Commercial bass cabs loaded with fifteens.

[Bill Fitzmaurice]

When looking at an SPL chart ideally it should resemble a Kansas skyline: flat as far as the eye can see. You’ll only find such a chart with the finest hi-fi speakers. Where pro-sound is concerned an acceptable chart more resembles the ocean: a few ripples here, a few swells there. And then there’s the chart that looks like the view from the top of Mount Everest. Unfortunately, if you’ve got a fifteen combo chances are the response from your cab most closely resembles the last scenario. This is the response of an Eminence Alpha 15 w/tweeter, in a 3 cubic foot (net) cab, both ported and sealed. Most fifteen combo’s have drivers with similar specs.



The sealed cab is actually better than the ported, with less of a hump in the midbass, so it will have less of a tendency to ‘boom’, and better low frequency extension. But with either the sealed or ported cab the low bass is weak, the lower midrange almost non-existent, and the peak at 1.8kHz would cause concern even to Sir Edmund Hillary. There is a major response dip between where the woofer stops and the tweeter takes over, and if you could see a chart showing dispersion you’d see that what midrange there is beams horribly. If there is one speaker configuration with virtually no redeeming qualities an inexpensive 1x15 combo would be it.

On the other end of the scale here’s a premium driver, the Eminence Omega Pro 15 w/tweeter, loaded in a 4 cu ft (net) cabinet, tuned to 40 Hz.



This is about as good as it gets from a relatively small direct radiator cabinet as far as the low end is concerned, and response to about 1.5kHz is quite good. However, the response dip between where the woofer stops and the tweeter starts remains. The only way to get smooth broadband response is to have a separate six or eight inch midrange driver.