Why is the box size needed so different for these two woofers?

[warnerwh]

I just ran the numbers for the Dayton Hi Fi 12". With a sealed box only 1.5 cubic feet you get an f3 of 38hz. Optimal box size was 1.7 or 1.8 without looking. In either case very small.

I'm in the middle of building a sub for the Dayton Hi Fi 15". The box I'm building is 8.5 cu ft. The f3 is 30hz.

I'm thinking I may have been better off building a sub with 2 twelves instead of the one 15. My box would have been far smaller and sensitivity would have been higher.

If my calculations are wrong please correct me. It seems I may have stumbled on a valuable lesson in subwoofer designs.

While I'm at it are there any other advantages of running two drivers as opposed to one?

Thank You

[peterS]

assuming you arnt mandated by an amps stability two 12" in separate boxes will be small of course but allow better placement too (think stereo)
seems the 15" has a very complient suspension- been a while since I've kept up on the ins and outs of t/s but the large Vas means a loose (complient) suspension- if im not mistaken

what amp are you using
what is your budget

[warnerwh]

I'm using an extra channel on a Earthquake Cinenova Grande 3 amp for a sub I'm in the middle of building. I also have another sub so will have two when this one is completed.

Thanks for the info on the suspension. I don't know much about drivers but thought that the same series albeit a different size wouldn't vary so much in the volume required in the cabinet.

Knowing what I know now I would have built a sub using 2 12" HiFi drivers instead. Mainly because it would be alot smaller. I'd also expect a higher output capability.

Live and learn

[Mazeroth]

Well your 15" setup is 8 hz. lower at the f3 point, which is a LOT for a sealed enclosure. Lower the enclosure size until it yields an f3 of 38 hz. like the 12" HiFi and see what size the enclosure is. Then you'll have a closer apples to apples comparison. :T

[Dennis H]

Theoretical F3 calcs don't really mean much with sealed boxes. All sealed boxes need EQ unless you make them infinitely big, i.e. an IB. So, you just pick a driver you like, pick a box size you can live with (bigger is better than smaller, everything else being equal), EQ it flat in the room and provide enough amp power to drive it to Xmax at the lowest frequency you want to play.