[Elecraft] (OT) CW Resonant Speaker

[stan levandowski]

A cylinder with a closed end is a "closed cylinder" and requires the 
formula that uses 2f instead of f.


The "real" formula accounts for lots of variables, including diameter of 
the sphere. But a ballpark formula that works just fine for less complex 
designs is just Length (in feet or fractions of a foot) equals the speed 
of sound in air (in feet per second which is approximately 1100) divided 
by either f (for an open end cylinder) or 2f (for a closed end cylinder) 
where f is the desired frequency of resonance you want.  Much like 
making a simple dipole, you can start with the formula but it takes 
trimming to get it optimized.


Example:  You want a speaker resonant at 600 Hz.  It is closed at one 
end ( the end in which you mount the speaker).  The tube is *about* two 
inches in diameter.  L=1100/2f  -- L=1100/1200  --  L=..916 ft.  -- 
 .916 inches x 12 inches = 10.9 inches.  


The preceding is not perfect but, like a dipole, it needs final 
trimming.  That's where an adjustable design (like the PVC versions with 
a sleeve) make it easier to trim vs. building a wooden box (like the 
KD1JV box design).


73, Stan WB2LQF


On Fri, Feb 17, 2017 at 06:07 PM, Mark Petiford via Elecraft wrote:

> I think a pipe with a speaker in the end is considered a closed end 
> cylinder, but I am not completely sure.  If so, resonant lengths are 
> shorter.  Here is the page from one of my favorite websites if you are 
> interested in experimenting with resonant speakers:
>
> http://hyperphysics.phy-astr.gsu.edu/hbase/Waves/opecol.html#c1
>
> Good educational website from Georgia State University.
>
>
> Mark,
> KE6BB
>
>
>     On Friday, February 17, 2017 2:14 PM, Mike Furrey  wrote:
>
>  I have not but you certainly can do it. The length of the tube will 
> determine the peak resonant frequency and you would have to experiment 
> with the length to tune it to the pitch you like best to listen to. 
> Remember the days you would blow across a bottle to make a tone? The 
> more you drank out of the bottle the lower the pitch. I like this 
> project and I am going to build one and it will be with a straight 
> tube mounted on a little stand so it aims towards me.
> 73, Mike WA5POK
>
>     On Friday, February 17, 2017 12:58 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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