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Old 16th January 2005, 04:14 PM   #1
sidd_raj2002 is offline sidd_raj2002  India
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Default help on ports

helo i had posted a thread on my 1st sub project earlier.

thing is i have built a cub of approz. 36lts and have put two 6"
drivers facing back to back on opposite sides. it is a sealed enclosure.
the mdf is approx. 18mm. the sub sounds pretty good right now.
but i think a port might pump up the punch of bass.
this sub was made very casually so dont ask me the qts and vts and all that stuff. iam a real amateur (17yrs old). all i know is the woofers have big magnets (sending a picture).

so can any one tell me the lenth and diameter of port that will give me the lowest frequency possible. cuz i am hooking it up with my home theater.

if u can tell me the lenght and diameter of one port and 2 ports also.
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Old 16th January 2005, 06:57 PM   #2
Bill Fitzpatrick is offline Bill Fitzpatrick  United States
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You need the T/S parameters of the driver to do a ported box.
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Old 17th January 2005, 10:12 AM   #3
rabbitz is offline rabbitz  Australia
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Without the T/S parameters you are pushing to get anything but since you like playing around and have built these without any calculations you might as well have more fun.

Stick to 1 port only and start off with a 90mm dia x 150mm long. If it sounds too boomy, make the port longer and if it is a bit light on the bass make it shorter. That size port is your standard PVC stormwater pipe and should not be too hard to get. If you can get one with the end joiner on it so you can add pieces of varying lengths. If you like sealed better just get a PVC cap to go over the port.

Have fun with it but spend some time eventually learning how to do it properly as you will get a much better result unless by all miracles you guessed right.
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Old 17th January 2005, 10:48 AM   #4
Circlotron is offline Circlotron  Australia
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Hi sidd_raj2002.

My feeling is that for unknown drivers that size you would want to tune the box to no lower than about about 40Hz. So....

Find yourself a demo copy of Cool Edit or some other program that lets your pc soundcard generate sinewave tones. Put a 100Hz to 30Hz gliding tone through your amplifier and into your speaker and watch the cone movement.

You will be able to tell what the box+port is tuned to because as you get close to this frequency (going down) the cone movement will stop getting bigger and actually start getting smaller again, becoming smallest at the frequency the system is tuned to. This is also where the port is pumping the hardest.

Below this frequency the speaker cone movement will increase very quickly again, so you can't push it very hard below this.

This setup may not increase the amount of bass directly, but it will definitely =reduce= the cone movement for the =same amount= of bass, so that means you can drive it way harder before it runs out of travel.

But remember, not =too= hard below the tuning frequency.
Best-ever T/S parameter spreadsheet.
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