Well, This is Weird!

[Michael Smith]

Yesterday I was giving my "new" amp it's first truly extended workout since I serviced it a week or so ago. I was hearing some strange "ghost" notes or something I can't fully explain, especially on higher notes on the high E string. I thought maybe there was something wrong with the tone stack so I tried the other channel (non-reverb and vibrato one). Same thing. Well, maybe it's fret buzz on the higher notes. Got out a different guitar, same thing. Something wrong with the speakers in my 2 x 12 cabinet? I was sitting in a chair about 10 feet from the amp, at about a 45 degree angle to the speakers. So I get up and move closer to the amp and I no longer hear anything out of the ordinary.

Well, it's been unusually hot here, and I had a box fan sitting on a chair a few feet away from me, more or less right between me and the amp. When I turned the fan off the weird notes were gone!. Somehow the higher frequency notes travelling through the fan blades was doing something to the sound waves, and that mixed with the direct and reflected sound hitting my ears was causing this weird effect. I'm glad I don't have to tear into the amp so soon after completing the service. Just move the fan, lol.

[phantomman]

If that fan hadn't been the culprit I would've suggested a microphonic tube.

Glad it all worked out for the better.

[Michael Smith]

If that fan hadn't been the culprit I would've suggested a microphonic tube.

Glad it all worked out for the better.

I'm sure someone with more knowledge than i have of physics or audio-acoustics could explain what was happening. I just thought it was weird, lol.

[phantomman]

An audible manifestation of the "doppler" effect no doubt.

[Offshore Angler]

An audible manifestation of the "doppler" effect no doubt.

Or "aliasing" due to the reflected sound waves off the blades more likely. Doppler would have been a pitch shift.

Similar phenomena happen at vane pass speeds (as the vane tips pass by the casing cutwater) on the centrifugal pumps in rocket motors, not that I would know anything about rockets, lol.



Chuck

[Michael Smith]

Or "aliasing" due to the reflected sound waves off the blades more likely. Doppler would have been a pitch shift.

Similar phenomena happen at vane pass speeds (as the vane tips pass by the casing cutwater) on the centrifugal pumps in rocket motors, not that I would know anything about rockets, lol.



Chuck

So there is a scientific explanation for the phenomenon I was experiencing! I thought I had screwed something up when servicing the amp.

I may have to fool around with different fan placements and speeds. Maybe I've stumbled onto a new "effect".

[Offshore Angler]

So there is a scientific explanation for the phenomenon I was experiencing! I thought I had screwed something up when servicing the amp.

I may have to fool around with different fan placements and speeds. Maybe I've stumbled onto a new "effect".

Yep, or could have been simple resonance.

[ch willie]

Can we market that phenomenon as a new effects pedal?

[Michael Smith]

Can we market that phenomenon as a new effects pedal?

We could, but it really didn't sound very good. Maybe call it the "malfunction pedal". I would be curious as to anyone else can replicate what I was hearing, or if it was unique to the size of the fan, the speed of the fan, distance from the amp, distance from me, etc.

This was the approximate setup. Speaker cab under the Bandmaster Reverb head.

[phantomman]

A stereo pedal combining tremolo and flange would be a close approximation I would think.

[ch willie]

A stereo pedal combining tremolo and flange would be a close approximation I would think.

. I’d think it’s a similar phenomenon



So Michael, are you saying you’re not a FAN of that sound?

[Offshore Angler]

Can we market that phenomenon as a new effects pedal?

Lot lighter than a Leslie!

[phantomman]

Easier on the roadies too!