port help with a Fi Q 15 with BP

[imhungnurnot 9]

I have a Fi Q 15 with BP power in about a 5 cuft box. 3.5 for the sub and the rest is displacements for sub and port. I have the box tuned to 31hz. I read the recommendations for the sub off of this forum and it says about 12-16 square inches of port area per cubic foot of volume. So that would translate from 42in-56in squared of port cross section and i have about 48 inches squared (its 13.75in W x 3.5in H x 36in L) and not very much air is moving through the port and it is not very loud. Maybe it needs more break in time?

Thanks

[streetbeater07 0]

I have a Fi Q 15 with BP power in about a 5 cuft box. 3.5 for the sub and the rest is displacements for sub and port. I have the box tuned to 31hz. I read the recommendations for the sub off of this forum and it says about 12-16 square inches of port area per cubic foot of volume. So that would translate from 42in-56in squared of port cross section and i have about 48 inches squared (its 13.75in W x 3.5in H x 36in L) and not very much air is moving through the port and it is not very loud. Maybe it needs more break in time?

Thanks

no, that would translate to 60-80 sq. in. of port area and your problem is probably going to be the length of the port....seems a little long for 31hz tuning? what formula did you use for calculating port length?

[imhungnurnot 9]

I have a Fi Q 15 with BP power in about a 5 cuft box. 3.5 for the sub and the rest is displacements for sub and port. I have the box tuned to 31hz. I read the recommendations for the sub off of this forum and it says about 12-16 square inches of port area per cubic foot of volume. So that would translate from 42in-56in squared of port cross section and i have about 48 inches squared (its 13.75in W x 3.5in H x 36in L) and not very much air is moving through the port and it is not very loud. Maybe it needs more break in time?

Thanks

no, that would translate to 60-80 sq. in. of port area and your problem is probably going to be the length of the port....seems a little long for 31hz tuning? what formula did you use for calculating port length?

How? 13.75 x 3.5 = 48.125 I used the formula off of JL's website.

Where Av is the cross-sectional area of the port (in square inches),

Lv is the length of the port (in inches) and

Vb is the enlcosure's net volume (in cubic inches).

I ended up with about 34.25 port length.. Then on jl's site it talks about end correction and it

says that if you use a side of the actual box as a side of the port like most people do you

are supposed to half of the Height to the Length. My height in this case was 3.5 and i added

1.75 (half of 3.5) to 34.25 equaling 36 inch length..... so im not sure.. Im pretty good with

math so i don't think i made a math error.. double check if you think i did.

Thanks

[BKOLFO4 29]

I come up with the port being too long. 36" is closer to 29 Hz.

edit - you subtract the 1.75", not add it, that is the difference. The effect length increases with a slot port, which means you can subtract it from the actual length.

tuned that low is going to gain bottom end, but lose some output where most song's have the strongest bass.

Can you post up full dimensions of the box for us to see?

Edited July 23, 2008 by BKOLFO4

[imhungnurnot 9]

I come up with the port being too long. 36" is closer to 29 Hz.

edit - you subtract the 1.75", not add it, that is the difference. The effect length increases with a slot port, which means you can subtract it from the actual length.

tuned that low is going to gain bottom end, but lose some output where most song's have the strongest bass.

Can you post up full dimensions of the box for us to see?

I'm still learning how to use Google Sketch Up but i have a basic model of the box

on there and im trying to figure out how to "take a picture" of the box so i can put it up here.

But I wasn't sure about the end correction wether i was suppose to add or subtract that.

Thanks, i'm gonna try to figure out that program and get a pic up here!

[BigPerm 0]

32.625" long = 31hZ for your box.

I've been told by a reputable builder (Woodlawn Cabinetry) that end correction is BS. Maybe it is, maybe it isn't. I

don't bother with it.

[imhungnurnot 9]

32.625" long = 31hZ for your box.

I've been told by a reputable builder (Woodlawn Cabinetry) that end correction is BS. Maybe it is, maybe it isn't. I

don't bother with it.

Alright. But what formula did you use to get that length? Is there a good online calculator where you can plug in the

variables and will be acurate or am i better off using my graphing calculator with the formula that i've been using?

Well BKOLFO4 seems to believe in it. Maybe this is true when one wall of the port is actually a wall of the box? I mean if JL has it on their site i would think it has some truth to it. I mean if you don't take it into acount it'll only throw off your tuning by about .5 hz. So maybe that why people say it is BS.

Well i'm going to see if i can get the top of that box off without damaging it too much and take the port out and cut it to length. So this should make it move more air throughout the port?

Thanks

[BigPerm 0]

32.625" long = 31hZ for your box.

I've been told by a reputable builder (Woodlawn Cabinetry) that end correction is BS. Maybe it is, maybe it isn't. I

don't bother with it.

Alright. But what formula did you use to get that length? Is there a good online calculator where you can plug in the

variables and will be acurate or am i better off using my graphing calculator with the formula that i've been using?

Well BKOLFO4 seems to believe in it. Maybe this is true when one wall of the port is actually a wall of the box? I mean if JL has it on their site i would think it has some truth to it. I mean if you don't take it into acount it'll only throw off your tuning by about .5 hz. So maybe that why people say it is BS.

Well i'm going to see if i can get the top of that box off without damaging it too much and take the port out and cut it to length. So this should make it move more air throughout the port?

Thanks

A good calculator is a free download called Winisd Pro Alpha.

http://www.linearteam.dk/default.aspx?download=winisd

I only use it to get a port length though. You have to lay out your box and calculate everything

else like sub/port/bracing displacement.

It was explained to me that subtracting or adding port length for "end correction" doesn't make any difference because you're also subtracting or adding to your internal volume by changing the overall volume of the port.

Check your PM

[imhungnurnot 9]

A good calculator is a free download called Winisd Pro Alpha.

http://www.linearteam.dk/default.aspx?download=winisd

I only use it to get a port length though. You have to lay out your box and calculate everything

else like sub/port/bracing displacement.

It was explained to me that subtracting or adding port length for "end correction" doesn't make any difference because you're also subtracting or adding to your internal volume by changing the overall volume of the port.

Check your PM

To tell the truth when i was thinking about it in my head i realized that about the end correction.

I don't have any new messages. What do you mean?

[BigPerm 0]

My bad, check it again.

[appleyard 0]

I used the WinIsd alpha over the years with success especially for port size and length.

I always counter check it on here

http://www.carstereo.com/help/Articles.cfm?id=31

Normally I would get the same result except in 1/100 decimal place. Also Scott did mention that its not recommended to have a very long port which I forgot why though.

[BKOLFO4 29]

I just use:

http://www.carstereo.com/help/Articles.cfm?id=31

As far as end correction - It seems to work with ports up to 3-4" wide, but beyond that the extra wall does not have as much effect. I never take more than 2" off for end correction on a slot port.

Brian

[imhungnurnot 9]

I tore it down and re ported it to be at about 33Hz with 3.5 net volume

with 14.75 cubic inches of port area per cubic foot of net volume.

Sounds beautiful on the low end but a little harsh on the higher side.

Tearing the face of that box off was rather interesting!!! ha

By the way the white line of caulk was where the first port was

and i took off a little bit of air space due to the smaller port.

[imhungnurnot 9]

Ha by the way the front of this box looks like a DA*M headboard off a bed!!!!

With that said. It also follows the contour of the dash beautifully!!!!!!!