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Old 10-21-2008, 03:23 PM   #1
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Wattage

I know this sounds like a dumb question, but how do you find the total wattage of amp connected to a cabinet, like if the head is say, 30 watts and the cabinet is a 4x12 and has 120 watts, what is the formula for total watts?
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Old 10-21-2008, 09:41 PM   #2
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The output of the head doesn't increase just because you plug it in to a cabinet with a greater rated wattage, if the head's output is 30 watts that's the most it will put out. Whether it will put out 30 watts into a particular cabinet is a different question; you need to know at what load the amp is designed to put out 30 watts and what the impedance of the cabinet is. This information is usually marked on the back of both items. If this sounds complicated, bear in mind that the maximum output of the head is arrived at when the amp is running at its most efficient loading, which for bass players usually means into a 4 ohm load (I think for guitar amps it's 16 ohms but don't quote me). If you plug an amp, rated at let's say 500w at 4 ohms, into a cab rated at not 4 but 8 ohms that will double the load on the amp and will typically reduce the wattage of the amp by up to half. (Since the audible difference between 250w and 500w is 3 decibels, or about as small a difference in volume as most people can perceive, this may not matter as much you might think.) You should avoid running an amp into a load less than the amp is rated for (e.g. a 4 ohm amp into a 2 ohm cab) as this will probably damage the amp.
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