In a recent exercise, I took a long search of available 12" drivers available on the market to try to find the best DIY for the buck. Although I ended up going with a used 410 for economy reasons, I thought it would be interesting to note a few findings and address the blanket statement that always come up when it comes to car subs and their efficiency. For the most part, the blanket statement that car subs are inefficient is true of any subwoofer (vs. a woofer). To get useable output at or near 20Hz, the cone has to have a low resonant frequency (added moving mass) among other necessary design specs that make for a very inefficient speaker (Sensitivity in the mid to high 80's). However, there are exceptions. Some subs out there have efficiencies in the low 90's. A decade ago, Cerwin Vega and Lanzar used to put out highly efficient subs - but by design they had very little excursion, requiring large banks of them to move any air below 40Hz without bottoming out. Mutually exclusive design properties are a beeyatch. Other brands had efficient subs that could go low somewhat efficiently - if you put it in a box the size of a walk-in closet. These days, there's a LOT of deceptive practices in sensitivity listing. Rather than stick to the standard 1W/1M (as flawed as many think that is), many companies are now listing their driver sensitivity at 2.83V regardless of speaker impedance. When most speakers were 8 ohms, 2.83V was equivalent to 1 Watt. But these bastids are using the 2.83V standard on 4 ohm and even 2 ohm voice coils, padding their sensitivity numbers with up to +6dB. Pretty crappy for those who aren't familiar with circuit theory. The giveaway is that their 2 ohm voice coil model magically has double the sensitivity of their 4 ohm model. So now you can rate a subwoofer at it's arbitrary resonance peak at say 1KHz, giving you a +6db gain over the actual frequency range it's intended for. Then you rate it at 2.83V which inflates another +3dB on a 4 Ohm speaker. That's a lie of +9dB, making your 86dB speaker look like it has a sensitivity of 95dB! Major suckage.