Speaker Building

Treble, Mid/bass spacing

A loudspeaker using a single full-range driver has the advantage that all the sound frequencies are emanating from an approximate point source. One major effect of this is that 2 separate sources producing the same frequency will cause cancellation in some areas of radiation at certain frequencies.

Many fine treble units made today have a wide faceplate that ensures stability and provides a baffle for the unit. Unfortunately, this faceplate obliges builders to accept a minimum spacing for drivers that is actually quite high.

The disadvantage of wide spacing is graphically illustrated below, though this example is quite extreme.

The wide space between the Mid and Treble unit is causing bands of cancellation and quite a shaky wave. With the Mid and Treble units close together the cancellation occurs outside the listening area.

Keeping the crossover frequency as low as possible helps to reduce the problem of cancellation related to the distance between drivers.

I also used another improvement on my own speakers by buying a spare pare of faceplates for the treble units and cutting out a segment to match the mid/bass driver. This reduced the spacing of the drivers by 2cm. Please note that the mid/bass is magnetically shielded which avoids the problem of the magnets interfering with each other at such close proximity.

The front baffle on these speakers is 42mm thick and is made from a sandwich of 2x12mm and 1x18mm MDF. The smooth curvature is achieved with 'Plastic Padding' used for car bodywork repair.

The inside of the baffle is carved out to allow the mid/bass pressure wave to move freely away from the driver.

These speakers are covered inside and out with heavy carpet tiles stuck to the MDF. This is the single best mod I have found for improving the sound of loudspeakers. Inside the cab there are 2 layers. Not very pretty, but effective. Even when playing at volume, an ear pressed against the side of the cabinet hears very little sound emanating through the cabinet walls.

These medium sized speakers (12 litres) weigh 24lbs each. (apprx 11kgm)

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