I'm good at ideas, not electronics! Can someone help?

[David]

We've wrestled, figuratively and literally, with using or emulating a certain electromechanical tremulant device which is housed in a heavy, fancy wood cabinet.  I hesitate using the name because I don't want any patent lawyers coming after me.  I have a couple of ideas for a micro version of said device.  I believe I've done all the due diligence that was available, so now it's time to ask questions.

It seems to me that one could make a version of this well-loved effect by driving a speaker with a Little Gem or other low-power amplifier such as Javacody's 386 amp with EQ.  One could then have the speaker firing into some kind of baffle (maybe a DC-powered computer fan?).  I know that this baffle would have to rotate at 60 r.p.m. for the slow speed and 340 r.p.m. for the fast speed.  I would think that speed of a DC motor could be set and/or varied by using pulse-width modulation or the "inductive load-rated zero-crossing relay" documented in a thread on the SSR.  One would then mike this small device to get the swirl.

I'm guessing that what I'm suggesting here must be too simplistic an approach or someone much wiser than I would have done it by now.  Messrs. Hammer, Keen, Orman, petemoore, and anyone else who has ever tried this:

Am I barking up the wrong tree?  If so, why?
Is this worth taking further?  Can someone tell me what the next step might be?

[petemoore]

Not too sure I follow so...
 Are you talking about running airborne sound [liike in front of a speaker] through a channel which can be alternately opened and closed using rotory doors? something like Beatles "blue Jay Way" effect that sounds like singing into a fan?
 Tolerances with something like this would be paramount. Flat fan blades should take much of the air flowing sounds from the effect and make it easier to align the spinning blades through the slice of the chamber [Sounds like something from "Pit and the Pendulum".]
 Another way would be to have a plate that has close tolerance to the chamber walls fit with bearings and spinning like a furnace vent tube valve.

[Ansil]

We've wrestled, figuratively and literally, with using or emulating a certain electromechanical tremulant device which is housed in a heavy, fancy wood cabinet.  I hesitate using the name because I don't want any patent lawyers coming after me.  I have a couple of ideas for a micro version of said device.  I believe I've done all the due diligence that was available, so now it's time to ask questions.

It seems to me that one could make a version of this well-loved effect by driving a speaker with a Little Gem or other low-power amplifier such as Javacody's 386 amp with EQ.  One could then have the speaker firing into some kind of baffle (maybe a DC-powered computer fan?).  I know that this baffle would have to rotate at 60 r.p.m. for the slow speed and 340 r.p.m. for the fast speed.  I would think that speed of a DC motor could be set and/or varied by using pulse-width modulation or the "inductive load-rated zero-crossing relay" documented in a thread on the SSR.  One would then mike this small device to get the swirl.

I'm guessing that what I'm suggesting here must be too simplistic an approach or someone much wiser than I would have done it by now.  Messrs. Hammer, Keen, Orman, petemoore, and anyone else who has ever tried this:

Am I barking up the wrong tree?  If so, why?
Is this worth taking further?  Can someone tell me what the next step might be?

i feel what you are saying i will draw up something tonight.

[Paul Perry (Frostwave)]

I suppose a rotating speaker gets a lot of its effect by changing the path length of the audio from speaker driver to listner. Now if you has a bunch of vacuum cleaner hoses of different length, and a rotating culinder with a holes in it so you could switch between various lengths, then maybe that would work. I can see having a small primary speaker, then a mic at the output & then putting that thru the main amp. The kind of technology you have in the talk box might be appropriate.

[aron]

They do have portable leslie simulators that you can carry now. Motion sound, makes one I think.

The idea of a tiny one is cool though. You should make it.

[David]

Aron:

I know about the Motion Sound unit.  It's too expensive.  Actually, it's also too big.  I'm envisioning something about the size of a Pignose.

I do want to take a crack at building this thing.  I just have so much I want to build and so little time that I don't want to waste any of my precious bench time chasing down dead ends.

To continue:

I haven't heard anyone shoot my idea down.  All right, on to the next step.  This is where I have no experience or knowledge at all.  As Dr. McCoy might have said, "Dang it, Jim!  I'm a systems analyst, not an electrician!" Anyway, supposedly the "baffle" has to spin at 60 r.p.m.
for "slow", and about 340 r.p.m. for "fast".  If I'm using a DC motor (I'm thinking I could do this with a low-voltage fan), can I just vary the speed with a resistance? Or do I need to get into using PWM or that zero-crossing relay thing?

Here's another question:

Is there an easy way to measure the r.p.m. of the motor?  I never bargained on needing a tach to build effects!

[petemoore]

And put a brake on it...you should be able to slow it down but it may be tricky to get a stable RPM that way.
 Many fans have the three way speed selector...but they go probably from very fast to way too fast to so fast it might as well be still?
 Voltage divider?  OK...I'm shooting straws...

[Darren N]

since I posted this:
http://www.diystompboxes.com/sboxforum/viewtopic.php?t=9610&postdays=0&postorder=asc&start=26
I've had the chance to see a real Leslie in action. I realised that while you can get pleasing effects by spraying your sound all around a room, the real magic in a Leslie comes from the Doppler effect.  The amount of frequency shift is dependent on the linear velocity of the sound source with respect to the listener. The linear veocity of the end of the horn on a leslie is dependant on the rate it's spinning and the length of the horn. They have to be as big as they are to get the same depth of modualtion.

So in theory it won't work, but since when did theory and practice ever agree? Build it.

The kind of technology you have in the talk box might be appropriate.

Just last weekend I was swinging the hose of my talkbox above my head (much like I had seen the Doppler effect demonstrated in high school except they used a whistle into a hose). Pity there was no-one around to hear it and it doesn't work if you're in the middle of rotation.

Darren

[David]

Instead of a fan, the speaker could dump into a piece of PVC pipe that spins at the appropriate speed.  There's the Doppler effect!

[R.G.]

... There's the Doppler effect!

The Doppler effect is duplicated exactly by a varying time delay as in a flanger or even some phasers set for "vibrato" by removing the dry signal from the output mix.

Leslies are more than that. There's a web page somewhere that addresses some of the subtleties of the effect.

A good leslie simulation is remarkably hard to do in a non-stereo, non-mechanical effects box. You have to simulate the varying frequency Doppler effect (easy), the varying amplitude as the horns/bass rotor face toward/away from the listener (simple, if harder to do well), the spatial effect of early and late reflections from walls and ceilings (hard to do without at least stereo and maybe some DSP). Leslies give a major workout to the human ear's psychoacoustic frequency sensing and localization mechanisms.

Leslies have been popular enough that if it was simple to emulate, there would be Leslie simulators everywhere.

The simplest way to do a Leslie simulator is  - build some variation of a rotating speaker setup. That one should work well. I've seen some things that rotate speakers in a vertical plane instead of a horizontal one.

[David]

OK, R.G., I read the reference you mentioned.  Hope my customer doesn't noticed that my delivery date just slipped.  I see that a Les*&^ is more than just Doppler effect.  Actually rotating a speaker or pair of speakers would involve some kind of arrangement of "points", probably some kind of vibration dampening, bearings, and now I'm rotating more weight, so I have to come up with a bigger motor.

That should make me quit, but dagnabit, I have a feeling there's a way to make this work -- at least for a guitar, which is all I want.  And by the way, thanks for bringing me back to earth.

Any ideas about controlling DC motor speed and braking?

[R.G.]

The way the Leslie-ish things I've seen do it is with a bass speaker mounted on the bottom of the cab, firing upwards into a styrofoam cylinder with a port cut from the bottom center curving up and to one side. The styro cylinder rotates, the speaker doesn't. One of them had what looked like a styrofoam cylinder that was cut at a slant across one end, and the slanted end pointed to the bass speaker. Same principle - the opening rotated, not the speaker.

I wonder if you couldn't get the same effect with a 5 or 6" speaker and a 6" pvc  tee fitting set up to rotate.

The highs are done with two smaller horns mounted on a rotating disk or arm.

The low frequency and high frequency rotors are independent, driven (by belts in some units) by AC motors. The motors are set up so they are merely switched on and off. The ramp-up/ramp-down speed thing is done by the mechanical inertia that the motors have to pull - the motors are not variable speed, just highly loaded.

[David]

I wonder if you couldn't get the same effect with a 5 or 6" speaker and a 6" pvc  tee fitting set up to rotate.

That's exactly what I was thinking!  Yee-hah!  I'm on the right track!

Now, I understood your comment about braking -- the weight of the baffle contraption IS the brake.  Logical.  OK, so now I have to find a motor with the cojones to spin this PVC tee.  Further, I have to have a way to spin this baby at "fast" and "slow".  Would it work to use two high-wattage resistors to select the appropriate r.p.m., or am I still missing something?  I don't expect this to be invented for me, I just need a little push over the rough spots.

By the way, I'm NOT thinking about using an AC motor.  12VDC or something similar is more what I had in mind.

[gez]

If anyone's interested here are a few links:

http://theatreorgans.com/hammond/faq/mystery/mystery.html

http://www.dairiki.org/HammondWiki/Leslie

http://www.soundonsound.com/sos/jan01/articles/vintage.asp

[Ansil]

this isn't acutally what you said to the detail this is something i just did a while back for shits and giggles. and to agravate my room mate.  i have actually not heard a leslie cabinet in person.  so i dont' claim that it sounds like it  i have in fact three peoples opinions here on it.


1. it sounds amazingly like a leslie.

2. it sounds  nothing like a leslie but very interesting indeed

3. it has a unique sound to it that does in some ways mimic a leslie.



my personal opinion.. it adds a cool effect for movies and stuff. as well as guitar sounds.  

the way i went about this is like this.  the positive and negative signal are applied to the red and green terminals respectively.   the two motors are runn off seperate controls


and they spin opposite each other.


http://www.geocities.com/austenfantanio//rotocabtypethang.htm


updated. i added an inside view of the box i am building it into.

[casey]

there is a company that has already done this......
the size is a mere  8" x 8" x 12", weighing in at 7 lbs.

here is the link!
http://www.songworks.com/index1.htm

they also have one that is slightly larger too.

super cool company.

[casey]

look to the left....it's called "rotary wave."  they have a 6.5" version of
it. and an 8" i think.

[David]

If only I could afford that...

[Paul Perry (Frostwave)]

Doesn't seem to be much in that RotaryWave thing.. anyone seen inside? if it is just a spinning baffle (like the bottom half of a real leslie) then anyone could make one, pretty easy. Maybe from a fan with a carved chunk of polystyrene on it! and a speed control.

[R.G.]

Instead, why don't we do this:

1. Crossover split the input signal, about 600hz like the real Leslie
2. Use a phaser (p90, p45, univibe, etc.) in vibrato mode for the frequency/Doppler shift and run the highs through this.
3. Use a tremolo circuit on the lows
4. Use just a hint of tremolo on the highs to fake the amplitude modulation in sync with the LFO for the highs
5. Mix all the stuff back together

For extra credit -

Make two, use one feeding one side of the room, one feeding the other through a different amp/speaker and at a slightly different frequency.