Luckythedog, whoever really wants to can relatively easily make amps which are completely stable into even highly reactive loads. This obviously implies amps which are highly load tolerant, which in turn can never be unless they have very significant current capabilities. Even the Japanese mass manufacturers, such as Kenwood/Trio, Yamaha, et al. have been quoting power ratings into 2 Ohms as per IEC standards since the early 80ies.
The there's the current freak company of Harman/Kardon, their trade mark being very high current capability amps from the lowest to the highest model, although their "HCC" (High Current Capability) is not at all clear under which conditions was it quoted. Into what loads and for how long is altogether missing, but from personal experience, they are usually capable of prodigious impulse currents "as is" from the factory.
And they are far from being alone. NAD and Rotel amps usually do well in this respect.
The there's the current freak company of Harman/Kardon, their trade mark being very high current capability amps from the lowest to the highest model, although their "HCC" (High Current Capability) is not at all clear under which conditions was it quoted. Into what loads and for how long is altogether missing, but from personal experience, they are usually capable of prodigious impulse currents "as is" from the factory.
And they are far from being alone. NAD and Rotel amps usually do well in this respect.
Last edited:
Richard,
So glad to hear you have water for the dispenser and ice maker!
(A great uncle was one of the two fellows who laid out the route for the dam at boulder to L.A.)
Canyon,
Attached is a picture of the heatsinks being used. One per 12706 device. The fan attaches directly to the fins. It was designed to cool a pentium so the 20 watts each one sees doesn't appear to be an issue. At 200 watts it is designed to keep the contact surface be under 47C.
Now the use of a linear power supply is actually a bit much. All I really need is a center tapped transformer and pair of low Vf rectifiers. I use the devices well below ratings at 6 volts. They seem quite happy there.
But by all means do let me know where I am foolish. (Not counting spending time here.)
Also attached is my basement lighting under construction.
So glad to hear you have water for the dispenser and ice maker!
(A great uncle was one of the two fellows who laid out the route for the dam at boulder to L.A.)Canyon,
Attached is a picture of the heatsinks being used. One per 12706 device. The fan attaches directly to the fins. It was designed to cool a pentium so the 20 watts each one sees doesn't appear to be an issue. At 200 watts it is designed to keep the contact surface be under 47C.
Now the use of a linear power supply is actually a bit much. All I really need is a center tapped transformer and pair of low Vf rectifiers. I use the devices well below ratings at 6 volts. They seem quite happy there.
But by all means do let me know where I am foolish. (Not counting spending time here.)
Also attached is my basement lighting under construction.
Attachments
Last edited:
Vacuphile,
So if you used a FIR filter that had enough time to correct for the 180 out of phase port output how long a filter would that take, could you possibly use that audio to match up with a video output or would you now also have to delay the video signal to sync them up? I would think you are talking about a very long delay at the bass resonance frequency to correct this. I would imagine that you would end up worse off than leaving this all alone and just accept the acoustical load just the way we always have. Otherwise use a seal alignment and more power in the amp and much more excursion of the driver, take your pick.
So if you used a FIR filter that had enough time to correct for the 180 out of phase port output how long a filter would that take, could you possibly use that audio to match up with a video output or would you now also have to delay the video signal to sync them up? I would think you are talking about a very long delay at the bass resonance frequency to correct this. I would imagine that you would end up worse off than leaving this all alone and just accept the acoustical load just the way we always have. Otherwise use a seal alignment and more power in the amp and much more excursion of the driver, take your pick.
I got Merilainen's book on current drive* after seeing a couple of his online posts, and was pleasantly surprised at his coherence, despite (see my Amazon review as Bradley Wood) he has the vibe of the fanatic, and one would probably dodge him at a convention or some such unless one was prepared to spend some time patiently listening to a diatribe.
His virtual certainty that he can hear all the benefits he cites (besides the easily-assented-to elimination of voice-coil self-heating-induced resistance changes) is well and good, but consider how difficult they would be to prove in a manner convincing to "scientists". Since virtually all loudspeakers are developed for voltage drive, of course we can't just hook them up to current-output amplifiers without gross effects on frequency response (and Merlainen is keenly aware of this). So how do we do any kind of comparative testing? It's apples and oranges in principle.
I tried to get Olive and Toole to consider the approach and didn't get a peep out of them. Voltage drive is just so prevalent, and the feeling that things are good enough is also nearly as prevalent. Then there's the tendency we have to partition systems into blocks, and when someone attempts to integrate any of those blocks the independent block designers bridle at the invasion of their territory, and the audiophiles are upset as they don't want their playthings taken away. So powered loudspeakers all fail in the marketplace (we'll see how the M2 does in the long run, given that you have to buy specific amplifiers and with specific, albeit not-too-brutal equalization). When I mentioned what in my opinion was a marketing mistake with the bundling of the amplifiers, Sean said "Well these amplifiers might not be good enough for you", thus completely missing my point ( he was corrected speedily). They would probably be FINE for me---but at least for the home system business model, this is not the nature of the high end (some would say fashion audio).
It would take a number of loudspeaker designers and a number of amplifier designers to adopt the current drive approach for anything to begin to evolve. The market needs to be able to play and mix and match. I think Merilainen has done a good job of outlining---even to the point of publishing circuit board layouts!---what approaches might work, even if his style, perhaps borne out of frustration (note the alarming pictorial on his book cover, which was doubtless a strong factor in the AES rejecting his ad) is unduly abrasive.
*ISBN 9781450544009
Brad,
I have that book and though a lot of the electronics mathematics goes over my head I get the premise. What I couldn't get so far from the book and I am still reading and re-reading it is what you would do differently on the speaker side of things besides raise the impedance of the voicecoil higher than normally used for a voltage amplifier. I couldn't see what else he really thought that you would need to do to make a speaker capable of working with his concept.
I have that book and though a lot of the electronics mathematics goes over my head I get the premise. What I couldn't get so far from the book and I am still reading and re-reading it is what you would do differently on the speaker side of things besides raise the impedance of the voicecoil higher than normally used for a voltage amplifier. I couldn't see what else he really thought that you would need to do to make a speaker capable of working with his concept.
The need for equalization is prominent, as well as, for a given output power amplifier, a means of preventing thermal runaway from voice coil overheating. The higher impedance is perhaps a convenience but in principle not a necessity.
His discussion about back emf is also quite interesting.
BTW we will get together---I haven't forgotten about you. Just very strange times of late.
Thank you for this post Brad.
I understand your concerns, although I have no interest for marketing strategies in the world of Hi-Fi.
I consider all the earlier moves toward a ‘system design’ (active loudspeakers) a technically justified engineering approach turned into a honest marketing move.
I am sure that the people who tried it were aware that they would not turn the market upside-down but they felt the need to do the proper thing, despite the complexity and high cost (brave men).
In the very near future due to technology advancement and it’s shrinking cost , there will be only a very few loudspeakers that will be offered DSP and amp -less.
Very true.
George
Brad,
Thanks for the answer and I haven't forgotten about getting together. As you just said about how you need to equalize the speaker for current drive it just seemed that all the real changes to use the current drive were really on the electronics side, the eq and coil heating were all done by measuring and compensating outside of the speaker itself, so again I don't see why he keeps saying that the speakers are designed for voltage drive when there is no basic change on the mechanical side that I see? Yes we can change the suspension to tilt the response curve differently if that was a help but otherwise he never states what he would do to a speaker.
I was just looking at local California colleges to see who is working or would work with dsp applications to audio applications. Anybody here in California have any personal experience in this area and our state colleges and universities? I see perhaps USC and UCSD, perhaps UCSB?
Thanks for the answer and I haven't forgotten about getting together. As you just said about how you need to equalize the speaker for current drive it just seemed that all the real changes to use the current drive were really on the electronics side, the eq and coil heating were all done by measuring and compensating outside of the speaker itself, so again I don't see why he keeps saying that the speakers are designed for voltage drive when there is no basic change on the mechanical side that I see? Yes we can change the suspension to tilt the response curve differently if that was a help but otherwise he never states what he would do to a speaker.
I was just looking at local California colleges to see who is working or would work with dsp applications to audio applications. Anybody here in California have any personal experience in this area and our state colleges and universities? I see perhaps USC and UCSD, perhaps UCSB?
Yes they were brave indeed. And some people I know have put a great deal of effort into achieving perfect on-axis response, but in the absence of powerful modeling programs and anechoic chambers with easily-manipulated microphone positions and data acquisition, have fallen short of good off-axis behavior, so their creations have not necessarily been that satisfactory in real rooms. And room EQ doesn't help off-axis deficiencies, and indeed may make things a lot worse.
Kindhornman,
Presently, I am tunneling my way into the theoretical and practical side of FIR filtering, so I stand to be corrected by those with further advanced understandings.
Let's take an example of a 180 degree phase shift at 20 Hz, which is a wave with a period of 50 ms. It follows from first principles that the minimum delay required to straighten this out is 1/2 of 50 ms = 25 ms. To this should be added the inherent latency of the DSP to do the calculations, store and retrieve data, etc. In couple of weeks time I hope to be able to inform you in terms of (n-1)/2 samples, where n is the number of taps, but I am not yet at the point where I can calculate the number of taps required to realize this filter.
At any rate, this delay is longer than the refresh interval of your video output, so delaying the latter will be required for optimal enjoyment.
If you approach current drive for a convential two- or three-way loudspeaker with an internal conventional crossover, it's hopeless.
If you have access to the individual drivers then no longer hopeless---but it means either a very different crossover or a plurality of amplifiers. so a loudspeaker is most likely either designed for current drive and will sound awful with voltage drive ( an orange) or for voltage drive and will sound awful with current drive (an apple).
All that's out there right now afaik are apples. Tasty ones, some bland but pretty to look at and accompanied by lots of preconceptions, and some pretty rotten ones.
And we haven't even spoken about motional feedback techniques, certain to be anathema for the feedback-averse. Not only is the dog chasing his tail, he's getting poop in his mouth when he manages to catch it
Well having a push pull system driving the speaker with symmetrical current drive on both sides, bridged, and including this into the feedback loop, oh my.
I can ask the questions, and have them, but will I understand the answers!
ps. Vacuphile, thanks your numbers, it helped to put it into perspective, it is a long delay. But truly why, is it worth the trouble in reality?
I can ask the questions, and have them, but will I understand the answers!
ps. Vacuphile, thanks your numbers, it helped to put it into perspective, it is a long delay. But truly why, is it worth the trouble in reality?
Last edited:
JC said he didnt think integration was a good thing (re HiEnd) when I said it would go that way. In fact, it is well along in going/being that way. More and more integration and mobility.
In video, I'm holding out for beyond 3-D.... it's in the works.... holography in the home theater.
THx-RNMarsh
Last edited:
- Status
- Not open for further replies.