[CW] Resonant CW Speaker

[D.J.J. Ring, Jr.]

Much of the following has been shamelessly copied from the SKCC
reflector but at least I've given most acknowledgements, to any I have
forgotten, "Your names will be written in Morse code Heaven, I'm sure
of it and "thanks" from all of us."

The resonant CW Speaker is featured in the February 2017 issue of QST.
The author says that listening to Morse through it would make
listening through other speakers unacceptable. The old SkyTec speaker
from the late 1970s had quite a following, people said it made signals
peak out of the noise.  I've always wanted one after I heard people I
knew talk about it.  Too little money at the time i believe was my
excuse.

You can change the author’s RCA jack to mono or stereo ¼ or 1/8 jacks
if you want to.

Adding a 2” PVC coupling between the speaker base and the street elbow
will get it to resonate around 600 Hz for those who like a lower tone.

Andy, K2OO added a small sheet of Plexiglas about 6 inches square from
the local hardware store instead of the recommended CD cover, it’s not
as brittle and easier to work with.

Other designs for such a speaker:

http://www.wcarc.com/images/elmer-files/CW%20Resonant%20Speaker.pdf
and
http://kd1jv.qrpradio.com/resonatespkr/CWSPKR.HTM


The SKCC group had a discussion on its email list about the hole and
it was thought that the hole in the plastic CD cover (or substituted
Plexiglas) was to seal the base of the tube acoustically and by doing
so lower the resonant frequency as sealed tubes have twice the
resonant frequency as open tubes. (Organ specialists are invited to
correct me.)

Dana Browne AD5VC, notes: “If you have a top-firing speaker on your
rig, simply buying a 4" PVC elbow and setting it on the speaker
produces a resonance in the 650-750 Hz range. I call this the "Passive
Vocal Clarifier" speaker accessory, or "PVC" for short (grin). If you
want to lower the pitch. try setting the elbow on a ring of styrofoam,
or just spacers. To raise the pitch by 50-75 Hz, cut off about 1/2
inch from the lip of the elbow.”

Ed, AD7GR gives some info and a spreadsheet: According to the math...
Using the formula F=122.4/(L=(0.3*D)) where F is frequency, L is
length of the tube and D is diameter of the tube, as you decrease the
length of the horn the resonant frequency will increase. So, if you
decrease the length to 5.73" the frequency should be 759 Hz.   If you
were to have a length of 5.73" and increased the tube diameter to
2.25" you would have 750.5 Hz.

Ed uploaded a spreadsheet, I’ve copied it here:
http://qsl.net/n1ea/tuned_speaker_calc_ad7gr.xls

There are some videos on this subject:
https://www.youtube.com/results?search_query=resonant%20cw%20speaker


73


DR

N1EA