Rotating cab, Concept

[Earthscum]

I was setting up mics on my drummer's set the other day and was thinking about how to minimize picking up reverb from the walls, and started thinking about eqing. Every time I think about my mic setup I start thinking about the effects of a rotating cab.

Well, I was thinking about the rotating cab idea and came up with an idea. First, we need a pair of bandpass filters, maybe with a notch to generalize a speaker response. That's finite details, though. So, the cab facing forward would be an in-phase response. The cabinet facing backwards would have an inverted phase response from bouncing off the back wall. If we use these two filters in a setup like Anderton's Bi-Filter Follower, only controlled with a LFO, we would be part way there.

Now we need the phase shift from the side walls. If we use a single phase shift that is out of phase in the low frequencies, and in phase on the highs, we can sweep the response up and down to simulate the rotation in and out of phase with the back wall. As a matter of fact, we can use the same LFO we use to sweep the phased bi-filter.

When the cab is facing forward (in-phase amp is active), the phase shift circuit will have a low frequency shift, causing a low-end cut. Cool. Now, as the cab rotates backwards (the in-phase filterbecomes inactive and the out-of-phase filter becomes active), the phase shift circuit wilraise it's corner frequency, and when the OOP filter is fully active (cab facing backwards) it will have a high cut, muffling the sound. As long as the phase shifter doesn't reach too high of a frequency corner, it should simulate the muffled highs very well.

Another idea is to make the phase shift lag behind by a hair to get a full rotating effect as if you were standing to the side and not a mathmatical standing directly in front of it kind of response.

To control the LFO speed, I was thinking you could use a large capacitor/resistor to slowly ramp-up the ground voltage when you stomp on a momentary. When the capacitor is at full charge, the cabinet would be running full speed, and when you release the momentary, the capacitor slowly discharges and simulates the motor ramping down.

And, of course, uber awesome millenium bypassing switch.

What do you all think? I'm sure someone else has already thought of this, so if anyone has a schematic, that would be awesome. If not, let's try it?

[petemoore]

  Manyones have thought and worked on that one.
  I used HDuty lampcord, hung and twirled the cabinet...not recommended in amp warranty.

[G. Hoffman]

I went to eBay and bought the mechanical bits from a Leslie home organ speaker unit (an OEM thing they sold to home organ manufacturers like Wurlitzer and such) that someone had parted out.  I built a box around it, and it sounds amazing!  The only problem I've had with it is it only has a fast motor, so I need to replace the motor at some point - either with an old Leslie stack, or a DC motor - or make a variable frequency drive for the induction motor that came with it (no, I can't just put a pot on the motor - induction motors don't work like that.  Why does everyone ask this?)  It's pretty small, and pretty light, so I have no problem carrying it around - and I pull things around in a bicycle trailer!


Gabriel

[PRR]

> how to minimize picking up reverb from the walls

Cover them with fuzz. Packing blankets, old fur coats, wool socks, heavy drapes. There's surely a space-age polymer product ("foam"), but beware of fire danger.

> a rotating cab... a pair of bandpass filters

Delay lines and low-pass filters. Trivial with DSP. Probably preset #67 in those 99-setting $99 amp/cab simulator pedals down in the toy aisle in Banjo World; also many plug-ins for P-Tools.

NOTHING else ever sounds JUST like a Leslie. Real rooms, stages, gigs are too complicated to "model" reasonably. And because of our heritage (hunting for mice and fearing tigers), our ears are awful good at scoping-out an acoustic space.

Sure fun to play with. But it isn't a new path.