Large vs Small ports?

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Poormanq45

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Posted: June 02, 2005 at 2:35 PM / IP Logged

What's the difference between a large port and a small port.

Is it similar to a decrease/increase of cone area? Meaning a greater increase in output from larger?

Also, square vs round. ANy difference?

DYohn

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Joined: April 22, 2003

Location: Arizona, United States

Posted: June 02, 2005 at 2:50 PM / IP Logged

In general there is no real difference in SPL between large and small diameter ports. The difference is in the noise the port makes. Smaller diameter ports cause the air to move fasteer so the volume being affected can get in or out, and they make much more noise. Larger diameter ports allow the air speed to remain low so they make less noise. A properly designed square port will sound exactly the same as a properly designed round port in a subwoofer enclosure. For a midrange ported enclosure, a round port tends to sound more musical than a square port.

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Poormanq45

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Posted: June 02, 2005 at 2:56 PM / IP Logged

Thanks for the quick reply.

So the only difference is that the smaller port will make a bit more noise.

I thought there might be an SPL difference, but if there's not, then why do people usually lean towards larger ports, which require longer lengths?

DYohn

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Posted: June 02, 2005 at 3:31 PM / IP Logged

Because small ports can make a LOT of noise, not just a bit more, and in some cases a very annoying "chuffing" sound that is louder than the tone the port produces. Using the largest diameter you can make fit is usually the best way to go. This is also why so many enclosures use slot ports. It is easier to make a large surface area fit into an enclosure with slots.

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DYohn

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Posted: June 02, 2005 at 3:57 PM / IP Logged

Here's the math behind port size calculations, and how to determine minimum diameter to limit port noise (you can never really fully prevent it.)

http://www.diysubwoofers.org/portcal.htm

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Nodestiny

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Joined: May 26, 2005

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Posted: June 02, 2005 at 3:59 PM / IP Logged

You actualy can gain a small amount of dB at a certant point by making a larger port, making the peak a bit peakier :D. The downside is you will loose an increadible amount of low end (anything about 10Hz below tuning will become more and more dangerous on the sub, nearly freeair with enough port size) and you can loose SOME high end... basicly larger ports are for SPL.

Generaly aim for 20-50% of the cone area... in your average install

Port size doesnt always make your noise differances... rounding edges the best you can or using the correct type of ports make a huge differance.

Depending on the install, Aeroports or square ports can be better. Generaly, i use square ports because its easier to get a larger volume without spending a lot of money (aeroports can be expensive, a peice of MDF is fairly cheap)

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Poormanq45

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Posted: June 02, 2005 at 11:14 PM / IP Logged

Is there any problem with using PCV for the port(s)?

sedate

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Location: Colorado, United States

Posted: June 02, 2005 at 11:38 PM / IP Logged

I use PVC for my ports and it.. well its really easy to work with. I've never heard any port noise but up until my last box, which I've not installed yet, I always used 4" ports and those things are huge.

Nodestiny:

I *love* your attention to grammer... capitalization and judicious use of paratheses... Looking at ur pagination it looks like a post I wrote. =)

U seem like u know ur stuff, what you think this box will sound like? (It's sitting in my garage waiting for sunny day... I really wish God would start running the weather by me in the morning..) its a 1.75 net internal with a 3" (carefully rounded off, of course) port tuned to about 28 hz for a JL Audio 13W6.. I built a slightly smaller box with a 4" port tuned almost twice as high... (about 48hz) and it sounded .. well it sounded horrid. Whatcha think?

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Poormanq45

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Joined: October 27, 2004

Location: United States

Posted: June 02, 2005 at 11:51 PM / IP Logged

Ok, now about port placement?

Where should it be placed? Is there a minimum distance it should be away from the sides? The sub?

Also, how should I round off the ends? Should I just round them like I would when doing plumbing? I mean with a file?

sedate

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Joined: July 03, 2004

Location: Colorado, United States

Posted: June 03, 2005 at 1:15 AM / IP Logged

Poormanq45:

Between DYohn and stevdart I've gathered that:

The port should be placed on the side of the box with the radiating cone... on the same side as the speaker..they work together to produce sound. The port should terminate no closer than the diameter of the port to the inside wall of an enclosure... as far as from the sub itself? I'd prolly use the same rule of thumb.

Yea man.. I mean.. I just use sandpaper to round off PVC pipe. A file prolly work better.

"I'm finished!" - Daniel Plainview

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