Re: A simple PVC PIPE audio filter for the Cricket

Charles W. Powell

I made a pair of these Dixie Cup resonant speakers today.  Remarkably, they have a very sharp peak at 600 Hz (my preferred center frequency).  I opened up the filter on the KX3 and found that the speakers were better than tightening down the filter on the radio.  It is the equivalent of about a 100 Hz filter, but much better sonic quality.  I am impressed!  Now I have extra Dixie cups for summer as well. (I made two because the KX3 needs “stereo” to work “Dual Watch” mode.

One suggestion that was not shown in the YouTube video: After attaching the speaker to the cup, place another cup underneath it, up against the bottom of the speaker, and hot glue it in place.  I found this narrows the bandwidth considerably, and fortunately at just the right frequency (for me, anyway).


Charles - NK8O

On May 3, 2017, at 9:22 PM, 'Sam Neal' n5af@... [4sqrp] <4sqrp@...> wrote:


I made it's el-cheapo little brother ( some old issue of Popular Electronics )
out of a Pringles potato chip can and the speaker out of an old CB radio. That
sounded very good, so I can imagine that it's big brother from QST will be
much better.


Sam Neal N5AF
Celebrating 60 Years In Amateur Radio

------ Original Message ------
Received: Wed, 03 May 2017 05:36:31 PM CDT
From: "Charles Moizeau w2sh@... [4sqrp]" <4sqrp@...>
To: "4sqrp@..." <4sqrp@...>, "wa0itp@..."
Subject: Re: [4sqrp] A simple PVC PIPE audio filter for the Cricket

By all means have a look at the February 2017 issue of QST, pages 43-45, "A
Resonant Speaker for CW", for good ideas and a nicely crafted result.


Charles, W2SH

From: 4sqrp@... <4sqrp@...> on behalf of WA0ITP
wa0itp@... [4sqrp] <4sqrp@...>

Sent: Wednesday, May 3, 2017 3:10 PM
To: 4sqrp@...; Charles Powell; Walter - K5EST
Subject: Re: [4sqrp] A simple PVC PIPE audio filter for the Cricket

Lets build one!

A hunk of pvc pipe works very well, and is plenty stiff enough. I built one
some years back, and if I could find it, I'd use it. The volume of the pipe
doesn't matter, only the length, so I'll let the size of the junk box speaker
dictate the diameter of the pipe. Easy calculation too, length of
pipe=1100/2f. Think I'll build one specifically for the Cricket, but it will
need a little outboard amp (tape it to the filter) to drive the speaker. This
thing could be built similar to a trombone, so I may include a sliding insert
(or an outside tube) that changes the resonant freq from abt 800 cycles (8.5")
down to 400cycles (16.5"). It will work for any rig that will drive a

I'm off to the junque box to find a speaker, anyone else want to build one
too? Anyone have some good construction hints?

I love this radio stuff.<><>


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On 5/3/2017 12:44 PM, Charles Powell
doctorcwp@...<mailto:doctorcwp@...> [4sqrp] wrote:

I had forgotten about this. I made one years ago when I first started in
radio, and used it with my FT-101EE. As i recall, it worked quite well and
the video bears this out. I have a boatload of small speakers around here
somewhere. I made a tuned speaker from PVC that also works very well - almost
as well as the filters on my K2.



On May 3, 2017, at 12:34 PM, Walter - K5EST
walter.k5est@...<mailto:walter.k5est@...> [4sqrp]
<4sqrp@...<mailto:4sqrp@...>> wrote:

Keeping in the minimalist fashion, my old friend the Red Solo Cup Resonance CW
filter does a great job at nearly no expense. The design has been around for a
long time. The URL is to a U-Tube video.

or if can get away with a scavenger hunt in the kitchen.....

Happy Walter - K5EST

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