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Bose Acoustic Waveguide Theory

by David Lipscomb

Bose speakers use proprietary engineering designs to achieve a large amount of sound from smaller speakers. Most of these designs revolve around use of folded transmission lines, which Bose calls Acoustic Waveguides. These designs allow compact enclosures and use of inexpensive drivers. The theory behind use of this design choice is an essential and defining element in the Wave radio, so named due to the use of their Waveguide topology. Other small Bose products such as the SoundDock iPod base also use transmission lines to produce large sound from smaller packages.

How Transmission Lines Work

The back wave of a speaker driver is equal in intensity to the front wave. Manipulated properly, this back wave can be used to reinforce output from the front of the driver. This is the key theory behind any transmission line design. By deploying a tuned chamber inside a speaker enclosure, the air pressure from the back of the speaker is slowed or sped up to a precise speed. Coiling the chamber as Bose does allows this precise tuning to fit into small enclosures, such as on the Wave Radio.

Bose Execution

Two 26 inch Waveguides are coiled to increase the amplitude of the small 4 inch speakers at the front of the Wave radio. This use of acoustics to amplify speaker sound reduces the need for large amplification, impractical in a small chassis. These Waveguides are made of plastic, either molded as part of the chassis or found as flexible tubing.

Horn Speaker Design

Speaker designs that use transmission lines are by definition horn speakers. Any horn must shape the sound to achieve the target sound as intended by the manufacturer. Horns in the case of the Acoustic Waveguide may be "selective" in terms of which frequency bands to reinforce, and which to leave alone. This is how Waveguide-equipped speakers produce big bass from small enclosures while not sounding thick and distorted.

Why Waveguides?

In order for a smaller audio system to find penetration into as many bedrooms, kitchens and offices as possible, big sound had to be stuffed into a small package. For many, a larger audio system is intimidating and, more practically, simply will not fit into some small rooms or spaces. The folded transmission line Waveguide may solve this issue for you, producing output similar to speakers many times their size.

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