I'm getting in soooo much deeper than I had planned . . . ;-)
Keep your ears and your mind open.

Passive xover components and impedance will also change, so this needs to be taken into consideration also.

Eat Mo' Hot Sauce,
crazychile

Dan

Sounds like this ones gonna be loud.

I am not the best person to get into this, but in case noboby brings this up I want to mention the "array" issue. With 15" drivers I think you will have to cross over below 800 Hz. The difference in distance between the two drivers off axis can do nasty things at higher frequencies due to interference. So if you had them alligned vertically the sound of the mids would get nasty if you stand up (or if you sit close). However, if your design permits the low crossover you will get more juice from your amp from a 4 ohm load, and some increase in sensitivity.

I think that your observation about reduced excursion is astute, but I can tell you in my setup there just isn't any meaningful excursion at any volume most people will allow. If you need high output though, more drivers is better than overpowering fewer drivers. You'll get less power compression and less distortion.

You may want to search the archives here for posts on 2.5 way systems. I find them fascinating.(2 woofs, 1 crossed at say 1.6 KHz, and one crossed say 500 Hz. If you use woofs with louder midrange or are going to put them far away from walls, this works well.)

Thomas

Questions:

Do you already have a driver?

Do you have a target box size?

Will it be used with a solid state amp?

I would bet there is a Pi with your name on it. Most of the 15" Pi's could do well as a sub. Just delete the High frequency horn and crosover.

JBL = pricy but real good. downside is not so much deep bass, but what you get will be as good as it gets.

Eminence = cheaper, deeper and amazing sound for the money.

Then what size box can you handle, and hey maybe a cornerhorn sub pair to get the best bass and keep the horn theme going. Now im getting carried away. (one can always dream/maybe I'll build some next year)

Thomas

You can get 6 dB (= 4 times) extra output by using two instead of one bass unit. 3 db from the extra sensitivity gained from better acoustic loading of the units, + 3 dB from the doubled power handling - in all, 6 dB.

But why not build two? Then you have a stereo pair & will then be able to go higher in crossover frequency if necessary...