4th order port area question

[BMAN 0]

i bought a 4th order box from someone and i want to make the port bigger but not sure how much port area i should have. i was told by a couple people that for a 4th order i should have around 20 square inches per cubic foot of the ported section. the ported section of the box is 13 cubes so i figured 9" x 29" would give me 261" of port which would be 20" per cube. right now i only have 198" of port which puts it at just over 15" per cube. im not sure if this is the correct way to do it so i was hoping someone on here could help me out with this thanks.

[Julian 641]

What subs are you using and what size?

[BMAN 0]

subs are 4 incriminator death row 15's

[Julian 641]

i can't find the xmax on the woofers, do you know by any chance?

[Kanaworm$ 292]

I would say roughly 19-21 mm

[Julian 641]

Also, whats your desired tuning?

[BMAN 0]

incriminator wont give anyone any of the ts parameters. they say to use their recomended box sizes but they dont give anything for bandpass enclosures. i dont know much at all about 4th orders but i didnt think the port size varied with each sub

[BMAN 0]

right now box is tuned to 43.5 and i want to keep it about the same because i like how it sounds in my truck

[Julian 641]

wow that is high... alright, MINIMUM I would suggest 358.05 in^2 ... You could use less port if you dropped your tuning however, say you tune at 35hz you will be able to use 291.44 in^2

[ibanender 2]

incriminator wont give anyone any of the ts parameters. they say to use their recomended box sizes but they dont give anything for bandpass enclosures.

There is a reason for that. Maybe it's worth paying attention to what they're telling you instead of what you're wanting to do

[ibanender 2]

wow that is high... alright, MINIMUM I would suggest 358.05 in^2 ... You could use less port if you dropped your tuning however, say you tune at 35hz you will be able to use 291.44 in^2

You do realize bandpass tuning isn't he same as ported tuning, right? A 35 hz tune would give him NO passband at all. If the sealed chamber is reasonable, it would play the hell out of about 30-40 hz and nothing else, and won't be loud doing it. The front chamber needs to be tuned much higher, like 55-60 hz.

[BMAN 0]

wow that is high... alright, MINIMUM I would suggest 358.05 in^2 ... You could use less port if you dropped your tuning however, say you tune at 35hz you will be able to use 291.44 in^2

You do realize bandpass tuning isn't he same as ported tuning, right? A 35 hz tune would give him NO passband at all. If the sealed chamber is reasonable, it would play the hell out of about 30-40 hz and nothing else, and won't be loud doing it. The front chamber needs to be tuned much higher, like 55-60 hz.

thats what i was thinking. ive always been told 4th orders shouldn't be tuned below 47hz. mine performs really well between 28 and 52ish i only have 2 subs playing right now and im sure it will change when the other 2 are in and playing. i want it to play low and get somewhat loud and i want more port area if thats possible

[Julian 641]

are you talking a 4th order bandpass or a regular 4th order?

4th order = ported box

4th order bandpass = ported box with a sealed portion.

[BMAN 0]

are you talking a 4th order bandpass or a regular 4th order?

4th order = ported box

4th order bandpass = ported box with a sealed portion.

sorry 4th order bandpass

[ibanender 2]

are you talking a 4th order bandpass or a regular 4th order?

4th order = ported box

4th order bandpass = ported box with a sealed portion.

Nobody ever refers to a ported box as a 4th order. I'd bet there are few that know 4th order (without bandpass name) is ported, so when they say 4th order it's assumed 4th order bandpass.

[Julian 641]

are you talking a 4th order bandpass or a regular 4th order?

4th order = ported box

4th order bandpass = ported box with a sealed portion.

Nobody ever refers to a ported box as a 4th order. I'd bet there are few that know 4th order (without bandpass name) is ported, so when they say 4th order it's assumed 4th order bandpass.

Just because it's never referred to a 4th order it indeed IS a 4th order (Ported), regardless.

[edouble101 314]

General rule of thumb is to go with the biggest port you can. I have read that over 3' in length the port starts to act like a horn so watch out for that plus the gain stats to flatten out.

[///M5 2,833]

Nobody ever refers to a ported box as a 4th order. I'd bet there are few that know 4th order (without bandpass name) is ported, so when they say 4th order it's assumed 4th order bandpass.

Disagree. A TON of people refer to ported boxes as 4th order. I do, just not here as people misread it

General rule of thumb is to go with the biggest port you can. I have read that over 3' in length the port starts to act like a horn so watch out for that plus the gain stats to flatten out.

ALL rules of thumb in audio are wrong regularly.

[RAM_Designs 25]

I try to have 1/2 the sd of the woofer(s) as my minimum. Without tuning unreasonably low it shouldn't have to be too long.

Edited January 21, 2011 by RAM_Designs

[ibanender 2]

Disagree. A TON of people refer to ported boxes as 4th order. I do, just not here as people misread it

Do you also refer to sealed boxes as "acoustic suspension" all the time? That would certainly lead people to believe you feel you have superiority.

General rule of thumb is to go with the biggest port you can. I have read that over 3' in length the port starts to act like a horn so watch out for that plus the gain stats to flatten out.

Wouldn't you WANT it to act like a horn? You'd gain lower end extension and efficiency. You can have too short of a port, depending on the tuning frequency, but I don't think there is such a thing as too long. You always have proper wavelength reverberation.

[Duran 387]

Misconceptions cause problems, things get lost in translation, and sooner or later people start confusing a 4th order to a 4th order bandpass, they are vastly DIFFERENT, hence the correction was made.

The issue is now done with, back on topic.

[Julian 641]

Misconceptions cause problems, things get lost in translation, and sooner or later people start confusing a 4th order to a 4th order bandpass, they are vastly DIFFERENT, hence the correction was made.

The issue is now done with, back on topic.

Thank you +1 for you sir..

[bassahaulic 155]

Re-building the whole box is needed to change any part of it.

I'm sure it's not fully correct anyway.

General rule of thumb is to go with the biggest port you can. I have read that over 3' in length the port starts to act like a horn so watch out for that plus the gain stats to flatten out.

ALL rules of thumb in audio are wrong regularly.

Thank you!

[BMAN 0]

i guess ill just leave it the way it is until im ready to do 8 15's