[CAUT] Re. Lack of low-frequency response

[Richard Brekne]

Hi Jim.

Thanks for the post.  I understand your bottom line of course.  The
point that has been raised to me is off on a somewhat different track
tho and I'd like your thoughts on it.  Regardless of the overall
stiffness of the bass end of the soundboard... if the cross grain
stiffness gets too different from the along the grain stiffness... can
this cause the boards resonance capabilities to break up into many
smaller areas and hence inhibit low end response ?

I'm going to take a couple quotes from Conklin and Wogram below for your
edification on this thread.. Particularly Wogram points in the direction
I am thinking along here.

    "The modal frequencies are determined by many factors, the primary
    ones being the material, size and shape of the soundboard, its
    thickness and grain direction, and also the material, dimensions,
    and placement of its ribs. Secondary factors include the
    characteristics of the rim or case to which the soundboard is
    attached. In general, the thicker the soundboard, the louder the
    piano but the less the duration of its tone. Soundboard design is
    often a compromise." -- Conklin

    "A stiffening of the soundboard would improve the sound radiation
    efficiency, as a stiff soundboard is less inclined to subdivide into
    small vibrating areas. One purpose of the ribs is precisely to
    stiffen the soundboard, which indeed is thin in proportion to its
    size. Another purpose is to "homogenize" the soundboard by
    equalizing the difference in bending stiffness (elasticity modulus)
    parallel to and across the grain." --  Wogram

    Jim Ellis writes:

        I have been "reading the mail" on this subject, and I see a
        tendency to
        over-simplify.  There is no single answer.  It's a very complex
        issue.
        Begin with the soundboard modes themselves before any
        stringing.  After
        stringing and full tension, everything changes.  Down-bearing,
        string-tail
        length, board mass, board stiffness (including ribs), and the
        possibilities
        go on and on.  The "bottom line" is, what is the compliance and the
        resonant frequency of the board after all is said and done?  At what
        frequencies do the board's vibrations break up into standing
        waves, and
        where?  Whatever the resonant frequency is, and how wide or
        narrow its
        bandwidth is will determine the dominant part of the tonal
        spectrum.  I
        would not dare try to tell you what the solution is, because the
        problem is
        so complex.  But the general "rule-of-thumbs" is:  The stiffer
        and less
        compliant the bass-end of the board is, for whatever reason, the
        less
        low-frequency response it will have.  The more compliant it is,
        the more
        low-frequency response it will have, but the faster those low
        frequencies
        will decay.

        Sincerely, Jim Ellis