capo buzz

[Overs Pianos]

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At 11:57 AM -0600 16/10/03, Fred Sturm wrote:
>
>Lance,
>	70's through early 80's there was quite a fad of filing capos 
>"to a point," by people following McMorrow's book. Then lots of 
>techs found that the wire shortly buried itself in said point (ie, 
>created grooves while being tuned and played), with associated loss 
>of clarity and power and return of noise. Then some folks got the 
>bright idea of hardening sharpened capo. Which solved one problem to 
>cause another - increased string breakage.

Hi Fred and all,

We have done a lot of work on this problem over the years. Yes, if 
the bar is hardened without paying careful attention to both the bar 
radius and the string approach angle, string breakage will be a 
problem. However, if addressed appropriately, it is possible to use a 
small radius hardened profile bar without experiencing premature 
string breakage problems.

We have found that the following factors contribute to string noise;

The radius or profile of the bar (both the capo and front duplex bars)

The length of the font duplex segment (shorter is better, longer is 
more prone to noise)

The accuracy of the duplex segment to a harmonic length of the 
speaking length (the closer the duplex segment is to a harmonic of 
the speaking length the greater will be the propensity to produce 
string noise).

When rebuilding grand pianos with cast in front duplex bars we;

* Remove the front duplex bars (with a small angle grinder) and build 
up the plate to enable the fitting of new 'de-tuned' front duplex 
bars.

* After measuring the string scale (before the piano is pulled down), 
using a spreadsheet which is designed for the purpose, we select 
appropriate front duplex lengths which will be as short as practical 
while at the same time set to a length which is out of tune relative 
to the harmonic lengths for each note.

* Manufacture new front duplex bars (which are also hardened - SAE 
1040 key stock is a suitable and economical material from which to 
make the bars), varying the heights so that the string approach angle 
is uniform and between 12 - 15 degrees (preferably 12 - 14).

* Shape and harden the  capo bar (this is a once only job since there 
will be no grooving of the bar after hardening, so subsequent 
re-strings will be a simple matter).

For those of you interested in hearing a recording of a piano fitted 
with this type of font duplex system, you can hear samples of our 225 
(7'4") piano no. 3 at;

http://overspianos.com.au/samp.html

Best,
Ron O.
-- 
OVERS PIANOS - SYDNEY
    Grand Piano Manufacturers
_______________________

Web http://overspianos.com.au
mailto:info@overspianos.com.au
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