[Elecraft] (OT) CW Resonant Speaker

[Joe Subich, W4TV]

The wavelength and frequency of musical notes can be found here:
    http://www.phy.mtu.edu/~suits/notefreqs.html

A closed end pipe as used in the resonant speaker is a half-wave
(half the given dimension).

Note also there will be some "end effect" because the sound continues
to vibrate past the end of the pipe - which means the pipe will need
to be somewhat shorter than the true half wave.  End effect is
generally about 20% of the pipe diameter (from reading up on pipe
design).  I don't know what the effect of a 45 degree "end" would be
but I suspect you would want to make the mid-point of the cut about
where a square end would normally fall.

One could also experiment with *closed end* pipes ... pipes with the
far end plugged and a notch or hole near the speaker.  Closed end
pipes are a quarter wave long which would significantly reduce the
size for those using low frequency tones.  An open 700 Hz pipe is
49.5 cm (without end correction) - an open 440 Hz pipe would be 78.5 cm
and a open 300 Hz pipe would be about 115 cm (nearly four feet!) long.
Unfortunately, I have not seen any information on the sound port
(notch) design for closed end pipes - or whether they can be driven
by a speaker.

73,

    ... Joe, W4TV


On 2/17/2017 1:56 PM, P.J.Hicks wrote:
> Has anyone built the resonator with a straight length of tube? Perhaps terminated with a 45 deg. cut?
> Might be an interesting experiment.
>
> The 45 deg long radius street elbow in 2" is an order only item in my area so thought I'd substitute a straight length.
>
> PJH, N7PXY
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