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Thread: $5,000 for one compression driver?

  1. #16
    Senior Member Steve Schell's Avatar
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    Hats off to Leo Bostwick

    The W.E. 596A and 597A (differing only in style of connectors, I believe) were an important milestone in loudspeaker development; they were literally the world's first tweeters.

    In L.G. Bostwick's article "A Loudspeaker Good to Twelve Thousand Cycles" (Bell Laboratories Record, May 1931) he describes his driver as having a response from 3,000 Hz. to 12,000Hz. with an overall efficiency of about twenty percent. He states: "Twelve thousand cycles is within the highest octave that can normally be perceived by the ear, but yet it has been found that certain musical instruments and voices, and many common sounds such as jingling of keys or coins, have overtones or harmonics that make such a loud speaker necessary for perfect reproduction." It is hard to imagine now, but he was writing this at a time when people had never heard such sounds reproduced properly before.

    As Marty pointed out, these drivers were way ahead of their time, reproducing mostly noise in the early Vitaphone sound sources. They were installed in the W.E. "Wide Range" theatre sound systems of the early to mid 1930s, which augmented the earlier "Voice In Action" full range snail horn systems by adding woofers and tweeters to a flat baffle mounted under the large horns.

    Bostwick was well aware of the problems of such extended frequency response. He concludes his article with these thoughts: "...a loud speaker efficient at high frequencies introduces other difficulties that would not be encountered if the high frequencies were suppressed. For example, amplifier overloading becomes much more strident, and noise may increase to an objectionable extent. A loud speaker of the type described, therefore, cannot be used to full advantage in systems where these factors are not favorable."

    While I'm sure that others would have developed tweeters eventually, Mr. Bostwick did it in about 1930! Here is another example of so many good things, speaker wise, tracing their origins back to Bell Telephone Laboratories.

    I have listened to a 596A. I sounded very sweet, perhaps not as extended as some more modern tweeters, but not the least bit raspy either. Although its 180 milligram moving mass should allow response higher than 12k, the single slit exit path probably introduces a phase cancellation that knocks out higher frequencies.

    The high prices paid for these are mostly fueled by their rarity and value as status symbols, but this would not be the case if they did not sound very good to begin with. I'll bet that Mr. Bostwick would enjoy watching these auctions if he was still with us.

  2. #17
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    Propagation delay

    Not only was there a problem with high frequency noise and pops from the soundtrack, but the propagation delay differences from that little horn and the large wood horns is/was terrible, the audio equivalent of not having the film in sync with the sound. The same problem occured when the cone woofers were added. The "Wide Range" systems seem to have been a flop.

    Those little tweeters are very cute, however, I didn't think that they sounded much different than the 075, and the 075 was much easier to find.

    For as "rare" as these are supposed to be, they seem to show up on ebay about every other month.

  3. #18
    Marty
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    Quote Originally Posted by Steve Schell
    ... its 180 milligram moving mass ....
    The W.E. 596/597 used low mass duraluminum diaphragms
    Like the ALTEC 3000 ? Which uses an aluminum microphone diaphragm ?

    One could make custom Horn Supertweeters by starting with a microphone or headphone motor assembly
    and adding a horn with a 'bullet' phasing plug

    I have dismantled FISHER & MAGNAVOX Horn Tweeters from the 1950s - they had phenolic diaphragms (disappointing)
    and similar 'bullet' phasing plug like the W.E.. These components could be used for custom Horn Supertweeters.

  4. #19
    Senior Member Steve Schell's Avatar
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    Marty, the use of a phenolic diaphragm does not necessarily imply a crummy tweeter. Many of the best ones, like the EVs and the Jensen RP-302 used a linen and phenolic diaphragm. RCA claimed a higher stiffness to weight ratio for the material compared to metal way back in the 1930s, and it has better self damping properties as well. I have a big 70lb. slab of phenolic material out in my shop. It just goes "thud" when hit with a hammer. I'd hate to hear the sound of a similar sized piece of aluminum!

    Phenolic diaphragms have been used in lots of cheapo drivers because they are easy and inexpensive to produce. They are also very resistant to heat and fatigue, which is why they are used in most high power paging drivers.

  5. #20
    Senior Member 4345's Avatar
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    t350

    Steve - Did the E.V. T350 use a phenolic diaphram? I think I recall it did. My friend has a pair of Cornwalls with this tweeter. After seeing the diaphram material, I was very surprised at how nice the high frequency was.

  6. #21
    RacerXtreme
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    3 days 4 hrs to go..............

    3 days, 4 hrs to go.......... the Ebay ad that started this post is up to

    $7300.00







    Do you think it will hit $10,000 ?

  7. #22
    Marty
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    Quote Originally Posted by RacerXtreme

    Do you think it will hit $10,000 ?
    Get ready for 12 Kilobucks

  8. #23
    aust-ted
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    I actually have one of these

    Hi

    I actually have a 597A which I acquired at a swap meet some years ago along with a matching 12" electro magnetic bass driver. Couple of problems with them though. Although the voice coil seems intact, it had become separated from the diaphragm, I suspect because the glue used had failed over the years. I have not dared try to fix it.

    The bass driver unit sadly has the nameplate removed from the back of it but am pretty sure it is a WE unit because of the label near the tube socket for the rectifier which is attached to it. I gather the 597A gets its DC power from here also. It has a leather surround. Not sure if that is original or a mod.

    These units originally came from a picture theatre in NSW from the early days of the talkies.

    With these prices perhaps I should put them on eBay

    Regards
    Ted

  9. #24
    Marty
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    Quote Originally Posted by aust-ted
    Hi

    I .. have a 597A ..from a picture theatre in NSW ..

    Ted
    Hi

    Since you can see inside it, what is the VC diameter ? What is the suspension/surround:
    radial-spiral like W.E. 555 & Altec 802, or roll-suspension like W.E. 594 & JBL 375 ?

    Yours seems to be repairable. There's a guy in Calif who repairs Altec 3000's (similar diaphragm?)

    The LF driver would be a TA-4151(A) or TA 5153(A) with on-board W.E. 275A rectifier bottle.
    (used in W.E. 'WIDE-RANGE' sound system)

  10. #25
    Senior Member Steve Schell's Avatar
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    4345, I've never had a t-350 apart, but believe that all the EVs used a phenolic diaphragm. The good phenolic tweeters do seem to have less coloration than those with metal diaphragms. I have noticed that metal diaphragms do sound metallic after one has been listening to phenolic diaphragmed drivers for awhile.

    Aust-ted, I have a friend in Sydney who is a highly skilled speaker restoration expert and historian, the world's best in my opinion. He has repaired 597As in the past; perhaps he could restore yours to working condition. If you like I'll put you two in touch- please contact me at [email protected].

  11. #26
    Senior Member edgewound's Avatar
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    Antiques education....EV tweets

    Great thread guys...I 've learned lots today.

    The EV T35, T350, ST350 does use phenolic diaphragm with a 1" voice coil, with no coil former bonded directly to the diaphragm. I've repaired lots of these for both pro-sound and hifi systems. Klipsch used these in at least the Heresy and the La Scala as well. They seem to be smoother and less longterm fatiguing to list to....and a heck of alot tougher that aluminum or titanium units. But hey...who's to say what's better? Sometimes I like Merlot, other times I want Pinot Noir.

    Great stuff guys,

    Edgewound

  12. #27
    Senior Member Steve Schell's Avatar
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    All good points, edgewound. I've been a Merlot hound for awhile, just beginning to discover Pinot Noir. Have you seen the movie "Sideways"?

  13. #28
    Administrator Mr. Widget's Avatar
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    Phenolic is smooth eh? Rolled off perhaps, I've used dozens of T35As with alnico and ferrite mags and never thought of them as particularly smooth.

    Beryllium is where it's at... now that is smooth.

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  14. #29
    Senior Member Steve Schell's Avatar
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    Hi Mr. Widget,

    Your plot looks like the T-35 rolls off above a mass corner of 8kHz. or so. This doesn't look so great on paper, but note the lack of response peaks up high; this driver probably maintains piston response through the audible range and will sound very clean if a bit dull. The rolloff could be corrected with some simple EQ. Many metal diaphragms will measure hotter on top, but this response is often achieved through break up resonances, creating the characteristic "tsss tsss tsss" spitty tweeter sound. Beryllium diaphragms probably do the best job of the metals of maintaining piston response, but I haven't found any I can live with as easily as the phenolics. As edgewound said, merlot or pinot?

  15. #30
    paragon
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    Thats what i heared

    Thats what i heared in the early 80 `s in a disco with a pair of E-Voice Sentry 3 (may not be for home listening) standing 12" above the ground. No Highs, only mittle and bass. Thats when I think that the 075 (2402) is much better (heared in an other Disco) than the E-Voice T35.
    Love the Sentry 3 off course !

    Eckhard

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