51 replies to this topic

[D34M0N.inc]

Thats with the box slid out so far ^

And i would go the XXX for sure mate.

[KungFucius]

So what ports would everyone recommend, a slot port or 2x 4" adjustable jaycar ports?



Or other suggestions?

Edited by KungFucius, 11 February 2012 - 11:35 PM.

[Lunchbox.inc]

i would definitely look at either a slot port or drop in square port, as 2x 4" aero's won't be anywhere near enough IMO...

a slot or square won't make a huge different with what your looking at, the only reason i suggest a square port is for ease of use, IF you decided you want to tune it differently, then doing so with a slot port isn't easy, whereas if you have a removable square port, you can pull it out and change it around...

if your set on your tuning then i would say go with a slot port, as they're a no brainer really, if you want the ability to change your mind down the track, then a drop in square port would be my suggestion...

a rule of thumb for working out port size, is that you want around 15-18 square inch of port, per cubic foot of enclosure space, so if you have a 7cf box your going to want around 100-130 sq. inch of port... you can have more, or you can have less, it will still work just fine, but thats your standard "rule of thumb" for port area... you'll find generally less port area, can result in a slightly "choked" result where the sub doesn't flow as well and output can suffer, sometimes an audible "chuffing" results... and too much port may increase output, but at the expense of reducing your usable bandwidth, as the woofer will have less "under/above tuning" support, being that it will unload easier and closer to your tuning frequency, as that is the point where your enclosure provides the most mechanical dampening...

it's rather simple to work out the size needs of your square/slot port, for example 2" across and 5" up and you have yourself 10sq inch of port, simple, but if you were to go with an aero port, it's a little trickier...

the formula for working out the area of a circle is as follows...

A = (pi x R)^2

A = Area, R = Radius...

so say you have a 6" round port opening, the radius would be 3"

3 x 3.14 = 9.42 then from here you basically times your result by itself so 9.42 x 9.42 = 88.73 and there you have your area...

BUT to save time and render all of the above moot,

a single 4" aero is roughly 39sq. inch
a single 6" aero is roughly 88sq. inch...
a single 8" aero is roughly 156sq. inch...


*deep breath* OK... epic long rant of useless information complete... i know i usually don't have to post so much, but it's 5am, i have yet to sleep, and what started out with just saying that " 2x 4" aeros won't be enough so go for a slot port ", has turned into this...

now... for sleep... or more Star Trek TOS...? i just can't resist a Star Trek... hmmm...

[RAD]

I think you're a little off there dude. 4" is 12.5sqin, 6" is 28sqin, 8" is 50sqin.

[Captn_Awesome]

^Ross is right.
You've multiplied by your area not your depth

[KungFucius]

It's piR^2 so yeah, an 8" aero would be ~50sqin.

Ok, for a 7cf box, I'd be looking at having ~115sqin of port area. So with a slot port in a box that will, most likely, be 20" tall I'll need a slot port that's about 5.8" wide. (that's a wide port!)

Now, tuning, how would I go about tuning it to 26-27Hz? ie what length does it need to be?

Edited by KungFucius, 12 February 2012 - 06:06 PM.

[RAD]

for a 26-27hz tune, you need to reduce your area, you can't go by the optimal 16sqin per cube rule.

70sqin for a 7cuft NET box will need 30" port length, and thats a lot.

[Lunchbox.inc]

see... this is what happens when your over tired trying to give advice.... lol, i did say i was up late didn't i..? maybe that post should have gone in the "drunk" thread, i'm sure my tired-ness was equal to at least a few pints... hahaha


wow upon further re-reading i really was WAY off... ignore me... lol

Edited by Lunchbox.inc, 14 February 2012 - 12:32 AM.

[KungFucius]

for a 26-27hz tune, you need to reduce your area, you can't go by the optimal 16sqin per cube rule.

70sqin for a 7cuft NET box will need 30" port length, and thats a lot.

So you're saying a smaller port because bigger box?

So that would mean a 6" aero port would need to be 30" in length for 26-27Hz?

[RAD]

smaller port because of lower tuning... and honestly, with a box that large, port area isnt as critical as say, a 2cuft box.

You would need two 6" aero's, which is only 56sqin... which would tune even lower, or reduce your port to about 24".

[KungFucius]

smaller port because of lower tuning... and honestly, with a box that large, port area isnt as critical as say, a 2cuft box.

You would need two 6" aero's, which is only 56sqin... which would tune even lower, or reduce your port to about 24".

Is 150mm pvc piping readily available or doesn't it come on that size?

Also, how does one calculate how long a port needs to be to tune to a certain freq.?

[RAD]

To the general public no, but having worked for a pipe company, you might find a company that screens and threads PVC pipes, flash the cash and they might sell you an offcut.
Or, find a new suburb and see what you can grift.

As for calculating the port length, try this: http://www.carstereo...icles.cfm?id=31

[Lunchbox.inc]

To the general public no, but having worked for a pipe company, you might find a company that screens and threads PVC pipes, flash the cash and they might sell you an offcut.
Or, find a new suburb and see what you can grift.

As for calculating the port length, try this: http://www.carstereo...icles.cfm?id=31

i've picked up 150mm PVC from bunnings on several occasions... i could be wrong but i'm sure 150mm is rather easy to get a hold of...?

[RAD]

Some bunnings are different, but i've only ever seen 90mm/100mm largest at bunnings.

I was going to say, if you live near some new housing estates, you could find some short lengths VERY very cheeep.

[Lunchbox.inc]

bahahahahaha bobblehead.inc...

i must be pretty lucky with my local bunnings/mitre10/home hardware as they all have 150mm, BUT there's is definitely a much larger abundance of 100/90mm piping as well as the elbows etc...

[KungFucius]

Some bunnings are different, but i've only ever seen 90mm/100mm largest at bunnings.

I was going to say, if you live near some new housing estates, you could find some short lengths VERY very cheeep.

hehehehe yeah

[im45pl.inc]

if you want 150mm go to reece plumbing they stock heaps

[KungFucius]

if you want 150mm go to reece plumbing they stock heaps

Cheers mate.

[KungFucius]

WATCH THIS SPACE!!

For a link to the build thread I'm going to start when I begin installing my system

[D34M0N.inc]

Hellz yeh llook forward to it

[KungFucius]

Gotta wait for my goddamn pods before I even consider starting >: (

Edited by KungFucius, 28 February 2012 - 08:01 PM.

[KungFucius]

Here ya go, guys!

http://www.mobileele...r-the-vl-wagon/