# Help with sub box design



## Slam-Hog (Aug 12, 2010)

I got a PPI pcx122. Recommended box specs for a ported box is 1.25cf with a 2.6" diameter port. 

I've always been told to fallow manufacturers recommendations, but wtf is with the 2.6" port. That seems way under anything i've ever come across in the past. Not to mention the 1.25cf box size, which is also slightly smaller than what i've dealt with in the past.

What I want out of is it good sound quality, with some bass. I'd like a ported box for maximum spl, but i'm still concerned about SQ, so I plan on tuning the box to 32 or so hz. 

So basically my question here is, should I fallow manufacturer recommendations, or just build a 1.8cf box with a 4" port and tune the port to 32hz?

What are the ups and downs of larger/smaller box size and larger/smaller port diameter?


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## Pat @ Pitt Soundworks (Nov 14, 2008)

Ported enclosures have to have a certain port area or else you will get port noise. For whatever that enclosure is tuned to, a 2.6" diameter hole is what is required.

4" is a lot of port for a single 12.

Larger/smaller box: efficiency. The bigger the box, the less power you need to reach maximum excursion. ALSO, the bigger the box, the easier it is to reach the thermal limits of the sub. For sealed enclosures, larger enclosures also change the dampening force on the sub and frequency response, but for ported enclosures it's not such a big deal (unless the box volume gets silly small).

more/less port area: the more port area, the lower you can tune the enclosure before hearing the port chuff. Port area can also change the amount of output (volume) the enclosure will produce. If you go with too much port area, the enclosure begins to act like a dipole box. IF you go with too little port area, the enclosure will act more like a sealed box. More port area also requires a longer port for any given tuning frequency.

Here's some graphs of different enclosures, estimated for cabin gain.









and just an FYI, that bandpass enclosure won't fit in the trunk easily.


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## Slam-Hog (Aug 12, 2010)

Not going bandpass.

So I guess you're saying I should go by manufacturer specs?

Is there a general rule as to the height/width ratio of a slot port? My design would be 12.5 tall which would make it only .625 wide.

Heres a link to the pdf for the sub. Its the 122. http://www.precisionpower.com/Manuals/Subwoofer Manuals/Precision_Power_PCX Series Subwoofers.pdf


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## Pat @ Pitt Soundworks (Nov 14, 2008)

If you use a slot port 12.5" high, use a width of at least a 2" and no more than 3".


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## Slam-Hog (Aug 12, 2010)

pi R square finds the area of a circle, correct? The round port to slot calculator I was using online must have been wayyyy off. it gave me a .625 x 12 slot for a 3.2" round port.


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## Pat @ Pitt Soundworks (Nov 14, 2008)

That's right, but a slot port has a lot more surface are compared to a round port. More surface area = more friction. A port of 12x.625 would react the same way as a leaky sealed box. It needs more port area.


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## Slam-Hog (Aug 12, 2010)

I'm using this calculator http://www.the12volt.com/caraudio/boxcalcs.asp

I figured port area of 3.2" round. Box volume is 1.32cf. tuned to 30hz, 15" long port. okay, sounds correct.

Same port area on a slot, 1.875x13.5", 1.32cf box valume, tuned to 30hz... *port 53" long*

WTF? 

I dont know why i'm having such a hard time with this one. Never had a problem in the past. Maybe i'm getting too old for bass.


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## Pat @ Pitt Soundworks (Nov 14, 2008)

Why 1.32 cu ft? Stay with 32 hz. There isn't enough of a difference between 32 hz and 28 hz to warrant the longer port length with this sub, let alone anywhere in between. And what's with the 3.2" port?

I'm getting for 1.32, 30hz, 3.2" a 16" port length. 8" sq inches port area.
for 1.875x13.5 (again, what's with the odd number choice?) I'm getting 53" port length and 25.3 sq inches port area.

As I said before, as port area increases, so must port length.


This was 1.25 cu ft, 28hz tuning, 2" x (I think 10") port for two 8s.


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## Slam-Hog (Aug 12, 2010)

Heres how I came up with the numbers. 

pi R ^2 of a 3.2" (which is what we just agreed is the area of a circle) is 25.3 square inches. 

The inside of my box is 13.5 tall, so thats one port dimension x 1.875 to get the 25.3 square inch surface area.

How'd you come up with 8 square inches of port area with a 3.2" port? I'm obviously doing something wrong here. MasterCam is also giving me 8.04 for a 3.2" port.

So that goes back to my origional 12.5x.625 port area.  I'm so confused. I need a nap.

Ok i see what i was doing wrong now. I was doing pi x r = 5.024 x 5.025 = 25.24
R square x pie = surface area.


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## Pat @ Pitt Soundworks (Nov 14, 2008)

Diameter = 3.2"
Radius = 1.6"
pi = 3.14

3.14 * 1.6 * 1.6 = 8.0384

8/12= .667"

25.3sq in port are would be a 5.67" diameter port.


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## Pat @ Pitt Soundworks (Nov 14, 2008)

Here's some free box designs:

1.25 @ 32hz









1.6 @ 32hz









source:
http://www.caraudio.com/forums/enclosure-design-construction-help/137804-free-box-plans.html


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## Slam-Hog (Aug 12, 2010)

Them things are huge. You think port chuff would be audible with a 1.3cf box and 3" round port tuned to 32hz? It's not like I got an orion hcca here.


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## Pat @ Pitt Soundworks (Nov 14, 2008)

Probably not. If it does, you won't hear it in the trunk.


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## Slam-Hog (Aug 12, 2010)

That about does it. Thanks for the insight.


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