posted
After reading a few post on programs not calculating for port and driver displacement this leaves me to ask.. What is the correct way to get the port where you want it. If my box is 4.6ft^3 before port and driver displacement, so I subtract driver displacement and say ummm 4.3ft^3 now for the port, I figure the port for a box that is 4.3ft^3 but after port displacement the box is now 4ft^3 does this raise my tuning freq? Anyone get what im saying? "hope so"
posted
Depends on how accurate you want it. Figuring in the sub displacement is good, try to get the port displacement in there as well, but don't worry too much if you're 0.1cuft out as it won't affect the sound much. Colin
------------------ Spy Shots Warning SPL in my car exceeds government health guidelines, civilians are advised to proceed with caution. Failiure to comply may result in serious injury or death.
pr = port radius in inchs vb = box volume in cubic feet after woofer displacement fb = tuned freq in hz
This is the formula I use from maple 5.0 to figure out port lengths exactly. You can get a "demo" version of maple that will do this for you for free from their site. Very fast way of doing it. Should be very acurate. Let me know if you have any questions.
Port displacement becomes very large very quick when you start talking anything over 4-6" round port.
[This message has been edited by TGuY (edited 04-20-2001).]
Posts: 736 | From: Albertville MN USA | Registered: Mar 2000
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posted
Well I will be using slot ports. The reason I ask is because it will be a switchable SPL to daily drive port. So for SPL the port will be upwards of 100in^2 which could hender alot of air space in the box. What is the website for that program?
posted
net volume and total volume can be considered two different things to clarify box building. remember, the driver wants 4.6 ft^3 of air. If your square port has a volume of .3 ft^3,and your driver displacement is .2 ft^3, then add them all together. Just make your box with an overall internal volume of 5.1 ft^3 and you will be set. These last two volumes are guesses, so just replace them with the proper volumes.
i've used it to calculate ports on three boxes now and all are tuned right (cones don't move when played at port tuning freq
------------------ Team "Under Pressure"--coming soon to SE Minnesota for a summer tour wall w/three shocker15's and a cadence a7hc...in a tiny corolla
If the application is particularly important (IE you want to dial in a peak response or best response in the car, etc) I suggest changing the port length.. Use the equations to help you find how much length to cut off per experiment, and see what sounds the best/gives you the highest SPL
ShadowStar
------------------ Still looking for that CHEAP Thunderdome :D
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Posts: 2578 | From: Somewhere In the Northeast | Registered: May 1999
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posted
ya, I agree.... EXPERIMENT> but as far as calculating things correctly, its an iterative process. You use a given box size, figure out the correct port. then calculate the correct box size with that port and find the port size again. if the new port changes your box size again, do it again. If you use slots against a wall in your enclosure your gonna have to experiment anyway. there are equations for that, but a lot of prople on here told me to ignore them which I did. End result, my enclosure was tuned to 45Hz instead of 62-63hz.
------------------ 2-DD 9512's 2-2000X's (for now) 8.0ft^3 box in a civic trunk One big ass port ?????dB's
It's not the size of your woofer, It's the size of the waves your woofer makes!
Posts: 1259 | From: Fullerton. CA ,USA | Registered: Oct 1999
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