BillFitzmaurice.info

Hello,

I'm looking into making a large AT for the back of my Ford Flex. I can go 40" wide on it and would like to do so. Would it be reasonable to run 3 10" drivers or stick to two? How does widening the box affect the tuning?
I am currently planning on using my Boston Acoustics GTA-800M amp for 800W RMS @2ohm. Be it a single 750-800W sub, two 400W subs, or 3 250-300W subs. If need be I will buy a new amp. I listen to mostly rock, metal, and EDM.

The drivers I'm looking at are automotive class but meet the requirements:
JL Audio 10W1v3-2: 11mm XMax, Fs 25.23 Hz, Vas 44.15L, Qts 0.436, 300WR/600WP $250
Alpine R2-W10D2: 20mm XMax, Fs 31Hz, Vas 18.2L, Qts 0.47, 750WR/2250WP $400 - NOTE, requires spacer on baffle as top mount depth is 5.92" if I used a 1/4" riser ring would the 20mm excursion be more of a problem?
Kicker CWR102: 17.5mm XMax, Fs 33.1Hz, Vas 26.38L, Qts 0.473, 200-400WR/800WP $136
Hertz MPS 250 S2: 16.8mm XMax, Fs 28Hz, Vas 24.5L, Qts 0.41, 500WR/1000WP $500
Cerwin Vega V102DV2: 17mm XMax, Fs 29.1Hz, Vas 39.6L, Qts 0.469, 400WR/1100WWP $130
Earthquake Sound Subzero-10: 31.75mm XMax, Fs 28.72Hz, Vas 30.67L, Qts 0.472, 750WR/1500WP $600 - something tells me the xmax alone is an issue, then I would need a 3/4" riser as the sub is 6 1/2". Is there a way to increase the chamber size?
This one doesn't meet T/S params but is intriguing: Earthquake Sound TNT-10S: 50.8mm XMax, Fs 35Hz, Vas 18.06L, Qts 0.624 (booo!) 300WR/1000WP, $107.

The width range for one driver is 15 to 20 inches, so the range for 2x10 is 30 to 40 inches. There's nothing to be gained by using a third driver. There is also nothing to be gained spending big bucks or having to make modifications using auto sound drivers that are optimized for use in a small sealed enclosure. They have massive xmax because in a small sealed box they have to. You also won't need more than 100w per driver. Most of the time you won't be exceeding 50w. Whatever you've read or experienced with direct radiating speakers doesn't apply to a horn.

Bill Fitzmaurice wrote: ↑Wed Mar 04, 2026 11:22 am The width range for one driver is 15 to 20 inches, so the range for 2x10 is 30 to 40 inches. There's nothing to be gained by using a third driver. There is also nothing to be gained spending big bucks or having to make modifications using auto sound drivers that are optimized for use in a small sealed enclosure. They have massive xmax because in a small sealed box they have to. You also won't need more than 100w per driver. Most of the time you won't be exceeding 50w. Whatever you've read or experienced with direct radiating speakers doesn't apply to a horn.

So the Dayton DCS255-4 is an ideal subwoofer. What effect does the wider box provide? I seem to recall reading that going to a wider box lowers the output frequency. Is that correct or am I mistaken?

Wider increases sensitivity at the bottom end of the horn's frequency range. It does not change the "tuning frequency".

I'd consider four eights if it pencils out. I originally planned on four eights, two in each 20" wide cab to fit between the wheel wells of my Jeep Cherokee. But, after building the first cab of two eights, I never built the second cab... it was enough output for me to not make it worth the time to build the second one. Not that I didn't want more output. Who doesn't, especially when it this clean and luscious? It just wasn't worth my time to build another one at that point. Maybe I shoulda done like you and went 40" wide right outta the gate.

No issue with two ten's. You'll be very happy. Just mention the eight inch option for the sake of options.