More responses needed

[Carl Meyer]

Okay,  I don't argue that cracks affect the tone.

If you want to use the speaker analogy.  The reason a speaker with slits
will reduce the loudness is because of the air pressure bleed around  to the
back from the front.  That's why speakers are put in a box to increase the
distance the sound must travel from the front of the cone to the rear.  This
becomes increasingly important at the lower frequencies.

So, when the soundboard rises pushing air up, the air is attracted to the
bottom of the board which is now creating a vacuum.  If there is a crack
allowing the air to reach the bottom of the board the sound is canceled.  It
now has a direct path rather than over the rim, down the  side and under the
piano.

I doubt that you'd notice it for small cracks.  I'm sure it could be
measured.
Again, let me say that it will be progressively noticeable at the lower
frequencies.

If you have ever listened to a speaker in open air and then in a suitable
baffle, you will notice the dramatic difference.  The speed of sound being
approx 1100 feet per second you can see that the time to cancel is enhanced
at lower tones
and will allow significantly more cancelation at the bass notes.  There can
be some significant cancellation when the phase of the two signals are 180
degrees
apart.  Hence a complete hole in the response at that frequency.

Ah! Acoustics!  What a wonderful thing!

Carl Meyer







----- Original Message -----
From: Wallace Scherer <p003520b@pb.seflin.org>
To: <pianotech@ptg.org>
Sent: Thursday, May 03, 2001 9:41 AM
Subject: More responses needed


> Dear list members,
>
> A recent discussion I started about applying epoxy to cracks in the
> soundboard of an old Winter piano which had strings and tuning pins
> replaced by another technician about 5 years ago, led to the conclusion
> by about 5 or 6 people who responded that repairing cracks in soundboards
> is mainly for cosmetic reasons and will not affect the tone significantly.
>
> To me this goes against the whole purpose a soundboard exists! Take the
> analogy of a speaker cone:
>
> Lets say that we have a radio or other sound producing device whose sole
> output is through a 15" woofer loudspeaker. If we then take a razor blade
> and make a series of randomly spaced  slits about 2" to 3" long around
> the sides of the speaker cone, wouldn't we expect the tonal quality of
> the speaker's output to be diminished considerably? And if, then, we
> proceeded to seal those slits in some manner so as to come close to
> having the speaker cone intact again, wouldn't we expect an improvement
> in the sound from when the cone had the slits in it?
>
> The reduction in sound (volume, tonal quality, etc.) of the speaker with
> the slits is due to its not being intact - the movement of the cone does
> not faithfully reproduce the sound it is supposed to make because its
> surface area does not respond uniformly.
>
> In like manner, especially in the lower frequencies of the bass notes of
> a piano, when the larger area of a soundboard must faithful reproduce
> those lower frequencies and transmit them to the air without
> interruption, if the surface area is broken up by cracks, the movement of
> the soundboard is impeded, therefore greatly reducing the volume of the
> sound reaching the hearer.
>
> Because of the basic physics of sound production, it therefore does not
> make any sense to me that repairing the cracks of a soundboard (assuming
> that the bridge, ribs, strings, etc., are all in good condition) would
> not somewhat improve the sound of the bass section.
>
> Since so few of you responded to this, I would like to ask more of you to
> respond, especially those who have had considerable experience in
> repairing cracked soundboards.
>
> The question is this:
>
> Assuming that the ribs, bridge, and strings are all good, would only
> repairing 10 fine, but rather long (10" or more) cracks in a soundboard
> make a noticeable difference in the bass section of a piano? (Let's also
> asume there is little or no crown.)
>
> Thank you.
>
> Wally Scherer
> Palm Beach County, Florida
> -----------------------------------------------------------------------
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>
>