Idea - making a doppler loudspeaker that isn't a Leslie

revsorg

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.

Gagaryn

Easier just buying a Yamaha rotary speaker I would have thought if Leslie is out of reach. The Yamaha's are cheap enough...

revsorg

I'm not looking for easy   I'm interested in making something.  Uncle Doug has made a home-made Leslie: 

Ravenous

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...

Ravenous

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...!)

revsorg

So, the inside of the cabinet could be a bit like the inside of the Trash Compactor?

revsorg

One of the things that appeals to me about this idea is that it's all about the way it sounds in the room, and it's likely to sound different depending on where you are. Miking it up would be a challenge.

Ravenous

revsorg said:

One of the things that appeals to me about this idea is that it's all about the way it sounds in the room, and it's likely to sound different depending on where you are. Miking it up would be a challenge.

Crazy idea... I wonder if anyone has tried to move the mic while recording... on a rotating boom perhaps...

ICBM

Apparently in the early days of Jethro Tull, they wanted a Leslie sound when they were recording but didn't have one available, so they got a roadie to stand on top of a normal cabinet and swing a microphone round and round it by its cable...

olafgarten

I always thought it would be a good idea to make a really small Leslie and amplify it through a Stereo PA

EricTheWeary

Yeah, the physical thing in the room is great - by the time it has been recorded I'm less sure it's worth the effort.

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. 

robinbowes

Vibratone on slow speed = Best. Chorus. Sound. Ever. 

thermionic

I found out at a relatively early age that if you stand in a smallish room and spin round when playing your guitar, you get a very cool Leslie-type sound!

octatonic

I don't bother with delay pedals- I just play things twice, the second time slightly softer.

ICBM

octatonic said:

I don't bother with delay pedals- I just play things twice, the second time slightly softer.

You are Bruce Hornsby and I claim my £5.

Rox

octatonic said:

I don't bother with delay pedals- I just play things twice, the second time slightly softer.

When I started playing guitar when recording, this is what I did because I didn't know that guitar pedals - let alone delay pedals - even existed. 

Not sure if I should be proud or embarrassed about that...?

EricTheWeary

There's a great clip somewhere of  Aziz Ibrahim doing faux effects like dub style delays and sitar noises just with the guitar. I'll have to look it up again someday.

Rox said:

octatonic said:

I don't bother with delay pedals- I just play things twice, the second time slightly softer.

When I started playing guitar when recording, this is what I did because I didn't know that guitar pedals - let alone delay pedals - even existed. 

Not sure if I should be proud or embarrassed about that...?

revsorg

Just going back to my original idea for a moment - I'm not sure which of the ideas that have been proposed would achieve a doppler effect. I figure that if I am going to establish this there are two ways - get input from someone with real or scientific understanding of all this, or go the Barnes Wallis route and start building some prototypes. 

Sporky

I think you could get close with a speaker with something like a slow fan in front of it. The blades will reflect some sound back, but that'll vary with the rotation and the pitch of the blades.

EricTheWeary

http://www.in2guitar.com/sidewinder.html

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. 

Nomad

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.)