[CW] CW Resonant Speakers

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

From
https://www.eham.net/reviews/view-product?id=5998&__cf_chl_tk=xxjwfye5iqyyqwa8lu0zpmmpqilexeamt52co2bdqng-1744514228-1.0.1.1-cumxyol3_b5ps3qv3afrdbpmervdqvkfykmkfldkooc

If you're reading-up on the Skytec CW-1 Speaker because you're thinking of
building one yourself then you need-to-know that the Skytec speaker that
you see in the pictures is the outer 'cosmetic' housing. The Skytec speaker
consists of a tube-within-a-tube ... the somewhat 'fat' outer PVC pipe
housing and a narrower (also PVC) pipe inside.

When you look at the pictures that show the front of the Skytec speaker
that smaller 'pipe' sticking out the front (in the middle of the dark
plastic 'surround') is the inner portion that provides the acoustic
resonance. The inner pipe is built with the same (roughly) 30 degree 'bend'
upper section just like the outer pipe; the inner pipe is concentric within
the outer pipe but I don't believe that has any effect on performance.

The outer ('fat') PVC pipe has a 3 1/2 inch outer diameter (OD) and the
inner (resonant) pipe has a 1 7/8 OD (inside diameter is about 1 3/4
inches). The actual electrical speaker is sitting down at the base of the
inner 'pipe' (pointing straight up).

(as has been mentioned by another reviewer) The Skytec speaker is tuned by
adjusting the length of the inner pipe - the portion that sticks out the
front (in the midst of the dark 'surround') is a sliding piece that fits
(fairly tightly) inside the portion that is just protruding out from the
dark plastic 'surround'.

In my situation I have been experimenting with different audio frequencies
for CW reception, specifically that are slightly lower than the 700-750 Hz
that used to be considered the 'standard'. I wanted to see if I liked a 600
Hz note (tone) and to get the Skytec speaker resonant at that lower
frequency I made a replacement (longer than the original) slider-piece out
of a length of toilet-paper tube (I slit the tube along-its-length, cut out
a narrow sliver, and then taped the tube back together so that its OD fits
tightly inside the Skytec speaker's inner 'pipe' that is sticking out of
the dark 'surround'). With that (slightly) longer 'slider-tube' I can now
tune the Skytec speaker to 600 Hz.

Here is some good reading material for acoustically resonant CW speakers:

An Electro-Acoustic CW Filter
QST Apr 1983

A Resonant Speaker For CW QST (Hints & Kinks) Dec 1987

More On Resonant Speakers QST (Hints & Kinks) Jan 1989

Additionally, here is a good article that discusses how to build a robust,
wooden cased,
speaker.

A High Quality Speaker System
for the Ham Shack
OST Oct 2004

It does not have an acoustically resonant speaker but when I read the
article I kept thinking that it would make an excellent 'surround' for an
acoustically-resonant design.

- Paul, WB5AGF
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