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View Full Version : Ported box help needed!!



badazzDD
01-03-2003, 09:42 PM
Ok, i am in the process of building my box. First, i need to make sure i have all the tools needed..

MDF 3/4"
Jig Saw
Silicone
Wood Glue
Nail Gun

I am going to make a ported box for my JBL GTO1220's.. The recommended specs are 2.25 cu ft per sub with a port dimension of 4 in diamater, and 13.31 in long tuned to 30 hz.

Questions:
1. Do i need to make a 4.5 cu ft single chamber with 2 of these size ports for the 2 subs?
- if i make the box bigger and add in a 3rd, or even 4th port, will the SPL increase?
2. What is the best material to use for the circular ports?
-Would it be better/easier to make a slot ported box?
3. Do i need to secure the ports in place?
4. For the finishing touch, what other than carpet can i use? Anything spray on?
5. How do i tune the port???

Pretty much, everything i need is here: (exept the lengths of the wood)
http://manuals.harman.com/JBL/CAR/Boxes%20and%20Parameters/GTO1220.pdf

Thanks in advance for any help!

badazzDD
01-03-2003, 11:58 PM
Originally posted by Jmac
1) Yes, you need to make two ports of that size.
2) Making the box bigger will increase SPL. Adding more ports will reduce port noise (Bigger boxes create more port noise, so more port area is needed).
3) Flared ports are the best.
4) It might be better to use a slot port.
5) Yes, you need to make sure they can't move.
6) Tuning the port is kind of complicated, but it is based on the internal volume of the box, the port area, and the port length.

Now, for my questions ...

1) How large is your trunk/how much of your trunk do you want to use ?
2) What amplifier are you powering them with ?

1. Trunk is HUGE! I can use up to 5+ cu ft and still have plenty of room for cargo.
- useable dimensions: no bigger than 34" L, 17" H, 15" W (roughly)
2. JBL 1200.1 - 4 ohm mono (for now) wanting to get 2 more 12's and run in 2 ohm mono
- subs are 2 ohm single voice coiled - 300w rms, 1200w max

badazzDD
01-04-2003, 01:06 AM
design for 2.. will keep and design another for 4.. but i wont have the other 2 for awhile.

I tried using WinISD Beta.. but i havent used it enough to completely figure it out.. from what i can tell, i will get a 5.01 db increase at 43.5-47.7 hz over my current box. not too bad.
(if i did it right)

badazzDD
01-04-2003, 02:52 PM
Originally posted by Jmac
Option #1

Construction Material = .75" MDF
Box Height = 17"
Box Width = 34"
Box Depth = 15"
Number of Ports = 2 (Round, one per chamber)
Diameter of Ports = 4"
Length of Ports = 11"
Port Area = 25.13 square inches
Box Volume = 3.63 ft^3
Box Tuning = 36.53 Hz
WinISD Estimated Peak SPL = 44.6 Hz
WinISD Estimated 3 dB Down Point = 35.8 Hz
WinISD Estimated Peak Port Velocity = 34.2 m/s @ 35.9 Hz

Option #2

Construction Material = .75" MDF
Box Height = 17"
Box Width = 34"
Box Depth = 15"
Number of Ports = 1 (Slot)
Diameter of Ports = 15.5" x 1.75"
Length of Ports = 22"
Port Area = 27.125"
Box Volume = 3.29 ft^3
Box Tuning = 29 Hz
WinISD Estimated Peak SPL = 45.8 Hz
WinISD Estimated 3 dB down point = 30.1 Hz
WinISD Estimated Peak Port Velocity = 26.7 m/s @ 24 Hz

is this showing that option 1 is a 2 chamber box and option 2 is a 1 chamber?
Also, would the box volume be before or after configuring displacement? Also, on the estimates SPL peak.. the 44.6 and 45.8 .. are these supposed to represent 144.6 and 145.8? By the way, i am only powering these with 600W not the 1200W..

thanks for all the help, and im sorry im asking so many questions. This is the first box ive built and i want to get it right.

i have measuerd my useable trunk space and i was off some:
my box useable space
L - 32" 40"
W - 17" 17"
H - 14" 18.5"

If i bolt my amp on the side ofthe box, i can only use 38" of length.. or, i can use all 40" and bolt my amp on the back (if i can get to it!)

I want to make sure i get the most possible SPL out of the restriceted measurments .. sicne im only using 600W

badazzDD
01-05-2003, 04:16 AM
Now, when you say most SPL, do you mean most SPL peak or most SPL possible over what frequency range ? [/B]

I mean i want the most possible gain night over the longest frequency range i can get. Since this wont be a competition setup, im not too worried about just peak spl.