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Discussion Starter · #1 ·
Is 1.5 cf ported too small for a Shiva in a car?

I've been running the idea through my head of putting 2 Shivas in my car. My amp had to be sent back for repairs, so my Revo 10 is also out and I'm getting to upgrade bug.
I designed a box that fits flush in my trunk that will be 3.194 cubic feet and I'm going to port it around 30-32 hz. I have a little 1200 watt amp already.
 

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Discussion Starter · #3 ·
Thank you, but I read that already :( I see all the recommendations, but I don't see anything about what I'm after.
 

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Thank you, but I read that already :( I see all the recommendations, but I don't see anything about what I'm after.

Sure.... you can port it and run it with a high tune. You get a huge hump in the response which is not unusual for car audio ported designs. If that is what you are after, go for it.

Kevin Haskins
Exodus Audio
 

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Discussion Starter · #6 ·
Sure.... you can port it and run it with a high tune. You get a huge hump in the response which is not unusual for car audio ported designs. If that is what you are after, go for it.

Kevin Haskins
Exodus Audio
Yeah that is a low tune for cars actually haha. Most guys actually tune higher in the 30s. Supposedly the cabin gain makes up for sub 30hz stuff. I just didn't know if the subs would be starving in 1.5 cf ported. That huge hump is what gives us car guys 140+ db :)

How much port area will you be using?
The box is like a funky part triangle design which really limited my ports. I'm going to go with two 2.5" ports that will be 7" long, leaving about 2" behind each port. I'm hoping I don't get any chuffing with the 2.5" ports. I could go with a 3" or 4" port but I don't think I have the length for it (that's what she said).
 

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With 1200 watts you'll need a hi pass filter at about 18 hz so the subs don't bottom out. With two 2.5 inch ports 7" long the port air speed is 80 m/s, that's way beyond port chuffing and into freight train territory. You need to rethink this. Two 2.5" ports have less than 10 square inches of surface area. You need at least 25 square inches of surafce area for this setup, more would be better.
 

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Discussion Starter · #8 ·
Well poo. If I used larger round ports they would end up being too long to fit. The only way I can increase port area is going with a T shaped slot port, which would be a pain in the butt to build. :(

I guess I could do the hair trick anyway, right? :p
 

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Just keep in mind that most car audio ported designs would not be considered acceptable to our general rules of thumb concerning port size. There is just no way to have a large diameter port + small box and get a useful tuning frequency. So most of the ported car audio designs you see are probably port limited.

There is nothing wrong with that if you know it going into the situation. You build with the largest port you can manage, and accept the port limitations. It will chuff and compress at maximum port output and that is lower than what the driver can provide but many designs still take that tradeoff. We do the same thing with the really large drivers and ports. An 8" flared port has tons of output before the port becomes and issue so even though the model shows high port velocity at maximum output, you ignore it knowing that the building will be quaking and stuff falling off the walls well before the port starts chuffing.

Kevin Haskins
Exodus Audio
 

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Discussion Starter · #11 ·
At that size. I'd consider sealing the sub. You get a lower roll-off and no ports to worry about.
I don't want to do another sealed system. I went from sealed to ported, back to sealed, back to ported, back to sealed lol. These were all different builds, btw. I guess going ported fits my pattern?

Just keep in mind that most car audio ported designs would not be considered acceptable to our general rules of thumb concerning port size. There is just no way to have a large diameter port + small box and get a useful tuning frequency. So most of the ported car audio designs you see are probably port limited.

There is nothing wrong with that if you know it going into the situation. You build with the largest port you can manage, and accept the port limitations. It will chuff and compress at maximum port output and that is lower than what the driver can provide but many designs still take that tradeoff. We do the same thing with the really large drivers and ports. An 8" flared port has tons of output before the port becomes and issue so even though the model shows high port velocity at maximum output, you ignore it knowing that the building will be quaking and stuff falling off the walls well before the port starts chuffing.

Kevin Haskins
Exodus Audio
That is very true. My last ported box was 3.4 cF tuned to 32hz with a little 4x4" wide, 7" long square port. Pretty small port, but that system sounded amazing. If that port ever chuffed, I didn't notice it over the vibration in my eye sockets. :p That box, though, was in a Firebird, which is a hatchback and is almost like a mobile horn haha. The cabin gain in that car was just crazy.

I would just forget the Shiva and go with a sub that is designed to be in a small ported box, but I've lusted after XBL^2 since the Brahma days and I really want it in my car! I'll have to start the build when I go on vacation next week.

Thanks for the replies!
 

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Discussion Starter · #13 ·
That box had a couple different setups. It first had two 12" Ascendant Audio Assassins. I believe AA makes Epik subwoofers don't they? They're also "partners" or something with Fi.

I also had two 12" TC sounds db-500s in that box too. The db-500s could have used a bigger box and a little more power, but that box was the biggest box possible that could fit in my trunk.

Here is a pic of the db-500s with the old amps and before I carpeted the box:
http://www.fquick.com/garages/viewgallery.php?action=viewimg&id=29598

I'm sure it could have been done better, but that was the first ported box I designed and built myself :)
 
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