Port Tube Too Close To Sub?

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mrmsudawgs

Copper - Posts: 145

Joined: February 22, 2005

Location: United States

Posted: March 08, 2005 at 3:37 PM / IP Logged

I'm using WinISD to size a vented sub enclosure. The calculated port tube length is about 20" of 3 inch diameter round tube. The port tube is not installed on the baffle board (the board the sub is mounted to). Rather, it is mounted at the end of the enclosure 90 degrees to the baffle board. This causes my port length to extend into the box towards my sub. The end of the tube is only about 2 inches from the back of the sub. Is this too close? Can I use some elbows in my pvc to angle away from the sub?

Thanks!

Mike

Poormanq45

Silver - Posts: 597

Joined: October 27, 2004

Location: United States

Posted: March 08, 2005 at 4:16 PM / IP Logged

Do NOT, I repeat do NOT use a port that is 20inches long! Numurous tests have been done that showed that "long" ports, which 20" is, will create a reverberation in the port. THis reverb will create a noticable distortion.

I suggest that you use two ports instead of one. Just make sure that the overall internal volume of them combined is equal to that of the original.

stevdart

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Joined: January 24, 2004

Location: Pennsylvania, United States

Posted: March 09, 2005 at 1:09 AM / IP Logged

Volume of the air in the port is not the basis of a port. You don't want to think that as long as the volume is the same that the port size (diameter, length or number of ports) can be changed. Check that out with port calculators. I don't know of problems associated with the length of a 20" tube port.

Some port calculators can be found here.

As to the question, the end of the port tube is actually a real part of the port's function, and has to be at least the diameter of the port in distance from any object inside the box. Also, the port should be place away from the wall that same minimum distance. Use elbows as necessary. Measure the port length through the center of the tube and elbow.

mrmsudawgs

Copper - Posts: 145

Joined: February 22, 2005

Location: United States

Posted: March 09, 2005 at 1:34 PM / IP Logged

I find it hard to believe that port length may induce extra noise. Look at the Bose Wave Radio. It's port length is about 3 ft long and it sounds great.

My port calculation came from WinISD. Its help file mentions nothing about a maximum port length.

As luck would have it, I can no longer use a 3" diameter port. Instead, I have to use two 2" diameter ports due to size restrictions. I should be able to elbow around inside the box much easier with the smaller diameter pipe. That is if I don't lose patience and throw the entire thing in the trash then go out and buy a prefab box! Port Tube Too Close To Sub? - Last Post -- posted image.

Port Tube Too Close To Sub? - Last Post -- posted image.

DYohn

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Posted: March 09, 2005 at 2:01 PM / IP Logged

FYI, the Bose systems are not ported, they are transmission line systems, which is a different animal altogether. Long ports can create strange noises and resonances, but 20" should not be bad at all. Yes, you can bend the port inside the enclosure if necessary, but you want to minimize this since they work best when there is the least amount of air flow restriction.

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Port Tube Too Close To Sub?

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