PDA

View Full Version : port help



mabel4life
03-14-2005, 09:10 PM
im building a box for 2 12" powerbass PB-B125D
here are the specs
50 oz. magnet dual 4 ohm vc
power handling 250 watts/ 350 watts peak
sensitivity 87 dB @ 1W/1M
FS= 29.8 HZ, QTS= 0.78, VAS= 118.9 Hz
Frequency Response 30 Hz - 1 kHz

what size should i make the ports?

joeldirt
03-14-2005, 10:00 PM
The size of the ports should be 4 inches in diameter where ever possible. The larger the port, the lower the port noise. But the length of the ports depend on how large or how small the enclosure is and what the tuning frequency you want. Let us know if you are going to put the subs in a box with individual chambers, or one large one, and what the dimensions you have to work with.

mabel4life
03-14-2005, 10:23 PM
the box will be one large one that will sit behind my back seat in the trunk. It will be around 36" long and 16" in heighth.

joeldirt
03-14-2005, 11:06 PM
the box will be one large one that will sit behind my back seat in the trunk. It will be around 36" long and 16" in heighth.

a suggestion:
36w X 24D X 16 tall outer dimensions using 3/4" MDF will give you 6.5 cu ft. which is good, now oyu can add in the bracing to reduce vibrations. Keep reinforcing until you reach a 5ft3 box lets say you want to tune the box to 32hz.........

if you were to use four 4" ports, the length would have to be 23.5 (you would have to put them side to side rather then front to back so they wont bump into back wall. ( I wouldnt suggest this design)

if you had three 4" ports, they would have to be 16 7/8" long

two 4" ports= 10 1/8 long.

http://www.audiobahninc.com/tech/Calculators/PortLengthCalc.htm
http://www.the12volt.com/caraudio/boxcalcs.asp

a slot vent 3" wide would have to be 15 13/16
4" wide would have to be 24 1/4

every one does things different, so you should have a few people putting in their input. what you decide to chose is up to you. Good luck

mabel4life
03-14-2005, 11:10 PM
would you suggest a slot vent over ports. keep in mind this will be in my trunk. thanks for the info

joeldirt
03-14-2005, 11:47 PM
would you suggest a slot vent over ports. keep in mind this will be in my trunk. thanks for the info

Even when you know, you never know.... you know? No one has all the answers, every one only holds thier own opinion. I always use round ports. I never used a slot port. Slot ports are suposed to be good to reduce port noise. I never have any problems with port noise in the round ports, because I always round over the ends. I also wrap the ports with 3/4" weather strip to help take away vibrations in the port. The round port requires PVC obviously, so if you have MDF laying arround scrap, you could probably jsut use that without having to buy PVC. it is in the trunk so asthetics aint a big issue, unless you plan on showing off your work. I think round ports look nicer thats why I always use round ones. As far as difference between the two.... as long as there isnt anything miscalculated, or assembled poorly, There really is no difference. Both things I guess slot ports may help with reinforcing the box if you think about it, that is a plus, But I flush mount the internal ends of the ports into a suport or internal brace so I can round over the edges cleanly and give suport in the box, while also reducing port vibrations. SO both have their plusses. I guess the disadvantage in my own opinion in slotted boxes is the way they look. I for some reason don't like them that much. Disadvantage of a round port may give more port noise. key word "may". take a few extra steps and it won't be noticable at all, or very little.

mabel4life
03-15-2005, 12:09 AM
thank you. your info is much appreciated.