Effect of Changing the Number of Frame Holes

In our simulation the frame has 13 holes whereas the real driver has effectively 9 holes, 8 round and 2 semicircular closest to the electrical terminals.

The number of holes in the simulated driver was reduced to 8 holes to investigate the effect on the frequency response.

The result of reducing the number of frame vent holes is to reduce the frequency of the dip from 2.9kHz to 2.3kHz and to separate what was degenerate peaks just above 3kHz to become a distinct feature.  Separation of these features is revealing and illustrates the individual contributions of the frame vent resonance and bass port resonance as they act against the air in the cavity behind the diaphragm.  The enclosed air directly behind the driver, the frame vents and bass port operate as a multi-port Helmholtz resonator.

The effect of reducing the number of damped frame vents appears to be a tiny increase in the low frequency output at ~50Hz, decreased midband output and a damped frame vent resonance producing a weak dip at 1.5kHz and a weak peak at ~2.9kHz.  The sharper resonance feature at 3.5kHz to 4kHz is the bass port.