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.

Tuesday, October 7, 2014

Even More on the Plywood Horns

I needed to make more experiments with the "poor man's" midrange horn driver concept.  I regard the matching plywood horns as a prototype not to be further altered.  They sound quite fine the way they are.  I needed a quick and simple way to fabricate a spare midrange horn to work on and try some new inexpensive drivers with.  Searching online, I came across a technique for building a horn using a combination of plywood or MDF panels and foam core panels available in almost any art supply store.  Here is a photo showing the horn glue setting:


Foam Core Midrange Horn I
Foam Core Midrange Horn I
Here is another photo showing the pine mold inside the foam core construction.  It requires many elastic bands to hold the glue joints.  Particularly on the narrow sides with the sharpest curve, it really helps to carefully score the foam core parts so they will bend easily into the shape you are trying to make.
 
Foam Core Midrange Horn II
Foam Core Midrange Horn II
I already had some 3/16 inch black foam core.  I will post more pictures of this later after it comes off the mold...

Bass Horn Project - Part Three

A Fully Horn-Loaded Loudspeaker Made Entirely From Parts And Materials Recovered From The Dump.

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

Part Three was supposed to be about constructing the third "throat" section of the Bass Horn.  Instead, the present two-thirds of the Bass Horn are now set up as the bass portion of a fully horn-loaded speaker in the barn attic.  The bass driver currently connected to the Bass Horn is a twelve-inch woofer taken from a KLH model CL-3A.  The woofer is connected to the crossover network also removed from the CL-3A.  The plywood midrange horn is connected to the midrange wiring in the same crossover and the Sansui tweeter is connected to the tweeter wiring.  I set the midrange and tweeter horns on a box so they are about the same distance from the listening area as the Bass Horn driver.

Horn-Loaded Speaker System - View 1
Horn-Loaded Speaker System - View 1
Horn-Loaded Speaker System - View 2
Horn-Loaded Speaker System - View 2
Horn-Loaded Speaker System - Plywood Midrange and Tweeter Horns
Horn-Loaded Speaker System - Plywood Midrange and Tweeter Horns
Horn-Loaded Speaker System - KLH CL-3A Crossover Network
Horn-Loaded Speaker System - KLH CL-3A Crossover Network
Horn-Loaded Speaker System - Lepai 2020A Amplifier
Horn-Loaded Speaker System - Lepai 2020A Amplifier
I am listening to the speaker powered by one channel of the Lepai 2020A Class "T" amplifier.  I have only one speaker like this right now so I have been listening mostly to monaural LPs recorded in the mid 1950s.  The sound is surprisingly good.