Quote:
Originally Posted by pKelly
From a customer's standpoint, on what order will the output be compromised by going with only two BM's as opposed to 4 BM's, assuming all other factors are constant?
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Well lets take a look at how the 4 drivers vs. 2 drivers quandry works out:
4 drivers are double the displacement compared to 2 drivers. Double the displacement (surface area and stroke) equals a significant 3 dB increase just by itself. Keep in mind this is assuming that your power input is the same even though your impedance has changed going from 2 drivers to 4 drivers.
Taking a look from sheer surface area alone lets look at the BM's. Each BM has an Sd of 420 cm^2. Two BM's have 840 cm^2 of surface area. Four BM's have 1680 cm^2 of surface area. Double the surface area equals a 3 dB increase.
Now, depending on how you have the drivers situated on the baffle you can get a significant increase from coupling affect too. When you cluster drivers together (in this case it would be two woofers on top and two woofers directly underneath) coupling affect adds a few dB to your output. Typically with 4 drivers vs. 2 drivers you should only see a 3 dB increase in output. Clustering the drivers together you can see gains in the 4-5 dB neighborhood. The reason for this is the air inbetween the drivers tends to get excited as well, which accounts for the increase in output. The increase in output also brings with it increased bottom end because instead of 4 12's you now have slightly more air being excited by the cluster of drivers and you end up with more bottom-end output by more air being excited than what 4 12's would typically do.
However, you get a little bit of coupling affect even if they're side-by-side. You won't see the extra 1-2 dB on top of the 3 dB from doubling your surface area when you have every driver next to each other like you will with four drivers clustered on top of each other, but you will see a tad more than expected. The major benefit no matter how you orient the drivers is low-end output. The low-end is always more solid, louder, and more controlled. Remember that every time you double your surface area that each driver has to work half as hard as it did before. Having to work half as hard means your drivers stay more linear (less Xmax per overall output), which means they stay more accurate.