port velocity help please

[brent379]

so I have my 4th order pretty much designed and im stuck on the porting part... I have three choices and don't know which one will be the best. box will be 2 cubes sealed and 4.2 ported after sub displacement....but that's not including port displacement. ive been modeling the ports on win isd and my options are:

1) square interchangeable port tuned to about 42hz... will give me the highest peak... +6.3 db at 37 hz and yield an f3 of 28hz and puts the port velocity at 63ft/sec at 36hz.... but this port also takes up the most amount of displacement...takes away 1.7 cubes and leaves me with a net volume of about 2.5 cubic ft.

2) 5-4 inch aeros 22.25 inches long tuned to 40hz...the peak is at +5.8db at 36hz and yields an f3 of 27hz and puts the port velocity at 88ft/sec @ 35hz and would give me a net volume of about 3.3 cubes after all displacements.

3) third option is 2-6 inch aeros 19.5 inches long which tunes to about 38hz.... peak is at +5.1 db at 34hz and yields an f3 of 26hz... but the port velocity goes wayyyy up to 96.5ft/sec at 33hz but leaves me with a net volume after all displacements of 3.5cubes...

ill be running 4 sundown sd 10s on an aq2200d at 1 ohm just in case ur wandering.

I just don't know which port is the best way to go. im not really going for pure spl...I wont be competing or anything I just want to be as loud as possible and I don't want my box to sound like a fart box lol just want a loud crisp clean sound. any help will be greatly appreciated!!!!!!!!!!!!!!!!!

[98GCLimited]

I had asked a similar question in the past and was told 1 6" aero would not be enough port area for a pair of 10s in a 4th. And 5 4" is barely bigger than 2 6" probably not enough port area either, so probably go with the square port (though you didnt mention what size).

I think a good starting point is half your total cone area in port area tuned to your sealed resonance and adjust from there.

With your square port your at about a 1:1.25 ratio though.

Are you at max dimensions with this box size or can you make the box bigger to compensate for the volume taken up by the larger port?

[brent379]

Ok I don't understand that 1:1.25 ratio can u explain that to me??? I've never understood that lol.

And yes I'm at the absolute biggest I can go. I've thought about going with just a ported box but on win isd it's nowhere near the output of a 4th at the frequencies I want so that's why I'm trying to go with a 4th.

[stroupe79]

1 to 1.25 is your sealed/ported ration..... 2cubes sealed to 4.2cubes ported is not a 1/1.25 ratio by the way...it's 1/2.1 again before port displacement

as for your port, I would go with a square port tuned to your resonant frequency

what frequencies are you trying to play that a regular ported box won't perform like you want?

[Bradprobert]

I would use port design one because you want to aim your air velecity right at 6% the speed of sound or slightly lower. Box ratio is determined between your ported compared to your sealed chamber or vise versa. The box ratio changes your bandwidth of the frequency response. the higher the ratio of ported to sealed the peakier of response and smaller bandwith. The smaller the ratio the flatter response and wider bandwidth. A good daily box will usually have about a 2:1 ratio. An spl oriented box will be 3:1 or higher. Also the port should be tuned to the resonant frequency of the car. If you cant overcome all the obstacles of designing a good forth, a ported box will be your best bet. the biggest issue is finding space; somehow i managed to get one under my back seat lol!

[brent379]

Oooo I got ya. I was thinking of something different with the ratio thing lol

And my goal with this box is for it to be really loud from about 30-40hz. I don't really care about anything higher because I mainly listen to rap hip hop and dub step.. Stuff that plays low. The resonant frequency of the sealed side is about 53hz. That's a little too high for what I'm looking for. Tuning my box around 40 ish puts the peak around 34-36....

[brent379]

And ya I understand how the 4ths work. I love em. Just a little confused on the port because I'm trying to use the biggest port possible without losing too much volume

[Bradprobert]

Well another big question is what subs are they?

[brent379]

4 sundown sd2 10s ran off an aq2200d at 1 ohm

[brent379]

And my total cone area is 268 sq inches