How do Tectonic DMLs generate the sound pressure levels (SPL) of cone and dome drivers from a rigid panel?

September 28, 2018

It all comes down to surface area.

Tectonic DMLs are physically bigger in area than conventional drivers. As an example, the Tectonic DML has approximately five times the radiating area of a 12″ driver, therefore the DML’s total movement need only be one fifth of that to shift the same amount of air.

Imagine a 12-inch bass driver being driven quite hard so that it moves +/- 5mm back and forth. This will produce high SPLs. So we can ask; how much does a DML need to move to shift the same amount of air?

A bit deeper:

The radiating area of a 12″ driver is about 0.05m^2. The radiating area of the Tectonic DML is approximately 0.25m^2. If the 12″ driver is moving +/- 5mm, a DML only needs to move +/- 1mm to shift the same volume of air. For the DML to produce the same SPL as the 12″ driver, it only needs to move about a fifth as much.

However, the surface of a DML does not usually move as a rigid piston and the comparison shown above is only true for lower frequency operation of the DML. At higher frequencies, the surface of a DML is undergoing complex vibrations with multiple regions moving with different phases, so the total net radiating area is reduced (although both sides of the DML are now contributing). But remember: we are no longer comparing a DML with a 12” bass driver because a 12″ cone cannot radiate above a few hundred Hertz. In the mid-range, a conventional speaker system is likely to use one or two 3” drivers, each having a radiating area of around 0.0033m^2. (Compression drivers / horns take over from there.)

Comparing these drivers with the radiating area of a DML (0.25m^2 x2 = 0.5m^2 for both sides remember) we can see that this is equivalent to 0.5/0.0033 = 150 midrange drivers. So even if just a portion of the radiating area of a DML is contributing to the on-axis output, there’s easily enough area to provide sufficient output.

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