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Multi-Way Conventional loudspeakers with crossovers

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Old 23rd July 2008, 06:32 AM   #4311
Lynn Olson is offline Lynn Olson  United States
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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.
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Old 23rd July 2008, 07:19 AM   #4312
mikey_audiogeek is offline mikey_audiogeek  New Zealand
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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
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Old 23rd July 2008, 07:26 AM   #4313
Lynn Olson is offline Lynn Olson  United States
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That mouse (Steamboat Willie) has a lot of power.
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Old 23rd July 2008, 09:08 AM   #4314
Brett is offline Brett
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Quote:
Originally posted by KBK
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.
Please share any links, pics or scans you might have as this is the area of my designs I am currently working on.
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Old 23rd July 2008, 01:34 PM   #4315
John Sheerin is offline John Sheerin  United States
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Quote:
Originally posted by Lynn Olson


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.
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...

Quote:
Originally posted by Lynn Olson


the inductance is quite nonlinear (and has high-order distortion terms), removing it is a gain all around.

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.


Quote:
Originally posted by Lynn Olson

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?

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.
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Old 23rd July 2008, 08:27 PM   #4316
nickmckinney is offline nickmckinney  Barbados
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Quote:
Originally posted by John Sheerin
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.


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.
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Old 23rd July 2008, 09:25 PM   #4317
John Sheerin is offline John Sheerin  United States
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Quote:
Originally posted by nickmckinney




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.

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).
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Old 23rd July 2008, 09:34 PM   #4318
Lynn Olson is offline Lynn Olson  United States
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Quote:
Originally posted by John Sheerin

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.
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.
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Old 23rd July 2008, 09:55 PM   #4319
bigwill is offline bigwill  United Kingdom
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Small world, my dad used to know Arthur Radford. We used to live in Bristol and he repaired lots and lots of Radford valve amplifiers and at one point probably had the biggest collection of Radford amps in the world!
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Old 23rd July 2008, 10:11 PM   #4320
Lynn Olson is offline Lynn Olson  United States
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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).
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