15inch sealed enclosure

[Spldecendant 10+ year member]

I picked up 4 kicker comp single coil 15's. The box I plan on putting them in is a sealed enclosure that is 40.5w,16h,32d now after speaker and brace displacement I will get about 2.5 per driver. I know a lot of 15's sealed like 1.5-2.25 sealed, but then I read kicker recommendation of 2.25 minimum and 5 cubes max why do the kickers differ so much and how will they perform being in 2.5 per driver.

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[Jeffdachef 5,000+ posts]

I picked up 4 kicker comp single coil 15's. The box I plan on putting them in is a sealed enclosure that is 40.5w,16h,32d now after speaker and brace displacement I will get about 2.5 per driver. I know a lot of 15's sealed like 1.5-2.25 sealed, but then I read kicker recommendation of 2.25 minimum and 5 cubes max why do the kickers differ so much and how will they perform being in 2.5 per driver.

2.5 to cubes sealed is normal for 15s. I personally wouldnt go any lower than that. BTW you are at 9.98 cubes BEFORE any displacement. You'll want to include subwoofer displacement and a 2nd baffle or else that box will fall apart. You are looking at 2.2 ish cubes per sub after accounting in displacement. I'd make the box a bit bigger to compensate or stuff with several pounds of polyfill. If you have some room make it into a ported box. You'll enjoy it a lot more.

 

[Spldecendant 10+ year member]

2.5 to cubes sealed is normal for 15s. I personally wouldnt go any lower than that. BTW you are at 9.98 cubes BEFORE any displacement. You'll want to include subwoofer displacement and a 2nd baffle or else that box will fall apart. You are looking at 2.2 ish cubes per sub after accounting in displacement. I'd make the box a bit bigger to compensate or stuff with several pounds of polyfill. If you have some room make it into a ported box. You'll enjoy it a lot more.

I would love to make it ported but this is max dimensions, also I will be using half inch birch with a 2 by 4 in each direction for brace all put together with pl. It will be 2.48 cubes per driver after 2 by 4 and speaker displacement.

 

[Jeffdachef 5,000+ posts]

I would love to make it ported but this is max dimensions, also I will be using half inch birch with a 2 by 4 in each direction for brace all put together with pl. It will be 2.48 cubes per driver after 2 by 4 and speaker displacement.

Even with bracing, 0.5 thickness is waaay too thin, the box will flex and you will lose output even if you line the inside with fiberglass resin. .75 is the bare minimal for any sub size above 10 inches. Especially 4 15s. If you are maxed out already you need to rely on polyfill. Build the box properly strong the first time to avoid headaches later on. 4 15s produce a lot more vibrations than you would think.

 

[Spldecendant 10+ year member]

Even with bracing, 0.5 thickness is waaay too thin, the box will flex and you will lose output even if you line the inside with fiberglass resin. .75 is the bare minimal for any sub size above 10 inches. Especially 4 15s. If you are maxed out already you need to rely on polyfill. Build the box properly strong the first time to avoid headaches later on. 4 15s produce a lot more vibrations than you would think.

I added an inch in hight making it 17 tall which makes it 10.66 with .75 birch then it is .115 per driver and then the 2 by 4 braces bring it to about 10 cubic ft after displacement. How much poly fill should I add

 

[Jeffdachef 5,000+ posts]

I added an inch in hight making it 17 tall which makes it 10.66 with .75 birch then it is .115 per driver and then the 2 by 4 braces bring it to about 10 cubic ft after displacement. How much poly fill should I add

Just shove enough to fill the box, shouldn't need too much after the added height. Make sure its far away from subwoofer vent holes and voice coils.

 

[n2audio 5,000+ posts]

Generally when a sealed box is smaller than ideal the low end rolls off a little faster and the freq. response becomes a little more peaky in the middle range of it's output - usually 50-70hz range.

The ideal volume is 4.1.

The 2.48cf box costs you about 2.3dB at 30hz and gains about 0.5dB at 70 hz. The crossover point (where the SPL is the same) is 47hz.

Effectively very little difference until you get close to 30, even then barely audible -- especially assuming some degree of cabin gain.

Polyfill wouldn't be worth the effort IMO, but if it makes you feel better go for it.

 

[germanyt 10+ year member]

I'd run 2 of those 15s in a large ported enclosure. Instead of having X amount of power on 4 subs you'll have X on 2 subs. The increase in power per driver, increased efficiency due to enclosure, and the nature of ported in general will likely be louder than the 4 sealed. Especially since you're sacrificing build quality to conserve space on a sub that already likes a large sealed enclosure.