[fredk]

Posts in another thread got me to thinking about design tradeoffs to achieve an objective.

Out of curiosity, I modeled two 15" CSS SDX15 vs 1. The gain is reduced excursion (and thus distortion) and no need for something like the Rekhorn1 for a highpass filter. It also reduces the needed amp power for a given spl level. The cost is slightly more money and a lot more space.

I am curious about the reduction in power. The dual driver model requires half the power to deliver the max spl of a single driver setup. I know that you gain system efficiency as you increase box volume. I also remember reading that you gain ~6db from a second sub if co-located [driver coupling] vs 3db if not co-located.

The dual driver model gains 6db for a signle box of twice the volume. I am wondering the following:

Will co-locating the drivers in a single box give you even more gain, or will you lose some of that 6db if drivers are spaced far apart? You could build a 7' box with a driver top and bottom vs two drivers at the bottom.

Here is the excursion difference at equal volume 1,000w single vs 500w dual:

 

[fredk]

+3db sensitivity due to cutting resistance in half, meaning you get 2x more power (so 500w to 1000w)

OK, I live in the land of the electronically challenged. I'm guessing this is the same thing as, or closely related to, impedance? Hmm... So, if it was a dual voice coil driver and I wired it such that the impedance remained the same as for a single driver I would lose the extra power handling and this 3db??

The interesting part of modeling two drivers vs one was that I could get the max spl of the one driver configuration on half the power. This left me wondering if this had something to do with box size increasing, or if it was just due to the increase in cone size.

 

[fredk]

Thanks Mike. I am usually good with technical stuff, but I seem to find electrical theory a challenge. It took me a bit of suplemental reading to understand the impedance/current/voltage stuff. I'll have to work on the 14 space half space stuff another day.

 

[fredk]

While you fellas are discussing the finer points of acoustic space and mass loading, I am still pondering the application of simple electronics.

I still don't understand why the power, as measured in watts is halved when I use two drivers in the model above. I went back and re-read some basic electronics stuff. IF I understand correctly, there is a defined relationship between watts, resistance and current. As the number of drivers is doubled, given the wiring scheme WinISD assumes, the resistance is halved and current is doubled leaving the number of watts consumed for a given spl level should remain the same.

What am I missing?? :huh: