compression waves

[Phillip L Ford]

On Sat, 24 Nov 2001 00:10:17  
 John Delacour wrote:
>At 6:44 PM +0000 11/23/01, Phillip L Ford wrote:
>
>>...but could someone please explain to me the utility or application 
>>of the results of this discussion.
>
>I think it has more utility and application than many threads in this 
>list,

Perhaps.  I wasn't trying to belittle the discussion.  It
was an honest question.  But I am having difficulty seeing
the utility.  The discussion seems to be more of one along
the lines of knowledge for its own sake rather than
knowledge that has an application.  There's nothing wrong
with that but it doesn't interest me.  It's the difference
in personality between the scientist and the engineer.  I'm
an engineer.  That doesn't make me better than the scientist,
only different.  The reason for the question was that I
thought I might be missing something or failing to see
something that someone might be able to point out to me.
>From the replies I've concluded that I haven't missed
something.

> but it does require the time and willingness to experiment and 
>to find and read the background literature.  A few of us seem to be 
>interested enough to do that and I'd hardly expect more than a 
>handful of people to take that trouble since it is a question mainly 
>of piano design rather than maintenance, though I think an awareness 
>of the existence of these waves can help the tuner to explain some 
>otherwise mysterious nastinesses such as falseness and the 
>unpleasantness of short grands.

If it could explain these sorts of things then I would
see the utility of it.  At present I'm having trouble
understanding a connection.

>
>>As I see it the items on the table are:
>>
>>1.  Are longitudinal modes in a real piano string determined
>>by the speaking length or the total length?
>
>Yes :-)  To what extent either is true is the only question that is 
>of relevance to the pianomaker and this discussion is moving towards 
>a way of answering the question.

Why is it relevant?  If it turns out the longitudinal mode
is determined by the speaking length would you design the
string differently than if the longitudinal mode is
determined by the total length?  In what way would your
design be different?

>
>>2.  Are the vibrations in the 'duplex' portions of the string
>>caused by transverse vibration of the speaking length of the
>>string and/or soundboard or by longitudinal vibration of the
>>string, which seems to be caused by unknown means?
>
>One cause of the l. waves is the sudden change in tension of the wire 
>when the hammer strikes.  Only transverse waves can disturb the air 
>and cause an audible sound but the two modes interact.  The 
>soundboard is irrelevant since it acts simply as an amplifier (or 
>absorber) of the string's vibrations and creates none of its own 
>initiation.

Two things here:
1.  I don't see that the soundboard is
irrelevant.  If the bridge moves up and down then the string
attached to it has no choice but to move up and down with
it which will cause transverse vibration of the speaking
lengths and the back scale.
2.  OK.  Let's say that the two modes do interact but the
longitudinal mode can not cause audible sound.  Then we are
back to the original discussion about whether the transverse
vibrations in the duplex portions should be tuned or untuned.
If the modes interact then the transverse vibrations in the
duplex segments will be excited whether or not they are
tuned.  Since you say that the l modes don't cause audible
sound then the sound we are hearing must be only influenced
by the transverse vibrations of the duplex segments and it
seems the only way to influence tone quality is change the
parameters of the duplex - either make them tuned or untuned.
In what way would understanding that there is an interaction
between modes enable you to change the design of the duplexes
or their relationship to the speaking length?
>
>>3.  Are the vibrations excited in the duplex portions
>>transverse or longitudinal?
>
>Both.

I thought there was some dispute about this.  I thought that
was one of the reasons for the length of this discussion.
I thought some were saying that transverse vibration can not
'bleed' across the capo or the bridge and therefore these
segments only have longitudinal vibrations.  And I thought
others were saying just the opposite.
>
>>4.  Do the vibrations in the 'duplex' portions of the string,
>>caused by whatever means cause the speaking length to vibrate
>>in its own fundamental and harmonics or in the fundamental
>>and harmonics of the 'duplex'?
>
>By design the two will coincide.

If you use a tuned duplex.  I didn't think that this had
been conceded.
>
>
>>If this summary is correct would someone please explain to me
>>how answering any or all of the above questions would
>>influence the scale design of a real piano.
>
>Harold Conklin explains how he actually did this at Baldwin's.  I 
>don't think anyone here is rushing to imitate his method and to me 
>the interest of his method is extremely marginal.  Ellis' approach is 
>interesting.  Neither would have bothered to get patents if 
>longitudinal waves in piano strings did not, in some areas, cause 
>problems,

Perhaps.  Or perhaps there weren't really any problems
and they thought they had come up with a great idea to
improve the piano.  Most piano patents that I have read
are answers to questions that nobody is asking.

> and the piano builder should be aware of the phenomenon and 
>be prepared to meet any problems it causes.

Being aware of the phenomenon and using that knowledge
to solve a problem are two different things.  I'm aware
of gravity but I'm not sure how I would design it away. 

> Theodore Steinway's 
>Duplex Scaling claims to improve piano tone by a certain treatment of 
>longitudinal waves.  Whether the claim is valid or not, such a widely 
>imitated icon of piano design, which for whatever reason has a huge 
>effect on the singing and ringing properties of the grand piano, 
>deserves some attention.
>
>JD
>
I agree it deserves some attention.  But I'm still right
back where I started - what do I do with this information.
Let's say CFT is right.  How do I use this fact, or the
knowledge gleaned from his patent to influence a piano
design.

Phil Ford