My last controversial discussion went over like a fart in Sunday school, with people accusing me of promoting something I was actually cautioning against: http://www.talkbass.com/forum/f15/car-subwoofer-sensitivity-1040006/ Time for some more controversy by touching upon another divided subject from a scientific point of view: Cabinet sensitivity and its relation to actual usable volume! So right up front, I'm discussing: Cabinet specifications, not specifications on drivers Sensitivity in standard SPL @ 1W/1M, not some random contrived rating Passive cabinets, not combos Sensitivity ratings for a cabinet are an indication of how much volume will come out as measured from 1 meter away with one Watt applied. The ratio of amplification to output is approximately +3dB for every doubling of power. So if I have a horrifically inefficient cab with a sensitivity of 88 dB (my car subwoofer home practice cab), and a 125W amp, then the extrapolation is roughly: 1 W 88dB2 W 91dB4 W 94dB8 W 97dB16 W 100dB32 W 103dB64 W 106dB128 W 109dB If you compare that to SPL levels necessary for a gig, such as those listed on the Greenboy Fearful page, you can see why this was built as a home practice amp with no further aspirations: http://greenboy.us/fEARful/faq.htm So another way of looking at amplifier power is in dB gain from 1W as measured from 1M away. Thus, a 125W amp gives you approximately 21dB gain potential, while a 500W amp gives you 27dB gain potential. This is all ideal calculations in an ideal world - in which we don't live. In fact, many folks here completely dismiss SPL sensitivity ratings and say they're meaningless. Why? While I don't believe in throwing the baby out with the bathwater, there are many reasons why folks are dismissive of sensitivity ratings, and why a cabinet rated at 104dB sensitivity and 500W capability might never come close to the calculated potential of 131 dB: Power rating is not realistic for actual live music. That 500W is really an occasional peak, but only 150 useable Watts can be run before one or more speakers melt The sensitivity rating is not guaranteed across the full range, and is likely just the highest peak somewhere at 2KHz. Lowest frequencies are hardest to produce loud, and the cabinet is only good for 1/4 rated power below 100Hz Volume rating at 1W/1M directly in front of the driver of choice gives no guarantees of off-axis response. So from the above, it's clear that the efficiency rating of a cabinet is no guarantee of how loud it will get in a specific application. It only tells you the volume produced at 1W from 1M away sitting in front of it.