[CW] Headphones or Loudspeaker?

[pa0wv]

Acoustical resonators are interesting, BUT I suppose
it is hard to influence parameters to determine the ringing, bandwidth 
and so on. You just can narrow the bandwidth and the detection of CW 
does not increaase in error rate,

As generally known CW is detectable in a wider (3 kHz) bandwidth 10 dB 
higher noise level, because your brains detect them just like in narrow 
band. Agree? When you narrow the band before the sound is presented to 
your ears, the error rate does NOT change because your brains does the 
narrow filtering already.

MY QUESTION:

Does a resonant speaker have any influence, that is better compared with 
an electronic band pass filter in the audiosignal followed by a wide 
band speaker?

Test your ears with a chirp increasing from 0 to 20 kHz with an 
increment op 100 Hz per second with the soud file available on 
http://pa0wv.home.xs4all.nl/wouter/CHIRP.WAV

Just download the file and start it, watch the time on your watch, every 
second it is increasing 100 Hz so you can determine the frequency bt 
watching the time.

PA0WV





> The acoustical resonator goes back a long time. Long ago I found an
> article from someone at M-G-M, I think, about a resonator to fit on
> the Western Electric condenser microphones they were using in the late
> 1920s. It had a tube and baffle to reduce the cavity resonance of the
> mic (nearly 10db at about 3Khz). This was before the method of design
> of electrical filters was generally known. I have no idea of how well
> this worked but suspect they had problems with the directional
> properties of the combination.  The idea for the speaker is to put a
> simple Helmholtz resonator in front of it. The resonance is controlled
> by the volume of the chamber in front of the speaker and the length of
> the tube. All good physics and should work. It seems to me that T.R.
> MacElroy sold a code practice oscillator with some sort of resonator
> on the speaker. Not sure how he did that.
>     There were a couple of brands of headphones in the 1920s that had
> adjustable resonance. One used adjustable spacing of the diaphragm.
> Never seen one in the flesh.
> 
> On 6/15/2018 11:02 AM, D.J.J. Ring, Jr. wrote:
>> Steve N4LQ has a wonderful video about resonant speakers.
>> 
>> He has a SKYTEC speaker and he took it apart and made a practical 
>> copy.
>> https://www.youtube.com/watch?v=MF8bk6958Hg
>> 
>> *Magical Audio Filter
>> *
>> MAGICAL AUDIO FILTER USING MC1458 &
>> ​ ​
>> MAX295 IC1s BY JIM PEPPER
>> ​  BOARD FOR $6.50  available from faircircuits​.net 
>> <http://faircircuits​.net>
>> 
>> 
>> 73 Nov 96 
>> <https://archive.org/stream/fea_The_Magical_Audio_Filter/The%20Magical%20Audio%20Filter#page/n0/mode/2up> 
>> https://archive.org/stream/fea_The_Magical_Audio_Filter/The%20Magical%20Audio%20Filter#page/n0/mode/2up
>> 
>> DESCRIPTION: This circuit uses two MC1458, one LM386, one MAX295, 
>> 78L05, and 78L12.
>> 
>> Note: Maxim has obsoleted the Max295 IC's; Make sure you can get the 
>> IC's before ordering the board!
>> (The MAX 295 is available on eBay for two for $13.00.)
>> 
>> ​Milestone Technologies sells a CW filter, too.
>> https://www.mtechnologies.com/misc/filter.htm
>> 
>> 73
>> 
>> DR​
>> 
> 
> --
> Richard Knoppow
> 1oldlens1 at ix.netcom.com
> WB6KBL
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> =30=