need help building a box

[korn0310]

I'm just gettin started with puttin additional audio equip in my 97 formula I bought today. I have 2 kicker comp(8ohm) 12"s, 1 600.1 jbl amp and a 300s rockford amp. i need to come up with a box design with messurments and should i use the 300s on some highs? Please help.... korn0310@yahoo.com right now I'm most worried about building the box

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[indosia 10+ year member]

To detirmine cubic ft multiply L x W x H then divide by 1728 = cubic ft. For example: 30 x 16 x 12 = 5760 divided by 1728 = 3.33 cubic ft. if you are using 3/4 inch thick matirial you would subtract 3/4 inch from each dimension to find the internal cubic ft of a the box. Sealed boxes are small and easy to build. ported boxes are more difficult and less forgiving of minor errors. same with bandpass. larger woofers like 12s sound better in ported boxes than sealed.

 

[ss3079 5,000+ posts]

If you dont want to build a box JL Audio, MTX, and Q-Logic probably have stealth enclosures for your vehicle.

 

[vasyachkin 10+ year member]

its not true that larger drivers are better ported, but it IS true that larger BOXES are better ported than small boxes. in fact with drivers its the opposite, you're better off porting a small driver in large box and having a large driver in small box sealed.

free software abounds to model subwoofer boxes ... thats how i designed mine - that is THE way to do it, but simply following manufacturer recommendation for volume can be OK. the problem is neither manufacturer recommendation nor software can account for your cabin's size, only for the sub box itself -- this is where sometimes brains have to be used //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif haha

 

[indosia 10+ year member]

Large woofers were designed for high output and low frequency extension which makes them more suited for ported boxes. Although they are often put in small sealed boxes to fit in cars.

 

[vasyachkin 10+ year member]

ported boxes are used with drivers that otherwise have LESS bass extention and port extends it. a driver that already has deep bass does not need a help of the port - its used sealed.

bigger magnet usually means less bass extention THATS RIGHT.

larger cone usually means more bass extention.

so what should we do, use large cones and small magnets ? NOOOOO because that will require boxes the size of refrigerator. confused ?

i could suggest you read a page about all this on my little website, i doubt you can handle it though - its probably too technical for you

http://sdf1.cc/~neowall/vas/phy.htm

 

[indosia 10+ year member]

Sealed boxes are not used much outside of car audio. Most all recording studios and manufactures of home speakers use ported boxes. One 12 in a ported box = 2 12s in sealed. Except the ported will play lower with less distortion.

 

[vasyachkin 10+ year member]

its true ported boxes are popular with home speakers, precisely because they make speakers louder BUT its not true that sealed speakers are not used. in fact BEST home subwoofers (velodyne and sunfire) are sealed.

for reasons that i can explain if you want, sealed box is BEST in car environment PROVIDED THAT you have enough money to get enough drivers and enough amps to power them, and provided that your goal is sound quality, not volume.

i am using ported myself though, because some of my friends are crazy and nothing is loud enough for them.

 

[ss3079 5,000+ posts]

Originally posted by vasyachkin for reasons that i can explain if you want, sealed box is BEST in car environment

Lets hear it.

 

[vasyachkin 10+ year member]

sealed box is a second order system meaning it has 2 * 6 = 12 decibels per octave bass rolloff below "corner frequency."

ported box is a fourth order system meaning it has 4 * 6 = 24 decibels per octave rolloff below corner frequency.

corner frequency is the resonance frequency by the way.

a cabin with windows closed is also a sealed box in itself and has a 12 decibels per octave BOOST below a certain frequency determined mostly by the largest dimension of the cabin. approximately where the largest dimension of cabin is half the wavelenght of a certain frequency - that frequency is the corner frequency for cabin's boost. by matching the corner frequency of a sealed box to that of the cabin you can cancel the box's bass loss with cabin's bass gain and achieve near-flat response to almost zero hetz. on the other hand you can NOT do that with ported box because 24db per octave does not equal 12db per octave.

 

[indosia 10+ year member]

That may work in one or two hatchbacks, but not in most vehicles.

 

[vasyachkin 10+ year member]

thats the problem - bass is very cabin-dependent and cabins are different.

you will not really see a 12 db boost suddenly starting at some frequency - rather it will begin higher and more gradually, becoming steeper as it goes down the frequency but never really reaching full 12 db per octave - it will also be superimposed on various peaks and dips related to various cabin resonances ... never the less you can still use this knowledge to your advantage if are willing to think about it.

 

[indosia 10+ year member]

A ported box may have a steeper roll off but it starts at a much lower frequency. A 12 w6 for example in a ported box is - 4 db @ 30 hz. 12w6 in sealed is - 8 db @ 30hz. Most sub bass is between 30-80hz.

 

[vasyachkin 10+ year member]

true, but if there is high bass energy below ported box tuning frequency the subs can be damaged. a good sub amp or processor might have subsonic bass filtering for this purpose and a good sub if designed specifically for ported boxes will have very stiff spiders to protect it from overexcursion when unloading.

if all these requirements are met, then ported WILL be louder, that i agree with.

 

[indosia 10+ year member]

At higher volume a sealed box woofer will have more distortion because of increased xmax. A woofer in a ported box can have high output with very little cone movment. So when you turn the volume up it sounds much cleaner than sealed.