what is a bad port ratio?

[scoobywrx05]

ummm so youre saying a port that is 10 x 10 will have less restance than a port that is 20x5.............

Less surface resistance only. If you have turns or flares or else in one port and not in the other, then that's different.

ok explain to me how the same amount of port area can have different surface resistance

Ok. Surface area resistance is equal to the area inside the port. An example. A 10x10x20 long port and a 5x 20x 20 long port. The tuning on the 5x 20 is actually a little bit higher then a 10x10 at the same length. A 10x10x20 has a port area of 800 where a 5x 20x 20 has a port area of 1000. Less area = less resistance.

[will77530]

ummm so youre saying a port that is 10 x 10 will have less restance than a port that is 20x5.............

Less surface resistance only. If you have turns or flares or else in one port and not in the other, then that's different.

ok explain to me how the same amount of port area can have different surface resistance

Ok. Surface area resistance is equal to the area inside the port. An example. A 10x10x20 long port and a 5x 20x 20 long port. The tuning on the 5x 20 is actually a little bit higher then a 10x10 at the same length. A 10x10x20 has a port area of 800 where a 5x 20x 20 has a port area of 1000. Less area = less resistance.

not by any calculations i know

[Joe X]

For all rectangles of the same area a square will have the least perimeter, the surface area of the port is the perimeter times the length. So for a given port area and length the square port will have the least surface area.

[scoobywrx05]

What is 10 times 20, then multiply that by 4. That will give you the internal surface area of the port. Now do the same for the 5x 20.

[scoobywrx05]

For all rectangles of the same area a square will have the least perimeter, the surface area of the port is the perimeter times the length. So for a given port area and length the square port will have the least surface area.

I think he's just getting port area and port surface area confused is all. No biggie. Just trying to help him understand the difference between the two.

[Joe X]

I think this is hardly useful information to the OP. So to the OP:

Acceptable port area ratio is: Height/Width <= 9 or Width/Height <= 9

Preferred port area ratio is: Height/Width <= 6 or Width/Height <= 6 ( according to some )

In most applications, basically daily, the above will work very well, competitors wanting to squeeze the last 1/100 dB surely will not want a 8:1 port.

[john253a]

Joe is very correct on that 1

A 10x10x 20

Has a ratio of 1:1

Port area of 100 (10x10)

Port surface area of 800 (10x20 + 10x20 + 10x20 + 10x20)

A 5x 20x 20

Has a 4:1

Port area of 100 (5x20)

Port surface area of 1000 (5x20 + 5x20 + 20x20 + 20x20)

A 11.2r x 20 aero port

Has a ratio below 1:1

Port area of 100

Port surface area of 700 (11.2x pie x 20)

But will have a much lower tune so it will be even lower

That's where port ratio comes into play

Aero 9-12aq" per ft

Slot 12-16sq" per ft

Because of the efficiency it allows a small port to be used

[brian222]

freakin aye! i found the holy grail finally after literally more than 12 hours probably closer to 16 hours of surfing the net forum after forum (ok probably more like four or five hours cumulative lol) but I was trying to figure out if round ports or the same as slot or square ports in relation to area needed per box sqftage think i found gold in these parts hope its accurate lol I'm just wrapping up my first build for 12 in a ported box they're really cheap subs just $40 power acoustics just so I could of get the hang of it without spending a lot of money but anywho I was trying to figure out the necessary port sizes for the size of my box I only have two chambers two subs per chamber and 4 cubic foot per chamber again these are only $40 subs so I know if one blows though both blow which like I said I don't really care I'm just trying it out but after making one Aeroport of 4 inches and thinking that I had it tuned right I started thinking maybe I need another port heck mayb 2 more lol because I know with slot ports you usually run 12 to 16 square inches per square foot but I didn't know if that rule applied for round ports also, but thanks for the post! ...ps -- I'm only running about 450 RMS to eat sub so like I said I don't know if that comes into play either with needing more ports? :-/ any feedback is greatly appreciated I'm excited about doing other builds like I said I picked the harder one that I should have for my first one should have just went with a sealed enclosure but that's just boring anyways next bill is two fifteens in a dual slot ported box then I'm going to dust off my three audiobahns and build a bandpass box wish me luck on that and like I said any feedback is greatly appreciated I've been seeing different ratios on bandpass boxes and I don't know what to go with a 1 to 1.5 or 1 to 2 ratio cannot really go any bigger than a 2 to 1 but ok I'm done rambling for now...