[CAUT] Lack of low frequency response

[Richard Brekne]

Hi CAUT-ees   This post came in on piano tech and I thought it worth
posting here.  Interesteds will please read Franks contribution below
before reading my reply just after this comment.

Cheers
RicB

Hi Frank.

Yes. I think the basic question I'm asking  is... can a lack of cross
grain stiffness at some point create a situation where the difference
between cross grain and along the grain stiffness becomes large enough
that the soundboards ability to vibrate well at lower (large) modes
becomes inhibited.  One of the points in the Five lectures is that cross
grain stiffness is needed to equalize stiffness in both directions
exactly because of the need to get the total vibrational area of the
soundboard vibrating.

I'm downstringing to do a couple things over/better on the instrument I
am working on... so I can try spreading sand or glitter on the panel and
hit the mid-low tenor area of the long bridge to see where it gathers.

Aside from the specific job I'm on... this is really interesting as it
touches on why older pianos sometimes start developing this kind of
sound.. why some new ones seem to have it built it... and suggests a
possibility of dealing with the symptom without removing the
soundboard.  It also adds argumentation on both sides of the CC and RC&S
discussion.  And on top of that it starts clearing up (in my mind at
anyrate) some of what possible reasons designers have had through the
years in selection of grain orientation and rib patterns along with rib
orientation relative to the grain.

So... do you think then if one goes too far (as you put it) in reducing
stiffness in the area of the soundboard at question here can cause this
kind of thinning / nasalness of the sound ?  And if so, does the idea
that the lack of cross grain stiffness being enough relative to along
the grain stiffness fit in here ?

Thanks for your thoughts

Richard Brekne



    ---- Richard Brekne <ricb at pianostemmer.no> wrote:
    >I'm wondering if a nasal sound... with little or no apparent low
end
    > response can have to do with LACK of stiffness in the fat part of
    > the soundboard... i.e. in that section that is somewhat front of
    > the long bridge and bass bridge.... low tenor area. I know this
    > seems to go contrary to the usual conclusions we'd jump at.... but
    > it connects with aging soundboards and why they start sounding
thin
    >and nasal...

Frank Emerson replies:

    I can't find the exact posting, but earlier in the thread it was
    suggested that the soundboard might divide into many small
    "tweeters" and thereby inhibit the full vibration of the soundboard,
    as a "woofer."  Forgive me if my memory has misconstrued the intent
    of the statement.  I have seen studies of soundboard vibration where
    black glitter is sprinkle over the entire surface of the
    soundboard.  As different frequencies are introduced at different
    locations along the bridge, the glitter moves to define nodal lines
    on the surface of the board.  The patterns came out differently for
    different frequencies.  It seems to me that these nodal divisions of
    the board do not inhibit the fundamental frequency, but work
    concurrently with it, in much the same way as a sounding string has
    a complex envelop of multiple partials at multiple frequency.

    Regarding reduction of stiffness in the bass region of the board, I
    believe you can go too far in that direction.  I am reminded of a
    piano that makes much ado about its reverse crown and floating
    soundboard in the bass.  To me it sounds much like an old upright
    where the bass bridge has come unglued from the apron.

    Frank Emerson