[Elecraft] (OT) CW Resonant Speaker

[Joe Subich, W4TV]

On 2/17/2017 6:56 PM, stan levandowski wrote:
 > A cylinder with a closed end is a "closed cylinder" and requires the
 > formula that uses 2f instead of f.

A cylinder with a speaker in one end and open in the other is an "open"
cylinder (open pipe).  It is a *half wave* in air which means the
formula uses 2f instead of f.

A "closed cylinder" is excited on one end and the other end is closed
(plugged).  A closed cylinder is a *quarter wave* in air - its formula
would use 4f instead of f.


73,

    ... Joe, W4TV


On 2/17/2017 6:56 PM, stan levandowski wrote:
> 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.
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