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View Full Version : How do you pick port area?



Exaran
10-18-2004, 11:19 PM
I've looked around, and found all kinds of equations and calculators for determining the length of a port based on box volume, tuning frequency, and port cross-sectional area...

How do you know how much cross-sectional area you need? Or do you just make it as big as you can fit?

This will be for an SQ oriented daily driver

Norcalracer283
10-18-2004, 11:21 PM
BBP

10 chars

Exaran
10-18-2004, 11:53 PM
?? Que ??

What you talkin about, willis?

jellyfish420
10-18-2004, 11:54 PM
power?driver?

Exaran
10-18-2004, 11:57 PM
Its for an RE8, at 200W RMS. I kinda wanted to know how i would go about figuring it out for any sub tho too

jellyfish420
10-18-2004, 11:58 PM
i was always told same area as the driver.

Exaran
10-19-2004, 12:04 AM
wow, that sounds pretty big for a .5 cube box

jellyfish420
10-19-2004, 12:12 AM
i think the re8 is .5sealed and 1ft ported. correct me if i'm wrong.

Exaran
10-19-2004, 12:25 AM
.21 sealed .5 ported at 32hz from their site

After fiddling with WinISD I came up with .5-.6 ported at 28hz for some good low end

I think the RE10 is .5 sealed 1.0 ported....

audioholic
10-19-2004, 12:31 AM
i was always told same area as the driver.

That cannot be right. If that were the case, the proper port area for a 15in driver would be 175 sqin. Way way too big.

Check with the driver manufacturer for their recommended port area.

DBfan187
10-19-2004, 12:44 AM
^^^I think that only applies for SPL only installs?

OLD_SCHOOL
10-19-2004, 04:28 AM
spl guys say use at least the sd on a driver... for a 15xxx thats like 125 in^2 seems a little much for a non comp box.

use a modling program and check the vent velocity at your power

BASS OUTLAW
10-19-2004, 05:07 AM
i thought that the air velocity in the vent should not exceed 10% , of the velocity of sound in air, thats why u go for more cross sectional area, to avoid whistling.
didnt knew it got SPL issues

jellyfish420
10-19-2004, 08:16 AM
WIth SPL, enclosure design plays a huge role (not just volume/port area/tuning) :fyi:
like what???

req
10-19-2004, 08:27 AM
i thought it needed an 8:1 ratio...

so what if you dont have BBP or winISD... where can i get one of these.. id really like to use them.



/offtopic
nice warning label jellyman =D

Nikuk
10-19-2004, 08:40 AM
like what???

think of it this way: if it were as simple as lots of port area & lots of wattage... wouldn't everyone be putting up 160's+?

Are they? No.

req
10-19-2004, 09:56 AM
so how do you guesstimate how much is a good port area? what factors come in to play that determine the SQ or SPL?

if its a daily driver, does it really matter as long as its large enough and the right tuning to eliminate port noise?

Nikuk
10-19-2004, 10:28 AM
so how do you guesstimate how much is a good port area? what factors come in to play that determine the SQ or SPL?

if its a daily driver, does it really matter as long as its large enough and the right tuning to eliminate port noise?

if i told you about "The One," perfect SPL port, I'd be lying.

And if i wasnt, the CA gods would slaughter me & my family.

If i told you about "The Perfect" ratio for an SQ or SQL port... see above.

Rule #1: different strokes for different folks/drivers/cars/tunings/weather/yougettheidea.

Rule #2: Study your physics.

req
10-19-2004, 10:38 AM
if i told you about "The One," perfect SPL port, I'd be lying.

And if i wasnt, the CA gods would slaughter me & my family.

If i told you about "The Perfect" ratio for an SQ or SQL port... see above.

Rule #1: different strokes for different folks/drivers/cars/tunings/weather/yougettheidea.

Rule #2: Study your physics.


for that i would have to say this;

i never asked for the perfect port ratio.
i never asked what anyones oppinion was.

i asked "what factors come into play when deciding on port cross sectional area" (well, not exactally like that but yea)

so, since there is no real 'perfect' awnser, what is YOUR oppinion on this matter? what do YOU like or use when you create a port? im not asking for a definitave awnser, but somthing that will point me in the right direction. :patrioti:

Exaran
10-19-2004, 11:04 AM
Ah ha! Found it myself ;)

http://www.diysubwoofers.org/portcal.htm

Look about 2/3 of the way down for "Minimum Port Diameter" ... It looks a little complicated, but should be do-able. This will tell you the minimum size to prevent most port noise

Looks like all it takes into account is Xmax and the diameter of the woofer

jemorgan85
10-19-2004, 11:15 AM
Scott Stoner just did a 150.8 with a single Mag D2 12 in a 11.2 cube box with 302 square inches of port area.

Nikuk
10-19-2004, 12:04 PM
Ah ha! Found it myself ;)

http://www.diysubwoofers.org/portcal.htm

Look about 2/3 of the way down for "Minimum Port Diameter" ... It looks a little complicated, but should be do-able. This will tell you the minimum size to prevent most port noise

Looks like all it takes into account is Xmax and the diameter of the woofer

the only real problem with that is you really wont see xmax @ tuning (which is when the port's working it's hardest). Otherwise, not too bad.


for that i would have to say this....so, since there is no real 'perfect' awnser, what is YOUR oppinion on this matter? what do YOU like or use when you create a port? ....

for "sql" purposes, I use 10-15 sq in of port per net cube of vB.
for "supplement" purposes (i.e.-my gf's car) i use 8-12 sq in per net cube.
for "my enclosures" 12-18 sq in / per.
for "comp" testing I use 3-36 sq in per net cube OR 40-120% of driver sd depending.

Depending on the output potential and Pe of the driver, these are adjustable.

Nikuk
10-19-2004, 01:27 PM
This formula assumes the driver is hitting Xmax at tuning, which is extremely difficult with today's high linear excursion drivers ...

With Sonys, this formula is great ... Not so much with W7s ;)


LoL.. exactly.

Exaran
10-19-2004, 06:11 PM
It did come out a tad big using the original formula... ~6" round port for an 8" woofer...

If xmax is too big, what do you think is a good replacement? ... maybe use 1/2 xmax?

OLD_SCHOOL
10-19-2004, 06:13 PM
the only way to find the best box for YOUR spl application is to either
1) know what your doing and use a ton of trial and error
2) have someone who knows what they are doing pay them a crap ton of money to find the best box for YOUR application

3) to put up good numbers in SPL comps goes way beyond knowing how to figure out ports and volumes... many things come in to play like nick said get real comfy with your physics books.
i am no expert on spl enclosures and i am even less of an expert on someoneelses spl enclosure i can draw up something i think will do very well in your car and it may turn out to not do well at all. or something i think may not do well turns out to be the cats azz

to make it simple it all in YOUR application.

when 1/10ths of a DB may make the diff between 1st and 1st looser you better be ready to use up some mdf and some serious time

jellyfish420
10-19-2004, 06:16 PM
think of it this way: if it were as simple as lots of port area & lots of wattage... wouldn't everyone be putting up 160's+?

Are they? No.
my question was what kind of "special" things go into hitting higher numbers? i know its just not all about port and power. but for example what are some of the design "tricks"?

OLD_SCHOOL
10-19-2004, 06:22 PM
jelly you might as well be asking to have *** with someones wife... cause they are more likely to to tell you yes there then to come of with that kind of information.


but i will say this air flow , port linearity are a couple biggies

Nikuk
10-19-2004, 06:28 PM
Duct tape.


sssshhhhhh....

Exaran
10-19-2004, 06:30 PM
the only way to find the best box for YOUR spl application is to either...

STOP right there! :)

I'm just looking for a good starting point for making a daily use SQ sub... I know everybody gets excited about SPL on here, but can anybody help me out?

I'm kinda getting a feeling that if i'm not competing there is some give in how big I make my port... so I just need a ballpark

Thanks guys

([edit] I appologize if the above quote wasnt directed at me)

OLD_SCHOOL
10-19-2004, 06:31 PM
dammit you might as well let out the secret that using black paint in the port and a clean but crack gives at least 2 Db

OLD_SCHOOL
10-19-2004, 06:34 PM
STOP right there! :)

I'm just looking for a good starting point for making a daily use SQ sub... I know everybody gets excited about SPL on here, but can anybody help me out?

I'm kinda getting a feeling that if i'm not competing there is some give in how big I make my port... so I just need a ballpark

Thanks guys


there is a TON of give some people say 13 SQ inches of port to every cube of VB. i say use a modeling program and look at the port velocity cause if you not competing then you don't need to worry about squeezing every single 1/10th of a db out

jellyfish420
10-19-2004, 07:54 PM
jelly you might as well be asking to have *** with someones wife... cause they are more likely to to tell you yes there then to come of with that kind of information.


but i will say this air flow , port linearity are a couple biggies
i wasn't asking for detailed secrets. but air flow and port linearity. those are some good starting points. just wondered so i can try some diff things on my own. linearity...you mean a straight port(no bends)? and how much of a gain will see with these tricks?1-2db? or bigger, if you know some better secrets?