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DIY sub


NBPK402
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I am going to be building a Home Theater out of our 2 car garage soon, and I am thinking of building a new sub. This is what I am thinking of:

1. Build out the garage wall 5' deeper, and 17' wide with a 8' ceiling (garage door will become a screen wall with my 3 La Scalas and 2 Heresy HIPs behind a AT screen).

2: The garage and new room will be double wall constructed with 1 layer of OSB, 2-3 layers of sheet rock with Green Glue. The ceiling is currently 9' and will have about a 6" thick additional ceiling due to 3 layers of sheet rock and Green Glue.

What I am thinking of doing is using the whole addition room for a IB type sub but make the exit point of the box into a horn. I would build boxes that would enclose the 5 front speakers and seal them into the front wall. The front wall would only have a hole in it for the sub/horn to exit the room, and the AT screen would conceal the whole affair. I currently have the PSA Triax sub and it is great. I figure when I move to the larger room I will need more subs and I would like to have a sub that will give me the low frequency performance of the Triax (or better) without using a 4000w continuous 8000w peak amp (x2 if I have 2). I would like to be able to do it with a single amp of under 500w if that is possible.

I was looking at building dual Gjallarhorns, but I am thinking that this might be easier to build and give me the same performance.

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The space behind the screen will be 4-5' deep, 8' tall, and 17' wide. In the space though will be 3 La Scalas and 2 Heresy HIPs. If I do the IB route I will seal off the screen wall and build boxes for the front 5 speakers to sit in.

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To determine rear space needed, take the Vas of one driver, multiply by the number of drivers (typically 4) and multiply that by 10. Using 18" Ficaraudio drivers for example, I come up with 538 cu/ft. It seems that the 680 cubic ft that you'll have available will work just fine.

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If I calculated correctly... I would have about 60 cubic feet less after accounting for the speaker boxes. So that would still be enough... Correct?

How do I figure out how much power it would take to hit 115db @10-15hz?

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600 cubic ft would be fine.

IB sub drivers reach their mechanical limits WAY before they reach their thermal limits so all you can do is look at the driver specs and see how much wattage you need to drive them. How big will the finished room be? Will it be sealed or have openings?

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600 cubic ft would be fine.

IB sub drivers reach their mechanical limits WAY before they reach their thermal limits so all you can do is look at the driver specs and see how much wattage you need to drive them. How big will the finished room be? Will it be sealed or have openings?

Both rooms will be sealed... The Theater room will be around 14' wide x 20' long with a 8' ceiling. I have not finalized the dimensions as of yet... We will be building a double 2x4 wall within the 2 car garage.

Edited by ellisr63
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A 4 driver IB in that space will be plenty, possibly scary. For reference, my living room is 20 x 21. The walls end at 8' and taper up to 12 in the center'. There are 3 openings in the room. I've hit 110 dB @ 10Hz and 120 dB @ 20 Hz measured 14' from the drivers.

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I went and re measured and I came up with these dimensions 16' wide, 23' 4" long, and 9' ceiling... The ceiling will end up at 8' due to the new ceiling and sub floor. The The room will end up at approximately 22' 10" long, 15' wide after walls are included into the equation.... Which will put it at close to 3000cf.

The area behind the screen will be 19' wide, 5' deep, and 8' tall... So we will have around 700cf after accounting for the speaker boxes. :)

Edited by ellisr63
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A 4 driver IB in that space will be plenty, possibly scary. For reference, my living room is 20 x 21. The walls end at 8' and taper up to 12 in the center'. There are 3 openings in the room. I've hit 110 dB @ 10Hz and 120 dB @ 20 Hz measured 14' from the drivers.

How much power did you need for your subs to hit that level?

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I am confused now... I saw this guy on another forum running 8 FiCar IB3-18 woofers with a 300cf room. Here is his graph.

http://s191.photobucket.com/user/spinefixr/media/c-weightwithnocalfiles.jpg.html

What is the advantage to running a bigger room behind the drivers... Efficiency?

After you hit the 10 x Vas threshold, there's no advantage. You just want to be sure the drivers are in free air.

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I am confused now... I saw this guy on another forum running 8 FiCar IB3-18 woofers with a 300cf room. Here is his graph.

http://s191.photobucket.com/user/spinefixr/media/c-weightwithnocalfiles.jpg.html

What is the advantage to running a bigger room behind the drivers... Efficiency?

After you hit the 10 x Vas threshold, there's no advantage. You just want to be sure the drivers are in free air.

But the FiCar IB3-18 woofers have a VAS of 381 for one driver... Am I missing something here?

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