Aprons and holey bridges

[John Delacour]

At 9:40 AM -0800 26/2/02, Delwin D Fandrich wrote:

>There is no particular need for high mass in the bass bridge, but it's not
>particularly bothersome (or noticeable) either. Remember, mass has more
>effect on the higher frequencies and springiness on the lower frequencies of
>the piano's energy spectrum.
>
>No, I haven't tested and/or documented this, but I have replaced a lot of
>bridges both with and without all the fancy holes drilled in them that are
>obviously intended to lighten them up. I've never noticed that the holes
>made any difference at all.

Maybe not in some cases, but I wouldn't say that they are necessarily 
"obviously intended to lighten them up".  The holes will also have 
the effect of altering the flexibility of the bridge (in some cases) 
and in all cases of changing the path of the vibrations and 
"filtering" or "mixing", as in the case of the fiddle bridge.  The 
cutting out and dowelling at the tenor of a Steinway O could hardly 
be intended merely to lighten the bridge in that section.  I've not 
had time to study exactly what is aimed at here, but maybe you can 
explain it.

Tests (Wogram) claim to have demonstrated that the quality of a note 
is affected if the string is situated above one of the nodes of the 
soundboard's free vibrations and that the position of the node can be 
changed by a slight redistribution of mass.  It seems to me that the 
node could be taken out of the direct line of fire by means of bridge 
incisions.  This would be an interesting experiment.

>I see no reason why a bass bridge body could not be made out of spruce or
>maple or beech or ash or everyone's favorite--Select Hardwood--for that. I
>doubt the acoustical differences would be all that noticeable. The choice of
>material used in the body--either good or bad--will certainly be less than
>sticking a cantilever under there.

I've read a few anti-apron posts of your and Ron N.'s and would like 
to hear precisely what the argument against the apron is.  I have 
seen so many pianos that behave excellently with a suspended bridge 
and yet from the very beginning of my career it has always seemed to 
me that a direct bridge was preferable, maybe even in spite of the 
evidence!

I have two 133 cm. uprights here, a Lipp and a Knauss (not a big 
maker but all fine pianos in my experience).  They both have an 
exceptional bass.  The Lipp has an apron  widening to 70 mm. and the 
Knauss has a curved solid bridge which is canted at about 15 degrees 
to bring the gluing probably 25 or 30 mm. inboard  -- which is very 
nice and rather unusual.  Unfortunately the Knauss is at the store, 
otherwise I'd put on identically designed strings to those on the 
Lipp and make a comparison.  My gut instinct tells me the Knauss with 
the direct bridge will be richer in the upper partials and less 
"plummy", but I'm not at all sure I'd be proved right.  What do you 
say?  And why?

You may have noticed I mentioned that the Ibach from which I have 
just removed the soundboard has an apron only 4 mm thick!  I bought 
this piano cheap and sounding as bad as any I've ever heard.  The 
reason became clear as I removed the bass strings and the bass bridge 
fell off the apron.  Generations of tuners had not detected this and 
I found at least twenty corks, wedges and pedal springs propping up 
the board all over the place when quite possibly there was nothing 
else wrong with it.  We shall never know.  I bought the piano in 
order to fit my experimental board, so the old board was coming out 
anyway, though Ibach had made sure it would take me a long morning by 
mortising it into the outer rim all round.

JD



JD