Don Leslie's other designs- The electrostatic upper rotor.

[paulj0557]

Donald Leslie might have stayed up many a night trying to improve an invention that needed little improving, but that was his nature. It seems to be the nature of most creative inventors. On July 9th,1956 he applied for a patent- number 3,058,541. The patent was awarded on October 16,1962. This patent was for an electrostatic upper rotor. It's easier to show it than explain it, but the proposed advantages were that it didn't share the same electrical resistance problems that a magnetic speaker put into rotation created. The Leslie's most people are used to consist of stationary low rotors with a baffled drum rotating below the downward facing speaker, and an upper mid to high range horn driver facing up into a horn baffle counter balanced by a dummy horn. So these systems don't have actual speakers in rotation. However there is another type that does put the actual speaker in motion- the Leslie Rotosonic. These are speakers mounted in a drum and then the drum rotates and thereby spins the speaker. It is a single 6x9 mounted vertically and behind a vertical slot in the drum where the speaker is recessed slightly. There is a Merco-tac that is used to allow the input to the speaker ( see image).
The electrostatic rotor seems interesting and I wonder if any were ever actually built. I have a pair of Magnaplaner Magnapan Smga's which are large flat speakers that speak out of the front and back. Some day I might experiment and put one in a tall vertical cylinder drum with either one long vertical slot on one spot on the drum and then rotate the drum around the speaker to see if it sounds good. I could also put a barber's pole type of slot around the 2 tall cylinders and have them synchronized so that they compliment each other somehow. It's just a thought...
BTW, Donald Leslie was a big theater organ buff so this might have had theater organ intentions.

Here's the page of Leslie's patent. Read the text below too. Please comment on this:-)

http://www.hammond-leslie.info/DonLesliesPatents/3058541_rotary_electrostatic_spkr.pdf

[torea]

Very interesting. I'd love to see one, I always have a bit of trouble trying to visualize it through the patent drawings. Wonder if any were ever made.

It's pretty amazing the stuff they came up with to make this awesome Doppler vibrato/tremolo effect. I still love the genius of the Wurly Spectratone unit that uses a rotary transformer to mount a pair of spinning speakers.

[Jan Girardot]

Fascinating! Paul, how did you happen on to that Leslie patent?

Re: rotary speakers: have youse guys seen the Baldwin Leslies? To me it seems their engineering department was trying to reinvent the wheel; what do you think? And, of course we musn't ignore the Yamaha "planar" rotary unit. Anyone know if Yamaha had to pay patent royalties to Magnaplanar for that and their "Natural Sound" speakers?

BTW: if anyone is interested, I have a WurliTzer SpectraTone unit out of a 4700 for sale. Contact me at jan@theorgangrinder.net if interested.

. .. Jan
the OrganGrinder

[BlueOliveB3]

I used to own Magnepan SMG's. They perished in an unfortunate home-studio accident (when bringing up the control room, make sure to disarm any tracks connected to open mics!) In retrospect I should have saved them and sent them to Magnepan to be rebuilt, but I tossed them. The tweeter voice grids burned out to protect the 50 cent fuses. I've never found speakers I liked as much as my old Maggies. The soundstage and smoothness was to die for, though the sweet spot is pretty narrow with them, the best stereo image is pretty much for one listener. But music just sounded "alive."

TP

[toasterDude]

Wow that is different, a whole new take on the problem. Thanks for posting this PJ57.

This brings up a related question for me, though. I was just working on an Allen "Gyrophonic" cabinet last weekend. These have a similar design concept, except the speakers are actually mounted in the rotating baffle; contact is maintained by brushes. But what struck me about it was that it uses DC motors, not AC like in the classic Leslies. It seemed like a more elegant solution in a way: just by varying the voltage, you can get different speeds (three different speeds, in this particular cabinet) from the same motor. Again, definitely less clunky than the little slow AC motor piggybacked on the larger fast motor. So it left me wondering why D.L. wouldn't have used DC motors too? Were DC motors not in use yet, when he first invented the "Vibratone" in ~1940? Or were they prohibitively expensive?

I just wondered if anyone might have any insight into the choice of AC vs. DC motors.

cheers,
td

[andyg]

I used to sell something very similar in the music storeI worked for back in the early 70's. Flat panels that stood on the floor, very slight curve to them. Sounded wonderful to me at the time. Not called Magneplanar, though. Did they license to technology to other companies across the world, I wonder?

[SimonB]

Andy,
Your description sounds like the classic Quad Electrostatic. They still sound good if working properly.
People would always mistake them for a heater http://quad405.com/first_el.jpg

[paulj0557]

Andy,
Your description sounds like the classic Quad Electrostatic. They still sound good if working properly.
People would always mistake them for a heater http://quad405.com/first_el.jpg

Ha ha that's funny, I found my SMGa's on the side of the road one evening while riding around with my buddy Charlie, better known as 'Mower-man Charlie'. Charlie had recently had surgery so I offered to ride on his thrash route looking for thrown out lawn mowers. This particular night I spotted what looked like office partitions, but as we got closer I knew better. " What do you want with those old office things?", Charlie said. They were laying flat on the ground and upside down. The plate on the bottom has a glass fuse exposed and two screw terminals. I was very surprised they worked perfect. At the time I was renting a small room so they seemed to dwarf the space, but the sound was huge! The best part was how they seemed to push a large mass of air without needing the amplitude, so to the listeners in the room the range was a full and crisp stereo image that seemed loud, yet on the other side of the door you could barely hear them. They are the perfect dorm or den speaker. It has my curiosity up, maybe I'll look them up and see what sort of dispersion they have on paper. The Magnapan speakers use what's called a dipole voice coil, but unlike a voice winding wrapped around a thin cardboard or paper covered aluminum cylinder, instead these windings are laid flat and adhered to a stretched piece of flat Mylar. The windings start at the top, then go to the bottom, then s back up, and so one all the way across. Behind the Mylar are slots with magnets which are staggered +-+-+-+-+-+-. So if you use your imagination you can begin to visualize that just as a traditional speaker moves the cone as a reaction to the constantly changing polarity set up by the windings placed in a magnetic field, so will the Mylar move in this constant opposition...

Okay, so do you think Mr. Leslie ever pondered a 360 degree speaker that can change it's focal point and spin the sound around the room just as high or low rotor, but with no moving parts? The Thomas Californian spinet did this using 2 speakers and used photo cells and light bulbs. Then by using negative feedback, phasing, and varying amplitude they were able to create a pretty cool sounding stereo ( and then quad on the Quad Californian) tremulent effect by sending the signal back and forth at various rates and with different electronic treatment. The user can adjust all of the parameters inside the organ by turning the trimmer potentiometers. The tone is a very shimmering. I think everyone should at least try to play a Thomas Californian spinet at least once...you'll probably buy it! Put the following line in forum's search bar:

Records Records Records! Post'm to Youtube & put 'electronic organ' in title! [/B

Then listen to the very first Window of Harry Wach playing a Californian spinet. BTW [B]ALSO listed three more organ records today scroll to the last post on that thread. Walter Wanderley Cheganca- whole record! Don Baker Hammond organ whole record, and Lenny Dee...1 track on 8-track. Enjoy:-)
Of course the simpleness of the motor driven high rotor is so effective it's likely Donald didn't lose a lot of sleep over the success or failure of his other ideas.

[paulj0557]

Wow that is different, a whole new take on the problem. Thanks for posting this PJ57.

This brings up a related question for me, though. I was just working on an Allen "Gyrophonic" cabinet last weekend. These have a similar design concept, except the speakers are actually mounted in the rotating baffle; contact is maintained by brushes. But what struck me about it was that it uses DC motors, not AC like in the classic Leslies. It seemed like a more elegant solution in a way: just by varying the voltage, you can get different speeds (three different speeds, in this particular cabinet) from the same motor. Again, definitely less clunky than the little slow AC motor piggybacked on the larger fast motor. So it left me wondering why D.L. wouldn't have used DC motors too? Were DC motors not in use yet, when he first invented the "Vibratone" in ~1940? Or were they prohibitively expensive?

I just wondered if anyone might have any insight into the choice of AC vs. DC motors.

cheers,
td

My guess on why Don opted for two AC versus a variable DC motor, at least early on was that he experimented with ideal rotations and two speeds ( a second motor was added later, not sure if solid state variable DC supplies were cost effective or reliable by then) were adequate for the Hammond- his target buyer. DC motors required a DC supply and added components to the situation. In early 40's they didn't have solid state variable supplies, or SS diodes, so to use one motor at a varied rate would mean at least one more tube unless the DC were to come off of the high voltage DC supply used on the amp, then it would need a step down transformer...in the first designs 2 AC motors made sense. Using a resistor array, or an L-pad to vary speed on a single AC was also a bad idea due to the tendency for an AC motor to speed up as the ceramic cools, more regulating tube circuits would have been more money. Bottom line, the old tube amp designs were extremely reliable, and for the most part so are AC motors. Remember, the first Leslie's were one speed and a standard 110 AC motor was a natural choice.

[paulj0557]

Don Leslie was a theater organ buff. My theory for the reason he invented the electrostatic upper rotor was in an attempt to overcome the shortcomings of the Hammond/Rotosonic combination in playing theater organ arrangements. Although the Rotosonic gives the desired bulbous tremulent tone, there is something missing ( besides the lack of reed,strings, diapason, and horn voices). I currently have no high rotor so I have no idea if my theater organ playing would benefit with a high rotor or not. The Rotosonic cabinets don't have upper horns, or low rotors. They have upper stationary 6x9's and a lower rotosonic. So come to think of it, this invention of his had a standard low rotor with a downward facing 15" ( or 12"?), and an upper electrostatic rotor. The fact that there are many electronic theater organs (ETO's) with standard low rotors that sound extremely theater makes you wonder anyway, this could have been invented for another brand of organ all together, like the 101, 102, and 103 were developed for Gulbransen (Lowrey too?).
All I know is my Hammond Elegante would benefit from a high-rotor, but not sure if it would make it more theater like...something is not quite right sounding for theater organ playing, even with the diapason,reed, horn, strings on. I really like Ethel Smiths playing and tone and I'm sure that a high rotor would at the very least get my Elegante closer to that tone anyway (...I didn't say it would get me there, just closer).

Anyone have any ideas what this electrostatic upper rotor would sound like on a tone wheel Hammond, or another make?

[BlueOliveB3]

The Rotosonic cabinets don't have upper horns, or low rotors. They have upper stationary 6x9's and a lower rotosonic.

Leslie made a bunch of models with Rotosonic lower rotors and upper treble horns. The 710, 715, my HL-722 and HL-822, and several others. The correct Leslie for your Elegante is the 740 or the 750, both of which had Rotosonic lower rotors and upper treble horns. You can also use a 715/HL-722 or similar but you'll need one of the piggyback cabs (515 or 540) to get the other stationary channels out. To hear what the 740 and Elegante sound like, search YouTube for the user ElegantePlayer. That's what he has. He's a great cocktail-lounge supper-club organist from back in the day.

TP

[jdoc]

Don Leslie was a theater organ buff. My theory for the reason he invented the electrostatic upper rotor was in an attempt to overcome the shortcomings of the Hammond/Rotosonic combination in playing theater organ arrangements. Although the Rotosonic gives the desired bulbous tremulent tone, there is something missing ( besides the lack of reed,strings, diapason, and horn voices). I currently have no high rotor so I have no idea if my theater organ playing would benefit with a high rotor or not. The Rotosonic cabinets don't have upper horns, or low rotors. They have upper stationary 6x9's and a lower rotosonic
710 and others have the Rotosonic, I pulled mine, and like many others; the crappy speaker was badly deteriorated fwiw.
I was so bad I never got a chance to test it, and I have seen others equally shreded, maybe with a good 6x9 and some rebalancing, I did keep the parts for the Leslie Lab.......

[paulj0557]

Leslie made a bunch of models with Rotosonic lower rotors and upper treble horns. The 710, 715, my HL-722 and HL-822, and several others. The correct Leslie for your Elegante is the 740 or the 750, both of which had Rotosonic lower rotors and upper treble horns. You can also use a 715/HL-722 or similar but you'll need one of the piggyback cabs (515 or 540) to get the other stationary channels out. To hear what the 740 and Elegante sound like, search YouTube for the user ElegantePlayer. That's what he has. He's a great cocktail-lounge supper-club organist from back in the day.

TP I think I was referring to my 705 which doesn't have a low rotor or high rotor. I've listened to Eleganteplayer and like his style. It would be interesting to hear a modded, or well adjusted Elegante through a nice old tube Leslie w/ hi/low rotors. I have two 540's and the 705 so it will work fine with the Elegante. I need to build an adapter for using it on the Elegante too, the Rialto II is what it's hooked to now, but an adapter should be simple enough. Just made an adapter so I can play my Wurlitzer 625t through it. My 625t is such a great sounding organ. After doing several repairs I've seen several places where I can add extra control over the mix of the voices. Wurlitzer is already pretty good with this, as they have always added 'accent' tabs to boost a rank of tabs, but would be nice to have individual control. Although the 625t is not a traditional individual transistor oscillator design, it is individual opamp circuits, post LSI TG's.

[BlueOliveB3]

Ah, gotcha. You know, since you have the 540's a 715/HL-722/815/HL-822 would really sing with that Elegante. You can often find them pretty cheaply, they're underrated Leslies. Run one of those along with the 540's and the 705...wall of sound! :D

TP

[andyg]

Concordes and Elegantes sound very nice through a 145, though obviously it only takes the place of the rotary channel's Rotosonic. The rest of the sound stays with the organ's main speakers. You can also hang a 145 or 147 on the end of a big Gulbransen, Conn, Thomas or big Kawai in the same way. Although there's no bass to be dealt with, the 15" speaker in the 145 adds to the depth of the rotary channel's signal, smoother than the 6x9" in the Rotosonic, for example.

[thetrader]

Sort of off topic but Don Leslie was a genius. Can you imagine. It's the depression, you go out and by a Hammond organ only to have it sound bad(in front of your wife) and you invent the best d_ mn sounding organ speaker ever made. In the 30's! Absolutely amazing!

[Derbig Mooser]

The thing about a Leslie which amazes me, almost more than how it enhances the Hammond Organ sound, is how a Leslie (working only with physical processing of the sound) minimises the sonic shortcomings of a Hammond Organ.
Notice that in an unhacked Leslie, there is no direct path from speaker to ear, and sound must be reflected many times before it reaches your ear. That principle was used for pipe organs, too.

But the organ the Hammond was designed to replace was not the pipe organ for the most part. It was the reed organ. At one time reed organs were almost as popular as pianos for the home. Many of them had 2 manuals and some had 32 pedals! By the time Hammond came along reed organs could be electrically blown.

[paulj0557]

Don Leslie taught us all a big lesson- there is always room for improvement. Another lesson was that common sense designs are available to all of us to think of and make. The Doppler effect is a simple principle and corresponds directly with the definition of vibrato. One could very easily 'dream up' a vibrato machine just by pondering a simple experiment of making a speaker's sound point to one direction in a room and then shift it's aim to another. In conceiving a contraption the first thing that might come to mind is mounting a speaker box to a Lazy-Susan and spinning it around. The problem of the wires going to the box getting tangled in the spinning could be overcome by making the speaker stationary...and the rest is history,right? Yes, and no. Don had a musical sense as well as his practical scientific sense. He took these concepts and refined them. The problem with many scientific thinkers these days is they will spend thousands of dollars exploring a concept and make absolutely nothing practical or useful come from it.

I'm curious, has anyone ever put a rotating drum with a 4-6" vertical slot, over a stationary box with a speaker facing out each side?