Ideal port sizing?

Is there any best port size to aim for if your making a slot port? Obviously you want one tuned to a certain frequency but there is a few ways to do that.

I know flared ports perform better (i.e. flared slot ports or aeroports) but is there a formula that you should try and aim for.

(i.e. surface area should be 1.5 x woffer size and width should be half length? Or something similar)

Example
The Ford TX-5 I am working on with 2 x 15” woofers in ported box aiming for tuning of 52-53htz

Assuming you know the frequency your building it for and you have plenty of room to make it then should it be 1.5 times the surface area of 1 woofer?
Or the same area as one woffer? Or twice the area of one woffer?

Should the port width be half the length ?
Is there an ideal depth?

I know you need at least the port width clear behind the port so there is no restriction.

My box is approx 221 litre’s
360 x 180 x 155 gives a tuning of 52htz
So does
400 x 200 x 235
So does
300 x 150 x 73

Now in this example the 400x200x235 won’t fit anyway but I am just wondering what the best rule of thumb for port size is….

Just for those of you interested.
http://www.caraudioaustralia.com/forums/in...45&#entry630345

is the car in question

That tuning seems a bit high, are you sure it's correct?

Phil

Slot Port, 2 flared ends, bass box pro 6 says 52.1htz....

freom my testing bass box always seems to pump out a slightly higher number then what it appears. but thats cool.

also i have done testing in the exact same car.
a crx style box was loudest but to get volume the box ends up to close to the rear and puts too much pressure on the car and the res freq drops severly.
i was burping out 145 at 40hz from 1kwrms.
the only way to know for sure about port lengths is to test in car.. all the cars i have worked with have worked differently.
currently the charade has 2 12" subs and a box about 3.6cuft and a single 6" port with 2 aero's slapped together.
in my rolla it was loudest with a 4.5cuft box with 2 6" ports about 8 inches long.
same gear.
from my testing in my mazda it hit highest with around about 14sqinches of port per cuft. and ports were about 10" long flared both ends.

So your saying perhaps tune a little higher like 54-55 and it will end up being 52ish…?

I know it will be trial and error anyway once I get the box finished. (which I hope will be by the comp this weekend)


Thanks for the detailed response.

What exactly is meant by a CRX style box?
So did you find rear loading was best or port and subs firing up like in a mirage ?

We had 148htz in a box with the 2 woofers firing up about the middle of the cabin with the port firing backwards, but the box was too big for the subs (9c/f internal)

I meant that tuning seems too high for that car.

If a car "hits" at 54Hz, then usually around 40Hz tuning works best.

Generally about 1/4 octave below the peak is the best tuning.

Phil

Yeah sorry your right, (late night) I mean I will be playing around 52-54 and port tuning will be around 40htz, your correct.

Either way is there a rule of thumb for initial port ratio to woffer ratio?

As I've said before, it's all about testing, some cars I've built have lost as we increased the port area, some have gained.

I've normally found that keeping the port length under 400mm is an advantage.

Phil

The "DD Ratio" is 15 sq.inch per 1 cube, so thats 117 sq.inch worth of area for your box.

All depends on your subs, car and amps tho.. I've always had more success with stupid large port area than small port area's, Shieldsy finds the opposite works, and lots end up inbetween. Start with a lot and work your way down if you have the time. If not, try the above amount and go from there.

Cool, thanks.

The box is prety shallow only 310mm heigh (to comply with no wall criteria, so deepest i can go on port is around 170mm.

230 x 115 x 115mm deep gives me a tuning of 40.5htz
220 x 110 x 100mm deep gives me a tuning of 40.5htz

So i'lll start with the first one (largest area) and go from there.

For example, we run 650sq" in our 28 cube SS1-2 car, tuned to 45Hz, it makes 158.8 @61Hz from 4000W.

Ripped in our SS3-4 wagon runs around the same (as big as can fit) for it's 40+cube box and makes over 164dB at 54Hz.

I've found bigger is normally better, but you can't beat testing!! Start as big as possible then plug it with heavy foam or MDF to change tuning and area.

Phil

Ok well there are a few limiting factors

Box depth internal is 300mm so max port depth can be (depending on port size obviously) is 125mm, however it can be any width or length

Other option is to have the woofers on top of the box and port rear loaded, so they are not on the same face.

This has the advantage of being able to have a much larger and longer port but don’t get the subs and port loading off the same face with subs firing up and port rearwards.

This is what is known as a CRX box

Important question.

How do i9 calculate port tuning if I use 1 side of the box as part of the port?

I stick the sensor inside the port and run a low volume sweep

Do what i do .

GUESS .

I start with tuning generally 10hz below the resonant frequency and then i throw some bricks in the box to reduce box volume and increase tuning. This then gives me a result and i write down results see if it gets me louder if it does, i make another box this time smaller with lower tuning port yet again and start with the bricks again.

This helps me find the right box for the car.

Cool well in this case that is pretty simple since i can move the back wall in and change port pretty easy so i can try as i go.