Port Area?

[Lets Get It 10+ year member]

Do the more port area you have mean the louder its goin to get? all variables are the same

ex.

sub in a 3 cube tuned to 40 with 35 sq in of port

vs.

sub in a 3 cube tuned to 40 with 50 sq in of port

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[Lets Get It 10+ year member]

bump..

 

[skmfkr 5,000+ posts]

first one doesnt have enough port area. 16 square inches per cubic foot

 

[gsuchyta 10+ year member]

A lot more factors to count in than just port area, but typically you want 14-16 square inches per cubic foot. More would be better, but I wouldn't go over 20 square inches per cubic foot.

The more port area it does get louder, but don't get rediculous with 100 square inches of port or anything for a 3 cube box

 

[Lets Get It 10+ year member]

i know just tryin to get a general idea

 

[2000LaDe 10+ year member]

A lot more factors to count in than just port area, but typically you want 14-16 square inches per cubic foot. More would be better, but I wouldn't go over 20 square inches per cubic foot.The more port area it does get louder, but don't get rediculous with 100 square inches of port or anything for a 3 cube box

if thats the case alot of sub companies give bad recommended enclosures then because its not always 14-16 per cube. i know of a few that are less than that. like my SSi's recommend a 2.5 cube box with 25 sq in of port.

 

[Rashaddd 5,000+ posts]

Shouldn't it be based on how much air the sub is going to be moving, not how big the box is? Or do we just assume that the box is also based on how much air the sub moves, and therefore is proportionate to necessary port area?

 

[2000LaDe 10+ year member]

ive never based my box designs like that. maybe thats why im so quiet? i dunno

 

[Lets Get It 10+ year member]

so is it based on the sub or the box? i was told it was based on the box volume

 

[skmfkr 5,000+ posts]

mostly box volume, but obviously if a sub is moving 3inches peak to peak and another is only moving 1.6inches or so, then the 3inch peak to peak is gonna move more air

 

[helotaxi 5,000+ posts]

There are a ton of variables. Box volume is one. Relative tuning is another. Power applied is yet another. You can use a pretty small port if you only run a small amount of power. Flaring the port can let you use a smaller port area as well. Borderline too small and you get port noise. Much too small and the port packs and the result is a leaky sealed box. Too big and not only is the port insanely long, but it fails to load the box correctly and can either act like a transmission line or like an open baffle.

 

[Immacomputer 10+ year member]

Shouldn't it be based on how much air the sub is going to be moving, not how big the box is? Or do we just assume that the box is also based on how much air the sub moves, and therefore is proportionate to necessary port area?

You are thinking correctly; everybody who recommends the 14-16/ft^3 is just spouting out bullshit spawned from DD because it works with their subs for their recommended enclosures. When I say bullshit, I mean coming from people who say this for any speaker/enclosure combination. When DD recommends it, they recommend certain subs for that specific enclosure. They are taking the two as a system and to simplify it for people who want a slightly odd volume but they don't want those people to **** up the port area calculation. Dumb everything down for people and you will get them to do what you want them to. Take a look at all these "truths" associated with DD like the whole "DD subs must be tuned to 40hz" and the like.

Box size will affect the air velocity but it is NOT the end all be all factor when deciding port area. Box tuning, driver excursion, applied power, driver/enclosure alignment, driver motor strength, and cone area will all be larger and more important factors than enclosure volume.

Saying that, it is better to have more port area than too little but you can still suffer going too large and creating an air mass that a small motored or underpowered driver can't move. For example, I built a 5 cubic foot enclosure and only used 36in^2 of port. Oh noes! That port must be way too small and have horrible port noise because it only uses 7.2 in^2 of port per ft^3 right?!?!? Wrong. It sounded excellent and there was no port noise at all at full tilt right at or below tuning.

So do take it with a grain of salt when people swear that 14-16in^2 is the only way to go. That much is not always needed and it really depends from application to application.

 

[gsuchyta 10+ year member]

Yes a lot of factors to consider when calculating port area

 

[tcguy85 10+ year member]

i'm using 7 sq inches of port on my box.... no port noise here.

 

[helotaxi 5,000+ posts]

^^^ 3" PVC I assume?