The RMS and peak wattage rating of a subwoofer (or any speaker) show afaik how much power it can safely handle without damaging it. But is this true for both sealed and ported enclosures? (assuming the boxes are build to the recommended dimensions)
There are several ways to damage a subwoofer, but the one I'm concerned about is exceeding the maximum excursion. When you have a subwoofer in a sealed box, the air inside the box acts as a spring, resisting movement from the speaker cone. With a ported box, this effect is much less, resulting in a larger excursion for the same amount of work.
I have a Hifonics mxz12d2 http://www.audiodesign.de/downloads/datasheets/Hifonics/MXZ12D2.pdf with an amp more then capable to deliver 1000 watts RMS. My plan is to use a sine wave, attach an (true rms) amp meter around one speaker wire and a volt meter over the two amp connection points. Then I increase the amp gain until I see the speaker uses close to 1000 Watts rms. But is this a safe way of setting the gain for this subwoofer if it's in a ported box?
Best Answer
Wrt excursion you'll find that any enclosure will affect this at a given input level. The closed enclosure will provide damping of the excursion all way down, while the ported version will provide little or no damping below the resonance frequency of the port.
I would suggest to do a frequency sweep with the driver mounted in the actual box to be used, starting at reduced input level. You should test for power as you have suggested, but also for excursion.
You will need a way to determine when Xmax is reached, and one way to do it is to use light weight pin. The pin should have a rounded head and be fixed loosely in e.g. expanded polystyrene or the like. You need to jerk the pin in and out some times to get it loose enough. The idea is that the pin is fixed at a distance from the dust cap, and when the desired excursion is reached, the pin will be displaced. Remember that polystyrene will easily move with the displaced air, so it should be a little as possible and held in position by a device made of high density material.
If you do this together with measuring the power, you will get the info you need for safe operation.