Direct Acoustics

In the late 70’s, my friends in Toronto, George, Ian and Robert, had started a business, Audio Products International, and had achieved considerable success in selling a line of speakers under the Burhoe brand name, which we had developed jointly, and considerably more success with another brand name, Sound Dynamics, which they had developed on their own.

Sound Dynamics was a line in the tradition of Cerwin Vega, large enclosures, large woofers with a horn loaded tweeter. When I visited them in 1978, I found that they were well along with a third product line, which they were calling Energy and had come very far in the design of a product they called the Energy 22.

They were unhappy with the performance of a new tweeter they were designing for this new energy line, and I volunteered to take a look at it. The problem occurred primarily at about 8,000 Hertz. Using a microscope and an oscilloscope synced to the 8 kHz frequency, I was able to view the motion of the cone which was causing the problem and redesign the profile of the tweeter to eliminate the problem. At the same time I designed a groove in the cone to accept snugly the voice coil, which allowed useful performance well beyond the accepted limit of human hearing 20 kHz.

Another innovation was in the use of magnetic fluid surround the voice coil not only to provide a heat sink so that it would not burn up with high power amplifiers but also to use its variable density characteristics to physically center the voice coil during production assembly.

The woofer was already well designed, based on the best British technology using a polypropylene cone and PVC surround. In my first departure from sealed box bass technology I participated in a bass reflex design.

The final step was to design a crossover which would seamlessly blend the frequencies of the woofer and the tweeter. To this end, we decided to rent the facilities of the National Research Council, which had an acoustic department which was charged with helping the development of Canadian loudspeaker technology.

Floyd Toole was the director and he had created a wonderful facility with a large anechoic chamber for testing in one building and a carefully designed listening room for subjective evaluation in another building. We spent about a week in the Ottawa winter carrying our speaker and its elaborate crossover, wires and coils and capacitors hanging out from it in the snow between the two buildings. It took many iterations of modifications, acoustic testing and music listening before we came to our ultimate design.

Unbeknownst to us, at the same time that we were finalizing our Energy 22 design, Floyd was conducting an international test of studio monitors for the CBC (Canadian Broadcast Company, I think.) In the elaborate process of double blind speaker comparisons of the best speakers in the world, Floyd sneaked in our Energy 22 prototype. It was our speaker that won the contest. We promised Floyd that we would make no changes to the sound quality in subsequent production.

Subsequently the energy 22 received many rave views and great commercial success in Canada.