I know that the Zapco says that their DC1100 amp puts out 1100 watts rms but they actually put out btween 1500 and 1700 watts rms. Im just curious if any one knows if the Audison amps are underated also and by how much. And what is the relationship between a ported box and a sealed box in terms of the amount of RMS watts they can handle.
Do a forum search for Audison.
There is no set standard by any manufacturer for "underating" an amplifier. The actual output is solely the judgement of its users. What some of the higher quality houses do, however, is limit their power bragging to very exacting criteria. If a user's definition of power isn't as precise as the manufacturer's, he may believe he is getting more than the amplifer is rated for.
Woofers in sealed boxes can generally withstand more power than in vented. But that's very general. Choose the proper type and size of box for the particular subwoofer.
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Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.