS sub that would beat it. But Duke was running a controlled experiment in a virtual laboratory; I was look for the best bass performance from boxes of, probably, radically different designs. We weren't on the same track and it took me awhile to figure that out. My bad.
I wouldn't do this either:
A purely theoretical exercise to prove a point that probably wouldn't net the best speakers anyway, given that's not even the objective of the exercise. I didn't quite understand where Duke was headed or we could have stopped a few posts earlier.
Duke, you asked about my listening system; thank you. Sharpen the pitchforks. The irony? We were arguing about bass and I have none. I've had it before and may again, but currently listen to a small, active system set up in the near field.
The digital front end is a MacBook Pro loaded with, ahem, redbook files. There actually are some hi-res files in there, but I hear the difference in the mastering, not in the numbers, and haven't even bothered to keep a plug-in like Pure Music in the system to play them in their native resolution. I've auditioned PM and Amarra. I've listened to native resolution, I've compared it, blind, to the same material converted to redbook. I remain convinced that the difference is in the mastering, not the digital resolution. YMMV. You won't be lonely if it does.
USB from the MacBook goes to a simple, but well made Chinese box that isolates, re-clocks, converts to optical and sends that directly to a pair of monitors manufactured by a small English company named AVi. The DAC and remote-controlled analog volume control are built into the AVis.
It sounds good. Clear. Precise. Coherent. The imaging and midrange clarity are pretty astounding, but not at all like the legendary midrange of low watt tube amps. I prefer low noise and crisp, 3-dimensional transients to liquid midrange, personally, and understand that what I prefer, and consider closer to reality, tube lovers often hear as bright.
But no deep bass at this point. Got to stop buying guitars and get a good sub one of these days.
Tim
I wouldn't do this either:
A purely theoretical exercise to prove a point that probably wouldn't net the best speakers anyway, given that's not even the objective of the exercise. I didn't quite understand where Duke was headed or we could have stopped a few posts earlier.
Duke, you asked about my listening system; thank you. Sharpen the pitchforks
. The irony? We were arguing about bass and I have none. I've had it before and may again, but currently listen to a small, active system set up in the near field.The digital front end is a MacBook Pro loaded with, ahem, redbook files. There actually are some hi-res files in there, but I hear the difference in the mastering, not in the numbers, and haven't even bothered to keep a plug-in like Pure Music in the system to play them in their native resolution. I've auditioned PM and Amarra. I've listened to native resolution, I've compared it, blind, to the same material converted to redbook. I remain convinced that the difference is in the mastering, not the digital resolution. YMMV. You won't be lonely if it does.
USB from the MacBook goes to a simple, but well made Chinese box that isolates, re-clocks, converts to optical and sends that directly to a pair of monitors manufactured by a small English company named AVi. The DAC and remote-controlled analog volume control are built into the AVis.
It sounds good. Clear. Precise. Coherent. The imaging and midrange clarity are pretty astounding, but not at all like the legendary midrange of low watt tube amps. I prefer low noise and crisp, 3-dimensional transients to liquid midrange, personally, and understand that what I prefer, and consider closer to reality, tube lovers often hear as bright.
But no deep bass at this point. Got to stop buying guitars and get a good sub one of these days.
Tim
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