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Old 2nd September 2005, 04:34 PM   #1
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Question Positionning the port on it...

Hello,

I am currently designing a TQWT for a friend, based on a Supravox 165LB. (I gave up the horn, way too big !!)

The previous enclosures I designed all used a frontal port, a solution that always gives satisfaction due to the synchronised driver and port waves.

My friend has a small room, and I'd like to take advantage of corner and floor loading in my design, involving rather a back or side port than a frontal port.

But I'm quite afraid to encounter phase problems and severe dips and peaks with a port that is not on the front of the enclosure.

I have also heard using a rear port could reduce the midrange output through the port, which is a very good thing.

I'm rather looking for a side port, because it doesn't involve leaving space behind the enclosure.


So I'm asking you, port experts, what you think about this port stuff, and what you tried with success !
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Old 2nd September 2005, 06:15 PM   #2
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Wavelengths at the frequencies the port is operating at are fairly long, so positioning isn't really a problem. The only issue I can see with side mounting ports is that box width is usually the smallest dimension, so if it's long, you might need to put a bend in the port.
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Old 2nd September 2005, 06:31 PM   #3
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Quote:
Originally posted by youyoung21147
The previous enclosures I designed all used a frontal port, a solution that always gives satisfaction due to the synchronised driver and port waves.
The back wave is out of phase with the front, so there is absolutely no guarantee that putting the port on front will make the two outputs in phase. To the contrary, in fact.

Rear-firing the port gives a little more boundary reinforcement for lows (expecially if near ground). It also attenuates some of the high freqs that aren't supposed to get through the port, but do.

Unless you plan on having the enclosure flush against the wall, I think rear-firing is the way to go.
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Old 2nd September 2005, 06:34 PM   #4
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OK I'll try the side port, so.

Length of the port won't be a problem, I find it even really short on my TQWT. TLs often have big and short ports.

Concerning the shape of the port, which is prefered ?

A tube, a slot, a vertical slot, several tubes ? (my port will not be at the end of the transmission line, but 8" above the the bottom.)
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Old 2nd September 2005, 06:43 PM   #5
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Quote:
Originally posted by youyoung21147
Concerning the shape of the port, which is prefered?
Round tube is easiest to predict, and I believe least likely to whistle. Flared ports are supposed to prevent turbulence at the ends, perhaps important for big vented subwoofer but probably not too important for full-range project.
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Old 2nd September 2005, 06:47 PM   #6
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Yes, round should be fine. It's also easier to tweak if you need to!
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Old 2nd September 2005, 06:50 PM   #7
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OK thanks a lot.

I'll go to a DIY shop this week end to see which diameters of PVC pipes are available. Cheap, solid and acoustically neutral .
Just what I need Hope they will have some 100mm + pipes lol !

Greets !
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Old 2nd September 2005, 09:56 PM   #8
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Just to add my vote for the round ports. Much less ripple as a rule than a slot port. Remember not to place it right at the bottom of the cab. though. 3" - 4" up is usually a good place to start.
Cheers
Scott
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Old 3rd September 2005, 08:10 AM   #9
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Yes, I placed the port above the bottom.

I just have a little question about the speaker's position :

How much space do you usually leave between the port and the wall, not to get a stuffy sound and uneven response ?
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Old 3rd September 2005, 08:26 AM   #10
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Good rule of thumb is leave at least the diameter of the port to the wall or any other obstructions. That also applies internally.
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