i need to make a dual ported box for my 2 12" infinity kappa 120.3se's. infinity recomends 2 cubic feet per sub... what i need is a formula to find the dimentions of the box. i've found plenty of sites telling me how to glue pieces of wood togather...
-DINGALING
Replies (3)
Swez on 08/7/2003 20:56:48
Simple deal... you have to run some numbers on the internal box dimensiions to figure out the internal size, then add wood thickness and port area to same for total external dimensions.
Here's the basics:
Internal dimensions/sub:
12" H x 12" D x 24" W = 3,456 cubic inches
3,456 /1728 = 2.0 cf internal then addwood thickness of each panel... typically 0.75" x 2 for sides, front & back
External dimensions/sub:
14.5 H x 14.5 D x 24 W = 5,046/1728 = 2.9 cf
Then have to calculate the port area inside the box and if you really want to be precise... a typical 12" sub has a displacement value of ~0.07cf
So roughly, you are looking at ~6.3 cf externally, to get a 2.0 cf ported enclosure. Be sure to add a center divider panel for strength and regidity and add that to that to the overall internal dimensions as well.
Let me see if I can give you something more concrete:
http://www.eatel.net/~amptech/elecdisc/spboxnew2.htm
A picture is worth many words...
Swez
DINGALING on 08/7/2003 21:28:29
k. thanks!! the calculator on the site was a massive help! just two more questions before i can go to home depot.
1. what guage wire should i use from the amp to the terminal cups on the box, and what guage from the terminal cups to the woofer, itself? i've heard 18 from many sites, but it does not clearly state whether these wires are for subs or regular speakers. i assume this would change the guage of the wire, considering that subs will be fed more power at once...
2. i know i'll be putting a massively awesome seal around anything that could come even close to leaking any air, so would you recomend using that polifill wool stuff? from what i understand, people use it to be able to make a smaller box, but still have the performance of a larger box...
-DINGALING
Swez on 08/8/2003 05:47:35
Wire gage depends on the power you are running to your subs. I generally use #12 gage wire for subs and #16 for interior speaks.
If you are running very high watts (>1000 W) to your subs, drop to #10.
As for sealing the sub enclosure, silicone (RTV) works great. Just be sure to let it cure over night before you install the subs.
About polyfill, yes... use roughly 1.0 lbs per sub chamber for a 12" sub. You can get this at WalMart in the fabric section or any good fabric store. I prefer the sheets (for quilts) about 1" thick or so
as opposed to the loose fill used in pillows etc.
Polyfill helps dampen the rear sound waves off the back of a sub and it slows the return wave reflections to a degree that the box will appear to be 5-10% larger.
FYI: A box does not have to be perfect on internal dimensions. You have fudge factor of +/- 10% internal air space recommended and the sub will still sound very good.
Finally, when tuning your ports, try to target your daily driver ports for ~35 Hz. Any signals below 35 will cause the sub excess cone movement (X-max) at even half the RMS rated power and high distortion values as well. Using a sub sonic filter is recommended for ported systems to prevent cone damage. Some amps already have them or you can by inexpensive add on filters as well.
Swez
-DINGALING
Replies (3)
Swez on 08/7/2003 20:56:48
Simple deal... you have to run some numbers on the internal box dimensiions to figure out the internal size, then add wood thickness and port area to same for total external dimensions.
Here's the basics:
Internal dimensions/sub:
12" H x 12" D x 24" W = 3,456 cubic inches
3,456 /1728 = 2.0 cf internal then addwood thickness of each panel... typically 0.75" x 2 for sides, front & back
External dimensions/sub:
14.5 H x 14.5 D x 24 W = 5,046/1728 = 2.9 cf
Then have to calculate the port area inside the box and if you really want to be precise... a typical 12" sub has a displacement value of ~0.07cf
So roughly, you are looking at ~6.3 cf externally, to get a 2.0 cf ported enclosure. Be sure to add a center divider panel for strength and regidity and add that to that to the overall internal dimensions as well.
Let me see if I can give you something more concrete:
http://www.eatel.net/~amptech/elecdisc/spboxnew2.htm
A picture is worth many words...
Swez
DINGALING on 08/7/2003 21:28:29
k. thanks!! the calculator on the site was a massive help! just two more questions before i can go to home depot.
1. what guage wire should i use from the amp to the terminal cups on the box, and what guage from the terminal cups to the woofer, itself? i've heard 18 from many sites, but it does not clearly state whether these wires are for subs or regular speakers. i assume this would change the guage of the wire, considering that subs will be fed more power at once...
2. i know i'll be putting a massively awesome seal around anything that could come even close to leaking any air, so would you recomend using that polifill wool stuff? from what i understand, people use it to be able to make a smaller box, but still have the performance of a larger box...
-DINGALING
Swez on 08/8/2003 05:47:35
Wire gage depends on the power you are running to your subs. I generally use #12 gage wire for subs and #16 for interior speaks.
If you are running very high watts (>1000 W) to your subs, drop to #10.
As for sealing the sub enclosure, silicone (RTV) works great. Just be sure to let it cure over night before you install the subs.
About polyfill, yes... use roughly 1.0 lbs per sub chamber for a 12" sub. You can get this at WalMart in the fabric section or any good fabric store. I prefer the sheets (for quilts) about 1" thick or so
as opposed to the loose fill used in pillows etc.
Polyfill helps dampen the rear sound waves off the back of a sub and it slows the return wave reflections to a degree that the box will appear to be 5-10% larger.
FYI: A box does not have to be perfect on internal dimensions. You have fudge factor of +/- 10% internal air space recommended and the sub will still sound very good.
Finally, when tuning your ports, try to target your daily driver ports for ~35 Hz. Any signals below 35 will cause the sub excess cone movement (X-max) at even half the RMS rated power and high distortion values as well. Using a sub sonic filter is recommended for ported systems to prevent cone damage. Some amps already have them or you can by inexpensive add on filters as well.
Swez
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