Geting Proper Port Area

[Dub7sonoma Premium Member]

I was never able to get a good answer on this either. According to this calculator, I'd need 69" of port area at 35 hertz for a single HDC3 12". I'm guessing that's because of it's high xmax. That port would be enormous.
Car Audio - PORT Size Calculations and Formulas for WOOFER and Subwoofer BOXES

Thats the calculator i use. It has always worked for me and given me AMAZING results

 

[ThatChevyGuy 5,000+ posts]

awesome, didnt know about that calc ^^

 

[Jeffdachef 5,000+ posts]

Poet area can be reduced if you have inner and outer flares. Radius determines area.
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so lets say my 2 18s require a minimal of 192 sq inches of port area, how much higher/lower can I go before it starts impacting sound in a negative way? No flares involved.

Thats the calculator i use. It has always worked for me and given me AMAZING results

There's a very small and negligible margin of error because the surface area of each sub is different. However, it does land you in the proper ballpark each time. Great tool.

*******To any newbie out there reading********

lets say an alpine type R or hdc3 18. Type R listed xmax specs is 20mm and the HDC3 18 is 36mm, Do not use those numbers, as they are two way travel. You need one way linear travel so divide it by two.

You need to make sure you find the one way travel X max for any sub or else you'll end up with ungodly amounts of port area.

 

[keep_hope_alive Premium Member]

Smaller means chuffing at low frequencies and that impacts performance. .

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[Jeffdachef 5,000+ posts]

Smaller means chuffing at low frequencies and that impacts performance. .
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how about when is it too big? Do you get any gains for higher amounts of port area or is it just diminishing returns or is there a point where you lose performance?

 

[tommymilan311]

Why go with a tube port and not design a rectangle port in your box?

 

[keep_hope_alive Premium Member]

No benefit going bigger other than lower port velocity. Too big and you csn have loading issues. Port placement is also important.

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[Jeffdachef 5,000+ posts]

No benefit going bigger other than lower port velocity. Too big and you csn have loading issues. Port placement is also important.
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Thank you!! Guess i'll keep around the minimum required, maybe a tiny bit more to be on the safe side, but no less

 

[garychurch84 10+ year member]

LinearTeam

Something to look into,its supposed to calculate if your going to have port noise or not

 

[poolman966554]

very interesting.

I just ran 2 sa-12 numbers on the calc psych0ticnemes1 provided, and it says the Sa's need 68.7" minimum port area.

The box plan suggested from sundown for 2 12's is only 55.25" (the box also is 3.5cu ft @33hz)

secondly, when sundown says Xmax is 19mm @70 % BL (motor force), is that 70% force at 600w? if so, would you adjust the xmax to compensate if your running 1000w per sub?

 

[Dmac1991]

quoted from over on SMD. Excellent read on port area. Port area. what does it affect? - Page 2 - SPL - SOUND PRESSURE LEVEL - SMD Forum

"Minimum port area can be found from a few variables of your system such as cone area in total, xmax and tuning frequency.

Using this:

Calculate the minimum port diameter from the following equations:

Sd = pi*(Dia/100)^2/4

Vd = Sd*Xmax/1000

Dmin = 100*(20.3*(Vd^2/Fb)^0.25)/Np^.5

where,

Dmin = minimum port diameter (cm)

For vented type speakers operated at full power that is, full excursion, it is possible to end up with audible noise from the air rushing in and out of the vent. For a given speaker system, the smaller the vent opening the greater the velocity of air in the vent and the greater the vent noise.

The main reason this ever became a topic is because Richard Small (the S in T/S Parameters) wanted to know the minimum velocity the air from the port could have without causing noise. This happens to be about 5% the speed of sound. That formula should get you close to it, but with modeling software you don't really need to use it, just make sure your port velocity is down.

There are other negatives from port compression such as added heat from inadequate air transaction and poor frequency responses due to it as well.

The Xmax is there to have it know your upper limit of excursion.

If you use less power you'll have less excursion to cause less air to move. So you could use a smaller port area, but when designing you design around your speaker not your amplifier, because what if you get a bigger amp.

If you could have too much port area then playing speakers at low volumes would sound absolutely horrible as the port area needed gets exponentially smaller as you use less power.

Unloading is based on port location not area.

Area can make positioning it hard to keep from unloading happening, but doesn't cause it.

No such thing as too much port area (at least within reason), there is such thing as too long of a port though, and since area and length are tied to tuning, you can definitely get yourself into a spot where your port is too big, because its too long.

Cone control problems will arise from not enough port area, not from too much.

Not having enough port will cause port compression. This makes your box start to act like a leaky sealed box. Output around tuining will drop, impedance will rise, output from your amp will decrease.

If your port is too long you run into trouble with pipe resonance.

Pipe resonances will produce extra harmonic waves and in extreme conditions it can adversely affect your overall output.

I believe I talked with Triticum about this at one point and I think I said that you don't want your vent length longer then 1/4th the length of the frequency you're tuning to.

And also impedance and tuning of your box changes when adding power."

 

[hispls 5,000+ posts]

Why go with a tube port and not design a rectangle port in your box?

Round is optimum. Fluid dynamics and all that.

very interesting.
I just ran 2 sa-12 numbers on the calc psych0ticnemes1 provided, and it says the Sa's need 68.7" minimum port area.

The box plan suggested from sundown for 2 12's is only 55.25" (the box also is 3.5cu ft @33hz)

secondly, when sundown says Xmax is 19mm @70 % BL (motor force), is that 70% force at 600w? if so, would you adjust the xmax to compensate if your running 1000w per sub?

When the coil is centered in the gap it has 100% bl. As it moves up or down from center you'll come to a point where the gap isn't full of coil but only part of the coil is in the gap. The accepted standard for x-max is the point where BL goes below 70%.

A lot of the conventional wisdom about box building has gone upside down and the folks who wrote the loudspeaker cookbook certainly weren't considering woofers with a 50 pound+ motor, 27mm x-max, and a suspension stiff enough to stand on. Fundamentals are still the same, but we've gained a bit of flexibility for our ported alignments.

If you use winISD and enter correct TSPs it's pretty good predicting port velocity to keep yourself out of the problem areas. I would agree that it's very hard to do "too big" and generally speaking too small will give you a lot more trouble.

The ratios of "15 square inches per cube XX inches long" were cookie cutter boxes for a couple different woofer brands (Shocker Mike was big into this and DD uses similar box). The ratio of area to space PLUS the length are to keep a tuning within where that driver wants to tune and does assume you're using the appropriate volume for each size driver. Mostly these "how many square inches per cube" rules will keep you out of trouble.

IMO go as big as you feasibly can. It's much easier to shrink a port than to make it wider. Also I've had a long day and am half asleep so if any of this doesn't make sense LMK and I'll clarify or edit.

 

[keep_hope_alive Premium Member]

Port Flares - Evaluation of noise

Flare-it - Free Speaker Design Software

this calculator works well and lets you experiment with radius.