Wednesday, October 22, 2014

The Sound Transformer - An Early Prototype

This is a continuation of Bass Horn Project - Part Three.

First a little review of how we got here.  A very long time ago, I developed an interest in high fidelity sound.  I plunged into the field at a very early age by removing all of the "recus" from my parents, record cabinet and spreading them around on the floor.  By the time my parents discovered this, I was sitting on top of a haphazard pile of 78 discs.  Later, when I could walk, I conducted an investigation of the loudspeaker in my father's Zenith Cobra Radio Phonograph.  This involved climbing up on a chair and poking a pencil through the grille cloth into the speaker cone.

A few years later, a very kind uncle kindled my interest even further by dropping off at our house several vintage audio devices for me to explore.  Those included a Webster-Chicago wire recorder, the precursor to tape recorders, an Ampex ten-inch reel-to-reel tape recorder, a Thordarsen twelve watt amplifier, and a Garrard record changer.  My first "hi-fi" was the Garrard plugged into the Thordarsen with a 4" x 6" speaker connected to the output.

I continued my formal education later on pursuing physics, mathematics, and electronics.

Finally, after all of this preparation, I am able to make a contribution to the field of high fidelity sound.  The "Sound Transformer" described below probably offers the most bang for the buck of any loudspeaker available today.  It is made of components removed from an "acoustic suspension" speaker, specifically a KLH model CL-3A.  The parts used include a twelve-inch woofer in the throat of the bass horn and the three-way crossover.  The midrange driver attached to the plywood horn is a two inch speaker removed from a small computer speaker box.  The tweeter is a Sansui unit removed from another speaker.

The Sansui tweeter is so efficient that it was necessary to use a dividing network to attenuate the treble response to achieve a balance across the frequency spectrum.

Sound Transformer - Midrange and Tweeter Horns
Sound Transformer - Midrange and Tweeter Horns

Sound Transformer - Showing Lepai 2020A and Crossover
Sound Transformer - Showing Lepai 2020A and Crossover
The plywood and Masonite panels used in the bass horn were recovered from scrap at local recycling and transfer stations.  Although large, the bass horn is light in weight and separates into two sections for transport.  The inexpensive Lepai 2020A amplifier provides the cleanest sound through this.

This assembly is called the "Sound Transformer" because the horns provide an acoustical impedance match between the relatively small speaker drivers and the air in the listening area.  The bass, midrange, and treble drivers are located in the same plane so the sound can travel from the drivers to the listener in the same length of time.