nickmckinney said:
This makes sense. As long as we work with the same materials (paper and aluminum) we're going to see problems at the same frequencies as the old-timers. And the promise of "miracle materials" remains largely unrealized - the new materials have new sets of problems with distortion, unexpected breakups at different sets of frequencies, weird new hysteresis modes that weren't there in the traditional materials, etc. etc. I found the new $60,000 TAD speaker (with its beryllium-diaphragm coaxial mid and tweeter) very disappointing, with audible breakups in the 3~5 kHz range, and deficient HF above 15 kHz. JBL fans consider the K2 drivers something really special, so I still want to audition them.
Phenolic and plastic-diaphragm compression drivers are the fallback position if the aluminum ones are just too hard to control. By avoiding the 10~12 dB HF boost and sharp-edged diffraction horns used in modern theater and SR applications, though, I'm hoping to sidestep the grit and harshness of modern PA systems.
I didn't find the sound of the vintage 288 and 1505 to be all that harsh - a little vague and diffused maybe, sort of on the romantic side, but nothing like the metallic tin-can coloration of modern theater-sound systems. The small and large-format Altecs are completely different animals in terms of midrange and upper-midrange sonics. I'm not that much into JBLs, so I can't comment on the sonics of small and large-format JBL compression drivers.
I guess part of the reason that I'm hard on the JBLs is that I really disliked the peaky midrange and treble of the L100 and L200 when they first came out, and I don't like modern JBL/THX theater-sound. Then again, I'm not a fan of the Altec A7, either. I like some of the old-timers, and don't like others. It all depends. If they measure rough in the 2~5 kHz region, I probably won't like it.
P.S. Not much to add on the active crossover - that'll be for the 18" driver, which will probably be the Beyma SM118N until the Lambda 18-incher comes into production.
I didn't find the sound of the vintage 288 and 1505 to be all that harsh - a little vague and diffused maybe, sort of on the romantic side, but nothing like the metallic tin-can coloration of modern theater-sound systems. The small and large-format Altecs are completely different animals in terms of midrange and upper-midrange sonics. I'm not that much into JBLs, so I can't comment on the sonics of small and large-format JBL compression drivers.
I guess part of the reason that I'm hard on the JBLs is that I really disliked the peaky midrange and treble of the L100 and L200 when they first came out, and I don't like modern JBL/THX theater-sound. Then again, I'm not a fan of the Altec A7, either. I like some of the old-timers, and don't like others. It all depends. If they measure rough in the 2~5 kHz region, I probably won't like it.
P.S. Not much to add on the active crossover - that'll be for the 18" driver, which will probably be the Beyma SM118N until the Lambda 18-incher comes into production.
"Yes rubber surrounds cause some amazing break ups. When I started down the low inductance road the first problem I found was that whatever was resonating in the driver showed mountain peaks in the impedance curve. I have never seen a worse set of impedance bumps than a prototype TD driver with a rubber surround. It took a special foam and special doping of the foam to get the impedance curve of our drivers smooth enough for my tastes, the foam itself had troubles also."
Interesting to hear that since most mainstream publications and even Lynn's website state that rubber has great damping properties.
Interesting to hear that since most mainstream publications and even Lynn's website state that rubber has great damping properties.
Thank you so much for your answers.
Regarding driver selection for midrange duties, I don't know if someone mentioned these: Fane Axiom series . Alnico motor, 1.75" voice coils for the 10" and 12" drivers, high sensitivity. Probably the best suited are the 12 (alnico) and the 15 (only ferrite) versions.
Oh, and because we have the luck to have some experts in motor design here, what do you think of this field coil design: HERE and HERE - prototype
It has a FEMM simulation also, not just a rendering.
Also here are some DIY projects of field-coil and alnico wide-rangers: Atelier Rullit . It's kind of one-of-a-kind
. I find it a great site, and very inspiring also.
Regarding driver selection for midrange duties, I don't know if someone mentioned these: Fane Axiom series . Alnico motor, 1.75" voice coils for the 10" and 12" drivers, high sensitivity. Probably the best suited are the 12 (alnico) and the 15 (only ferrite) versions.
Oh, and because we have the luck to have some experts in motor design here, what do you think of this field coil design: HERE and HERE - prototype
It has a FEMM simulation also, not just a rendering.
Also here are some DIY projects of field-coil and alnico wide-rangers: Atelier Rullit . It's kind of one-of-a-kind
. I find it a great site, and very inspiring also.
Caferacer said:
I am a lot more skeptical about wonder damping materials than I used to be. Although John and Nick didn't put up a big flashing sign, what was implied in their last post was the degree that woofer inductance masks serious resonances in the impedance curve.
Back when I was at Audionics in the mid-Seventies, I used the BBC chopped-sinewave technique to slowly sweep through the impedance curve and look for narrowband "buried resonance". And boy, were they there! A lot of them! What was surprising was how narrow these buggers were - maybe 50~100 Hz wide at 3 kHz, for example. That meant they would stimulated on a quasi-random basis when listening to music - classical music, with its dense spectrum, would be more likely to wake it up, while sparse music, like jazz or rock, would be less likely to stimulate the narrowband resonances. Thus, the preference for one kind of speaker for classical, and another for rock-n-roll.
With the exotic inductance control techniques of John, Nick, and presumably 18Sound, you get nearly flat impedance curves. Since the inductance is quite nonlinear (and has high-order distortion terms), removing it is a gain all around.
Being able to newly discover little bits of grunge is also a win-win situation - particularly if the voice coil, the spider, or the surround are the problem. Side-to-side rocking, or complex high-order vibration modes, do not readily respond to equalization except in the gross sense of flattening out the frequency response. Equalization does nothing for narrowband regions of high distortion, or narrow spikes in the directivity pattern caused by small regions of the driver breaking up. At the driver level, it's better to track these things down and do your best to get rid of them.
After-the-fact driver hacking tends to be a losing proposition - yes, you can coat the cone with miracle gunk and remove the dustcap (both of which destroy the resale value), but you can't do anything about the spider or surround, unless you go ahead and completely recone the driver. At that point you might as well design a new driver from scratch, since all you're saving is the motor and basket.
Edge termination has always been the trickiest part of driver design, going right back to Rice and Kellogg. It has been hostile to theorizing, and not all that easy to measure, either. The ridiculous variety of spiders and surrounds over the last 80 years is a comment about the difficulty of the problem, and the reason I have the greatest respect for driver designers who know what they are doing.
As a commenter on the audio scene, I'm always trying to break down the wall of secrecy that surrounds this aspect of driver design. I respect the principle of trade secrets, but the sad history of audio is that key design aspects are lost over time thanks to designers moving on and corporations going out of business. This results in the gradual loss of proprietary knowledge over the decades and the absurd spectacle of re-inventions of concepts that are half-a-century old (or older).
I got in trouble a little while ago commenting on applying Aquaplas on the surround vs the diaphragm, and Greg Timbers set me straight. All well and good. But the impulse data to support this statement is ... where? In the corporate archives? What happens twenty or thirty years from now, when all of us are gone, and all the people in the future have to go on are brief anecdotes sitting on a file server somewhere?
That's why I'm always pushing for more data. The big corporations bought TEF and MLSSA systems soon after they came out, but the data they were collecting remain in corporate archives, even for speakers that are long discontinued. As Altec demonstrates, audio corporations are not forever - and the knowledge of the original designers, as well as the data they collected, becomes dispersed and lost over time.
Retrospective measurements, and careful disassembly of the drivers, does not tell the whole story, nor does it reveal the intentions and goals of the designers. People all over the world are still doing archeology on Western Electric, Altec, and RCA theater sound equipment, more than half a century of after the drivers, horns, and amplifiers were designed.
Lynn Olson said:
And sharp slopes are no good as they capture, isolate and smear resonant energy beyond the crossover range. Besides the misbehaviour of the filter with the imperfect driver- as all drivers are. I do believe the most mis-applied crossover type known to man is the high order slope of 24db. It's funny how you can hear a 24db crossover at a show, long before you enter the display room. So bad, you don't even have to be in the room to hear it.
Anything done by Robin Marshall has always been a good thing to look at when pondering Surround/cone termination.
As for re-hashing, the best and most intelligent bracing I've ever seen in my life..I saw in a speaker from the 50's.
I should add the topic of loss-of-knowledge is a sensitive topic for me. Back when I was college, I took a summer job as a GS-4 Graphics Aide for NASA, during the summer of the Moon landings. Even though I was at NASA headquarters in Washington DC, it was still plenty exciting - and I was the presenter behind the rear-projection screen that showed the proposals for top brass at headquarters. I presented the NASA plans for the next thirty years - through the Year 2000.
The only element of those plans that survived the savage Nixon budget cuts was the Space Shuttle - in grotesquely altered from, with the JT79 hydrogen-fuelled jet engines deleted, and a pair of strap-on solid-fuel boosters added on. Continuously-occupied Moon bases by 1975, deleted. Earth-to-Moon Space Tug, deleted. Nuclear-powered rocket for missions to Mars and the fringes of the Solar System, deleted. Boeing 2707 Mach 3 titanium-skinned supersonic transport, deleted. Thank you very much, Nixon. Thanks to you, the future we could have had does not exist.
Guess what happened to the Huntsville team that designed the Saturn 5 rocket, still to this day the most powerful launch system ever built? Gone. Dispersed, the know-how scattered to the winds. If the USA wanted to go back to the Moon, it would take longer than the entire original Apollo program. In terms of aerospace, the USA is now further behind than we were forty years ago. Passenger planes fly slower and are no more comfortable. There no plans serious plans anywhere in the world to built an SST. The tooling for the SR-71 Blackbird, which is still the fastest plane in the world, was destroyed at the order of the Secretary of Defense.
Knowledge is really lost and destroyed, and re-creating it is fragmentary at best. The future of the movie 2001 was in fact a realistic projection based on the best available data from NASA at the time. The world has lost more than 40 years of potential technological progress thanks to the short-sighted budget-cutting of the early Seventies - instead, we now live in a world dominated by geopolitical and military competition for fossil fuels.
This is a dramatic example of what quietly happens in audio. Key aspects of knowledge really are lost over time, and forward progress is many times nothing more than marketing PR over the latest gimmick like iPods. Some fields advance - computers and the Internet, obviously - but other fields stagnate. The social communities of the Internet - like this one - can get around the institutional obstacles, exchange knowledge, and act as a collective memory for an industry that has a very long record of forgetting technology. With any luck, we can build things no corporation would take a chance on.
As for a return to space - well, I have a feeling it will be a Chinese rocket that offers the first commercial spaceflights to the tourist attractions of the Moonbase. Now there's a thought - Hong Kong on the Moon. Hollywood scriptwriters, you saw it here first.
The only element of those plans that survived the savage Nixon budget cuts was the Space Shuttle - in grotesquely altered from, with the JT79 hydrogen-fuelled jet engines deleted, and a pair of strap-on solid-fuel boosters added on. Continuously-occupied Moon bases by 1975, deleted. Earth-to-Moon Space Tug, deleted. Nuclear-powered rocket for missions to Mars and the fringes of the Solar System, deleted. Boeing 2707 Mach 3 titanium-skinned supersonic transport, deleted. Thank you very much, Nixon. Thanks to you, the future we could have had does not exist.
Guess what happened to the Huntsville team that designed the Saturn 5 rocket, still to this day the most powerful launch system ever built? Gone. Dispersed, the know-how scattered to the winds. If the USA wanted to go back to the Moon, it would take longer than the entire original Apollo program. In terms of aerospace, the USA is now further behind than we were forty years ago. Passenger planes fly slower and are no more comfortable. There no plans serious plans anywhere in the world to built an SST. The tooling for the SR-71 Blackbird, which is still the fastest plane in the world, was destroyed at the order of the Secretary of Defense.
Knowledge is really lost and destroyed, and re-creating it is fragmentary at best. The future of the movie 2001 was in fact a realistic projection based on the best available data from NASA at the time. The world has lost more than 40 years of potential technological progress thanks to the short-sighted budget-cutting of the early Seventies - instead, we now live in a world dominated by geopolitical and military competition for fossil fuels.
This is a dramatic example of what quietly happens in audio. Key aspects of knowledge really are lost over time, and forward progress is many times nothing more than marketing PR over the latest gimmick like iPods. Some fields advance - computers and the Internet, obviously - but other fields stagnate. The social communities of the Internet - like this one - can get around the institutional obstacles, exchange knowledge, and act as a collective memory for an industry that has a very long record of forgetting technology. With any luck, we can build things no corporation would take a chance on.
As for a return to space - well, I have a feeling it will be a Chinese rocket that offers the first commercial spaceflights to the tourist attractions of the Moonbase. Now there's a thought - Hong Kong on the Moon. Hollywood scriptwriters, you saw it here first.
A perfect example being that I JUST came up with something that in theory, should dramatically reduce transient distortion in drivers (standard design drivers, and a revealed adjunct to other unpublished stuff) Now, keep it until I can patent it, or blurt it out? My bar or needle and experience on that one is to keep it to myself as the ridicule suffered after revelation..or..conversely... the lack of recognition of the idea's origin point has always been an irritant. My experience in giving away patentable stuff that has been picked up and used by others is at about 8 items or so, when it comes to these forums. This concerns things that have been used and become viable commercial successes.
As a recent example, in the Blowtorch thread, about a day or two ago, I came up with a fix for volume controls to deal with transient originated distortions. I published it immediately on thinking it up, as I've done similar before. Right after I stated it, John said that it was one of the blowtorch's 'secrets'. Whoops.
As a recent example, in the Blowtorch thread, about a day or two ago, I came up with a fix for volume controls to deal with transient originated distortions. I published it immediately on thinking it up, as I've done similar before. Right after I stated it, John said that it was one of the blowtorch's 'secrets'. Whoops.
Well, one advantage of public disclosure (preferably with some kind of hard-copy backup, like a magazine article) is that it establishes priority. That may not sound like much, but it does prevent some greedy people from trying to patent your idea in the future, since all it takes is a photocopy of the (dated) magazine article to blow the patent, or patent application, out of the water. Firstest with the Mostest is what counts - and being seen as such. Visibility has its advantages.
That's why hobbyist magazines can actually be rather useful in establishing priority - as well as a low-cost form of self-promotion. Cheaper than advertising, and more credible, too. A win-win all around. Everyone thinks you're a good guy, when what you're really doing is self-promotion at very low cost (your time to write the article and make it interesting).
Be sure to throw in some snazzy graphics, everyone likes that, and it makes the written content more memorable. Speaking as a technical writer, I'd most often do the graphics first, then simply write the text to illustrate the pictures. It's also an easy way to do a presentation - graphics first, then improvise the talk around the pictures. That way you don't even need notes, just tell 'em what they're seeing. That's all I'm doing in the picture shown below, just making it up as I go along.
The magazine article can also be used as a citation of prior art, which can quite useful if you want to develop the concept a lot further and structure a new patent around it. Pictures make the difference!
I really think the common practice of trade secrecy has been quite destructive to the audio field - for one thing, many audio designers are such egotists that they have nothing but contempt for the ideas of others (present company excepted of course). Or if they copy it, it'll be such a half-***** job that it'll hardly work at all. This is a lot more common than you might think. Collegiality is all too rare, and that works against us.
That's why hobbyist magazines can actually be rather useful in establishing priority - as well as a low-cost form of self-promotion. Cheaper than advertising, and more credible, too. A win-win all around. Everyone thinks you're a good guy, when what you're really doing is self-promotion at very low cost (your time to write the article and make it interesting).
Be sure to throw in some snazzy graphics, everyone likes that, and it makes the written content more memorable. Speaking as a technical writer, I'd most often do the graphics first, then simply write the text to illustrate the pictures. It's also an easy way to do a presentation - graphics first, then improvise the talk around the pictures. That way you don't even need notes, just tell 'em what they're seeing. That's all I'm doing in the picture shown below, just making it up as I go along.
The magazine article can also be used as a citation of prior art, which can quite useful if you want to develop the concept a lot further and structure a new patent around it. Pictures make the difference!
I really think the common practice of trade secrecy has been quite destructive to the audio field - for one thing, many audio designers are such egotists that they have nothing but contempt for the ideas of others (present company excepted of course). Or if they copy it, it'll be such a half-***** job that it'll hardly work at all. This is a lot more common than you might think. Collegiality is all too rare, and that works against us.
Attachments
For anyone interested in reading more about loss-of-knowledge I can recommend this book: Free Culture: The Nature and Future of Creativity
Cheers,
Mike
Cheers,
Mike
Lynn Olson said:
Sorry, but why would this be? Mechanical resonances will be reflected into the impedance curve to be in series with the impedance of the inductance, so they should still show up as spikes. I guess I can see where the ripples in the phase might not be as obvious if the phase has a larger slope to it...
Lynn Olson said:
Do you have a reference or data for this? I ask because it's something I'm interested in, but most speaker distortion I have seen and measured has been low order. Typically the L vs displacement or L vs current are not functions with sharp corners so I wouldn't expect it to produce high-order distortion. I do think it makes a difference in the sound based on informal listening tests I've done.
Lynn Olson said:
Having previously worked as a transducer designer, I can tell you (and you already know) that every audio company in the world of any size knows that the average customer has, relatively speaking, no knowledge about audio. Most people don't know how to interpret a frequency response plot let alone more sophisticated measurements. Since it requires time and effort (ie, money) to publish everything that is published (literally, the company hires people to perform this function), there is no incentive for companies to publish more in-depth information, as it won't appreciably increase their sales. I can say that internally, many companies have documents called 'best practices' and 'knowledge bases' that try to document all those little tips and tricks that might otherwise be lost as engineers moved on or just to make sure good techniques are uniformly applied. However, as you say, these things will be lost when companies die. Of course companies are not generally in business to teach other companies how to design and build better speakers, so I wouldn't expect to see these things published any time soon. I think the only thing you can realistically do is figure it out yourself and publish it somewhere public. I know I personally would like to build and possibly sell my own transducers at some point in the future, and I can tell you that laying out a step by step explanation of all my experiments and my construction process doesn't sound very appealing even now from a purely hypothetical standpoint. I imagine I would publish more information than the average audio company, but that would be because my market would be people like you who would have enough knowledge to interpret some of it.
John Sheerin said:
Best way to test inductance issues on drivers I have found is a mixed signal of 2 sine waves, one at the lowest frequency and strong enough to take the driver to xmax and the other sine wave at the highest frequency that the driver is expected to reproduce. Then see if the higher frequency changes when the lower sine wave is removed.
A poor mans test is to play it full range and manually move the cone back and forth. With normal junk drivers on the out stroke the treble response is significantly improved.
nickmckinney said:
I assume you mean do that and look at the difference in the max and min values of the amplitude of the higher frequency tone compared to with no low frequency tone? That's a standard AMD test (albeit I've usually used AMD to see BL variation, but you can also use it to see Cms and Le variation). The best way I know to test is to use a Klippel analyzer and get a plot of Le vs X and Le vs I. It's a graphical representation of what causes the results of the AMD test, although it does separate things out a bit better. Of course that is the rich man's test - $35k and up for a system last time I got a quote. However that doesn't really address anything that I was asking about (high order non-linearities in the inductance and mechanical resonances that are reflected back into the impedance curve being masked by high inductance).
John Sheerin said:
Ancient Wireless World articles by D.E.L. Shorter that showed swept (not single-tone) distortion harmonics from the 2nd through to the 5th, from 50 Hz to 5 kHz. I read the articles a long time ago, some time back in the Seventies when I was working at Audionics, and sadly no longer have the originals, which went back another ten to fifteen years.
Audionics of Oregon imported Radford during the early Seventies, so it had a Brit connection, including visits to Ye Olde Country every couple of years to see the old man in his factory in Bristol. He liked to drive his Jag at insane speeds down the middle of those crazy three-lane roads - you don't forget that right away. The Radford factory was something else, some kind of sheltered workshop for the local crazies, with hunchbacked characters right out of Young Frankenstein.
Arthur couldn't understand why Americans thought Jags were unreliable, until he mentioned in passing the factory staff mechanic came through Bristol every couple of months and "tuned them up". We explained that the factory mechanics didn't do that in the US ... in fact, that Jaguars (and other English cars) were notorious for falling apart in the USA, particularly in the West, where people drove long distances in very hot weather.
Our little group (Charles Wood, Gene Still, and myself) were kind of goggle-eyed at the whole idea of the factory mechanic coming around on a regular basis and "tuning up" the product - it certainly told us volumes about different ideas of reliability. By contrast, the Japanese built cars, trucks, and electronics to be abused in Third World countries with basically no maintenance at all - and Americans don't like doing maintenance on a regular basis either. We had to explain to Arthur that Americans expected things to last forever, and certainly to never go back to the factory for repair or a "tune up" - it was Arthur who was surprised to hear that.
Of course, distances in the UK seem very compact for people who live in the Western part of the USA, where the nearest adjacent metropolis is hundreds or thousands of miles away. Where I am now, for example - there's Denver, 20 miles away, but the nearest cities that are bigger than Denver are in Texas, Illinois, or California - not exactly next door. "Just pop around the corner" has a different meaning here.
The Radford tube and transistor amps were pretty good for the day, and the TL-90 speaker was one of the true classics. Good sound, and Arthur was a real character who had seen it all. The people at Audionics felt privileged to be the US importer during the early Seventies.
Having grown up in Hong Kong and gone to King George the Fifth secondary school, I fell into the Brit way of seeing things easily enough. It didn't hurt that my hifi preferences were thoroughly Anglophile, listening to Quad ESL57's, B&W Model 70's, and Spendors at Radio People in Hong Kong. I still like that stuff - old school but superb on choral music and large-scale symphonic.
Speaking of old school - it just occurred to me I might actually have one of those KGV ties I had to wear every day, along with those silly blazers! KGV wasn't air-conditioned back in the Sixties, and Hong Kong has a humid subtropical climate. I should probably pick up a copy of this book, since it mirrors my own experiences growing up in Japan and Hong Kong during the Fifties and Sixties (minus the marital discord).
Having grown up in Hong Kong and gone to King George the Fifth secondary school, I fell into the Brit way of seeing things easily enough. It didn't hurt that my hifi preferences were thoroughly Anglophile, listening to Quad ESL57's, B&W Model 70's, and Spendors at Radio People in Hong Kong. I still like that stuff - old school but superb on choral music and large-scale symphonic.
Speaking of old school - it just occurred to me I might actually have one of those KGV ties I had to wear every day, along with those silly blazers! KGV wasn't air-conditioned back in the Sixties, and Hong Kong has a humid subtropical climate. I should probably pick up a copy of this book, since it mirrors my own experiences growing up in Japan and Hong Kong during the Fifties and Sixties (minus the marital discord).