Hi guys
I am sharing the results of a project I started back in 2017; I am calling
it 3S, super selective speaker. 5Hz to 10 Hz BW APF.
The idea of chasing an acoustic filter was motivated my early situations
reported by N4II Ed, and NX4D, Doug, when it was possible to copy a weak
signal far from the radio room, the walls was working like a filter removing
the QRM. The first project I should call beginners luck, worked straight
away. With two speakers behind my monitors, I was able to copy that weak
signal you can see on the SDR waterfall but not pull it out. Since I start
using the system, I and other friends here at my station were able to copy
any signal that we can see at the waterfall, I like to use HPSDR audio water
fall to identify the weak signals. Most of the time it was not possible to
copy the same signal with my IC7851using headphones.
In the last few months, I was recovering from an eye surgery, and I decided
to work on a new pair of speakers, for my surprise it was very complicated.
After a lot of try and building, now I can share the results with a huge
improvement from the original project.
This project was based on the work of Ed Loranger (WE6W), and N5FC Resonant
Speaker (N5ESE Prototype) found here >
https://www.n5ese.com/res_spkr.htm
Several deep diving on organ pipe builders, psychoacoustic, the human ear,
CW pitch and NASA 3-D initial work that today moved to multimedia, all that
results on the paper attached. The new 3S, or super selective speaker can
provide narrow bandwidth between 5 and 10 Hz with no ringing or
intermodulation.
There is enough information to build the system on the pdf attached. I used
PVC 2" sch40 because it provides the best Q, for lower CW pitch, like 200Hz
I used aluminum tube 3"x1/8 wall.
Enjoy it,
73
N4IS
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