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From Dennis, of course:
Subject: Platitudes! Science! Audio Religion! Politics! $ales!
Date: Thu, 29 Jun 2006 22:26:12 -0600
Good grief! The age-old battle between Super Scientist and Audio Religionist is mighty strange to me! Not that it hasn't been going on for almost a Century. WW2 ended and all the military-trained "experts" came home and built "ham" rigs. Soon, people again started living normally, and these "hams" turned their military electronics training into something they could listen to-- or something someone would hire them to design, so it could be sold.
The stuff to be sold had to have "specs"-- something the $alesmen demanded. Either you generated some "specs" or you got "canned". The military stuff and the engineering that went with it was to be scientific, reliable, repeatable, and correctible (repairable).
The ARRL Radio Amateurs Handbook made available to the new "ham" operators-- the mathematics and formulae of basic electronics. Many, many other authors soon developed their own sets of literature and dogma, and some of you know more of it than I do. Are these formulae correct? Yes-- mathematically they usually are, and we use them every day. But none of this was ever designed to really reproduce music well.
The art of doing that had grown up mostly around the movie industry both before and after WW2. The Lansing organization got started (JBL and ALTEC speakers) in the early days-- because MGM pictures didn't like hearing TWO taps for every ONE tap-- of a tap-dancer in their movies! Jim Lansing solved that problem, and speaker time-alignment was born.
But the amplifiers WERE NOT time-aligned....yet. For a while nobody cared. They weren't using much feedback in very many amps yet, and the W.E. model 91 (300B amplifier)-- was still in use in many movie theatres. This thing was very far from perfect, but it wasn't suffering seriously from too much negative feedback., and it was operated "Class A". Other W.E. amplifiers got used in theatres (and so did RCAs, etc.), but none of them ever sounded as "right" as the W.E. "91". Today, the TUBE-- (300B) is worshipped-- a mistake of course, but not a horrible one musically.
TODAY we have arrived at the point where we want AMPLIFIER time-alignment as well as SPEAKER time-alignment. We also expect this from wiring and interconnects. That is why you will find no shielding and nothing too close to anything else-- in all my designs. You must accomplish this and keep all wiring SHORT while you're at it. Also, no wire can come near another or to anything else-- regardless of insulation used.
The art of reproducing reality simply requires that the amplifying devices be allowed to do their jobs-- unmolested and not degraded by efforts to "help them" from self-appointed genius engineers who have no movie theatre experience, or maybe can't hear the problems they are causing. The circuits for reproducing reality best are EXTREMELY SIMPLE and depend upon proper use and placement of the devices, NOT upon any theories, or "proven" science.
After all, the idea was (and is) to recreate reality-- not to build monuments to scientific theory or genius. We have developed some very reliable, repeatable, accurate, good science for getting this done, and we express the results of this in audio listener terms, NOT in techno-speak and formulae, which can be irrelevant.
The need to "prove" everything-- so coveted in scientific circles is anathema to us because it makes a really simple job both overly complex and tampered with. When you are trying to reproduce reality, any form of tampering with the job that each device must do is truly counter-productive.. Also, the technical formulae are all available in any library, and we assume that the reader will get off his fat----------- and get it-- if he needs it.
"The need to "prove" everything-- so coveted in scientific circles is anathema to us because it makes a really simple job both overly complex and tampered with."
I can't help but respond to the irony here. You (Dennis) seem to be attempting to 'prove' something about science, exactly the failing you accuse it of. Meanwhile, the goal of engineering analysis is to take an apparently complex situation and make it understandable in a way that makes application simple; the exact opposite of what you accuse it of.
It is undeniable that there are still things to be learned about reproducing music, but I don't see how that can be used as an indictment of science. It would thrill me to understand why NFB seems to squash the music so often. The fact that my textbooks don't explain it does not make we want to throw my hands in the air and shout "science sucks!" It just makes me realize that there's more work to be done.
You are correct about it being TOUGH to get loop NFB right. Stu Hegeman could do it "falling out of bed", but he was 1 very special dude.
I'd like to think that the NFB loop in "El Cheapo" performs well. The loop is only around 2 stages and pains were taken to avoid phase shifts. There is but 1 cap. inside the loop and the feedback resistor is non-inductive. Starting with a reasonably linear open loop circuit helps too.
Now THAT was good. :)
"The art of reproducing reality simply requires that the amplifying devices be allowed to do their jobs-- unmolested and not degraded by efforts to "help them" from self-appointed genius engineers who have no movie theatre experience"
that the best audio reproduction is at movie theaters, you haven't gone to a movie theater lately. It's loud and boomy, but quality? Remember the speakers at outdoor theaters? Now there's quality sound ...
From Dennis :
Subject: WHAT ??
Date: Fri, 30 Jun 2006 14:14:11 -0600
AH! I GET IT! We go to a movie theatre and we get bad sound! Too bad, as the 35mm sound tracks that theatres use are far superior to L.P.s, CDs, and even most 1" reel recorders.
When in L.A. (California), you should get to a really great theatre and hear this stuff! Real fidelity and true-to-life dynamics. The 35mm prints made for TITANIC, FORREST GUMP and TOP GUN were done at Paramount Studios-- some really good sound people. You could visit!
What if you went to your local theatre and redesigned their playback chain? As a test, drag-in your best Hi-Fi stuff-- use their speakers if they are JBL or ALTEC. Play your best sources thru your chosen amps. Then, if their projector has really good tracking, connect the photocell output directly into your preamp. You will hear stunning dynamics that will put CDs and L.P.s out to pasture!
You could even own a movie theatre. You could run only the best shows, and you could design the entire playback chain! You'll never get sound that good in your home, unless it has the acoustics of a properly designed theatre building.
Sorry to burst any bubbles here, but the days of discrete analog magnetic tracks are in the distant past - 70mm mag-track movies started becoming rare by the mid-Sixties, and I think the last release of that format was Kubrick's "2001", which I remember seeing in 70mm at the Cinerama theatre in Washington D.C.
After that, all movies were released in monophonic optical sound in 35mm prints, with the widescreen effect coming from matting of the 35mm frame - although a few were released in the Panavision anamorphic process (but still using a 35mm frame). The net result of smaller screens in multiplexes, sloppier projection, and the regression to 35mm and mono optical sound was a backward move to quality somewhat worse than 1930's standards.
The release of "Star Wars" in the late Seventies finally brought stereo back to the big screen, via the Dolby dual-track optical process. By the mid-Eighties Dolby Stereo was replaced by Dolby Digital, leaving the optical mono track intact (and used as a reserve track in case DD failed during projection), and inserting the tiny digital data between the sprocket holes of the 35mm frame.
Since DD was originally developed for early HDTV proposals, and then re-purposed into a theatrical system, the data rate for all 5.1 channels is set to a rather modest 256kbps. With 2-channel Red Book CD's having an uncompressed data rate of 1.4Mbps, you can see how heavy the compression is for Dolby Digital.
Modern movies support several compressed-digital formats in the same 35mm frame: Sony SDDS is on one side of the frame, DD is still between the sprocket holes, the emergency mono optical-analog track is on the other side, and DTS is carried by a specialized CD that goes with the movie that is digitally synchronized to the picture.
Note that the only analog thing about this is the emergency mono-optical track, which is only briefly activated when the digital systems experience an irrecoverable data loss. In practice, since the optical and digital are synchronized, the audience only hears a very brief loss of quality, hopefully not in a major scene.
With the very rare exceptions of 70mm releases using the old mag-tracks, which can only be shown in a few theatres in the world, everything else - including IMAX - is compressed digital, with pretty high compression ratios, in the MP3 range. No tube amps anywhere, and the horns are modern constant-directivity types, optimized for uniform coverage, and designed to be used with digital equalization with multi-kilowatt Class AB transistor amps.
There's a reason modern films don't sound anything like the Todd-AO 70mm releases of the 1950's - the technology is completely different, from start to finish. Back then, it was all-analog, all-mag-track, with all-tube electronics for the entire signal chain. These days, it's all-digital, from start to finish, with heavy digital compression applied to the final mixdown, ultrahigh power all-transistor playback electronics, and digitally equalized multi-amped horns.
I gotta tell you, while I have great respect for the obvious and huge technical difficulties to be overcome in designing sound for big movie theatres, I can't say I like movie theatre sound itself; my heathkit aa-151 triode mod'ed amp, as low hifi as it is, is "yummy" to my ears; I ENJOY listening to all sorts of old vinyl on it, it bathes my ears in just wonderful sound - "yummy" is the only word I can think of that really describes it - and vocals are nice and clear, so it's not just distortion of a kind I like - or maybe it is, but in a way that preserves vocal information - but, while I get ACCURATE sound in a movie theatre, and LOUD sound in a movie theatre, and STARTLING sound in a move theatre, and gut-rumbling BASS in a movie theatre, it is NOT ear-pleasing sound, it is just good informational sound for the movie, and to me there is a world of difference.
"It ain't a comeback until it's left the shop" Jimmy Dunne, the first man to drive a VW Beetle faster than 200 mph, and he has the forehead scar to prove it; I will always honor him for taking a chance on me when I wanted to be an engine mechanic.
you realize that you just AGREED with virtually everything Dennis said.
The difference is you equate your 'megaplex 2000' experience with his...and your amp with his...or mine.
Happiness is the point. We all agree on that. :)
"Also, no wire can come near another or to anything else-- regardless of insulation used. "
How can that be done? Jeff-Dennis, I really need to have a look at the power transformers, output transformers and the chokes that you guys are using. I thought the wire in a transformer was wound around a core and the wire was wrapped tight against it's self.
Boy, am I confused. :-)
Better get rid on the line cord with it's parallel wires, Tre'. Use two (or three) wires seperataed by a few feet, minimum ...
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