The port area issue

[amangujral06 0]

Hi there, after trying to build my own ported box , with certain limitations, i came to ask myself that why do we need 12-16 sq inches of port are per cufeet ?

The answer was to avoid air shuffing.

BUT !

If a box is 3cufeet , the good book says to use minimum of 36 sq inches(minimum) port area for it, now if we use the same sub to play in a 5 cu feet box, port area increases to 12X5 = 60sq niches (minimum)

Now i am guessing that the subwoofer will not miraculously start to push more air ,and that we may have to increase the port area to avoid air shuffing. The sub should displace the same amount of air in a 3 cu feet box or 5 cu ft box.

So , why not use 36 sq inches port area also for a 5cufeet box? ( you may take FiQ 15" into consideration)

Thanks

Edited November 28, 2010 by aman gujral

[Hell-Razor 0]

Good question, Ill be watching and waiting to figure out why...

[NB50 206]

You kinda answered your own question. The whole port area and box volume are guidelines. Port area is determined by what speakers you are using.

[amangujral06 0]

You kinda answered your own question. The whole port area and box volume are guidelines. Port area is determined by what speakers you are using.

I totally agree that these are the guidelines, BUT, can 36 Sq inches port area on 5 Cu feet box drastically changes the performance Vs 60sq nch port area ? Again when we know that the sub is going to displace the same voulume of air !

Its a big question for me as this factor is affection my box design By using a lot of volume on port itself ! Any guys out there , who had already experimented with the same ?

Edited November 28, 2010 by aman gujral

[luckyishere 0]

Good Question !! The answer is gonna help me too as i am also trying to build an enclosure for my Fi Q's

[///M5 2,833]

ALL "rules of thumb" suck. None of them are right.

However, that does not mean that you won't need more port area. The larger the box, the more output at low frequencies for a specific power and along with it more air flowing through the port. There is a HUGE difference in air velocity (same port size) when you make a box larger. If you had ever spent even 2 seconds in a box modeling program you'd see that first hand.

[Argent Audio 54]

ALL "rules of thumb" suck. None of them are right.

However, that does not mean that you won't need more port area. The larger the box, the more output at low frequencies for a specific power and along with it more air flowing through the port. There is a HUGE difference in air velocity (same port size) when you make a box larger. If you had ever spent even 2 seconds in a box modeling program you'd see that first hand.

M5 is so very correct!

This is what I use WinISD for modeling port velocity. I don't like the program for much else.

Andrew

[low_bass_makker 0]

Good Question !! The answer is gonna help me too as i am also trying to build an enclosure for my Fi Q's

Like I mentioning to you yesterday the larger the box more amount of air will displace. Hence the larger port area !!!

[95Honda 486]

The port area versus enclosure volume is only meant to keep idiots from using a 1" I.D. vent with a high-stroke 18" driver..... Other than that, it is pretty useless....