Bandpass Dual Chamber Basic Theory:
The front and rear of the driver are mounted in separate enclosures and tuned to specific calculated values. Resultant output is suppose to be better than any of the other designs mentioned previously. Bose owns the rights to the exact details behind this design. They explain the theory like this, "The low-frequency speaker drivers are located between separate acoustic compression chambers inside a patented Bose Acoustimass module. As each speaker cone moves, it excites air in the chambers. Trapped in the chamber, this air acts as an acoustic spring, which interacts with the air in the port to produce more low-frequency sound with less power. The system is more efficient and requires less cone motion, which in turn produces less distortion. In the event that any otherwise audible distortion is produced, the patented design traps it inside the acoustic chambers -- so it never enters the room. The result is an Acoustimass module with no audible distortion that can be located anywhere in the listening area.
Bandpass Dual Chamber Advandages:
More efficient system within its bandpass. More control over cone movement. Less audible distortion. This doesn't necessarily mean that there is a true reduction in distortion from the driver, but that any distortion that is present form the driver can't be heard as well due to the chambers acting as filters on any unwanted noise. My opinion only.
Bandpass Dual Chamber Disadvandages:
Combined volume of both chambers may result in large overall enclosures. Very difficult to design properly. You may have to experiment a great deal before getting this design to sound acceptable. Results may vary substantially due to misalignment of both front and rear chambers as well as tuning frequency of each chamber. Drivers can be easily blown due to high compression factors because of lowered cone motion and thereby exceeding the thermal limits of the driver before exceeding its mechanical limits. The driver may in fact tear itself to pieces. There are no exact parameters or calculations for designing 6th order bandpass enclosures due to the patent owned by Bose. So if you build one, you're basically on your own. Original article sourse is danmarx.org.
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