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Mwm,

It's not difficult to figure out why your first build bit the dust quickly. The loading 'seen' by both drivers in your initial design is an acoustic short circuit - the same as a dipole loudspeaker. The distances between your 'taps' in the waveguide are not large enough to create significant phase differences between the diaphragm motion and the wave arriving at the tap as it passes down the waveguide. As a result, your drivers were probably way into overexcursion, and would eventually have ripped themselves to shreds. Much of what you might have been hearing from the enclosure would have been motor distortion - the woofer's final cry for help before mechanical damage or failure.

Hornresp does not do a good job of simulating the fact that the radiation surfaces in the 'taps' are mechanically coupled. It only simulates two separate radiators out of phase with one another. Otherwise, you would have seen extreme excursions in your diaphragm displacement plot in Hornresp.
 

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Mark,

In the first build, the inner driver is absolutely seeing a short circuit. The only way to acoustically load a driver is to make sure the rear of the driver never 'sees' the front side of the driver, or 'sees' the radiation from the front driver with the phase rotated to within 90 degrees of the rear driver - or else some part of the interaction between the front and rear of the driver will be destructive. In your first pictured build, there is less than two inches of baffle between the front and the rear side of the inner driver, which is absolutely a short circuit because there is no acoustic structure in the enclosure 'circuit' between the two sides of the interior driver.

I discussed this with you on DiyAudio - in your original build, you might as well omit the interior driver entirely. Hornresp's excursion predictions are invalid in this case because the exterior and interior drivers are not mechanically coupled - Hornresp simulates all the drivers in the system working as a single piston, not multiple diaphragms.


Best Regards,

Rory
 
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