|Bass Horn - Part-2-01|
I wanted to try a driver mounted at the throat to see how this might sound. I tried a wide range GE S-1201D featured in an ad in Audio Engineering February 1952. You will find an image of this advertisement on the page at The EH Dirt Road Special is Back for repairs posting. The S-1201D I tried is in an old open back baffle originally part of a Califone record player. Measured DC resistance of the voice coil is 8 Ohms.
Just about the time I got this lash-up ready, I realized that the power had gone off. So instead of plugging anything into the wall outlet, I set up my 12 DC marine battery with a small inverter and plugged into that. Here is a photo of the setup for testing:
|Bass Horn - Part-2-02|
|Bass Horn - Part-2-03|
|Bass Horn - Part-2-04|
|Bass Horn - Part-2-05|
Here are a couple of photos showing the interior of the horn after the eight cleats have been fastened:
|Bass Horn - Part-2-06|
|Bass Horn - Part-2-07|
This project is about a bass horn. However, preliminary testing with the vintage GE S-1201D with a variety of music indicates that, if you can live with a little directivity at the higher frequencies, this seems to work quite well as a full-range horn.
Sensitivity is extremely high. While working in the garage today about eight feet away from this horn while it was playing, I had the volume set for a comfortable listening level. Without changing anything, I connected an AC voltmeter directly to the amplifier speaker output terminals and measured peaks of about 200 millivolts going into the speaker. At 8 Ohms, this is the equivalent of 5 milliwatts of peak electrical power. While fastening the Masonite panels, I was essentially inside the horn listening to the music and I had to turn the volume down even further.
Before I set up the iPod music player, I tried a sine wave generator and got very strong output down to about 40Hz.
So far, this speaker is relatively lightweight. I will try to weigh it tomorrow. Using an SPL meter, it would be interesting to measure the efficiency of this speaker at several different frequencies. Another test I would like to try is applying a square wave and watching the waveform in the air in front of the speaker with an oscilloscope. Time coherence should be quite good because all of the sound is coming from a single driver without the need for any crossover. I will probably take it outside for square wave testing to avoid room boundary reflections.
Even without any further testing, the musical sound from this speaker is really stunningly good, especially from well-recorded percussion instruments.
This bass horn project continues with Bass Horn Project - Part Three.