Speaker Directivity Modifier, Part II

(By Jay Mitchell continued......)


Effect on Response

Response curves unmodified and modified (with 3/4" foam) cabs are shown below.

Unmodified

Response of an unmodified speaker/cabinet at 0, 15, 30, 45, and 60 degrees off axis. The black curve is the on-axis response

Response of an unmodified speaker/cabinet at 0, 15, 30, 45, and 60 degrees off axis. The black curve is the on-axis response

Note the vertical spread in the unmodified responses above 1500 Hz. The difference exceeds 20 dB at some frequencies.

Modified

Response of a modified speaker/cabinet at 0, 15, 30, 45, and 60 degrees off axis. The black curve is the on-axis response

Response of a modified speaker/cabinet at 0, 15, 30, 45, and 60 degrees off axis. The black curve is the on-axis response

Note the dramatic reduction in the vertical range of the responses of the modified speaker. At 2.5kHz, the differential between on axis and 45 degrees is reduced by 7dB. Between 3 and 4kHz, the difference is reduced by more than 10 dB. Note also the similarity between the responses of unmodified and modified speakers at 45 degrees off axis. Some adjustment to tone controls may be necessary after modification, but your tone will now be much more consistent at different positions.

Implementation Tips

The concept is almost trivially simple to implement. Here are photos generously provided by players who have made and installed modifiers in their cabs.

Egnater 20 Cab

emptycabinside

Empty cab prior to installation of foam. Note the obstruction caused by the backing plate for the logo mounted on the front of the cab. It is preferable to eliminate any such obstructions, with or without a directivity modifier.

emptycabwithfoam

Egnater cab with modifier installed. Ideally, the small gap on the right side of the backing plate should not be present. Practically, the effect is likely to be too small to notice.

Front-Loaded Cab Installation

mitchell-modifier1

mitchell-modifier2

The photos are self-explanatory. Note that, if there is room on the front of the baffle (i.e., the grille is not placed directly on the front surface), the modifier may take any shape that is convenient, as long as it completely covers the speaker.