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MMD > Archives > April 1997 > 1997.04.11 > 07Prev  Next

Resonant Sound Chamber for Music Box
By Robbie Rhodes

Greg Przyjemski is seeking design ideas for his proposed musical box.
At work today I spoke with a talented mechanical designer who built a
large Irish harp, and we discussed the classical design of the sounding
board and sound chamber.

The harps sounding board forms one surface of the long, slightly tapered
sound chamber.  The chamber is enclosed except for a port (or ports) at
the larger end, near the bass strings.  I suspect that the mid- and high-
frequencies are radiated by the simple drum-head mode of the sounding
board, but the low bass frequencies are transmitted via the chamber,
which is like a Helmholz resonator or tuned-port bass-reflex loudspeaker.

The "classic" Helmholz resonator is a crockery jug; the resonance is
determined by the enclosed volume, and modified by the port area.  The
sub-woofer loudspeaker (disguised as a compact coffee table) is a very
efficient Helmholz resonator, of one octave usable frequency range.

Perhaps a sounding-board-and-resonator for a musical box movement could
be designed like the harp and the Helmholz resonator, such that the
sounds of lowest bass notes would be "amplified" by a ported chamber
in which the sounding board forms one wall.  It might, or it might not,
be beneficial to incorporate the tapered sounding board shape of the harp,
but it certainly would look different!  The zither appears to be built
somewhat like this.

Robbie Rhodes

(Message sent Sat 12 Apr 1997, 02:04:03 GMT, from time zone GMT-0700.)

Key Words in Subject:  Box, Chamber, Music, Resonant, Sound

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