View Full Version : multi subs in ported chamber
hi, i have often heard that when you put multiple subs in a ported chamber then you need to double the volume of the box for each extra sub. say if one sub needs 1.5 in ported to opperate then two would need 3. they are in the same air space. and i have also heard that no extra is needed. also have heard that just add for the displacement of the subs. for air space. for ports i have heard about the same thing. two subs need two ports. two subs needs one port double in size for one sub. can someone help me on this. what i want to know and do is run two 12's in a ported box with shared air space. the sub requires 1.25 to 1.75 for ported and a 3"x7.5" round port. i want two in this box. please advise
03-27-2007, 05:59 PM
if u have 2 subs u need to double the air space.. in most cases... and in turn need a bigger port...
what subs you got that would help us a lot and don't listen to what the specs said... they usually give u a box too small and a tune it too high...
i am running audiobahn 12". aw1200q. the high excursion models. the ones that take a nonimal 700 watts and a max of 1400 watts. the amp is a soundstorm f2800. currently i am running it 2ohm mono to one 12 in a ported box. the box is just a tad over 1 qube and the port is 3x9 square and 7.5 inches deep. the thing pounds like crazy for one. but the problem is my amp is pulling too much current and even with 2 - 1fared caps the electrical system in my car is suffering. the sub is a dual voice coil dual 4ohm. i want to amp the mids and highs but with the current electrical draw i can't do that. any more suggestions on both problems will be appreciated.
by the way i drive a 2003 kis spectra. so trunk space is at a premium and electrical output is small.
03-28-2007, 11:55 AM
tYou definitely have to double the airspace when adding another sub. The port size will change but if you choose to use a common enclosure it may not be double the size. What you should do is call around to some local shops and see if they have a box building program. When you find one ask if they have the specs on the subs that you are using. If they don't you can get the specs on the woofers in the owners manual or find them online with the manufacturer. You will need the theile small parameters so they can tell the program what your subs specs are and can predict what the box design output will be. If you don't want to mess with that and like the way your current box sounds just build a box with the same airspace on each side of a divider and use the same size port that your old box has on each side of the divider. Make sure that your port is at least one thickness of the wood that you are using away from the sides and back of the box.
As for your "current" situation the power caps don't give you any extra current they just give your amp power faster and help to keep from beating the crap out of your alternator. Your options as i see it to fix the problem is to first upgrade the battery. I only use Optima batteries( the ones that look like a 6 pack). They are about 200 bucks but they work. Every battery that you add puts an extra 10 amp load on your alternator. I would just replace the stock battery if you are still using it with something better. Go ahead and keep using the power caps though.
If you still don't have enough juice you can try to add a second MATCHING battery. If you still have a hunger for power you may have to replace the alternator with a high output one. If there is an alternator/starter shop around they may be able to beef your stock one up for alot less than an out of the box high output powerplant($400-700). Hope i have helped. Power supply is just expensive but if you want everything to put out what it can you have to feed it the juice.
03-28-2007, 01:25 PM
keep it simple....double the box size and add another 3" port.
as for you power issue...caps are worthless...talk to anyone in high end car audio....sell them and get a high output alt. or get yours rebuilt. it's always best to fix the problem at the source....
03-28-2007, 01:27 PM
Make sure that your port is at least one thickness of the wood that you are using away from the sides and back of the box.
umm... you mean the diameter (or width) of the port...not the thickness of the wood.
03-28-2007, 09:37 PM
^^ yeap, it would be good to double both, as you add net volume to the box you should also add volume to the port.
03-29-2007, 08:07 AM
if you double box volume, you double port AREA....not volume. if you simply added volume by adding length, it would just change the tuning and still not allow proper air flow. double the area and then add the length (volume) according to the desired tuning freq.
03-29-2007, 08:57 AM
lol, I guess to help him out you are correct, but what do you think happen when you increase the width or diameter of a port?? it increases the AREA and net volume displayed by the port, you can't just have one... this is what I was referring to.
thanks for all the help. most of my concerns and questions were answered. with one exception. when sharing one chamber for 2 subs, one has to be wired in reverse polarity right. that is one thing that everybody has said. i can do all that and have a good idea what to do i just want some advice and talk from people that have done it before. and one final question. besides not having to take in account for sub displacement, what is the advantage of inverting the subs on the enclosure with magnet out. i have done this and cant really tell a difference. thanks for the help again.
03-30-2007, 01:02 AM
No, don't reverse the polarity of one. It would be counterproductive. Think of one sub going in while the other is going out. For an easy free program to calculate box tuning etc., download winisd pro. I don't know the site offhand, but search for it or linear team IIRC. As far as inverting, it doesn't affect the sound, other than the subs basket not displacing any air like you said (it actually adds airspace because of the shape of the cone/dustcap). Looks is the only advantage, and I liked having the huge basket/motor structure as a protective grill cause grills don't get much stronger than that;)
03-30-2007, 01:07 AM
Oh and like most said, if you add another sub, you'll want to double the area inside the box, and increase the port area to keep the port velocity reasonable (keep in mind that port area, enclosure volume, and port length all have an effect on the tuning, so when you change one you'll have to change at least one of the others to keep the same tuning)