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Old 7th March 2010, 12:26 AM   #1
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Default Damn Ports!!!

I've finally finished my project to realize that when I put the volume louder, there's alot of port noise. I then realized that I made a very weird mistake calculating port size and that the ports I have used are way too small. I have a 69L enclosure with two ports for this driver. I recalculated the port sizes to have 2 three inch ports of about 12 inches long. I only want to make sure that this will actually work since I don't want to cut a hole in my box to then realize that I made a mistake...again... Enclosure has 13 inches of depth inside. Will the new ports work? Or is there not enough space between the end of the port and the rear wall? Help!!
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Old 7th March 2010, 12:33 AM   #2
WRWSTD is offline WRWSTD  United States
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With an inch to spare, that is getting mighty close to the rear wall.
How big are the existing ports?
Are they flared?
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Old 7th March 2010, 03:19 AM   #3
GM is online now GM  United States
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Quote:
Originally Posted by fouchagalaga View Post
Will the new ports work? Or is there not enough space between the end of the port and the rear wall? Help!!
In theory you want a 3r spacing to any boundary, so with a 3" dia. vent you ideally need at least 4.5" to any boundary to ensure it doesn't affect tuning.

Note that vents can extend out of the box somewhat, so while it doesn't look good it's a viable solution to your problem.

GM
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Old 7th March 2010, 03:30 AM   #4
NEO Dan is offline NEO Dan  United States
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Quote:
Originally Posted by WRWSTD View Post
How big are the existing ports?
Are they flared?
Could you answer the above questions?
You may want to opt for an elbow and then extend the existing port.
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Old 7th March 2010, 03:45 AM   #5
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Default port clearance

Quote:
Originally Posted by GM View Post
In theory you want a 3r spacing to any boundary, so with a 3" dia. vent you ideally need at least 4.5" to any boundary to ensure it doesn't affect tuning.

Note that vents can extend out of the box somewhat, so while it doesn't look good it's a viable solution to your problem.

GM
The poster above is correct. The idea is not to get "too close" to a boundary. When you do, the air mass in the port is sort of coupled to the air mass around the boundary, effectively increasing the length by a small percentage. In your case, if the port is flared, with 1" space between the flare opening and the wall, you probably have the bare minimum for the port to work fine, without air flow restriction. Sure more clearance would be better, but you don't have too many options.

I would install the port to its full length. Then listen at top volume for noise issues. You can always shorten the port by up to 1". Because you are near the boundary, the port is effectively longer than it would be if it terminated in free space, e.g. not near the rear wall. Make sure to shorten in small increments, because it will affect both the length of the port and the amount of the boundary effect.

In the worst case scenario, you might have to shorten the port by a couple of inches and this will increase the tuning, how much depends on the total port length to start with, e.g. the percent change. You can do some rough calculations on this first to see if it would be acceptable WRT frequency response.

There are ports tube "systems" out there that include 90 degree bends, so you could also think about using one of them if there is room inside to accommodate the bend and this would solve the problem.

Just don't make anything permanent until it has been tested and you should be able to remedy your situation one way or another.

-Charlie
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Old 7th March 2010, 10:22 AM   #6
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The OP stated there is 13" between the inside walls. If he is using 3/4" material, that would give 1.75" of clearance for the port end.

I ran some sims with the driver specs and it wouldn't hurt anything if the port length had a small virtual increase from boundary coupling. With 1.75" of space, I don't think it would be much though.

Don't forget, longer ports (lower tuning) = less vent velocity as well.

Fb = ~33Hz with 12" long ports.
Fb = ~30Hz with 15" long ports.

IMO you should be OK just putting in the two 3" x 12" ports.
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Old 7th March 2010, 02:30 PM   #7
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the existing ports (which are way too small...) are flared and 1.75'' at the inside end and 5'' long. I havn't closed anything permanently on my enclosure so I could still work on it. I like the bended port solution but can any bended port work if they are the right size and lenght or is there something special about what port I am supposed to use? I will check for the 3''x12'' ports to see how well that would fit.

Last edited by fouchagalaga; 7th March 2010 at 02:38 PM.
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Old 7th March 2010, 06:37 PM   #8
WRWSTD is offline WRWSTD  United States
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In view of what you have to work with, I agree with theAnonymous1 and CharlieLaub.
I am no expert, however having an experience just like this one has taught me that the 3''x12'' ports with flares should work adequately.
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Old 7th March 2010, 06:39 PM   #9
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Have a look at these Port tubes, I think they might work out well for you.

btw - Solen, besides being in Canada, is reliable and easy to work with.
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Old 7th March 2010, 09:57 PM   #10
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cokewithlime, I wanted to buy exactly rthe same ports you have shown. I live 25mins from that company on the north shore of montreal. And also... I've talked about this with my dad (I'm only 17) and when I came back from work today.. he made some sort of port for me and had already drilled holes...... I was very mad but it ended up looking pretty good. I havn't tried them yet since he stopped drilling the 2nd hole from me being mad. I'll post a pic of what these ports look like.
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