Anybody Know leslie bass Rotor dimensions

[cgiff]

I'm in the process of building a modular leslie from Scratch. I'm building this specifically for guitar. I plan on using a 12 inch speaker to interface with the plywood bass rotor. Does anyone know the dimensions of a standard 15 inch leslie baffle so I can scale to 12 inch? Specifically looking for the height of the rotor.

Cgiff

[Earl Norton]

If you are not using a horn for high frequency, you should consider keeping the scoop as short as possible. A long scoop will act like a low pass filter. Other than that, the scoop should cover the 12 inch speaker...like 11 inches round or so.

[cgiff]

Got it I think

Thanks for the respone Earl, I have been doing some research on the leslie baffles. Don patented a variant of the rotor by adding a couple of deflectors in the scoop to capture higher frequencies, a patent was issued in the mid 60's. Ultimately I plan on using both a speaker and a horn on ths project. I'm going to experiment with a couple of different baffle configurations, using an aluminum and a plywood scoop. I'm toadd aluminum deflectors to a plywood scoop in an effort toobtain full range output as this is for a guitar application. I have reverse engineered some dimensions of a patent drawing scaled and curve fitted to obtain a 12" scoop that looks very close to the 15 inch standard. I would like to confirm the inside height dimensions of a 15 inch baffle just to confirm my assumptions.

[devnull]

Is this helpful?

http://www.theatreorgans.com/hammond...y/mystery.html

[Mark Hammer]

The intensity of the effect depends on the diameter of the rotor. Keep in mind that the rotation speed will be the same (one would hope), so a longer diameter rotor means that the rotor travels a greater perimeter in one rotation. This also means that the acoustic signal produced at point X, has travelled farther and faster, in time, than the acoustic signal produced just 90 degrees earlier in the rotation. Whatever notches are produced by the doppler cancellations will also extend lower down, yielding a more pronounced effect.

My sense is, as well, that a small part of the Leslie "sound" involves a small, but still noticeable, amount of amplitude modulation and lowpass filtering as the horn points away from and then towards the listener. A slightly longer diameter rotor will accentuate that a bit.

So, from where I stand, the rotor dimensions should not necessarily be scaled down for different sized speakers.

[oc disorder]

A couple of things you may not have seen
Copy of a 1968 article in Electronics Australia "Rotating System Loudspeakers For Electronic Organs"
http://ozvalveamps.elands.com/playma...leslie6803.zip
Leslie 122 Project
http://www.users.bigpond.com/johnacollins/hammond.htm

[Mark Hammer]

I snagged the first article a few years back, but was unaware of the second. Thanks! That's a very nice piece of work.

I think it is fair to say that the dimensions of the rotor that we are accustomed to seeing, are frequently a product of the dimensions of the overall cab required to house all that stuff, yet still be liftable.

[cgiff]

OK, it's been 10 years since my original request for rotor dimensions. I bought a Hammond x77 & Leslie off of Kijiji a year ago. I have salvaged the Leslie for the mechanical components. I have reverse engineered the drum rotor, with the help of a few friends. Designed and built fixtures to make the rotor, happy to say I was successful in making a plywood drum rotor for a 15 in driver. I used a seismic app on my tablet to assist in balancing the rotor. So now have a 3 piece portable full sized Leslie, horn,s rotor, JBL drivers, electronic crossover powered with a hacked up fender mustang V amp (hacked chassis, very low weight 2x75 watt power amp etc.). Arduino uno used for motor hi freq reverse phase angle control. (No motor stack due to weight) electronics allow min, max and ramp up down control. No it's not a real 122 or 147. But incredible for guitar. Heaviest component is horn / amp cabinet at 55 lbs. due in part to the additional weight of the JBL 2420 driver. K130 is used in the speaker cab for low or full range frequencies, depending on what I select. Rotor and motor are in a separate cab. I'll post a YouTube vid in the late fall.