port volume Q

[maniackilla 10+ year member]

i have read over many articles and never understood the EXACT reason behind port volume. i know if u have a box at say 5 cubes and you want it tuned to 30hz. you plug some numbers into a formula and it tells you exactly how much port area you need for that box to tune it to that freq *displacement accounted for*

but is there something else? does more port area increase something? i forget what i read but it was basically something like more port area is equal to adding cone area or something. you add up cone area and port area to get some number. so a 10 with more port area could potentially be the same as a 15 with much less port area if im understanding it right.

but wouldnt adding more port area in a box change the tuning? i think thats part of the reason my new setup isnt as loud as my old when it should be louder. the old box i had had a MASSIVE amount of port area and not so much volume for the actual subs. they were in a bed box. subs facing towards the middle of the box. they didnt have too much room behind them but there was easily a 8" or so gap between the faces of the subs from the front of the box to the rear *each side of the baffle was about 6" away from the rear of the box allowing the air to come up thru the middle between the subs*.... a few feet long. would that be port area, and in addition, account for more SPL?

i know u can just compare x sub in x box with x power and yadda yadda yadda. but i would think this setup would be a little louder.

Click to read more...

 

[jellyfish420 10+ year member]

try reading this

http://forums.caraudio.com/vb/showthread.php?t=69944

 

[maniackilla 10+ year member]

i read that ... even replied to it

i think i get it .... i was thinking port volume LxWxH ..... whereas area is LxW. so u can change area by making the shape longer and wider and still have the same tuning as long as the height is shorter *keeping port volume the same* correct?

so a 30" wide port thats 1" tall and 20" deep would **** as opposed to one with the same volume but different dimensions ... say ... 10" wide, 6" tall, and 10" deep. correct? and the area of the 2nd would be greater *since height, or in my case, depth* in the second would be greater since the LxW on it is *10x6* 60sq" and the first is *30x1* 30sq"

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[maniackilla 10+ year member]

i read that ... even replied to it
i think i get it .... i was thinking port volume LxWxH ..... whereas area is LxW. so u can change area by making the shape longer and wider and still have the same tuning as long as the height is shorter *keeping port volume the same* correct?

so a 30" wide port thats 1" tall and 20" deep would **** as opposed to one with the same volume but different dimensions ... say ... 10" wide, 6" tall, and 10" deep. correct? and the area of the 2nd would be greater *since height, or in my case, depth* in the second would be greater since the LxW on it is *10x6* 60sq" and the first is *30x1* 30sq"

??????????????

? ..... 10 chars

 

[OLD_SCHOOL 10+ year member]

the more port area you have the longer a port will be for example

using a port area of 60^2 and 29 hz in a 4 cube box

(60 * 1.84x10^8)/ (4 x 1728 (29/.159)^2) - (.823 * sqrt of 60 ) = 41.6386 inche long port

same thing only this time with 180 in^2 of port area

(180 * 1.84x10^8)/ (4 x 1728 (29/.159)^2) - (.823 * sqrt of 60 ) = 144.041 inches long

so as you can see increasing port area increases port length for same tuning

to determine the amoutn of port area you need involves several things such as your listening taste whether you want more spl or more Sq your car the amount of power your using... and the amount of port area needed to keep port noise down

you can tune a box using a 4 x 12.5 inch peice of PVC in a 4 cube box to ~23 hz but the port noise would be nasty

Mat

 

[jellyfish420 10+ year member]

its not really port volume that makes a diff, it port area. like old school said, the more area you have the longer the port is gonna have to be. also the more area you have, the more air it dissplaces around tuning. the box i just built for a friend for 2-10's has a 47.25in^2 port. the subs have 50in^2 area. so around tuning the port acts as a third 10(in a way)

 

[maniackilla 10+ year member]

oggg thanks u guys. how efficient is it giving up box volume for port volume? like ... any certain method when determining a ratio of box volume to port area?

 

[OLD_SCHOOL 10+ year member]

well the best way to do it is say you need a box that 4 cubes for your subwhich liek most peopel say for example re says liek 4 cubes a for xxx 15 .. well you want the sub to see 4 cubes of air space that does not include a port

so you would say 4 cubes of air space + port + sub +braces = overall volume

thats the ideal way

but sometimes it's just not possable

for example i am doing a box for a guy right now with a XXX 18 and he has very limited space re wants 7.5 cubes

we could get 7 + port and we had to bump up his tuning alittle and use wood braces inside the box + allthread and nuts and washers all the way through the box to preserve air space... we hope it's going to sound good and do well i think it will but as you can see sometimes you just gotta make some sacrifices

worst case for him is it sounds like poo he just build s a sealed box... never know until you at least try