I think I stumbled onto a way to get that “moving air” feel from an electric organ without a Leslie, and I’m buzzing to see if anyone else has tried something like this or can help refine it. I routed my organ through a simple 2-way crossover: lows to a small sealed sub tucked behind the bench, highs to two tiny nearfield speakers mounted on a silent, belt-driven cake turntable with curved foam baffles in front of each speaker. The baffles aren’t horns, just shallow S-shaped deflectors. With the rotor creeping at “chorale” and then ramping to “tremolo,” the sensation in the room actually feels like air is moving, even at neighbor-friendly volumes. It also changes how I play, which is the magic bit I’ve always missed with pedal-only rotary sims.
What I’ve tested so far:
- 850 Hz crossover point sounds most Leslie-like here; 600 Hz was muddy, 1.2 kHz got phasey.
- A gimbal BLDC motor with sine-drive ESC is dead quiet and ramps smoothly; steppers microstepped were okay but had a faint tick at certain speeds.
- A 3D-printed lazy Susan with rubber isolation grommets killed most cabinet buzz.
- Recording with a single mono mic a meter away gave that classic “folding image” when blended with a bit of close DI.
Questions I’d love input on:
- Is there a known “sweet spot” crossover for this kind of physical rotary proxy? I’m hovering around 700-900 Hz, but would love measured opinions.
- Any rules of thumb for the baffle geometry to mimic the HF horn vs LF drum? My shallow S-baffles seem to throw highs nicely, but I’m guessing surface curvature matters a lot.
- Accel/brake curves: what time constants feel right to you for 122 vs 147 behavior? I’m around 4-5 seconds up to fast, 6-7 seconds down to slow, but not sure if that’s psychoacoustically ideal.
- How are you taming Doppler vs amplitude modulation in DIY builds? Mic distance and directivity help, but I’m curious about diffuser materials or asymmetrical baffles to bias the effect.
- For live use, would dual counter-rotating baffles (lighter mass, lower speed) be more convincing than one heavier rotor? I tried counter-rotating at half speed and it got ultra-wide but maybe too chorusy.
- Best way to integrate expression so that speed ramps are linked to pedal position without feeling gimmicky? I’m considering a “hold at chorale unless pedal >60%, then ramp to tremolo” mode with a long brake tail.
- Any EMI gotchas with BLDC controllers around vintage tonewheel preamps? I shielded and grounded the motor assembly, but I’d love proven layouts to keep hash out of the preamp.
If anyone has measured polar plots of a Leslie horn/drum or has built a “quiet rotor” rig, I’d be thrilled to see geometry, materials, and speed profiles that worked. If this can get 80% of the vibe at 20% of the volume, it could be a game-changer for apartment-dwelling organ nerds.