Harmonic Distortion / Overdriving strings?? Noise Question???

[Ron Nossaman]

At 06:48 PM 3/6/99 -0500, you wrote:
>Hi All,
>
>I've run into a customer who has noticed a problem with his Boston
>piano.  It's a 6'4" grand.  Playing softly, the tone is good.  But on
>louder playing, and rapid repeated playing of particular notes, there
>comes an irritating sound from the speaking length of the string.  To my
>ear, it sounds like the string is being 'overexcited', or overdriven,
>beyond the point of a clear undistorted vibration.  Kind of reminds me
>of what happens when you overdrive an amplifier and hear the sound
>distort.  On the piano it tends to sound like a zing/ring.  (This is
>like trying to tell a person who has never been sighted what a rainbow
>looks like!)  Upon further examination, I've determined that the 'noise'
>is indeed in the speaking length of the string.  (Blocking out the
>duplex etc. has no real effect.)  Also, I've checked on about a half
>dozen other pianos for the same thing, all the way from Young Chang, to
>Wurlitzer & Baldwin, to Petrof and Steinway.  I was actually able to get
>the same distortions from ALL of them!  The Steinway required the most
>effort on my part to make it give off this 'sound', but I was able to
>get all of them to do it, and over quite a range.  The worst areas on
>most all of them was the range starting about an octave above middle C,
>and continuing up about an octave and a half, but it was indeed possible
>to do this 'overexcitement' over most of the range of the plain wire
>strings.
>
>I've not been able to put my finger on this one.  Some thoughts to date
>are scattered; hammers are too hard, (voicing seems to help a little,
>but it's still there), hammers striking the string in the wrong place,
>(haven't been able to play with this one yet), too much bearing, (I'm
>not sure how too much or too little bearing would affect distortion of
>the sound), poor scale design, (just because it says "Designed by
>Steinway", it doesn't necessarily impress me), poor bridge notching,
>(the notch does not drop away from the string in such a fashion to give
>a good termination point in my opinion, but I don't know what minimums
>would be.  I know I notch mine a lot more deeply and distinctly when I
>do them.)
>
>I just wondered if anybody had a thought.
>
>Thanks in advance.  (And also, thanks for all the good conversation.  I
>just found this list a few weeks ago, and am very happy to be able to
>read the conversations.  I've been learning. (Hope it never ends!)
>
>Brian Trout
>Quarryville, Pa
>
>

Hi Brian,
You left out the part about the short sustain in the same range. Welcome to
the killer octave. It's not the hammers, though voicing can sometimes make
it less awful. It's probably not the strike point either, though that can be
contributory. There's probably too little bearing, rather than too much,
because soundboards tend to go flat in that area first - sometimes before
the piano gets to the showroom floor. The scale design may not be too great,
but it's not that either. The bridge notching is noticeably different among
the pianos mentioned, yet they all make the same sort of sound. That's not
it. It's a soundboard impedance problem. A design flaw. A cast in stone,
fight to the last man, defend to the death, take no prisoners, by gawd
traditional, hang on like grim death design flaw. The real fix is to replace
the soundboard with one that's designed to work more like a soundboard should. 

Or you could tighten the plate bolts, seat the strings to the bridges, soak
the hammers in magic elixir, oil the casters, harden the capo, tune the
duplexes, put CA on nearly anything, polish the hitch pins, seat the strings
on the bridges again just for luck, and maybe kill a chicken or two late on
a moonless night. One never knows, it's a mystery.

Here's where we need the archives on CD. Thousands of words of detailed
explanation of soundboard impedance problems, cause and effect, have
appeared on the list. You might want to go back and read through some of it.
Read Del's articles in the Journal on the subject if you have access. He's
the guy who brought impedance to our attention in the first place. Good stuff.

  
 Ron