This forum has been great about answering technical questions so here's another one... Ok, lets say I have a 15 inch speaker that has a sensitivity of 100 dB at 1w/1m and a 500w @ 4 ohm amp. That gives me 126.9 dB. I understand that if 2 speakers should be 3 dB louder than 1, but how does wiring of a single 2 speaker cabinet figure into this. In other words, If I wire 2 8 ohm 15's in parallel to achieve a 4 ohm load is the cabinet going to be 3 db louder (129.9 dB) than a single 4 ohm 15 at the available 500 w? Does wiring the cab in parallel mean that each speaker is getting half the wattage that the amp is putting out, or is each speaker getting the full 500w? Now, how does series figure in? Would two 4 ohm 15s in series be louder that 1 8 ohm 15?

Hmmm, you managed to calculate decibels, but can't figure out power distribution. Odd. Anyway, if you parallel 2 identical drivers, each gets half the power. If each would get full the power, that'd be the solution to humanity's energy problems The phenomenon you're referring to is called mutual coupling. When 2 drivers are in close proximity, their combined cone areas are acoustically "coupled" meaning the acoustic impedance (the resilience of the cone-to-air transfer, so to speak) decreases. This means you'll get a theoretical 3 dB gain in the bass range, up until the frequency of which the wavelength is equal to 4 times the distance of the speaker cone centers. You also get a theoretical 3 dB increase, because the electrical impedance is cut in half, and a theoretical amp would be able to provide twice the power. In real life this is only about 1.5 dB So, this would add up to about 4.5 dB gain, because you're using two identical parallel drivers instead of one. Two of the same drivers in series (the way you describe it), will still sound about 3 dB louder.

Yeah, I wouldn't be able to calculate decibels if I hadn't found the formula in a thread on this forum. Anyway, I was thinking that wiring in parallel cut the power to each speaker in half and series effectively (or theoretically) cut the power in half by doubling the impedance, but wasn't sure. Thanks for the reply.

Sorry if that power distribution remark sounded harsh. It does, now that I read it back. The power is cut in half simply because there are two speakers. There's only a given amount of power, and each watt can only be "used" once.