laminated bridge question

[Delwin D Fandrich]

Stephen Birkett wrote:

> As we are talking about bridges, there is the acoustic issue which I
> hesitate to raise. It might be interesting to compare a solid maple beam,
> with laminated stacks glued with titebond, titebond II, and with hide
> glue. It's quite possible the dynamic properties of the four will be
> significantly different. Not having done this I can't say what might be
> the outcome. On early pianos there is a noticeable acoustic difference
> when bridges are sawn instead of bent...presumably associated with
> different impedance parallel to the soundboard.

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I have compared bridges with the following configurations:
1)  Solid maple bridge with no separate cap.
2)  Solid maple bridge body with a solid maple cap.
3)  Vertically laminated maple bridge body with a solid maple cap.
4)  Vertically laminated maple bridge body with a horizontally laminated maple
cap.  The laminations used to make the cap were 1.0 mm thick.
5)  Vertically laminated maple bridge body with a horizontally laminated beech
cap.  The bridge cap material was supplied by Delignit.
6)  Horizontally laminated maple bridge with no separate body or cap. The maple
laminations were approximately 3 mm thick.
7)  Vertically laminated maple bridge with no separate cap.
The same phenol-formaldehyde adhesive was used in all cases except for the
laminated beech cap which was made with some type of resorcinol adhesive.

With the exception of the two bridges using horizontally laminated caps -- these
bridges exhibited slightly better string termination qualities in the top two
treble sections -- there were no audible or measurable differences in the sound
or frequency/energy spectrum that could be traced specifically to the variations
in the bridge material or construction. If these widely disparate bridge types
did not appreciably affect the sound coming from the same piano, it's really
doubtful that the type of glue used to hold any part of it together would make
all that much difference either.

Del