[Elecraft] (OT) Follow-up on CW Resonant Speaker

[Vic Rosenthal 4X6GP]

I built one once with a 2-1/2" (6.4 cm) diameter PVC tube. Unfortunately 
I don't remember the exact length, but it was about 7" (18 cm) long. I 
simply glued a 2-1/2" speaker to one end. It resonated at about 600 Hz.

At one point I placed a tightly fitting lid from a spray can over the 
back of the tube and the speaker. It became significantly louder.

My experimental 2 cents.

73,
Vic, 4X6GP
Rehovot, Israel
Formerly K2VCO
http://www.qsl.net/k2vco/

On 19 Feb 2017 01:32, David Anderson via Elecraft wrote:
> Stan,
>
> Thanks for the video, most impressive.
>
> I have one comment regarding the need for an amplifier with the KX1
> /KX2 or KX3 radios, there is another YouTube video from a couple of
> years ago that appears to be almost what the more recent QST article
> is based upon and in it the constructor has it connected to a KX1 and
> it seems loud enough.
>
> https://youtu.be/4iNELueaU6M
>
> Then there is another video where another constructor dissects the
> original commercial design and makes one, this really shows how
> efficient the design is when at the end he compares the bare speaker
> on its own and how weak it sounds compared to when it resonates.
>
> https://youtu.be/MF8bk6958Hg
>
> The key seems to be that in both of the above cases the lower part of
> the resonant speaker is + not + sealed completely, air is allowed to
> enter and exit, though there is sound deadening material in the
> cavity. Perhaps that explains the greater sound efficiency?
>
> This is something I plan to investigate myself with my KX3, once I
> get the parts here, of course being in the UK we are now metric and
> so some slight adjustments are necessary as our pipe is 50mm and so
> on. A friend has offered the services of his laser cutter and 3D
> printer which will come in handy too!
>
> 73 from David GM4JJJ
>