Anyone care to explain end correction?

[Joe X]

Pretty self explanatory.

New here. Not to car audio, although compared to a lot of you guys, I could definitely be considered a n00b.

Anyway, I am wanting to get back into it. I am good with Sketchup. I'm good with math. I have been playing with winisd. Seems pretty simple. I've just never actually designed my own ported box before. I've either had other people from forums do it for me, or used the box calculator on the RE website, which is very limited to one design style, and I'm not very confident in its accuracy. The only thing I'm really lacking here to really get the ball rolling on designing some legit enclosures is the fact that I have no idea what end correction is or how to use it.

I watched a youtube video created by Mark at C.A.F. to teach myself how to use Sketchup, and he mentioned adding half the port width to the length of the port, which is what got the ball rolling in my head that I need to learn what this is and how to use it in order to design and create a properly tuned enclosure.

Thanks in advance!

Extreme tuning accuracy alone is not grounds for a box to perform as you want or even a correct design, the only people I know to need extreme tuning accuracy is competitors and usually a tunable port is used along with some measurement instrumentation to set it to work as needed. You can have any number of boxes with different parameters, layout and different subs, SAME tuning and will sound completely different.

[user18436572]

I got the formula rearranged to find just the end correction factor.

It does not appear to be constant as of a couple of practice examples.

This is what one of my source sites says on the subject.

The value for k, the end correction, can be fine-tuned by using the following values to derive the appropriate end correction figure for each end of the port, then adding them together

Flanged End: 0.425

Free End: 0.307

e.g. if both ends were flanged,

k = 0.425 + 0.425 = 0.850

if one flanged, one free,

k = 0.425 + 0.307 = 0.732

if both ends were free,

k = 0.307 + 0.307 = 0.614

Normally, k=0.732 is assumed

Does it count as both ends being flared if the inside end of the port shares a wall with the rest of the box and the other one is only slightly rounded just enough to remove the sharp edges? Like 0.375" radius (enough to make the end of the 0.75" board look like half a circle)

Pretty self explanatory.

New here. Not to car audio, although compared to a lot of you guys, I could definitely be considered a n00b.

Anyway, I am wanting to get back into it. I am good with Sketchup. I'm good with math. I have been playing with winisd. Seems pretty simple. I've just never actually designed my own ported box before. I've either had other people from forums do it for me, or used the box calculator on the RE website, which is very limited to one design style, and I'm not very confident in its accuracy. The only thing I'm really lacking here to really get the ball rolling on designing some legit enclosures is the fact that I have no idea what end correction is or how to use it.

I watched a youtube video created by Mark at C.A.F. to teach myself how to use Sketchup, and he mentioned adding half the port width to the length of the port, which is what got the ball rolling in my head that I need to learn what this is and how to use it in order to design and create a properly tuned enclosure.

Thanks in advance!

Extreme tuning accuracy alone is not grounds for a box to perform as you want or even a correct design, the only people I know to need extreme tuning accuracy is competitors and usually a tunable port is used along with some measurement instrumentation to set it to work as needed. You can have any number of boxes with different parameters, layout and different subs, SAME tuning and will sound completely different.

I understand that. I'm just looking to make sure if I'm trying to tune to 32hz that I don't end up at 30 or 34 or some shit. I just wanna know where I'm at.

[Triticum Agricolam]

...

Does it count as both ends being flared if the inside end of the port shares a wall with the rest of the box and the other one is only slightly rounded just enough to remove the sharp edges? Like 0.375" radius (enough to make the end of the 0.75" board look like half a circle)

...

...

I understand that. I'm just looking to make sure if I'm trying to tune to 32hz that I don't end up at 30 or 34 or some shit. I just wanna know where I'm at.

...

I think you may be confusing flared with flanged. If you port has at least one wall in common with the rest of the box none of the three values listed are going to be what you want.

If you are shooting for 32 Hz and end up at 30 or 34 you will never be able to tell the difference by ear.

[user18436572]

So...I started doing some math today on a box that I wanted to design. Using K=2.227 since my port runs along the side of the enclosure like most vented enclosures, and it shortens my port length by like 18 inches. That seems awfully drastic. That's like half the vent length or more. Does this seem right to you guys?

Again, not trying to accomplish extreme tuning, but cutting a vent length in half is going to affect the tuning frequency by a lot more than just a few hz. lol.

My port area is 51in², so that makes my diameter 8.058in. With an end correction factor of 2.227, that's 17.945in of "correction" on a port that was originally supposed to be like 27.5 inches according to winisd. Using the formula (confirmed my math with this link that does the math for you: http://www.calculatoredge.com/new/ventlength.htm ) I got a vent length of 39.5cm which is 15.5in.

Does anyone think this seems accurate? Sorry for being such a pain in the ass, but now I'm confused as to whether or not I'm even confused.

[user18436572]

Bump?

[Triticum Agricolam]

If you post all the specs on your box (net volume, tuning, port area, etc) I can check over your numbers and see if it looks good.

I can tell you from experience that using the appropriate 2.227 end correction can shorten a port by a lot, so I wouldn't be surprised if your results are accurate.

Nice CounterStrike avatar BTW :-) Those were the good 'ole days.

[user18436572]

If you post all the specs on your box (net volume, tuning, port area, etc) I can check over your numbers and see if it looks good.

I can tell you from experience that using the appropriate 2.227 end correction can shorten a port by a lot, so I wouldn't be surprised if your results are accurate.

Nice CounterStrike avatar BTW :-) Those were the good 'ole days.

Haha. Thanks. Good days, indeed.

Sub is RE SX 15 D2 (old design from like 06)

External restrictions: 33"w x 14.25"h x =< 24"d

which leaves us with....

internal dimensions: 31.5" x 12.75" x =<22.5"

and a vent port that is 12.75 x 4" for a port area of 51in²

Sub will be mounted face up. Would like to face the port to the back if possible; however, if I utilize the full 24inches of depth, there isn't enough space for the port to breathe if facing the rear, so it would have to be ported to the side. BUT....if that end correction value of 2.227 is right for my application and the port only needs to be like 15.5inches long, I can probably get away with port back.

[user18436572]

P.S. this is going in a trunk, and before you guys jump my shit about sub up, port back/port side not being optimal for a trunk application....I just want you guys to know, I'm just trying things out. I had this sub in this car once before in a box that was built for something else. Just so happened to be 4ft³ tuned to 35hz I think, so I tried it. It was just something I threw together real quick. Due to the dimensions of this particular box, the only way to fit it was sub/port up. It sounded pretty damn good. Especially down low, but there were parts of the higher end of the spectrum that I think were getting cancelled out. I then built a box to pretty much the same dimensions, but put the port and sub on the shorter side for sub and port facing rear. This reduced my internal volume to 3.5ft³ and I honestly don't really remember how it sounded. The amp I was using at the time took a shit (Sundown 1500v1 that I later learned how to fix) and having this set up facing the rear, it made the trunk latch rattle so fucking bad that it ruined the sound quality completely (I like to fold my seats down when subs face rear obviously) I should also note that the trunk panels don't really resonate like most cases, it was the actual latch. No amount of sound deadener can fix this. When I had the sub/port up, I was able to wrap electrical tape around the striker which was good for about a good day worth of beating before I had to rewrap it. lol.

Anyway...my goal here is to have the sub face up, because I am able to tuck it under my package tray and it doesn't rattle so much. But I want to try facing the port in different directions to try and cure this cancellation issue I had last time.

I am also trying to get a firm grasp on this box designing thing in general. I will soon be installing a couple Sundown 15s in my buddy's Jeep, and it caused me to have a relapse in my addiction to bass. I just want to know what I'm doing, so that I can get better at the art.

[Triticum Agricolam]

OK, so the dimensions you gave work out to 5.22 cubic feet gross internal volume. You didn't mention what tuning you are shooting for, but if you figured you are going to have around 4 cubic feet of net airspace with 51 sq in of port at 32 Hz that works out to about a 15-1/2" port using the formula Krakin listed. Or if you go by JL's formula 17-1/2".

[user18436572]

I was going for 32hz, sorry. Which formula do you believe is more accurate? 15.5inches doesn't seem too short for 32hz at 51in²?