Jump to content
Sign in to follow this  
pervitizm

Need help in figuring out port tuning and port area

Recommended Posts

I recently brought a pair of LvL 4 with LvL 5 coils to go with my single Autotek MM4000.1D amp. I want to put these subs in an 07 Chevy Suburban LT.The idea is to keep my third row seats. That was the main reason why I brought a suburban instead of a tahoe. So far this is what I've came up with. *Note all measurements are external*

Height: 23 3/8 inches or 28 1/2 inches if I go up to top of headrest

Width: 49 inches

Depth: 28 3/4 inches

I went to 12volt.com to use their volume calculator and it came out to roughly 15 cft of internal volume space.

image00oh7.jpg

I want to go ported with the 18's and I want to go both subs and ports facing up as apposed to subs up and ports to the rear.

So I created a couple different boxes using Sketchup and I used this box volume/port area thread on ROE to help me out with trying to figure out the tunning and port area.

The first box I did was a single port in the center of the box between the two subs firing up. Box external measusrments are 24hx49wx26d. Both the top and bottom are double boarded. The port opening is 5wx24.5hx10d.

dcbox3tw7.jpg

The second box I made was one where it had two ports. One on each side of the subs. Again both the top and bottom were double boarded and the ports were 2.5wx24.5hx10d

dcbox5mo5.jpg

The third & forth boxs are ones I did based off of some help I got over on SMD. I also need to note that I've only used the tuning formula and other tips from here on box 3 and 4. This box has an 8wx24.5hx13d port, which is a single port off to the side of the box.

rustyboxjh6.jpg

While this box is more of a CRX style has a port 8wx21hx13d.

rustybox2qi6.jpg

Now here is what I came up with as far as tuning when I plugged in the numbers for both box 3 and 4.

External

24Hx49Wx26D =17.7 f^3

Interneral (Before Displacement) = 14.14 f^3

21Hx47.5Wx24.5D

Port Opening is 8 iches Wide and the depth is 13 inches

Box 3 is 8Wx13Dx24.5H- port area is (8x24.5 = 196sqin)

Displacement: (8.75x13x24.5)/1728

Box 4 is 8Wx13Dx21H - port area is (8x21=168sqin)

Displacement8.75x13x21)/1728

Fb = 0.159*SQRT[(Av*(1.84*10^8)/(Vb*1728*[Lv+(.823*SQRT(Av))])]

LV is the length of the port

AV is your port area

VB is your boxes internal volume(every displacement accounted for)

Fb will be your tuning frequency once you work the formula through.

Box 3 Fb = 0.159*SQRT[(196*(1.84*10^8)]/(14.14*1728*[13+(.823*SQRT(196))])

SQRT (196) = 14

10^8 =100000000

Box 3 Fb = 0.159*SQRT[(196*(1.84*100000000)]/(14.14*1728*[13+(.823*14)])

0.823*14 = 11.522+13 =24.522

14.14*1728 =24433.92*24.522=599168.58624

Fb = 0.159*SQRT[(196*(1.84*100000000)]/599168.58624

1.84*100000000=184000000

184000000*196=36064000000

Fb = 0.159*SQRT[36064000000]/599168.58624

36064000000/599168.58624 = 60190.08

Fb = 0.159*SQRT(60190.08)

SQRT(60190.08) = 245.336667

Fb = 0.159*245.336667

Fb = 39.008hz

Box 4 Fb = 0.159*SQRT[(168*(1.84*10^8)]/(14.14*1728*[13+(.823*SQRT(168))])

SQRT(168) =12.9614814

Fb = 0.159*SQRT[(168*100000000)/(14.14*1728*[13+(0.823*12.9614814)])]

Fb = 0.159*SQRT(16800000000)/261442.944

Fb=0.159*SQRT(64258.8)

Fb= 0.159*253.493195

Fb = 40.305hz

Sorry for such an loooonnnng post, but I want to make sure I have the whole port area and tuning formula down correctly. If this is so then I'll know what to do to make port adjustments. As you can see both box 3 and 4 if the numbers are right are tuned really high. I was shooting for more of a 32hz - 35hz range.

Share this post


Link to post
Share on other sites

Maybe try starting from the other side of the design procedure, with your goals first.

What are you looking to achieve, most of all? Do you know the sound you're after? Also do you have any idea how many cubes each of your subs works best in, or do you have any T/S properties for your woofers? I haven't played around with these particular drivers so if you have any info from other guys who already have experience with them that could be very helpful.

Also, for the box I would probably do subs up, port back in your suburban. It tends to work very nicely in SUVs and I wasn't too fond of the subs up, port up when I tested that setup.

Share this post


Link to post
Share on other sites
Maybe try starting from the other side of the design procedure, with your goals first.

I think I pretty much laid out my goals, which is box for pair of Lvl 4 18's tuned around 32hz with both subs and port firing upwards. I guess after reading my post above I really didn't clearly stated what I was looking for out of this post. What I wanted to know was did I do the tuning formula correctly? If I have that fomula correct then I can redesign the box to meet my tuning tuning needs.

What are you looking to achieve, most of all?
Daily driver that tuned for music mostly hip hop, rap and r&b. However I listen to a lot of different types of music so I want it to still sound okay if I play some old Duran Duran or Korn. It just that 90% of the music I listen to is hip hop, rap and r&b.
Also do you have any idea how many cubes each of your subs works best in, or do you have any T/S properties for your woofers?

The T/S parameters can be found by going here. According to the T/S the subs need around 5.75ft^3 of space per woofer. So I wanted my box to fall right around that with bracing accounted for. so I figure if I can get around 11.5 to 12ft^3 of internal air space then I should be straight.

Also, for the box I would probably do subs up, port back in your suburban. It tends to work very nicely in SUVs and I wasn't too fond of the subs up, port up when I tested that setup.

Yeah, it appears that most of the folks I've talked to on all the other forms have suggested that I go for the more traditional CRX style of enclousre. So I haven't rule that out totally. I'm in the process of redesigning again just to see what I can come up with. Doing this is a lot cheaper than buying MDF and getting the box all wrong.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this  

×