Shell-speaker

Recently Joe Sousa sent me a link to the web-site with beautiful examples of see-shells, in fact snails, used to amplify the sound. Its cavity widens similar to the horn of a horn-speaker, so the same principle has been employed.

That brought my attention to a decorative item which stands on my shelf collecting dust.

This article describes what I have done with it.

First, I boiled it for 15 minutes in kitchen-vinegar to dissolve the lime scale, washed it and let it dry. Then, I cut the top with a diamond saw and removed adjacent part of inner cone using my PROXXON hand-tool. The hole I have made so was about 50 mm in diameter.

Preparing all necessary parts was the most difficult. The driver-element was an SAL wide range speaker YD78 (2W; 8 Ohm). I cut the wooden ring 8mm thick, 80mm outer and 50 mm inner diameter. With the lathe I made groove which fits to the front of the speaker. In a carved Chinese stand of 80mm in diameter a hole was cut to fit the speaker-basket.

The driving speaker was then fixed between the wooden disk and the stand using two-component polyester glue.

When dried firm, the competed driver-assemblage was glued at the cut surface of the shell with the same glue. Bottom of the stand was then covered with black cardboard, after soldering the connecting cable.

After it hardened, I took another stand of the same type and colour, but with the diameter of 150mm.

It was fixed with three screws from beneath for better stability and nicer look.

Now, it was time to test my shell-speaker. I used sine-wave signal-generator, tube-amplifier with ECL82 and digital oscilloscope to measure the output RMS-voltage by frequencies from 20 to 10000 Hz. The results are shown at the graph below.

Of course, sine-wave is one thing, but the real music is quite another! So, I tried it with a vintage-radio (via output transformer) and with my PIONEER tuner. You can see it and hear how it sounds by clicking here.

As you can hear, it is not a HiFi-sound, but quite good for such a gadget.

Try this and have fun!

Regards, Dejan

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