Bridge pressure bar

[Greg Newell]

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Alan,
         Comments interspersed below.



At 12:04 AM 4/13/2003, you wrote:


>Greg wrote
>
>        >  " In my view the only thing that you can assure with this pressure
>bar is string termination. At some point , though, you will simply crush the
>string into the bridge body and wind up with poor termination. "
>
>No! The string does not come into contact with the wood at all. There are
>bridge inserts on either side of the pressure bar, same as on a guitar, or
>similar to the rods inserted at the top bridge. The string is threaded over
>the front insert, then under the bar and over the rear insert.

This is a very much clearer picture if only in the mind's eye.


>          > "I still don't understand what this has to do with downbearing
>unless you are somehow adjusting the height of the strings with this bar,
>although I don't see how. Is the bridge body somehow height adjustable? "
>
>You can adjust the pressure of the bar same as on a normal top bridge.
>It does not affect string height.

I'm still not sure I would call this downbearing. It does seem as though a 
decent string to bridge coupling is achieved.

>             >"The second point you have is about a soundboard being able to
>be made perfectly flat as long as sufficient downbearing exists. The two are
>interrelated and depend upon each other for good piano tone."
>
>
>          >"If you had a piano with poor downbearing but plenty of crown the
>tone would suffer. In like manner if you had a piano with plenty of
>downbearing but poor crown you would, again, have poor tone."
>
>Correct me if I'm wrong but crown in a soundboard is a method of resisting
>the pressure of the strings i.e an arched object is much stronger than a
>flat beam.

As i understand it, and I'm very open to correction, not entirely. It is 
the very resistance, however, that causes a certain amount of stiffness in 
the soundboard making it a better resonating body.

>  String pressure is used as a means of ensuring good contact with
>the bridge so the string vibrations can be transmitted to the soundboard. As
>far as I know it is this string pressure that is known as downbearing. If
>you use downbearing as a method of bridge contact then you need crown in the
>soundboard to resist or counteract the pressure (otherwise the soundboard
>would simply go concave and negate the downbearing). If you used a different
>method of string contact with the bridge,(i.e. not use string pressure) then
>you would no longer need a crown in the soundboard.

I'm not sure this is true. If the board is completely flat with no 
perceivable crown and no induced stiffness then are large amount of this 
resonating bodies efficiency is gone. Being that others ave maintained that 
the soundboard is already a rather inefficient transducer then with the 
absence of any crown and therefor stiffness you may wind up with a dead and 
powerless carpet weight.

>       >"Please rethink what was supposed to be the benefit here and if
>possible could you provide a clearer, larger picture?"
>
>Picture on it's way soon but at the moment I have to churn out 4 quotes to
>the local university, the usual 100 year old pianos that only get serviced
>every 10 years, you know!........and look at the time!

I'll look forward to it! Good luck with the proposals!

Best,
Greg

>Regards
>Alan Forsyth
>Edinburgh
>
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>_______________________________________________
>pianotech list info: https://www.moypiano.com/resources/#archives

Greg Newell
mailto:gnewell@ameritech.net 

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