Port size question

[morris]

Would a 3" diameter port(flared on one end) be adequate for a 12 inch woofer? This would be for a 3 cubic feet box tuned to about 22 hz. What is your experience with using a 3" port for a 12" woofer...is the chuffing audible? I am thinking a 4" diameter would probably be better but it becomes longer than I want it to be...although I can find ways to make it fit if a 3" inch diameter port is a bad idea.

Thnks!

[morris]

"8 to 10" woofers will use a 2" flared port. 12 to 15" will use a 3" flared port. These are the pre-made, cut to size "Precision" ports. These are of course adjustable in the middle section. My own experience finds people making their ports *way* larger in diameter than they need to be, which which relates to longer ports."
-I cut and pasted this from Zaph's website. I think I will just go ahead and do a 3" diameter and flare it at both ends unless someone can convince me otherwise.
Silly me to ask such a noob question!

[johnnyrichards]

Well, a larger port diameter never hurts. It won't make it sound bad, there won't be any ill effects from using the four inch instead of the "recommended" three inch.

Years ago I went with the rule of thumb: "6-8" use a 2" port, 10-12" use a 3" port and use a nice sealed box for them big ol' 15 inch woofers."

That was then, this is now and fifteen years ago a 12" subwoofer with 7mm Xmax and 100 watts of power was a big one and today a 12" with 15mm of Xmax and 500 Watts is common place and a 3" port probably doesn't cut the mustard any longer.

YMMV so build it and give it a listen. It may turn out that your desired listening level would let you get away with a 2" port on a 15" subwoofer - or it may turn out that the 3" would huff and chuff on an 8" driver. How loud do you listen to stuff? Most vent models are done with maximum power at a single frequency - not realistic at all. Modeling software always assumes people crank the living hell out of their equipment and sit around all day listening to reggae at 115 decibels. So unless you plan on doing that, you can probably safely drop down to the three inch.

FWIW, I experienced major chuffing with two 5.25" Tang Band subwoofers in a 1 cubic foot box tuned to 33 Hz using a pair of 1.625" ports. However, I am one of those guys who cranks the living hell out of his equipment and sits around all day listening to music, loud.

Ramble on and on here... There isn't even a whole lot of information below 30 Hz, even in a lot of movie tracks and a lot of whats there isn't very loud anyway. You may just be fine with the 3", especially flared. Again, modeling software assumes the worst with the bottom octave.

I am in the process of building a PC sound system using two-way desktop speakers with 5.25" woofs and 3/4" tweets. The bass will be handled by a pair of Tang Band 8" drivers (W8-670Q 8 ohm subwoofer, nice) in a vented 1.75 cubic foot enclosure. Tuning will be in the low 30's and I am using the 4" precision port just because it will fit just fine in the box I plan on building. I'll use the full length. Not because I was overly worried about chuffing, but because the big port will look cool, and I can fit it in there just fine. Only a few bucks more than the three inch.

This is the best part about building subwoofers. Everyone has their own theories on the way to do things and at the end of the day the room you put it in kicks the sh!t out of your design anyways. So maybe worrying about theoretical port sizes should not be a primary concern - your room may destroy your design or it may naturally augment the bottom octave nicely to where the low tuning is a detriment rather than an asset (the bedroom sub I just finished has an F3 of 29 Hz. In my 15' by 12' by 8' bedroom it benefits a LOT from room gain).

So maybe you can tune the thing a little higher and use the larger port if your room is creating too much low frequency energy from the low F3 you have already designed. I know a low F3 is all the rage these days, but in certain rooms that room gain kicks in and a low F3 all of a sudden means one-note muddy noise.

Look at this rambling, obnoxious post... I need to sleep more.

[morris]

I never thought of it that way! Thanks, am a little more enlightened. I want to keep the port tuning lower at about 22 hz as per Curts recommendation in his website.
http://www.geocities.com/cc00541/Sealed_v_Vented_3.html
It is supposed to help with the vented woofers group delay. Whether that is audible, I do not know. I will just do it anyway. I do not listen to my speakers crazy loud anyway so I think I will stick to the 3 inch.
Thank you for your "rambling" it helped make me feel better about the 3" port diameter.

[Chris Roemer]

I never thought of it that way! Thanks, am a little more enlightened. I want to keep the port tuning lower at about 22 hz as per Curts recommendation in his website.
http://www.geocities.com/cc00541/Sealed_v_Vented_3.html
It is supposed to help with the vented woofers group delay. Whether that is audible, I do not know. I will just do it anyway. I do not listen to my speakers crazy loud anyway so I think I will stick to the 3 inch.
Thank you for your "rambling" it helped make me feel better about the 3" port diameter.

One the the 1st speakers I built (in 2000) used a 3" mailing tube in a 2 cf box with the Dayton 8" "Classic" (as it's called NOW) with an F3 below 30 Hz. It chuffed like crazy. When I rebuilt it a few yrs ago I ran a 1/4" roundover (router) bit around the hole and the chuffing was dramatically reduced.

My own ROT is to use a 4"d port with a 10" or 12" sub/woofer. If you must use the 3", I highly recommend exiting it out the back away from your listening position AND rounding over the hole where it leaves the box to help quiet down any chuffing.

Chris