ETM, looking again at a few pages in your book, it is amazing to me that you put so much into it, and can sell the book at such a low price. A small recommendation might be that you expand the general equation on p. 338 using dot notation, just like Rice and Kellog did in 1925, and added to by Manger in 1975, using M(x)(..)+B(x)(.)+C(x) = (force function), and showing the differences between current drive and voltage drive, if this is possible. Perhaps, if I just read the book, I would find that you have already explained it adequately. However, I suspect that this is the wrong audience for you to really be comfortable in. In any case, good luck with your book, it is more than most here would ever attempt in any case.
Why not gain some of the advantages of current drive within the speaker itself? My Iron Lawbreakers implement some unique design features to do so.
1) They use a maximally efficient bass driver (the JBL 2220A) and a compression driver (Altec 288G) /smooth horn in such a way that significant resistive attenuation (up to 8 db from the lower midrange on up) creates a source impedance at the driver that is closer to that of a transconductance amplifier than a pure voltage source type largely reducing magnetic circuit related distortion and thermal compression. Yet the overall speaker efficiency still is 100db/w/m referenced to its nominal 18 ohm impedance.
2) I have found a way to incorporate an air core transformer (which also serves as the series LP choke) into the bass driver xover in such a way (in conjunction with, within the cabinet, 30% activated coconut shell charcoal by volume in sealed bags with desiccant packets) such that the upper BR tuning impedance peak is eliminated and the measured overall impedance is 18 ohms +/- 20% from 40 hz to over 200 hz. A side benefit of the air core transformer in the xover is easy compensation of the cabinet baffle step. Resultingly, from this xover/damping approach more than unity voltage sensitivity is gained in the 50-80 hz region, usefully filling in the otherwise 'saddle shaped' response of its box tuning just above 30hz and giving usable bass response down to this frequency which is not what would be expected with a 100 liter box coupled with a 15" woofer having a Qts of 0.18. The overall bass amplitude is quite sufficient with this design (perhaps down by a db or so below 100hz, in the interests of full disclosure
), and is extremely tight, nonresonant and resolving of inner detail.
3) As mentioned above, a uniquely flat impedance characteristic is attained from 40 hz to over 200 hz for the Iron Lawbreaker (which could be extended to over 10khz with a reasonably simple zobel network for equivalent performance with voltage or current source amplifiers, although I haven't bothered to add such a network since I am currently using my DC Coupled OTL which is very much a voltage source amplifier. It's interesting that the influence of the air core transformer allows an effective impedance transformation of a bass driver having a Rdc of 6 ohm so that the overall speaker impedance above 40 hz never drops below 15 ohms, and this with series elements of only 600uF capacitance and a conventional series choke connection (of the air core transformer primary) and without any series resistance whatsoever in the LF xover. FWIW, I allowed an impedance droop to 12 ohms at the BR tuning frequency of 31 hz to get a bit more LF, before the impedance increases at 6db/octave at lower frequencies (the overall speaker is capacitively coupled with polypropylene capacitors, largely to minimize out of band bass driver excursion).
1) They use a maximally efficient bass driver (the JBL 2220A) and a compression driver (Altec 288G) /smooth horn in such a way that significant resistive attenuation (up to 8 db from the lower midrange on up) creates a source impedance at the driver that is closer to that of a transconductance amplifier than a pure voltage source type largely reducing magnetic circuit related distortion and thermal compression. Yet the overall speaker efficiency still is 100db/w/m referenced to its nominal 18 ohm impedance.
2) I have found a way to incorporate an air core transformer (which also serves as the series LP choke) into the bass driver xover in such a way (in conjunction with, within the cabinet, 30% activated coconut shell charcoal by volume in sealed bags with desiccant packets) such that the upper BR tuning impedance peak is eliminated and the measured overall impedance is 18 ohms +/- 20% from 40 hz to over 200 hz. A side benefit of the air core transformer in the xover is easy compensation of the cabinet baffle step. Resultingly, from this xover/damping approach more than unity voltage sensitivity is gained in the 50-80 hz region, usefully filling in the otherwise 'saddle shaped' response of its box tuning just above 30hz and giving usable bass response down to this frequency which is not what would be expected with a 100 liter box coupled with a 15" woofer having a Qts of 0.18. The overall bass amplitude is quite sufficient with this design (perhaps down by a db or so below 100hz, in the interests of full disclosure
), and is extremely tight, nonresonant and resolving of inner detail.3) As mentioned above, a uniquely flat impedance characteristic is attained from 40 hz to over 200 hz for the Iron Lawbreaker (which could be extended to over 10khz with a reasonably simple zobel network for equivalent performance with voltage or current source amplifiers, although I haven't bothered to add such a network since I am currently using my DC Coupled OTL which is very much a voltage source amplifier. It's interesting that the influence of the air core transformer allows an effective impedance transformation of a bass driver having a Rdc of 6 ohm so that the overall speaker impedance above 40 hz never drops below 15 ohms, and this with series elements of only 600uF capacitance and a conventional series choke connection (of the air core transformer primary) and without any series resistance whatsoever in the LF xover. FWIW, I allowed an impedance droop to 12 ohms at the BR tuning frequency of 31 hz to get a bit more LF, before the impedance increases at 6db/octave at lower frequencies (the overall speaker is capacitively coupled with polypropylene capacitors, largely to minimize out of band bass driver excursion).
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A slight error in the above. For the 2220A the network attenuation is primarily series reactive, not resistive, in the 1-2 octaves from the lower midrange to the xover point. This is primarily to compensate for on axis baffle step gain, contour the ultimate xover slope to what I call a quasi first order (which is a xover with first order passband characteristics and stopband characteristics that are comparable in overall attenuation to conventional 2nd and 3rd order types as applies to speaker xover applications) and to flatten the slightly rising response of the 2220A above 150hz.
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Hi Dave,
Well, it's difficult to remember exactly what forum a thread is in. So, in that case this is precisely the correct approach I guess. Certainly not to indicate how much "meat" is in the offering - which is what I was attempting to figure out. When you are asked to pay for something, it's nice to have an idea what quality you are getting.
The one thing I don't believe belongs here, which both ETM and JC are guilty of, is the intellectual snobbery that seems to come easily to them. The air of superiority that these two like to put on is distasteful, as well as unpalatable. Something that certainly does not help the cause in any way. For JC, this is expected.
I may buy the book, but it looks like it will have to be after a talk with someone who has read it. I have a full library here at home that confirms I do buy texts that I find informative. That's even after I read a version in PDF format, I will buy the book if it's worthwhile.
Enjoy the sideshow folks.
Well, it's difficult to remember exactly what forum a thread is in. So, in that case this is precisely the correct approach I guess. Certainly not to indicate how much "meat" is in the offering - which is what I was attempting to figure out. When you are asked to pay for something, it's nice to have an idea what quality you are getting.
The one thing I don't believe belongs here, which both ETM and JC are guilty of, is the intellectual snobbery that seems to come easily to them. The air of superiority that these two like to put on is distasteful, as well as unpalatable. Something that certainly does not help the cause in any way. For JC, this is expected.
I may buy the book, but it looks like it will have to be after a talk with someone who has read it. I have a full library here at home that confirms I do buy texts that I find informative. That's even after I read a version in PDF format, I will buy the book if it's worthwhile.
Enjoy the sideshow folks.
Chris, the google preview actually does show quite a lot of the book's contents. Worth a run-through. After reading it, I still have the same opinion as before- it's a worthwhile and valid system design option, but certainly not the ONLY correct way to do things, as (for example) thoriated's example illustrates.
Anatech, ETM and I are conversing at an 'engineering' level, so to speak, rather that a technician level. I try, on this website, to converse at a 'technician' level when I can, and I am usually successful. However ETM actually wrote a book at an 'engineering' level and getting through it takes both math and good analogies of speaker system behavior for it to make any sense. I was asking ETM for a better mathematical of speaker system behavior, with an example used by both 'Rice and Kellogg' (inventors of the direct radiator speaker model) and 'J. Manger' (developer of the first real change in loudspeaker design in 50 years since R&K), to give us a better feel of the tradeoffs in speaker drive. It is really a question to him, and not to everyone.
Hi SY,
Time is an issue - as always, but I'll have a look. Thank you for pointing that out again for me. One concern I have is that I won't learn much that is new, but it's always worth a look. You've seen the "library", so you know it has a lot of basic stuff in there as well. Nothing wrong with refreshing one's memory now and again.
I completely agree that current drive does have it's place among all the other tools at your disposal. One tool never suits every job, and that is also my view.
Hi John,
At least you know how to make me laugh. I really did enjoy your last comments - I really did. Right down the "John Curl alley" as it were. A technician who endeavors to converse at an engineering level, but attempts to talk down to a technical level where possible.
God, you're funny as hell John! I guess I'll take my drooling self on over to the sink to dry off before attempting to understand words from the gods.
Sadly, I suspect you really do believe your understanding and abilities are that far above most others around here. If nothing else, this can be a source of amusement for others you consistently sell short.
John, have a great day. Thank you for putting a smile on my face.
Best, Chris
Edit:
SY, amazing similar thoughts came to both of us.
Time is an issue - as always, but I'll have a look. Thank you for pointing that out again for me. One concern I have is that I won't learn much that is new, but it's always worth a look. You've seen the "library", so you know it has a lot of basic stuff in there as well. Nothing wrong with refreshing one's memory now and again.
I completely agree that current drive does have it's place among all the other tools at your disposal. One tool never suits every job, and that is also my view.
Hi John,
At least you know how to make me laugh. I really did enjoy your last comments - I really did. Right down the "John Curl alley" as it were. A technician who endeavors to converse at an engineering level, but attempts to talk down to a technical level where possible.
God, you're funny as hell John! I guess I'll take my drooling self on over to the sink to dry off before attempting to understand words from the gods.
Sadly, I suspect you really do believe your understanding and abilities are that far above most others around here. If nothing else, this can be a source of amusement for others you consistently sell short.
John, have a great day. Thank you for putting a smile on my face.
Best, Chris
Edit:
SY, amazing similar thoughts came to both of us.
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KEF published a white paper regarding activated charcoal used in speaker enclosures and released a line of speakers that included this material.
Perhaps nanotechnology can come up with an improved version of this. IAC, the use of coconut shell charcoal is one reason I call these speakers 'Iron Lawbreakers'.
Also, I question the assumption that tube amps necessarily have low damping factors. That is definitely not the case with my DC coupled OTL which will maintain a damping factor across the audio band in excess of 100 at 8 ohms without trimming and considerably better than that with adjustment
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Duality
Hi ETM,
I just leafed through your book at Amazon and it looks a very complete, very well written book. Congratulations with bringing such a difficult job to a good end. I have read part of this thread and have ordered the book.
Now, admittedly, I need to work through this to be able to give a well thought out view, but at this point something is bothering me.
You have stated that voltage drive and current drive are complementary views; for example, in current drive you can compensate for resonance peaks by parallel shunting away drive current, while in voltage drive you can do so by series attenuating the drive voltage. There are more examples of this dualism.
If this dualism is the case, one would expect that either method would lead to a similar level of performance, and not that one would be sort of ideal and the other sort of fundamentally flawed.
This is not a disagreement with you at this point, as I said, I need to read the book first, but it nags me.
jd
Hi ETM,
I just leafed through your book at Amazon and it looks a very complete, very well written book. Congratulations with bringing such a difficult job to a good end. I have read part of this thread and have ordered the book.
Now, admittedly, I need to work through this to be able to give a well thought out view, but at this point something is bothering me.
You have stated that voltage drive and current drive are complementary views; for example, in current drive you can compensate for resonance peaks by parallel shunting away drive current, while in voltage drive you can do so by series attenuating the drive voltage. There are more examples of this dualism.
If this dualism is the case, one would expect that either method would lead to a similar level of performance, and not that one would be sort of ideal and the other sort of fundamentally flawed.
This is not a disagreement with you at this point, as I said, I need to read the book first, but it nags me.
jd
Jan, I may be confused, but the dualism breaks when you contrast inductors vs. capacitors - electrostatic speakers and electromagnetic ones. If we note that current drive would be inappropriate for electrostatics, it seems apparent that voltage drive is inappropriate for electromagnetics.
However, this only holds true if coil force is directly proportional to coil current, and it was pointed out to me that this is not so.
- keantoken
However, this only holds true if coil force is directly proportional to coil current, and it was pointed out to me that this is not so.
- keantoken
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