On 8/1/96, Ronald R Shiflet rote: <<it needs to be brought up more often. I tuned a piano 2 weeks ago that was so close, I was able to spend my time fine tuning. Last week the owner called back to complain that it sounded terrible. I asked her to first check the sound with the fan on and then off. This has happened before. I wonder how many people get frustrated with us and go elsewhere when the fan is the real problem. A good lesson in communication. >> A strange but true phenomenon. Kent Weeb wrote about it in Baldwin's "Sounding Board". I recounted my own acquaintance with it in the 2/91 "Granite Action" (NH Chapt): "Close Encounters of the Salad Master Kind" I knew something was wrong as soon as I started in on the tuning of this 5-year old Yamaha U1, and I could already feel condolences for its owners. The tone in the third and fourth otcaves was anemic, washed out. Worse yet, a subtle flutter was showing up in the middle partials (3d through 7th) on notes in this region, maybe one or two partials per note. The partial number affected changed from note to note, and this flutter was independent of the tunings usual beat rates. Was this the reason I was called in on a pianos not badly out of tune? I listened around the room for other sources of pitch which might be interfering with the piano sound. The loudest electrical appliance was the ceiling fan which whispered innocently. I could still tune and so I did, until halfway through when I decided to shut off the fan, just on a hunch, mind you. Like magic, the sound turned froma cold drizzle to warm sunshine. This was one for Dr. Science, my neighbor, who is a black belt, 12-star radio engineer with a labor rate for servicing the region's electronic facilities twice my own. He's never forgotten a word he's read, and his hearing is so acute that on a visit to NYC American Museum of Natural Science's gem room, he compained to the guard that the ultrasonic security system was giving him a headache. Yes, Ira knew. Sound transmitted by or received from moving objects produces a Doppler effect in which frequency or phase is modualted. For all practical purposes, I the listener was stationary, as was the plane in which the turning fan blades moved. However the blades themselves were attatched to the hub with a slight pitch so as to push air. Consequently, sound from the piano was faced with a constantly changing distanceto the blades which would reflect them. Had the fan been unnecessarily fancy, the blades might have had a curved rather than flat cross section., which would have made theDoppler modulation non-linear. Regardless, the phase modulations were a product of the distance fromthe piano to the blades (fluctuating periodically within a fixed range), the motor's rpm, and the number of blades (these latter constant). All that was left was for these factors to combine in consonance with some partial on the note currently played. And I had noticed that as I moved from note to note the flutter would roost on a different partial (or partials). Shut off the fan and my headache was gone. Bill Ballard RPT NH Chapter "No one builds the *perfect* piano, you can only remove the obstacles to that perfection during the building." ...........LaRoy Edwards
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