"killer octave:

[Richard Brekne]

I would be glad to help out with measuring any data you need for your inquiries
Ron. I have 17 good to excellent quality grands, and 26 varying quality
uprights at my disposal for very frequent measurements at the university. You
just tell me what you want measured, and I'll send it along to you. I have the
RCT, and Tunelab to work with in this regard.

Hope you had a nice Christmas.

Richard Brekne
I.C.P.T.G.  N.P.T.F.
Bergen, Norway

Ron Nossaman wrote:

> >Thanks to all for making this as clear as mud for me!
> >
> >Rook
>
> The killer is where it is. It doesn't start at any specific note, nor end
> and any specific other. On any given piano, it will shift up or down scale
> with humidity swings. It will even seem to disappear altogether in some
> pianos during high humidity cycles. The root cause is the soundboard being
> too low in impedance in that area. The killer isn't in exactly the same
> spot from piano to piano, or even in the same piano from month to month
> because no two soundboards are exactly alike, even if the string scales are
> (nominally) the same, and no individual soundboard is the same at 30%rh as
> it is at 60%rh. The beginning of the killer octave corresponds, generally,
> to about where the tuned front duplex starts. It is my opinion that this
> isn't an accident, but that the duplex was designed to combat the already
> existing soundboard problem in this area. First came the basic soundboard
> design, then came the tuned duplex. Why would anyone go to the trouble of
> inventing the duplex if they weren't trying to shore up what they
> considered to be inadequate sound in that section? This is also the area
> that gets the most complaints regarding voicing. Consider all the different
> sets of hammers from all the different manufacturers, all nicely graduated
> in size from one end to the other. Why would so many of them have voicing
> problems in the same area of the scale, but some not? Why does extensive
> voicing, and even hammer replacement fail to fix the problem? If the
> hammers cause the problem, shouldn't the problem go away when the hammers
> are replaced? Why does rebuilding the piano, rescaling, renotching bridges,
> replacing the action, and shimming and refinishing the soundboard, too
> often result in a rebuilt piano with the same kind of tonal problems, in
> the same parts of the scale, as it had when it came in the shop? Why does
> no amount of tapping strings down on bridges tame the killer octave? Why
> does the soundboard go flat in the killer octave first? Why does that
> section go out of tune so quickly, and so far... and why almost always
> FLAT? That's because it's a soundboard design problem, not a voicing or
> tuning problem. The killer octave does exhibit tuning (as opposed to tuning
> stability)  problems though. This is the area where the unison pitch drops
> most as you tune the second and third strings to the first. Why is that?
> Doesn't that strike anyone but me as an odd coincidence? I think that this
> is likely to prove to be a soundboard problem too, though it may be as much
> related to resonant frequency as to impedance. I've been trying to get some
> folks with SATs and RCTs interested enough to help me chase down some data
> on this one. I've got some interested people, but no one has had the time
> this fall to chase anything down. I'm working on it though, and I'll
> eventually publish the results, whether I get anything conclusive or not.
>
> So there are a whole bunch of problems associated with this area. Every one
> of them is a result, not a cause. The cause is the soundboard design, and
> no matter what you do about the secondary effects, the only kind of fix
> that approaches the root of the problem is to install a more efficient
> soundboard. I know that's not a field repair, but the point is that there
> IS no field repair that's anything but a band-aid to disguise the symptoms.
>
> More mud, right?
>
> Ron N