Bending Slot Port

[Miller 10+ year member]

I need a port longer then the length of my box...Do I just bend it along the back??

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[junocdx 10+ year member]

Yea. They do make flexible port tubes but they're expensive. You could always go with a slot port!

 

[slipknot87420 10+ year member]

Originally posted by junocdx Yea. They do make flexible port tubes but they're expensive. You could always go with a slot port!

lol... he is going with slot port ... yes you can bend it but then you have to deal with end correction get somebody else on here that's bout as far as i can go

 

[Miller 10+ year member]

end correction?? your loosin me. anybody care to explain?? Also how would I measue how long the port is if I bent it?

 

[evo2k3 10+ year member]

Originally posted by Miller end correction?? your loosin me. anybody care to explain?? Also how would I measue how long the port is if I bent it?

end correction takes in acount that the air moving in the tube actully extend further than the slot itself (so it is a bit longer) if you dont deal with it, your tunning freq may be off by a fraction of a hert.....to messure the length, you messure the length that a particle would travel down the center(in all 3 demensions) of the port.

 

[more_spl 10+ year member]

i dont know what port correction is, but just add all dimensions for lenght

 

[Miller 10+ year member]

I'm pretty confused with this end correction so Let me just ask this... My box is 3.3 Cubic feet that will be housing 2 12" SE's. I want to tune it to 35 Hz using a slot port. The slot port with be 14.6 inches high and 2 inches wide. On Win Isd it says the port length should be about 15" long. My box is only 14" deep. So I would have the port run first along the side then bend and run along the back a little bit......How long should it run along the back??

 

[LoneRanger 10+ year member]

um....

how about you just layer the port?

go to EDs website and look at the plans for their 15A box.

the port looks like a rat maze, but it comes out to the right length and your tuning will be right on the button.

don't do what the guy said earlier about just cutting it short. you can't tell how much higher that will tune your box (remember, shorter port = higher tuning) and it will most likely cause you to have a box that's tuned so high that it will sound like ***.

 

[more_spl 10+ year member]

just change the length and height of the actual port hole.. that will determine how deep it should be also... i made like 6 plans before i got one that looked and worked good!!

 

[Miller 10+ year member]

What if I make it 2"x 14.6" and it says the port needs to be 16" long to tune it to 35 Hz. So my box is 14 inches deep. Would I just make it 12" into the box, then make a 90 degree turn with the port and go another 4 inches??

 

[tyranis]

Ok, when you "bend" the port you need the average length. so if you used a 14.6x2x15L port you need to subtract the width (2") from the port. Since it is also (I assume) using an outer box wall as a port wall, you need to subtract 1/2 the width from the port also (another 1" in this case). I did this on my last box and it was spot on. I used Term Pro to figure the length needed for my size box, displacements, and size port.

To test your box and KNOW what it is ported at use a test disc (I use db jams I bought from term pro) that has sine wave frequencies. Play at low volume but enough to have some noticable cone movement at SOME frequencies. Be sure your subsonic filter is not on, but be careful not to over power your subs. As your disc approaches the tuning of the box, speaker movement decreases. At the tuned frequency there will be almost no cone motion, but this is where there will be the most air movement at the port. Above or below this frequency there will be more cone movement.

In my box wich faces up, I put a few pennies on the sub, play at low volume, subsonic off, starting at 20hz, advanced the frequency/cd trac and at 35 hz (tune of box) the pennies don't move. At 33 hz and below and 37 hz and above the pennies bounce like crazy!

Hope this helps!

Jim/Tyranis

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[JeremyD 10+ year member]

The JL tutuorial gives a pretty simple explanation on end correction: http://www.jlaudio.com/tutorials/ports/

 

[Trixter 10+ year member]

Originally posted by JeremyD The JL tutuorial gives a pretty simple explanation on end correction: http://www.jlaudio.com/tutorials/ports/

I'm glad you dug that up 'cause I was just about to.

 

[nismboy6986 10+ year member]

thats helpful but the L1 and L2 thing has me confused. they say it is the measurement of the port length in the center of the port but their lines don't look centered up in the pic. for example if the depth of the enclosure (which would be H) was 8 inches, L1 is 5 inches and L2 was 5 inches, the effective port length woulb be 14 right [5+5+(8*1/2)}?

 

[Trixter 10+ year member]

H is not the depth of the enclosure, it's the width of the port.

With that in mind, if H = 2" and L1 = 5 and L2 = 5, your effective port length is 10".

When they say "down the center" they just mean down the center width wise. You don't have to take 1/2 of the width of the port. They just want to make sure that when you go around the corners, you are in the center so you get a true measurement.