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Discussion in 'Pro Audio Equipment' started by Jbrax, Jan 2, 2008.

  1. Jbrax

    Jbrax Guest

  2. bent

    bent No Bad Vibes! Well-Known Member

    Well...
    Have you been honing your welding skills?
     
  3. moonbaby

    moonbaby Mmmmmm Well-Known Member

    Well, I built a plate unit 'way back in 1976, with a partner who's now sadly deceased. He was an engineer with Southern Bell, and fairly savvy, techwise. We used an E-V 12" SRO speaker to "rattle" the plate, and Barcus-Berry transducers on the plate to serve as the return pick-ups. It was a real "trial and error" situation, with constant torquing of the hook-bolts we used to attatch the plate to the frame. We had a motorcycle shop weld the frame, and I can't remember what we used for the metal plate. I think he got it from a navy shipyard. Anyway, it was a NIGHTMARE, and although we ended up getting it to sound OK, it took entirely too much time and sweat equity. We ended up getting an Ursa Major, an early digital unit.
    The instructions you posted make it a LOT more user-friendly to build this.
    I have no idea as to your technical prowess with metalworking and electronics. And, in truth, this may very well be a personally rewarding experience that I wouldn't want to talk a person out of. From a strictly personal perspective, this makes an interesting and entertaining read, but I would never go through all of that work again. I think that plates sound great, properly built and adjusted.
    But these days, so do a number of digital boxes, especially Lexicon PCM's.
    And they don't require twistin' bolts...
     
  4. Jbrax

    Jbrax Guest

    well The thought did cross my mind.. I do have acess to the materials, and yes I can weld.. I do believe i can do it for cheaper and I love to tinker. Also I do happen to have a isolated room inwhich to put it in...
     
  5. bent

    bent No Bad Vibes! Well-Known Member

    Hey, if you've got the money and the time, I say go for it.
    Post pics of the progress for us to check out!
     
  6. Jbrax

    Jbrax Guest

    can do. I think this will be alot of fun
     
  7. RemyRAD

    RemyRAD Well-Known Member

    A little more information on this that you should know.

    Back in the early 1980s, EMT's 1958 patent rights of Dr. Kuhl's reverberation plate expired. I was considering building my own since I had been maintaining them since the mid-1970s. Yes, it looks simple but.... EMT used a cold rolled steel. Out of all of the plates that they manufactured, 60% of them were disregarded for inconsistencies! 60%! Another company out of Chicago, Studio Technologies (if my synapses are firing properly) started building plates of two different sizes, utilizing stainless steel. Those were much brighter and quite amazing sounding. They created a slightly scaled-down version, 3' x 6', which I purchased and managed to wrestle into the basement. It never quite had the same high-frequency decay as the larger version but was still an order of magnitude better than any spring unit that wasn't an AKG BX20E and even that didn't quite come close. I think I was the only " Project Studio" in 1983 that had one? I never knew anybody else except a large studio that had a plate. Digital reverbs except for the new Lexicon 224 which were $15,000 US were modestly sad imitations. And even that never quite sounded like the original EMT 140 tube much less the EMT 140 ST stereo transistor version. However, we could do things that were not possible in real life.

    Reverb time was varied by utilizing a piece of rigid fiberglass ceiling tile that was moved closer to and away from the backside of the plate but never to touch it physically. The original EMT plate utilized a speaker like voice coil that was glued onto an aluminum cone that was in turned, screwed to the plate. The voice coil magnet structure was supported by a pair of frame crossmember to support its weight and keep it rigid.

    Yes, Barcus Berry type pickups can be easily glued directly to the plate in two different positions. The original EMT plate utilized crystal pickups which were similar to crystal phonograph cartridges and a few enterprising engineers even mounted 2 more pickups for a quad chamber. We wouldn't use anything like that today. At one time a company that made a very nice acoustic pickup called FRAP (Flat Response Audio Pickup) were more sought-after for this application.

    The real trick is the tensioning of the plate within the metal frame. EMT utilized a pair of tensioning mounts at each corner. Their tensioning instructions were funny at best. You were to tighten the tensioning clips at only 2 corners. And you were to tighten them until they broke! You would then fit a new one on and tighten to nearly the same point without breaking the clips. It wasn't easy. I eventually tuned mine like doing pizichado on a violin E string. The Studio Technologies unit I owned utilized simple circular eye bolts which could destroy the plate before breaking! So be careful.

    Another funny fact was that the cold rolled steel was coated with linseed oil! It was awful! And many moron engineers cleaned this nasty sticky stuff off only to have their plate rust terribly. You were not supposed to do that! Even if you didn't, overtime, you'd still get some rust. In spite of that, some rusted plates still sounded good but that was the exception to the rule. Of course the stainless steel plate needed no coating and its exaggerated brightness wasn't all that flattering to classical music. Great for rock and roll! Eventually I sold that and purchased a Lexicon PCM 60 and PCM 70 and a pair of LXP1's. I sure do miss the EMT 140 ST.

    Because it is electromechanical, like moonbaby indicated, he merely utilized a loudspeaker to excite the plate, by pointing out towards the plate. As opposed to physically mounting a transducer to the plate. The biggest problem is that you must put this device in its own soundproofed room. That's a lot of real estate. Essentially a dedicated spare bedroom with a vertical bed, that must be kept closed.

    I actually think you could utilize a metal bed frame as the frame. We are essentially talking about a device that is the size of a queen-size bed on its side. You then mount that in a box and put that box in a room. Many studios actually hung them from the ceiling rafters with springs to isolate the device from structures ambient low frequency interference. These devices are by no means quiet like a digital unit is but there is no other kind of reverb that can compare to a good sounding plate. Unfortunately, your budget for coldrolled sheet metal may not be as great as the R&D department at EMT. And with much effort, you may end up with a truly mediocre sounding reverb unit not worth using. But you might have a lot of fun and learn a lot in the process. It's just that a 4 foot by 8 foot piece of sheet metal requires a 5' x 10' metal frame box.

    Without the rigid fiber glass ceiling tiles in close proximity to the plate, your reverb time will generally be approximately 4.5 seconds! A little long for most folks. Damping will probably be tricky? So for the actual steel plate, you may want to also consider stainless, instead of coldrolled steel?

    What a lot of folks don't know is that the drive amplifier utilized heavy high-frequency preemphasis which gave the plate that sizzle especially with sibilant vocals. I love that sound! A preemphasis curve that is reminiscent of the NAB 15 IPS record curve. Not a flat input, with quite a few watts of drive power were utilized.

    What you might want to do for a driver would be to consider one of the JBL titanium tweeters from a 4312 speaker? Those tweeter diaphragms are on a plastic frame that can be removed from the speaker magnetic structure. You could then Pierce a whole in the center of the diaphragm so that you could screw it to the plate. You would have to first make a mounting bracket to hold the magnetic structure to the frame that could be bolted on. You would mount the diaphragm first and then very carefully fit the magnetic structure to the frame and diaphragm bolting it into place. That's how it was done when you worked on a EMT and I can tell you it not only wasn't easy, it was easy to damage it. You might even be able to order the original EMT driver? That would certainly make life a lot easier if they still offer it?

    And no 2 plate ever sounded quite alike. The good high-end studios always got the best sounding plates. The rest of us got the ones that we could. Our 140 ST was quite good that never quite compared to the ones that I used at Media Sound in NYC. Those were uber Sweet. I remembered when the ass hole who ran the Peabody Conservatory of Music Studios sold their EMT 140 ST to Sheffield Recordings, so he could purchase a TASCAM model 10 audio console! LOL! WHAT AN IDIOT! Of course, John Ariosa of Sheffield Recordings of Phoenix Maryland, didn't complain. I forgot where we got ours?

    I still dream in EMT plates
    Ms. Remy Ann David
     
  8. Jbrax

    Jbrax Guest

    Thanks Remy!!!!
    Why did I know you would have knwn all about these...lol

    I will be making the 3x6 version, I have no room for 4x8..

    I do believe I can aquire all the parts nessesary from the link I posted above

    Im going to shoot them a email today to make sure...

    stainlees steel is pretty pricey, so Ill have to take my chances with the cold rolled steel.. This will be alot of fun to do and to experiment with.. I will keep you all posted when I get started...
     
  9. JoeH

    JoeH Well-Known Member

    Remy, seriously, you need to write all this down somewhere and perhaps make a book out of it all, before you (and the rest of us old timers!) forget it all. I don't want to be sitting in an old age home someday, trying to remember what you said about plate reverbs....hahahaha

    What fun it was to read all of that; talk about going full circle and coming out the other side! I too remember huge, dusty old EMT boxes hidden in back closets and other out-of-the-way places way back when. And tuning/maintaining those suckers was a nightmare, indeed!

    Makes me tired remembering all that work involved to just get a little reverb in yer life. :wink:
     
  10. RemyRAD

    RemyRAD Well-Known Member

    LOL! Thanks Joe.

    I hadn't checked the link out and found that old Tape-Op article and it was saying everything I was talking about. Of course mine was all from memory. Proving once again, that not all of my brain matter was removed in my brain surgery two years ago. That is I think I had brain surgery? I don't quite remember because I was asleep for it. But I was told I was there.

    I forgot to mention that most folks think that the plate vibrates back and forth since the voice coil is connected to it in that manner. But that's not how the sound propagates across the plate surface. It actually travels along the surface and reflects off the edges and so it vibrates, in a sense, perpendicular to the driver. A bizarre thought indeed. Who would have thought? And all of this back in 1958! Brilliant!

    Happy 50th birthday to the EMT plate!
    Ms. Remy Ann David
     
  11. Jbrax

    Jbrax Guest

    so should the pick-ups be closer to the edge Remy?
     
  12. RemyRAD

    RemyRAD Well-Known Member

    No, they should be placed in the mid left & mid right, on either side of the plate, on either side of the driver. You are still picking off those surface skating, dense waves. I would imagine that the R&D performed by EMT and all those Germans 50 years ago probably determined the density of the reverb was better, in the wider opening planes. Remember, this was first released as a mono device with tubes in just a single pickup! EMT actually sold an upgrade kit to convert old Mono tube units to the new fangled stereo transistor thingies. I never heard the tube units but can only imagine that the drive section was way sweeter as the transistor one would sound awful and crunchy when you would overdrive it, just like transistors do.

    Another little note of interest is that, our 140 ST actually had a 2: 1 compressor on the drive section that you could switch on. This was a factory thing and not a custom modification. It was interesting and we used ours both ways, even though you would have to go into the sealed plate room to throw the switch on the electronics. Generally, most folks left the switch off but you would get a cool extra exaggerated reverb with it on. It also help to prevent overdriving the driver.

    The original 140 also had a manual reverb time adjustment on the box that you had to crank by hand. Later, a motorized device, with remote control was offered. And when you changed the reverb time, it wasn't something that you could do, or use as an effect, because the motor would cause undue noise. It was like a Ron Popiel tabletop rotisserie.

    You set it. And forget it!
    Ms. Remy Ann David
     
  13. Jbrax

    Jbrax Guest

    I got ya! Thanks Remy
     

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