port frequency question

[Mathman 0]

Sooo, I am now in the process of designing my box for a single 10" sub down firing in a ported enclosure. I got the rough idea for the design from those AudioFire boxes for trucks. The sub will be down firing right behind the center console, the main box will go up to right above the rear seat from the ground, the port would then go from the box to the back of the seat and do a 90 degree and back towards the front seat. So, the port is going to be pretty much external from the main portion of the box....my question is, how do I go about figuring out the tuning frequency of this port? It is going to be a fairly thin port but pretty long and I am just not to sure.

At the moment I am planning on using either a Q or BL. I have a RF1000.1 to use.

Thanks for the help

Edited November 25, 2008 by Mathman

[95Honda 486]

Just use any of the box modeling programs on the net. It doesn't matter or change the tuning frequency if the port is inside or outside of the box. Just be sure not to exceed the ratio of 1:9 for your cross-sectional area of the port if it is rectangular (i.e. a 1" x 8" port is OK, but a 1" x 10" port could be a performance compromise).

[Mathman 0]

so if i were going with a 2" port in height, width could be no more than 16", correct? also, i am going to have a pretty long port and the box calculator isnt letting me design a 12" wide box with 18" of port length, unless you know of another box calculator that allows the option for longer ports that go outside the box.

at the moment, a rough estimate of the port would be like 2"x11" for the actual port, but the length would probably be pushing around 28".

Edited November 25, 2008 by Mathman

[KU40 173]

You can't just arbitrarily pick a port length. You need to decide what you want to tune it to and pick the port length from that. So you want your port to be 2" x 11" and 28" long, how big is the box going to be (net, that the sub will see)?

[Mathman 0]

I gotta figure all that out, I am just trying to get a rough idea, I would like it tuned to about 34 Hz, and after checking out a few quick sketches I am fairly sure the port would need to be around 2"x11". i will play around on thanksgiving and get some better measurements to throw up on here, so i guess till then no worries.

[hiloracerboy84 0]

.159* sqrt(1.84x10^8xport area)/((box cubic inches* (port length+.823*(sqrt(port area)) works for me. its the formula on the JL site under tutorials - ports

[BKOLFO4 29]

http://www.carstereo.com/help/Articles.cfm?id=31

[Mathman 0]

One more quick question....if I want my port to be external, do I have to have any part of the port inside of the box or can I literally build it directly off the box? I was hopin to build it onto the box, but if I have to put it inside the box some then so be it.

Thanks

[95Honda 486]

100% of the port can be outside the box, it doesn't make one difference at all... It actually makes things easier because you don't have to account for the port displacement with you box design...

[diablo_331 23]

i think a passive radiator would be a great idea here

[Mathman 0]

That is exactly why I wanted to put the port outside the box, would be easier to design. Passive Radiator, ehhhh. I'm just lookin for something decently easy to build that will get very loud for Truckaudioman while he is out of commission. slowly workin on his truck....been tough, 82 hrs weeks at work.

[diablo_331 23]

its your build but passives r VERY easy to build..build a sealed box with 1 10 and 1 12 cutout then tune the radiator then ur set

[Mathman 0]

I've never done anything with passive radiators, yet alone heard pretty much anything about them. Not 100% on them, but I will look up some stuff and read up more on them.

[Duran 387]

A passive radiator would work fine for you, theoretically porting an enclosure gains you 3 dB, same with doubling your power, a passive radiator just doubles your cone area, so it is the same as porting it.

[Mathman 0]

so, for me to use my 10" sub, I would then need 2 additional 10" PR's....is that correct? does it require any additional airspace to use PR's?

[Mathman 0]

Okay, now I have looked over some stuff I am a little interested in Passive Radiators....What would be a good PR to use with a Fi Q? Would I also need to double the cone area for PR's...ie. 2 10" PR's for 1 10" sub? I read somewhere that you would need to double it.