Millions of years ago I saw the Pat Travers Band and they had big
Leslie speakers on stage with their spinning speakers that achieve a doppler effect. Leslies give you a physical experience when you're in the room with them that IMHO any amount of digital modelling falls short of.
I have started wondering if it would be possible to make a speaker cab for a guitar amp that somehow achieves a doppler effect but in a smaller enclosure and that isn't a straight rip-off of the Leslie design. The reason being that I've got a tiny little Plexi 7 amp, can I avoid having a humungus speaker cab to accompany it?
I thought I'd just throw this idea out there see if anyone has any insights.
My idea is that you could use the
transmission line concept to reduce the requirement for a large enclosure. I had two ideas based on this:
1. You could have more than one transmission lines inside the cab, and using a mechanism route the sound from your speaker through the different paths, achieving a modulating sound. I wonder if a clever 3D printed shape might facilitate this re-routing of air. Rather than spinning, the shape might move back and forth. Maybe I shouldn't worry so much about a spinning thing being deemed a copy of the Leslie concept.
2. Have one transmission line, but have it variable in length. One way would be like the slide on a trombone, but with a bigger cross section. I'm imagining a sort of steampunk-like thing protruding in and out of your speaker cab, electrically powered, using a silent motor-powered mechanism.
You could maybe have more than one thing going at once - after all, the Leslie has separate bass and treble mechanisms.
My understanding of physics isn't good enough to know whether either of these ideas would actually achieve a doppler effect, something even vaguely like it, or even whether it might sound nice?
I'd be interested to hear anyone's thoughts.
Comments
Easier just buying a Yamaha rotary speaker I would have thought if Leslie is out of reach. The Yamaha's are cheap enough...
Make the transmission line section out of that flexible, corrugated plastic pipe they sell in pet shops for making guinea pig shelters. Then arrange a motor to sway it back & forth changing the length.
Possible problem: the corrugations make clicking noises when flexed, and these might crack after a bit of use. Maybe some kind of flexible pipe? Or something like a trombone? (obviously much larger bore so you don't get pitch shifting.)
Edit: Duh - the trombone idea is exactly what you suggested above. By the way maybe you could knock up a prototype with a tiny toy speaker and foam core board...
Or another idea - speaker in the top as usual, a fixed hole at right angles for the sound to come out, and inside that a board at around 45degrees, but it's made to pivot back and forth. A bit like a harmonica player waving the hand over the mouth.
(Though there's probably a very good reason nobody does them this way, that I can't think of right now...!)
Crazy idea... I wonder if anyone has tried to move the mic while recording... on a rotating boom perhaps...
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Motion Sound used to make rotary speakers for guitarists that were fat 1x12s, so I don't think they were enormous or that heavy. Some kind of rotary drum in front of the speaker. Looks like they only do big combos for keyboard players these days.
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Rox said:
That's an article on the old Motion Sound combo. It is something like a fan (some kind of rotary motor)in front of the speaker but instead of blades it's that drum type mechanism.
It's not clear to me how a transmission line will have the desired effect. In loudspeaker design, the job of a transmission line is to suppress emanations from the back of the speaker, which would otherwise get into the room and mix with the emanations from the front and cause various cancellations and additions depending on frequency, room specifics, location of the speaker and listener, etc. I don't see how connecting and disconnecting (or blocking and opening) a transmission line will result in the subtle vibrato effect that a Leslie produces.
That Motion Sound thing is like the bass rotor in a Leslie. Unless I'm missing something, it has no separately spinning high frequency component - proper Leslies have the bass rotor (basically an angled deflector plate that sends the speaker emanations out in a circular fashion, like a radar beam), and a spinning horn that does the same thing for the high frequencies. The Leslie effect has a couple of characteristic components: the horn system tends to spin at a higher speed than the bass rotor, and the rate of speed change between fast and slow differs - the rotor takes longer to speed up and slow down compared to the horn. The change in horn speed is very quick, while that of the rotor has a noticable transition time.
There used to be a budget Leslie that only had the big speaker (but full range) and rotor - no horn assembly. It didn'thave the characteristic sound. (It was bland shite, if I'm honest - when I bought my Hammond A100, that was the speaker on offer with it, and I turned it down. I later got a Leslie 145 which is bass rotor and horn, and has The Sound.)
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