what happens if the port isn't perfect?

[king alpha 0]

I'm building a box that's, according to my calculations: 1.9959 cubic ft (not including port and .12ft^3 sub displacement), with a port area of 28.75 square in, and port length of 33 in. This box should get me about 32-33 Hz. This box is for a single 12" SI Mag that's going to be powered by a Sundown SAE-1000D.

Anyway, this is only my second box build, and my box building skills ain't nowhere close to most on this forum. But I'm wondering how some of my problems will effect the actual sound of the sub.

My problems lie in the port, which runs through one side of the box, and continues around the back of the box. So, these are my problems with the port:

1. The port area is supposed to be 11 1/2 in. tall, and 2 1/2 in. wide. But after the glue dried, the height is still 11 1/2, but the width varies. The very bottom of the port is 2 1/2 in like I want, but it slowly get's smaller so the top is about 2 3/8 in. This issue is only with the part of the port running along the side. The part of the port going along the back side is 11 1/2 x 2 1/2 like I wanted it to be. (yeah, one day I'll have enough money and time to be good at this stuff)

2. I used Gorilla Glue. Well, the glue expanded and there's excess dried glue bubling on the connect points inside of the port. I'm guessing all that glue would create some sort of turbulence for the port air. And I cannot trim off the glue because my port hole is to small for my hand to reach all the way in.

So, the box ain't perfect, but how bad is it?

[Mike P. 0]

It's not bad at all. The 1/8th inch difference in port width and a little excess glue won't change anything. The tuning will still be in the 32-33 hz range.

[Peteyglad 2]

It's not bad at all. The 1/8th inch difference in port width and a little excess glue won't change anything. The tuning will still be in the 32-33 hz range.

I agree, that error is so small it will not make any audible difference.

[///M5 2,833]

Less port area = lower tuning, so at least your error is in the right direction.

[mrray13 30]

Less port area = lower tuning, so at least your error is in the right direction.

lol, but can add a bit of port noise.

but as mentioned, it honestly shouldn't matter.

i do have a question though. you mentioned the port bends along the back wall. did you measure the length of the port down the middle or did you build it with a total of 33" of inside port wall?

wheeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee

[king alpha 0]

Less port area = lower tuning, so at least your error is in the right direction.

i do have a question though. you mentioned the port bends along the back wall. did you measure the length of the port down the middle or did you build it with a total of 33" of inside port wall?

I measured down the middle of the port. I even drew a line on the box down the middle of the port before gluing and measured that line. The line is actually 31 3/4 in. because according to JLs tuturial I'm supposed to add half the width of the port if the port is running along one of the walls of the box. So, my port length is either 33 in or 31 3/4 in. I believe JL so, I say 33 in.

As far as port noise go, my first box was 2.6 cubic ft and has a 1 3/4 in x 11 1/2 in port. I can't hear port noise while I'm driving and didn't know it existed until I decided to take a few videos on my digital camera. So, at least for my car, port noise only happens when you pop the trunk and watch the sub play, but not when I'm driving.

Thanks for all the support, and hopefully this damn rain stops so I can finish building.

[mrray13 30]

kool. you should be good to go...and don't forget..

wheeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee

[king alpha 0]

kool. you should be good to go...and don't forget..

wheeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee

Ha, I see that pic all the time, but never thought about putting pics on this thread.

Anyway, here you go:

here's the dried glue in the port:

the bottom of the port with that line in the middle I measured for the port length:

The inside of the box:

here's the box with the front on, not glued yet (I chopped off the one end because it was really crooked, so I'll cut another small peice of MDF to glue there):

The Mag and brand the new, unused SAE-1000D sitting pretty, but not doing nothing........yet

And a pic of the old box that's supposed to be 2.5 ft^3 tuned to 32 Hz, but after measuring, closer to 2.7 ft^3 tuned to about 30 Hz

BTW, Am I allowed to put this much pics?

[platnum accord 0]

sandpaper on a steek!

[king alpha 0]

I finally got to install the box/sub/amp yesterday.

So, I went from:

1. 12" Mag in a box that's 2.6 ft^3 @ about 31 Hz, with a Massive P1000.1 amp

2. 12" Adire Brahma MK III (Fi reconed) in the same box above and the same amp (I had air leaking under the sub gasket because of a bad box build)

3. 12" Mag in a box that's 2 ft^3 @ about 31 Hz with a Sundown SAE-1000D amp

Here are my thoughts:

The Mag in the 2ft^3 box and Sundown sounds the cleanest. But the output is nowhere near the subs in the bigger box. When I have the time, I'll switch out the Sundown with the Massive and see what happens (maybe I'm setting the amp wrong or something), then after listening to that, I'll switch the Mag with the Brahma and try and determine if it is only the box that's causing the decrease in output, or if it's one of the other componants.

The songs I used for my output test

the songs on both Yung Jok CDs

Can't be touched by Roy Jones Jr.

The Hand Clap song by ?

Yeah, not much testing, but I'm a little busy to concentrate on this to much at the moment. Thanksgiving can't come sooner.

[George 0]

Less port area = lower tuning, so at least your error is in the right direction.

i do have a question though. you mentioned the port bends along the back wall. did you measure the length of the port down the middle or did you build it with a total of 33" of inside port wall?

I measured down the middle of the port. I even drew a line on the box down the middle of the port before gluing and measured that line. The line is actually 31 3/4 in. because according to JLs tuturial I'm supposed to add half the width of the port if the port is running along one of the walls of the box. So, my port length is either 33 in or 31 3/4 in. I believe JL so, I say 33 in.

As far as port noise go, my first box was 2.6 cubic ft and has a 1 3/4 in x 11 1/2 in port. I can't hear port noise while I'm driving and didn't know it existed until I decided to take a few videos on my digital camera. So, at least for my car, port noise only happens when you pop the trunk and watch the sub play, but not when I'm driving.

Thanks for all the support, and hopefully this damn rain stops so I can finish building.

i see this mistake all the time. your actually suppose to subtract half the port from the LV (port length) to get PLV (physical port length). adding physical port length to the port will effectivly lower your tuning even more. the point is you're suppose to try and shorten the port because the air is going to use part of that wall as the port, so you take away half the port width, so that your subwoofer still "see's"

example:

2^3ft @ 32 hz with a 4x10" port means you need about 47" of port length that the SUB will actually see. so the physical port length, ie, the length that YOU see, needs to be 45".

adding half the width would make the port take up more volume, and lower your net box volume as well. this would make your tuning drop (not by much in this example. only looking at close to .3hz,and would still put you close to the 31-32hz your were aiming for, and cause NO audible distinction). but it can add up little by little when you start making huge ports that add 3.5-4" to the port length.

i have no idea why JL states that, but i have a feeling they are saying the same thing just in a different way and it confuses people. then again they use a different equation as well. i use winisd (which claims to calculate end correction, but it seems to match equations that only calculate LV) and this forumla (depending on if i actually want to caluclate it out by hand, or use winisd to get me there)

Edited November 15, 2007 by George

[mrray13 30]

Less port area = lower tuning, so at least your error is in the right direction.

i do have a question though. you mentioned the port bends along the back wall. did you measure the length of the port down the middle or did you build it with a total of 33" of inside port wall?

I measured down the middle of the port. I even drew a line on the box down the middle of the port before gluing and measured that line. The line is actually 31 3/4 in. because according to JLs tuturial I'm supposed to add half the width of the port if the port is running along one of the walls of the box. So, my port length is either 33 in or 31 3/4 in. I believe JL so, I say 33 in.

As far as port noise go, my first box was 2.6 cubic ft and has a 1 3/4 in x 11 1/2 in port. I can't hear port noise while I'm driving and didn't know it existed until I decided to take a few videos on my digital camera. So, at least for my car, port noise only happens when you pop the trunk and watch the sub play, but not when I'm driving.

Thanks for all the support, and hopefully this damn rain stops so I can finish building.

i see this mistake all the time. your actually suppose to subtract half the port from the LV (port length) to get PLV (physical port length). adding physical port length to the port will effectivly lower your tuning even more. the point is you're suppose to try and shorten the port because the air is going to use part of that wall as the port, so you take away half the port width, so that your subwoofer still "see's"

good catch. i didn't really pay attention to where he said he "added" half the port width to make up for the rear wall.

wheeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee

[SQBMW 0]

using a router on the port exit will help reduce some of your port noise as well by reducing turbulence at the 90 degree edge.

Bob

[dropkick13 0]

using a router on the port exit will help reduce some of your port noise as well by reducing turbulence at the 90 degree edge.

Bob

I'm about to start my first ported box as well but I'm still in the learning stage. What is 'port noise' ?

Box looks good, hope my build will run smooth too

[///M5 2,833]

chuffing sound generated by high velocity air moving through too small of an area

[dropkick13 0]

chuffing sound generated by high velocity air moving through too small of an area

ah right, like farting with your cheeks pinched

[George 0]

Less port area = lower tuning, so at least your error is in the right direction.

i do have a question though. you mentioned the port bends along the back wall. did you measure the length of the port down the middle or did you build it with a total of 33" of inside port wall?

I measured down the middle of the port. I even drew a line on the box down the middle of the port before gluing and measured that line. The line is actually 31 3/4 in. because according to JLs tuturial I'm supposed to add half the width of the port if the port is running along one of the walls of the box. So, my port length is either 33 in or 31 3/4 in. I believe JL so, I say 33 in.

As far as port noise go, my first box was 2.6 cubic ft and has a 1 3/4 in x 11 1/2 in port. I can't hear port noise while I'm driving and didn't know it existed until I decided to take a few videos on my digital camera. So, at least for my car, port noise only happens when you pop the trunk and watch the sub play, but not when I'm driving.

Thanks for all the support, and hopefully this damn rain stops so I can finish building.

i see this mistake all the time. your actually suppose to subtract half the port from the LV (port length) to get PLV (physical port length). adding physical port length to the port will effectivly lower your tuning even more. the point is you're suppose to try and shorten the port because the air is going to use part of that wall as the port, so you take away half the port width, so that your subwoofer still "see's"

good catch. i didn't really pay attention to where he said he "added" half the port width to make up for the rear wall.

wheeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee

well i see the JL FAQ area say to add half the port width for end correction which is why people always add to it. i think the JL info is based on trying to find your tuning. for example, measure the port physically, add half the width to get what the sub would really see, and then plug it into the equation.

i dont really know. im sure JL has it right, just didnt put enough specific info to say what they were trying to accomplish.

[king alpha 0]

adding half the width would make the port take up more volume, and lower your net box volume as well. this would make your tuning drop (not by much in this example. only looking at close to .3hz,and would still put you close to the 31-32hz your were aiming for, and cause NO audible distinction).

Yeah, I kind of thought it wouldn't matter much with my box because I didn't have a huge port. But, I do have another question now about my box.

A few weeks ago I measured my SPL on a term lab (and met up with a bunch of SSA members in the process). Anyway, we did a sweep or something to see where my box peaked at, and it was 44 Hz. So, I got scored 134db @ 44 Hz. Is it right to tune a box in the low 30s and peak in the 40s? (BTW, I don't really care for pure SPL........but that was the first time I got to see a TL set up)

[mrray13 30]

yes, most ported enclosures (install dependant) will peak 7-11cycles above tuning. hardcore spl people aim for the peak of the box and car to match so that the sub is doing very little work while the box/port is doing the majority.

what you saw though is typical of a "daily driver"

wheeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee