Bronze Member
Username: Snarl2004

Post Number: 20
Registered: Dec-06
what is the general rule for tuning a box. I want to build a vented box. i want it 2.5 cubic feet and the vent to be around 50 cubic inches. i was wonder how to tune it so it will be 25-28hz.thanks

Gold Member
Username: Mr_kebo

Albertville, Al USA

Post Number: 1051
Registered: Nov-04
i would do 33-35hz

Silver Member
Username: Tanmanfosho

C Bang, Hardcore Iowa USA

Post Number: 377
Registered: Nov-06

mr kebo check ur e mail

Bronze Member
Username: Snarl2004

Post Number: 21
Registered: Dec-06
alright but how do i tune it so it is 33-35hz? i know it has to do with the port length but i dont know what exactaly it is.

Gold Member
Username: Bestmankind

Fi Audio BTL

Post Number: 9034
Registered: Oct-05
you can use this site to help you calculate your tuning.


Bronze Member
Username: Snarl2004

Post Number: 22
Registered: Dec-06
which would be better? A box that is 2.2 cubic feet and tuned for 38hz or a box that is 2.5 cubic feet tuned for 32hz? is there that much difference?

Gold Member
Username: Mixneffect

Orangevale, Ca. USA

Post Number: 1373
Registered: Apr-05
"what is the general rule for tuning a box"

The general rule for tuning an enclosure is to fine tune the F3 (the frequency where the volume drops 3 dB below average and declines furthermore below that point thereafter).

Port tuning is used to fine tune at or near the F3, but you need to know that porting will yield a 3 dB gain. Thats why they use the F3 theory. They realized that a port will gain about 3 dB so they said, hey why not tune at 3 dB below average, so that it will raise it back to par:-).

You want to build a 2.5 CF box with a 50 CI port, and want to tune it to 25-28 Hz.

Well if you are lucky, then you might get it, but you need to understand how an enclosure works.

An enclosure will have an air pressure that will make your speaker behave either stiffer or looser. A stiffer suspension will not yield lower frequencies. A looser suspension will yield lower frequencies, but will not control the speaker as well as a sealed enclosure would. So if you have an enclosure with a 3" hole without a port, you will have a speaker that is uncontrolled (for one), and it will sound out of tune. When you add a port, you will increase the air pressure inside the enclosure that will also help fine tune the sound as well as gain 3 dB at the frequency you choose. Choosing which frequency to fine tune is important. Ideally you want to tune near the cutoff (F3), but you may choose to go lower or higher but each one will compromise something.

If you tune above the F3, you will gain 3 dBs, which will probably sound boxy and/or boomy.

If you tune too low you will lose the speed of the speaker, and will have a softer impact.

The ideal tuning frequency is at or near the F3 (since this the natural limitation of your speaker), but then all speakers will behave differently, so you end up compromising.

Enclosures are designed based on the thiel parameters of the speaker, which will yield certain volume requirements.

You may find out that the optimum enclosure volume is 4CF, but you want to use it in a 2.5 CF enclosure, you will lose a lot of the low frequencies which cannot be brought back up to par by just tuning with a port.

You may go with a bigger enclosure (say 6 CF), but you will compromise speed, and probably even volume, but you will gain a lower F3.

Hope this helps:-)
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