[Elecraft] Cabinet resonance

[Ken Kopp]

The combination of the cabinet and speaker of my
K2 (#5665) has a VERY pronounced resonance at 
about 450 Hz.  How fortunate, as this is the frequency 
at which I like to copy CW. (:-)

The resonance is so pronounced that it would present
a problem if I wanted to use a higher frequency, say
600 Hz.  It initially caused me a bit of consternation as 
I was setting up the filters ... until I realized what was 
going on.  Even with the filter set up for 600 Hz I would 
still find myself tuned and listening lower than the "Spot" 
tone ... sort of a human AFC circuit. (:-)

Has anyone else noted this?  I wonder if all the speakers 
supplied with K2's are of the same design from the same 
supplier?

Mine -does- have all options installed except the battery
and I assume the resonant frequency of the box would be
different ... or non-existant ... with different "fillers" inside
the case.

I have two of the "old" Skytech variable-resonance speakers 
stored away that are fine examples of the application of 
housing / speaker resonance as a CW aid.  They use a sliding 
tube to "tune" the  assembly.

73!  Ken Kopp - K0PP
k0pp at arrl.net