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Good to know it can be done, I'll try to source some real Baltic birch and add bracing to the design, if it works well I may have a well drafted set of plans to share when I'm done :)

No prob.

When you are working on your design, make sure you use enough port area. It can be tricky to do with these smaller boxes. For a SA-8 on 750 watts I'd use no less than 15 sq in per sub.

"Nothing prevents people from knowing the truth more than the belief they already know it."
"Making bass is easy, making music is the hard part."

Builds:

U7qkMTL.jpg  LgPgE9w.jpg  Od2G3u1.jpg  xMyLoO1.jpg  9pAlXUK.jpg

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No prob.

When you are working on your design, make sure you use enough port area. It can be tricky to do with these smaller boxes. For a SA-8 on 750 watts I'd use no less than 15 sq in per sub.

O I was going by diysubwoofers.org and I though I wanted a 3 inch diameter port about 14 cm long if I recall correctly.

15 sq in per sub could be like having 4 separate 4" diameter ports or one 8" diameter port then, which is also doable. I like the aeroport idea because it will take less volume than a slot port. 15sqin per sub sounds excessive to me though, but if you are certain it will work I'll go for it.

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Yeah with a single 3" port you would pretty much have a sealed box, whether you want to or not.

While 15 sq in per sub may sound like a lot, to put it in perspective Sundown recommends 8-12 sq in for their E-8 sub, and thats and 300 watt RMS sub. You are going to be (potentially) running 2.5 times as much power. At tuning all of the output comes from that port, you don't want to be choking it off.

I think your idea of a single 8" port would be great.

Here is a calculator that you can use to give you an idea of proper port size: http://www.carstereo.com/help/Articles.cfm?id=31

With high Xmax subs (18mm or greater) that calculator tends to error on the high side, but its a starting point at least.

"Nothing prevents people from knowing the truth more than the belief they already know it."
"Making bass is easy, making music is the hard part."

Builds:

U7qkMTL.jpg  LgPgE9w.jpg  Od2G3u1.jpg  xMyLoO1.jpg  9pAlXUK.jpg

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What frequency are you tuning to?

91 C350 Centurion conversion ( Four Door One Ton Bronco)

250A Alternator (Second Alternator Coming Soon)

G65 AGM Up Front  / Two G31 AGM in Back

Pioneer 80PRS

CT Sounds AT125.2 / CT Sounds 6.5 Strato Pro component Front Stage

CT Sounds AT125.2 / Lanzar Pro 8" coax w/compression horn tweeter Rear Fill

FSD 5000D 1/2 ohm (SoundQubed 7k Coming Soon)

Two HDS315 Four Qubes Each 34hz (Two HDC3.118 and New Box Coming Soon)

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I just checked the link. It calculated I need an 8 inch port at 49 inches length. That's 1.5 ft^3 of my 2.5 available volume!!! How do I get around this?

Well unfortunately there really no way to "get around" it without paying a performance penalty somehow. Welcome to the difficult part of car audio enclosure design :-)

Whenever you are dealing with a situation where your space is limited, which is most of the time with car audio, the trick is figuring out what design compromises can be made that will have the least negative impact on performance. No matter what you do, performance is going to have to be sacrificed in some way, we just find to find the best way.

One thing you can do is decrease port area. This won't hurt performance at all at low volume, but at high volume it will eat your output for lunch. It can be quite detrimental.

Another thing you can do is reduce box volume, this will decrease output around tuning at all volume levels, but it will do so consistently, unlike reducing port area.

You can also tune higher, higher tunings require shorter ports, so you will save some space that way, also with higher tunings you can get away with smaller box sizes. The price you pay is decrease low frequency performance. Depending on the type of music you listen to tuning higher may or may not be a path you want to go down.

Lastly, you can reduce cone area, by either running smaller subs or running less subs. In your case dropping down to three SA-8s may be something to consider.

"Nothing prevents people from knowing the truth more than the belief they already know it."
"Making bass is easy, making music is the hard part."

Builds:

U7qkMTL.jpg  LgPgE9w.jpg  Od2G3u1.jpg  xMyLoO1.jpg  9pAlXUK.jpg

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I just checked the link. It calculated I need an 8 inch port at 49 inches length. That's 1.5 ft^3 of my 2.5 available volume!!! How do I get around this?

You have found out why 8inch subwoofers are useless in cars, even though they exist, they shouldn't.

Sealed enclosure (1 12inch) or 10inch ported are probably your only good options with the space you have available.

Anything else will not be efficient.

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Thinking is the root of all problems...

You ALWAYS get what you pay for.

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Hm you guys gave me lots to think about. Sounds like all of these setups could be adjusted for low volume SQ but it seems I become more concerned about spl. I'm not necessarily concerned about wattage efficiency or dollar efficiency as much as SPL to air space efficiency.

So maybe if I make a more specific question. If I were to focus on 35hz SPL, still with 2.5 ft^3 and a ported enclosure with proper porting. Should I shoot for a down firing sa-10" or sa-12. Or 2 x8 subs or 3 sa-8 subs (I'm assuming 3 sa-8 will be louder than 4 if I get the porting and airspace correct so I am abandoning the 4 sa-8 config if that is correct).

I'm open to other brands, I'm just naming sundown sub's because its where I did most of my reading. (8 inch sub's have no depth restrictions but 10's or 12's need to be in the ball park of 6" mounting depth and magnet profile starts to matter)

So far someone suggested ascension audio havoc subs, I think the 10 could fit but I haven't had a chance to go through the specs yet and fit it to my model to check clearances.

Edit: just looked up specs on more subs

I checked out most of the sub's on SSA and I'm thinking I could fit one of the following with proper space and porting.

I could fit ascendant audio's havoc 10 or possibly 12.

I could also possibly fit an icon 12 or 10

And also an xcon 10.

A DC lvl 4 10 is also possible.

Sundown sa 10 is possible.

Edited by somebodyelse
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OK I think I'm now officially torn between one havoc 12 or 3 sa-8's, after correct porting both boxes would have near 2 ft^3 of air with 6" or 7" diameter porting tuned 30-35hz (35hz for the 8" subs). 8s would be forward facing and the 12 would be down firing with about 1.5 inch off the carpet. What would flex the roof better?

Edited by somebodyelse
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we don't know. you'd have to build it and find out for yourself. perfect world, the most cone area in the closest to ideal box out of those two options would "flex the roof better".

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