View Full Version : Jmac, can ya help? dont worry im not askin you to make free plans.

11-01-2004, 03:56 AM
i just wanted to know if you can check this over and tell me if its good?

internal dimensions are 17"H and 28.5"W. the port area i wanted to use was 17x4 so 68 sq inches.

Lv=68*1.84*10^8/[4*1728*(30/.159)^2]-.823*sqrt of 68

Lv=44.061. so that means Physical Lv=44.061-2= 42 inches

now i did 42-21.5(any number smaller than Lv right?)=20.5". length for second wall.
and it displaces 20.5*4.75*17/1728=.9579

the first wall is 20-4=16" lenght for first wall
and it displaces 16*4.75*17/1728=.7476

now for all displacements we get 4+.9579+.7476+.21(for the sub) and that equals 5.9155. so i need an enclosure with a gross volume of 5.9ft^3

now to figure out the depth the box will be i need to do 5.9*1728/(27*17)=22.25

and now 22.25-4(for the port width)=18.25 which is the length for the first port wall

and 42-23.75=18.25 for the second port wall. now is this right or should the 23.75 be a different number? i wouldnt think both port walls would be 18.25" . thanks

11-01-2004, 04:36 AM
sweet man. thanks. i know your loosing money teaching people but your still helpin people do this stuff by themselves and it makes them feel good that they can get something right. btw, im sure this isnt the only car audio forum that has people needing box's designed for them... ;)

11-02-2004, 03:33 AM
just built the box, installed the sub and all that good stuff. hmm, the box just doesnt have the response i was hoping for. for example, late night tip, rep your city, and get low (three songs with some really low bass) dont play very well on this box. ive checked the SSF and the crossovers, but the lows just arent there. the box is supposedly tuned to 30hz but my 12" mag with about 1300 watts of power tuned to a little more than 29hz hit those low notes with authority while the 15" xxxwith over 2k watts just wont play them, and i KNOW this sub can hit them, so its either the box or some settings. anyone wanna help me figure this one out? or maybe is a port wall too short (im still unsure about that 2nd wall) and the tuning is actually way higher than what i figured resulting in really weak lows?

11-02-2004, 01:22 PM
I just caught a mistake ...
It should be 20 instead of 16" for the displacement ... why is that? i thought you could pick any number for the length as long as its shorter than port length, then subtract the port width?

So your actual net volume = 17*27*22.25-3270.375-0.21*1728 = 6579.495 ci (3.807578125 ft^3 (I thought it was 28.5" internal, BTW ?)) it is...isnt it?

edit: oh ok i see. i did the internals, but then i forgot that my exteral width was 30 and not 28.5. so i subtraced .75x2 (mdf) from the 28.5 and got the 27". so this means my box is even smaller than we thought right? and this would bring the tuning up even more?

So your enclosure is reallly 3.8 ft^3 tuned to 30.8 Hz (approximately) ...

That being said, it should still reproduce lows with authority ... This could be caused by lost energy (flexxing, inadequate sealing, etc.) ... maybe just because you're not really sending it the amount of power you think you are ?

i dont know. the amp is a power acoustik 3000db (or whichever the one that produces 2300 watts @ 1 ohm is). so if it doesnt do 2300 i can almost guarantee it does at least 2k. either way, the lows just arent there. the upper notes, like i would say the 40's are killer. i can easily say they are louder than the mag (as it should be considering its a 12" sub with less displacement), but the lows are almost non exsistant. my friend is happy as hell with the sub, but i KNOW that there is way more output down low that is untapped as of yet.

11-02-2004, 02:06 PM
Did you make the enclosure 28.5" internally instead of 27" internally ?

If so, your net volume would be greater and your tuning would be lower ...

Net volume = 4.136 ft^3
Tuning = 29.52 Hz

It could also be the difference in acoustical properties between your vehicle and his vehicle ... Your vehicle may emphasize the lows more ... Or his may be causing cancellation at those frequencies ...
i made it 28.5 internally. so i guess its 4.1 cubes at 29hz. wtf i dont get it. i dont think its really the difference between the vehicles as they are both explorers (but yes i did think of that). hmm, i have no clue what it is. i was gonna build him another box and make it more accurate, but i mean 4.1 @ 29 was one of our first ideas to do (actually 4 @ 30 but its close enough). i guess today well play with box positioning, and more and more crossover settings. anything else i should look for?

11-02-2004, 03:10 PM
thats what driving me nuts. i will definatly check for leaks altho i did my best to make sure there was none in the beggining, it never hurts to triple, or quadruple check ;). late night tip is definatly in the band but wtf. i mean im expecting almost the same sound (just louder and deeper) since the boxes for the mag and the xxx are ( was for the mag :( ) tuned to almost exactly the same hz while also being .1ft^3 more than the reccomended box volume.