Friday, May 12, 2006

Acoustic Tube

The acoustic tube (I also refer to it as the redirect tube) is a vertical plated brass tube brazed into the pole pieces in the 77DX. The radius of the tube OD fits the inside radius of the pole pieces and confines a small area of air behind the ribbon, which is only about an inch long. The top of the tube is closed, and the bottom of the tube is positioned above the entrance hole in of the Acoustic Labyrinth.

The acoustic tube has two slots cut into it: One is at the entrance, just behind the ribbon, and the other rear slot is on the opposite side of the ribbon, toward the rear. The rear slot is milled to have a flat surface on which the shutter rests and rotates.

The shot above shows a modeled acoustic tube and ribbon motor assembly used to characterize the geometry and acoustic Z of the basic 77DX design. One apparent shortcoming of the 77DX is reflection from the back of the shutter loading the adjacent ribbon. Here we have placed the ribbon about 2X the distance from the back of the tube, added an acoustic matching network, and tuned the acoustic load until the response is fiarly flat looking at a distant broadband source.


Anonymous said...

Hey I want to get those cad files are they for sale? Who is Transducer Associates and are they still in business?

Bob Crowley said...

Transducer Engineering Associates was the old name for the company that eventually became Soundwave Research Laboratories, Inc
The files are written in Solidworks and there are about a hundred along with a complete 77DX production file, bills of materials, and comprehensive engineering analysis. Please contact us at 509 231 4515 for rights to this package.