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Thread: Identify Theatre Speaker for me?

  1. #46
    Senior Member Woofer's Avatar
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    .... but if the JBL 2226 goes down to 40Hz, and the W only goes down to 50Hz, maybe you should be taking the measurement from a slightly further point.
    I don't think you're getting the full wavelength.
    Also, maybe try a reading with the box up on it's end.

    Plus, I'm a tad intrigued.
    You mention that you're going to cross these at 50Hz from your Sub.
    What are you using for a Sub?

    Cheers....

    ps: I do so hope you remembered to pull Dizzy out of the back of the box before you screwed the back panel on.
    I might be deaf, but I can still hear da bells! (Quasimodo)
    .... Oh, and the Kick Drum.

  2. #47
    Member 16hz lover's Avatar
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    Quote Originally Posted by Woofer View Post
    .... but if the JBL 2226 goes down to 40Hz, and the W only goes down to 50Hz, maybe you should be taking the measurement from a slightly further point.
    I don't think you're getting the full wavelength.
    Also, maybe try a reading with the box up on it's end.

    Plus, I'm a tad intrigued.
    You mention that you're going to cross these at 50Hz from your Sub.
    What are you using for a Sub?

    Cheers....

    ps: I do so hope you remembered to pull Dizzy out of the back of the box before you screwed the back panel on.
    The mic was only 5 ft from the front of the mouth.

    I've got two EV 18" S-181 subs to do the stuff below 50hz.

    Also all the measurements were with the back completely open when it was pulled out in front. The final response curve was with the bass bin against the front wall, so it would be similar to having a slotted back on it.
    Still searching for the perfect blend of SPL and SQ in a set of speakers.

  3. #48
    Senior Member Woofer's Avatar
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    Quote Originally Posted by 16hz lover View Post
    Also all the measurements were with the back completely open when it was pulled out in front. The final response curve was with the bass bin against the front wall, so it would be similar to having a slotted back on it.
    Shouldn't the back be sealed?
    I might be deaf, but I can still hear da bells! (Quasimodo)
    .... Oh, and the Kick Drum.

  4. #49
    Member Horn Savant's Avatar
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    Quote Originally Posted by Woofer View Post
    Shouldn't the back be sealed?
    Pre war stuff usually had open or vented back wave.
    So the 50 hz bump is probably the spkr resonance
    The first HF compression drivers were also vented rear cavity !

  5. #50
    Senior Member Woofer's Avatar
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    Quote Originally Posted by Horn Savant View Post
    Pre war stuff usually had open or vented back wave.
    So the 50 hz bump is probably the spkr resonance
    The first HF compression drivers were also vented rear cavity !
    I can see how that might be OK with low powered valve amps, but in a high power situation, I can see the speakers disintegrating in no time.
    Otherwise ALL 'W' type bins would be open backed wouldn't they?

    Cheers.
    I might be deaf, but I can still hear da bells! (Quasimodo)
    .... Oh, and the Kick Drum.

  6. #51
    Member 16hz lover's Avatar
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    another year has passed, and I finally got the Shearer up and running. I built a set of upper mid/tweeter open baffle cabinets to mount up on the side walls. I used 2- Audax PR170MO high efficiency midrange speakers and then crossed over at 5k hz to a Ciare 1.38 tweeter which is also 105 db eff.





    I got this concept from the guy on here who used to go by Mike Bates I believe, an elusive fellow whom I could never get in contact with...strangely enough. He preferred this setup to all the horns he said he had tried through the years, only he used a different tweeter. Anyway, I am using the Shearer from 50hz (which is it's cut-off freq) up to 400 hz, I'm using a BBE electronic crossover with 48db slopes to provide this crossover frequency, then the mid-tweeter cabinets take over. The Shearer in it's final resting place.


    So the whole system is about 105db/1 watt. We measured the response again with the XTZ PC software and microphone and this is the response we got. Remember that there is a noise floor below 50 hz showing up on this response curve. Kinda fun to watch it as cars go by....especially dump trucks with all their low rumbling going on.


    It's really nice sounding with only the 125hz Shearer hump sticking out. You have to get back and lean against the garage door to get far enough away from the Shearer to get good bass, and it would likely sound good with the garage door up and then stand down at the end of the street. It's just really stinking loud. At 70% volume, we measured an average 120 db, anything more I'm going to have to get some ear protection. I still haven't turned it up all the way...but it's just so clean sounding all over the whole spectrum. So now I'm working on building a subwoofer enclosure to handle the 50hz and below stuff. The enclosure will be the same 40" height as the Shearer and depth as it too ( 32") and will be about 24" wide and will be tuned to 20hz using two 18" custom built drivers from Sundown Audio with 30mm of linear travel, and driven by a Crown K2 amp.
    Still searching for the perfect blend of SPL and SQ in a set of speakers.

  7. #52
    Senior Member herki the cat's Avatar
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    Smile Diamonds in the dung!

    Quote Originally Posted by Hz lover View Post
    NOw that the thread has been diverted and killed.



    Also got this tube amp, haven't gotten any numbers or info off of it yet from my buddy
    The little RCA amplifier to to right is a two stage RCA 1620 pentode voltage pre amplifier serving the projector film sound track, and the Power Amplifier to the left is an "RCA MI-9354-C" 20 Watt Priceless Gem used almost exclusively in 1800 seat theaters from early 1930's to late 1940's just preceding the three-channel "Cinema Scope Movie" event. This amplifier features output impedance taps of 15, 50, & 250 ohm from four 6L6-G pentodes with regulated screen grids; you can see the gas - filled regulator tube behind the panel meter. There are two 5U4-A rectifiers. Also, poking out behind the chassis, there is a massive power transformer which yields less than 1.5 % AC distortion. All the filter capacitors are premium 20 year-life filter capacitors. For Large Speaker systems, RCA had the "highly sought after" 40 Watt power amplifier with a pair of 845 triodes driven by the MI-9354-C.

    This is an extremely sweet, clean-very low noise, tight amplifier with superb control of speaker motional impedance. I have six of these "RCA MI-9354-C" gems.

    RCA traditionally used a 250 ohm transmission line from projection booth to back stage. A typical dividing network had a second order configuration with a pair of LC's consisting of a "4 Mfd" oil-filed capacitor and a massive air wound coil. RCA also had "15 ohm cross overs" at 240 Hz & 300 Hz which employed massive tapped coils and multiple capacitors including the "XT-3083," 250 ohm matching transformers in a huge steel box.

    The box along side the amplifier has two RCA "XT-3083", 250 ohm line to multiple voice coil Matching transformers with secondary taps to accommodate any configuration of RCA horn LF & HF 30 ohm drivers such as the RCA MI-1432-A, or Mi-1444 and MI 1428-B or MI-1443 in RCA's Photophone Speaker systems with the RCA MI-9436-W folded bin horn designed by Dr. Harry Olson, which was licensed to MGM for manufacturing by Lansing as the "Shearer Horn" with the Lansing 15XS field coil drivers.

    BTW, all RCA 15 inch Photophone Drivers including the field coil MI-1432-A, & the Mi-1444 both with a phenolic spider and the MI-9449 of the late Ubangi horn all have identical, small mass, cone diaphragm design with free air FS of 60 Hz resulting in some 6 Db more sensitivity & better transient response than the Altec 803 / 515 series of 30 Hz free air FS. These RCA drivers match RCA's Ubangi Radial Horn designed by RCA Photophone chief engineer, Mr. John Volkman, and his brother in law, Dr. Harry Olson of the RCA Princeton Labs. The late A. J. May executed the Ubangi product design in Camden.

    The point here is that below 60Hz, the Ubangi Horn throat acoustic resistance component drops to zero, followed by a gently increasing mass reactance which reacts with the cabinet rear volume. It is well known in RCA that the seven foot width dimension of this enclosure is required well below 60 Hz. In fact, this Horn system is capable of excellent performance down to 30 Hz with very good phase linearity and low phase distortion.

    It is therefore a serious mistake to chop off one side, or both, of this Ubangi to accommodate Altec and other foreign drivers__ Not To Worry, Please!__ A. J. May found that CTS Inc,. has a 15 inch driver with cone virtually identical to the 60 Hz RCA Drivers. A. J. demonstrated to me__ excellent survival after pushing a CTS driver off the bench_ hard_ to the floor.

    One other Gem you can use__ I did snug up an Altec 515-B with cone flange tight against each of the slot ports of my Ubangi's__Awesome to say the least.

    Aside from all of this, if you don't have the original "Horn Honk - Free" RCA Mi-9448 or Mi-9458 or MI-9548 Phenolic Diaphragm HF Drivers, the JBL 2440 and 375 with original JBL Aluminum, still available, are excellent clones of the WECO 594-A.

  8. #53
    Senior Member herki the cat's Avatar
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    125 Hz Shearer hump sticking out

    [QUOTE=Hz lover;291727]another year has passed, and I finally got the Shearer up
    It's really nice sounding with only the 125 Hz Shearer hump sticking out. QUOTE]

    You know what? "That 125 Hz Shearer hump sticking out" is characteristic of the Shearer W bin horn which was originally designed by RCA for their own in-house RCA Photophone theater market & incidentally licensed to MGM to be manufactured by Jim Lansing as the Shearer Horn. RCA furnished _within their crossover networks_ a filter network to even out and reduce this 125 Hz hump. The the level of attenuation in this narrow spectrum was adjustable to accommodate any acoustic aberrations in this narrow spectrum otherwise contributed by the theater auditorium.

    Other than that, with the W bin sitting on the floor, there is a virtual image below the floor which acoustically doubles the single W bin horn mouth area, and the low frequency response will be the same as a horn of twice the size of the single W bin elevated above the floor. Simply stated, the low frequency response is more robust with the W bin on the floor.

    Cheers, herki
    Last edited by herki the cat; 11-18-2011 at 11:13 AM. Reason: NATHA

  9. #54
    Member 16hz lover's Avatar
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    wow herki.....an enormous wealth of knowledge you posess on these things.
    Still searching for the perfect blend of SPL and SQ in a set of speakers.

  10. #55
    Senior Member herki the cat's Avatar
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    Cats always need to know everything

    Quote Originally Posted by JBL 4645 View Post
    That’s a whopper of HUGE one and the cat is most curious about it bet it was sniffing at for hours and looking for way in though hole too catnap. What the cat’s name?

    Dizzy(Gillespie) is about 8 months old and believe me, he's already explored all the inside of the speaker. [QUOTE/]

    Now, This is (Robert) who came into the house in the palm of my hand at the age of four weeks _ tiny as a little mouse on his little back to have his tummy caressed. He is very intelligent & polite. He waits for his food sitting there with his tail curled around his front paws. herki[QUOTE/]
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  11. #56
    Senior Member herki the cat's Avatar
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    125 hZ Shearer Hump Sticking Out

    Quote Originally Posted by 16hz lover View Post
    wow herki.....an enormous wealth of knowledge you posess on these things.

    16hz lover;323439, Many thanks for the kind words.

    RCA always used the MI-493-A or MI 1265, 125 Hz, VOICE FREQUENCY FILTER in their 15 ohm MI-1481/MI-1484 cross over filters with two RT-492 Voice Coil matching transformers on the High Frequency MI-1428-A/MI-1443, 4 ohm Drivers, and the low frequency MI-1432-A/1444, 30 ohm Drivers.

    In order to achieve flat response to 40 Hz, the RCA W bin's require a large infinite baffle surface to attenuate the driver rear sound wave from canceling the W bin front sound wave.

    The W bin was elevated on a platform from the floor so that the center of the high frequency horn on top of the W bin was 2/3 of the picture height. The MI-1456 LF Baffle, a typical system, rests on a 24" high platform with a front vertical- frame surface covered with a panel extending from the floor to the bottom edge of the W bin, providing a very long rear to front path around the W bin. The 40 Hz infinite baffle was completed with a 24" wide left-hand wing extending from floor to the top corner of the W bin and a similar right-hand wing, 36" wide.

    This RCA W bin Speaker system is Excellent from 40 Hz to beyond 400 Hz, with a dynamic purity in the Mid Bass extending from 150 Hz to 500 Hz, including the "Human Voice Fundamentals Spectrum"_ You can't fool voice _ you have been hearing it all your life. .

    Your JBL 2226 LF Drivers appear appear to be excellent performers in your W bin. As an alternate choice, the Altec 515 B/G, & the 803 series Drivers __OR JBL EQUIVALENTS__ with FS of 30 Hz, are highly recommended for the W bin if the the RCA LF Drivers are not available. These excellent 30 Hz Drivers will extend the bass response operating as Direct Infinite Baffle Drivers from 40 Hz to 30 Hz where the W bin horn loading gives out.

    The beauty of these Alternate Drivers will eliminate _ Acoustical Cross Overs & Electrical Cross Over Circuits _ of heavy, Woolly, sluggish Sub woofers _ and provide tight clean bass transient response. Been there, & IMHO, with the Alternate Driver System savings, you can build a second W bin for stereo. All the parts are simple panels of wood with straight sides

    BTW, the CTS Inc,.[Chicago Telephone Supply Inc,.] 15" equivalent of the RCA MI-9449 Driver I recommended for the RCA Ubangi Horn in Post #52 was absorbed by Eminence Speakers, Inc,. an excellent speaker manufacturer.

    Keep an eye out for the 15" CTS speaker in yard sales, the Good Will Stores, & discarded Faux Mahogany-Monster Radio Consoles at the curbs, etc.The CTS has a huge square ferrite magnet and a cone very similar to the MI-9449.

    I have included the schematic here of the (RCA "125 Hz") VOICE FREQUENCY FILTER from a WECO /ERPIE/ (RCA) aka, Altec Service Co.,Theater Service Engineer's Manual, dating back to 1932... herki [QUOTE/]
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    Last edited by herki the cat; 11-22-2011 at 02:39 PM. Reason: NATHA

  12. #57
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    sounding panels

    Quote Originally Posted by Tom Brennan View Post
    It was his to throw away. It's just old stuff, not worth getting a grabber over.
    Don't forget that bass bin should have had two large panels .one for ea side ..if not ..
    they could be reconstructed

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