Effect of Short Circuiting Front and Rear Volumes

Below is the additional effect of adding an acoustical short circuiting system between the rear and front air volumes as described in the earlier model preparation video.

The short circuit effectively diminishes the bass performance, producing a slope towards a slightly raised fundamental resonance.  The upper densely modal acoustic of the front cavity also appears to be changed by the presence of the short circuit holes.

The graph below illustrates the effect of damping the short circuiting holes with volume absorbency.

Damping the short short-circuiting holes using the same absorbency as prescribed to the frame vents restores much the bass performance by controlling the amount of short circuit, however the 900Hz resonance is usefully diminshed, resulting in a flatter frequency response.

Taking a second look at the influence of the bass port in the context of this more complete system response, we can see in the graph below that blocking the bass port removes the bass enhancement.  This illustrates that the bass port, operating in tandem with other leakage control measures provides a valuable low frequency tuning opportunity.  In earlier analysis of the driver alone, it was difficult to see how important this device was.

The video below shows the acoustic phase contours for the system with and without bass port.  It is clear that the resonance at 32Hz (and bass boost) disappears when the bass port only is blocked.