Bandpass ported through rear deck. Questions.

[Evilthx]

For my '97 Mustang GT I'm going to do a bandpass enclosure using my extra JBL P1224 and port it through the rear deck between the rear speakers. JBL gives specs for the box so I'm going to use their recommendation.

My question is, what should the dimensions of a square port be? They give the specs for a round port of 7 inches long and 4 inches in diameter. I want to use a square port as it will ease installation, molding to the rear deck and enclosure.

Their specs on the enclosure are as follows:

Rear sealed chamber = 1 cubic foot

Front ported chamber = 1.75 cubic feet

Port = 7 inches long by 4 inches round

Does it matter if the port is actually outside of the enclosure or will that affect the tuning of the box?

Thanks everyone.

[ckeeler11]

a 4" round port gives you about 12.6 sq. in. so a square port the same area would be 3.25x4.

port outside the enclosure does not matter. just make sure you subtract what ever is inside to get the external length.

[Evilthx]

Thanks. Wow, that's a pretty small port for all that bass to come through. Is it safe to say that I could make it 4" square and 3.25" long? That box is going to be very close to the rear deck.

[Evilthx]

Looking at the port for the ported box the specs are 4" round by 10" long... the fB = 33hz but on the bandpass the fB = 55hz. Is this the tuning frequency? If so, can I make the port the same as the ported box to tune it lower?

[ckeeler11]

Im not a 4th order guy but the specs for ports given by manufacturers are generally on the small side. How much power will you be running?

I do know 4th can be tricky and alot of guys build it so they can change the ports out to get the tuning they want. Since you are running external that would be fairly easy. i would start with a port area around 30" (5.5x5.5) to see how it does.

Hopefully one of the more experienced 4th order guys chime in.

[Evilthx]

How much power will you be running?

An Alpine MRX-M100 (1000w rms @2ohm)

[ckeeler11]

See my edits above in previous post.

[Evilthx]

See my edits above in previous post.

I hope they chime in too. I thank you for your help. I am pretty sure the 1999 and 1997 Mustangs are the same interiors though the body changed. I have the '99 here to do some rough measurements until I get my GT here in the beginning of November.

[Triticum Agricolam]

Looking at the port for the ported box the specs are 4" round by 10" long... the fB = 33hz but on the bandpass the fB = 55hz. Is this the tuning frequency? If so, can I make the port the same as the ported box to tune it lower?

One 4" port won't be enough, which is why in that document you posted it says "2 Port". Even two 4" port is probably on the low side. Most manufacturer port size recommendations are based on using RMS power, you are going to be running over twice that.

You can make the port longer to tune it lower, but you aren't going to want to tune it that much lower. I'd suggest no lower than 45 Hz. Bandpass boxes aren't like a ported box where you want to tune to the low 30's. Also if you could make the port removable in some way so you could tweak the tuning once you get the box in the car and playing it would be a good idea. Bandpass boxes give you a "window" of frequencies that they play well, being able to move that window around a bit can be very useful.

[Evilthx]

Holy crap.... It does say 2 port. I could make it 6.5" square by 4" long. Man I need to read. Thanks for seeing what I missed.