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Multi-Way Conventional loudspeakers with crossovers

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Old 22nd June 2013, 07:24 PM   #8971
limono is offline limono  United States
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yes , not all polyester caps sound OK and I'm not that sensitive to sound of caps anyway just it's worth noting that there is a fraction which can't stand the sound of poly caps I think Peter Qvortrup wrote something about sound of thousands piercing needles. At the moment I'm looking for best bipolar electrolitycs in 8uF , 12uF and something smaller to make odd values . Anybody got those horrible standard blue Black gates ?
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Old 22nd June 2013, 07:30 PM   #8972
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The crossovers I opened dated from the early Seventies, long before anyone thought caps had any sound at all. Jung's article on caps was published in 1979, and that started people thinking about parts quality in a different way.

My disappointment when I opened the Altec A5 crossover cans was the sharp distinction between the quite expensive cast-aluminum box (cast aluminum was and is plenty expensive, even for Altec) and seriously cheapo parts inside ... and the dismaying discovery that caps appeared to be picked out of a random parts bin. Values were nominally the same, but the vendor wasn't. The L-pads between the 2nd-order highpass filter and the 288 compression driver were a step below Radio Shack quality, and were both severely corroded ... a pretty good indication that neither box had ever been opened.

Although I like Altec drivers, to be honest, the crossovers they used were very primitive ... textbook 2nd-order highpass and textbook 2nd-order lowpass, going back to the bad old M-derived filter-theory days of the Thirties. Altec (and JBL) were using textbook crossovers 10~15 years after the BBC (and other Brits) started using pretty sophisticated crossovers.

The Big Two West Coast manufacturers were coasting on the reputation built in the late Thirties, and were ignoring the Brits and the fantastic work of a local boy at CalTech, Dr. Richard Heyser. Looking back what Altec and JBL were doing in the early Seventies, it was very much a Not-Invented-Here town, with no attempt to make time measurements, much less CSD plots (which the BBC and Heyser were doing), and very simple 1st and 2nd-order crossovers that did not equalize the drivers.

None of that takes anything away from the drivers, which were designed in the mid-to-late Forties, and represented the best thinking of the time.

Last edited by Lynn Olson; 22nd June 2013 at 07:35 PM.
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Old 22nd June 2013, 07:53 PM   #8973
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Lyon,
Extrapolating from what you are saying I will add in that JBL and Altec at the time just acted as if the crossover components were completely interchangeable, that is what you are seeing. As long as the value was electrical component met a minimum standard like it was plus or minus 10% it was the same and would sound the same. We all know now that isn't true and I bet they more than likely did also, but just ignored it as they could get away with that. The same guys designing those great drivers of the time we just as capable as anyone at designing better crossovers. As you say Heyser was in California and there were just to many others who knew what was going on. When you control the market for the products why change was the thinking.
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Old 22nd June 2013, 08:16 PM   #8974
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Although Altec (and JBL) were using primitive crossovers, Altec did start to introduce Acousta-Voice 1/3 octave theater equalizers. I imagine there was a fair amount of market resistance, because theaters were scaling down at the time. Big theaters with 70mm 6-channel mag-track were phased out, replaced by mini-screens in multiplexes with 35mm optical-mono sound ... going right back to Forties exhibition technology. The so-called "wide-screen" movies (1:1.85 aspect ratio) were nothing more than matted-out 35mm, with the top and bottom of the frame blanked out, resulting in a movie frame with less area than the Forties-era Academy frame. Not an ideal market to sell better sound.

The A2, A4, and A5 were not flat, with a 3~6 dB peak around 1.5 kHz, and a HF rolloff above 3.5 kHz, thanks to the perforated screen. But in a sense it didn't matter, since movies made in the Forties, Fifties, and Sixties were mixed and equalized with the A-series in mind.

Sound quality in the Seventies could be described as low-fi, since quality 70mm mag-track exhibition had disappeared, and brutal-sounding Crown DC300 and Phase Linear 700's were replacing old, worn-out vacuum-tube amplifiers. A few theaters were Acousta-Voiced, but most weren't, since few movies had anything better than mono optical soundtracks. Star Wars was the first Hollywood movie to re-introduce stereo sound, after a long absence, and even that was simply Dolby stereo-optical, a technique first invented and patented by A.D. Blumlein in the mid-Thirties.

I can see why there was a push for some kind of improvement in the late Seventies and early Eighties (THX standardization). The 35mm theater owners were using the cheapest projectors and sound equipment they could get away with, while directors wanted to re-introduce stereo sound with the kind of quality associated with 70mm mag-track and good home hifi systems (which had long surpassed theaters in sound quality). Thus, THX certification, JBL theater loudspeakers, and the mixed blessing of heavily-compressed AC3/Dolby Digital sound.

Last edited by Lynn Olson; 22nd June 2013 at 08:31 PM.
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Old 23rd June 2013, 02:29 AM   #8975
BudP is offline BudP  United States
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Quote:
Although Altec (and JBL) were using primitive crossovers, Altec did start to introduce Acousta-Voice 1/3 octave theater equalizers.
And yet they used the most linear inductor style ever. And, they would not have been the least expensive.
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Old 23rd June 2013, 02:38 AM   #8976
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And different vendors? Who cares?
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Old 23rd June 2013, 03:05 AM   #8977
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Hi Bud, Do you mean they used air core inductors? The old drivers I thought were forgiving of this basic approach. Particularly when horn loaded. Pio caps and air core inductors in 12dB primitive style sound pretty good, but hoping to learn more from Lynn.

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Old 23rd June 2013, 03:17 AM   #8978
BudP is offline BudP  United States
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The Xovers I have seen, and not an abundance of them either, used a non saturable reactor. Somewhat of a misnomer, but they provide linearization of flux in the coil, including smooth settling, but do not suffer from the usual gaped choke problems or the nonlinear clumping of inductance in air coils.
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File Type: jpg non saturablre reactor pic.jpg (16.3 KB, 316 views)
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Old 23rd June 2013, 03:51 AM   #8979
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Looks like the I is on the back of the E. One big air gap? How do cored inductors behave on very low level signals, when the inductance drops off? I understood more constant inductance was the idea of air cores. But in a cinema probably that was not an issue. Or I maybe these are for lower cross over points than practical with air core perhaps.

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Old 23rd June 2013, 04:31 AM   #8980
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The effective permeability of a core constructed like this is 45, rather than a few, to many tens of thousands. What the core is doing is just ordering what is otherwise a disorderly rise and fall of inductance in the windings. Also, since the core is basically inert regardless of the frequency, the typical distortion addition is not a factor. You, of course, do not want to mount these onto a steel plate....
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