John Curl's Blowtorch preamplifier part II - Page 2832 - diyAudio
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Old 21st October 2012, 12:14 PM   #28311
wrinkle is offline wrinkle  United Kingdom
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But we are talking about 3% extra, over what is already produced directly by the driver itself.
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Old 21st October 2012, 12:18 PM   #28312
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About time alignment, it is a minimum requirement for a hifi home enclosure, of course. Not enough, on my point of view.
We can use use digital filters to linearize further both response curve (and reduce some room resonances) and group delay of the whole assembly. You can achieve this for the response curve (those curves are from the Moonlight project, i get similar results with my own system.):
http://www.moonaudio.fr/Photos%20tai...ence%20@2m.jpg
and this for the group delay:
http://www.moonaudio.fr/Photos%20tai...up%20delay.jpg
with as a result, on a 1KHz square wave:
http://www.moonaudio.fr/Photos%20tai...MaX%201kHz.jpg

Quote:
Originally Posted by wrinkle View Post
But we are talking about 3% extra, over what is already produced directly by the driver itself.
Each time i made distortions measurements, it is on an assembled system, one meter away. I don't know how to measure a distortion somewhere inside a driver motor. Yes distortion of the loudspeakers gives very bad numbers, whatever the technology, and i wonder how we can enjoy such numbers, while 0.1% in an amp can be so disagreeable....-)
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Last edited by Esperado; 21st October 2012 at 12:25 PM.
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Old 21st October 2012, 12:57 PM   #28313
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We used a lot of speaker cones in parallel to reduce the distortion to below 3-10% in the midrange that the horns produced. Horns and 10KW? I have some idea of the performance, as I spent the summer of '72 hanging around Kelsey and Morris in London, PA people for Pink Floyd at that time. They used horn bass bins and horn midranges, etc, driven by Phase Linear 700's. Not bad, but the GD wanted something 'better', and I found the weak spot in their system in the 1'' horn throated JBL horns that worked 1KHz and above. This is what needed 'fixing' and so we went to large arrays of direct radiators, and many paralleled horn tweeters (Electrovoice T35) above 4KHz.
Effectively, we removed the horn throat distortion in the critical 1K-4KHz region by using a very large array of JBL 5'' direct radiators, to replace the horns normally used by most PA companies. Worked pretty well too. That 'glare' from excessive energy in the 4-8KHz region was gone. The big trade-off was amplifier power needed for the midrange array. We NEEDED thousands of Watts, and so we had those Mac amps. We used tube Mac 3500 amps for the horn tweeters. Even the roadies could tell the difference between the transistor and tube Macs on the tweeters.
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Old 21st October 2012, 03:16 PM   #28314
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So, at the end, we are on the same wavelengths, John ?

Talking about distortion, of an electo-acoustic device is depressive. Cones or drivers give, at the end, and at the comfortable level we like, similar order distortions ( from my experiences and various measurements, i'm unable to make a decision on that criteria) ).
Cones or drivers present different issues. We Chose our poison. But talking about PA system with hight fidelity in mind is just a joke.. Agree ?

Let-us return to home systems.

Some will prefer to listen to classical "musique de chambre", and will be pleased with a sytem, low level, with very sweet trebles, and focus to detailed room reverberations. They don't care with impact. They will love Quad speakers,as an example.

I was a sound engineer, in contact daily with real instruments, mainly in the "Rock end Roll/ Jazz area. I was looking for a home (or studio) system able to reproduce at real level drums and basses, flat enough for i can judge the tonal balance of my mixs. Analitic enough for i can evaluate my work on reverberations and delays, with enough separation between instruments for i can follow each one with not too much effort to isolate-them in my brain.

I was very uncomfortable with most of the studio monitors, and, believe-me, bored with the harsh sound of compression drivers. Those awfull Tannoy, JBL, Urei...

If i had chosen my actual system, it is because it was the best compromise i found, after, may-be 20 different home enclosures.(from Quad to Elipson, Cabasse etc...) and a lot of mods on them.

My actual system will be the last one. Very dynamic, horns and drums are so real, killing, cymbals are like in the life, you can hear all the dimension and metal, with a clear impact of the stick on it. Not those pshhh pshh pshhh produced by dome tweeters.
Same with the piano. You believe a Steinway or a Bechstein is in your room. And you can immediately identify-them.
Presence of the voices are even too much. (apart Aretha and very few others, i do not care too much about singers).
You can hear the slightest breath and bubbles of saliva...Attacks on the guitar chords are impressive... each instrument is in the space, with space between them.
They don't go flat higher than 16Khz, they are not sweet, you cannot listen to music during hours.
They are two ways, because less crossover, better it is, and it was very difficult to achieve, at the limit of the speakers capability, a coherency. They use a horn for the 1500- 20000 range, but, believe-me you will never notice a Donald Duck "compression" sound in any manner.

You don't believe-me ? Here a revue of the big system (it is in French, use Google translation), build with the same concepts, driver and horn calculations, my enclosures sound very very close:
http://www.esperado.fr/temp/critique.html

Thanks to my very talented friend Francois Delamare for his exceptional talent, innovative ideas and help.
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Old 21st October 2012, 03:34 PM   #28315
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Quote:
Originally Posted by Esperado View Post
You can hear the slightest breath and bubbles of saliva...
Ewwwwww!

se
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Old 21st October 2012, 03:42 PM   #28316
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... The enclosures of this article were from "Maison du haut parleur." in Paris. They are still available under this reference. But do not try to listen to them or buy them any more. After François leaved the company, they have changed the bass speaker, and destroyed the sophisticated huge passive symmetrical filter with impedance compensation...
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Old 21st October 2012, 04:40 PM   #28317
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I built the same sort of design for Gunther Loof for the Paris studio, in 1975. The biggest difference is that I used an Emilar horn with a 1'' throat, and a super-tweeter.
John Meyer and I built the JM/C 3 horn (time aligned with a transient perfect xover) combination, at IHEM in 1974-1975. It was even better, but designed for MUCH higher output levels.
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Old 21st October 2012, 04:54 PM   #28318
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While 'time aligned' horn systems are ideal for home listening, they are almost impossible to build successfully. Either, the 'time alignment' and you get something like a K-horn, or you get a 'successful' 2 way horn-direct radiator combination with a complex crossover.
Transient 'perfect' or simple 6dB/octave crossovers create BIG problems with frequency cancellations due to imperfect acoustic summing of the horn to the direct radiator. I found that 3-pole Bessel filters in the crossover worked best.
Of course, horn throat distortion is relatively small with a home system, BUT when the same horns are used in PA systems, it dominates the distortion spectrum, normally.
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Old 21st October 2012, 05:09 PM   #28319
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I have tried an English translation of the revue here:
http://www.esperado.fr/temp/critique-en.html
(They don't talked about 3% distortion ;-)

Ps: the JBL 2426 J driver is an 1" 16 ohm, for the 6 ohm enclosure.

We had tried near all available driver at this time, before to chose this one.
Other 1" drivers where not good enough or able at low frequency (we do not wanted the bass driver to fractionate), and all the 2" unable to go high enough.
The quality's coherency of those drivers was problematic. Francois was obliged to go to Harman with his Bruel &kjaer equipment to measure and sort the drivers he wanted to order.
More than half of the membranes were rejected.
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Old 21st October 2012, 06:09 PM   #28320
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Esperado, it appears that you do not take horn throat distortion seriously, or have never read any engineering textbook that describes it properly. I personally measured 3% distortion with a similar JBL driver and an LE-85 horn connected, 40 years ago, at a sound check for the GD, with 2W input to the horn, with an oscillator and a wave analyzer. Referencing my measurements to Harry Olsen's 'Acoustical Engineering' and Beranek's 'Acoustics' at the time, I found a good correlation with their graphs of horn throat distortion.

Last edited by john curl; 21st October 2012 at 06:22 PM.
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