Port lenght VS baffle and air pressure - diyAudio
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Old 5th February 2004, 09:09 PM   #1
Guss is offline Guss  Canada
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Default Port lenght VS baffle and air pressure

Hi, well its a simple question and I hope there is a simple answer

When we design a port, most of the time we end up using big diameter tubes which demands long lenghts. Say my walls are 2'' thick so add 2'' to the total port mesure so the woofer sees the corect size... But adding up some more lenght add to air presure too... Can we say that the diam of a port stands for the tuning and his lenght for the air compression? Maybe not at all but... Some say that the woofer needs to ''see'' the port while winISD state that the box doesn't care wheter it's inside or outside of the box. Anyway we still have 2'' thick walls... When must I count the tube as baffle, port or air resist...
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Old 5th February 2004, 10:12 PM   #2
Guss is offline Guss  Canada
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WTH almost 2 hours and only 10 views, Ive always been bad at finding good titles , BUMP, at least if you could just read it and tell me what you dont understand lol anyway
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Old 5th February 2004, 10:35 PM   #3
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Port tube length is adjusted for tuning. To keep the length reasonable adjust the diameter as long as your air speed is kept under 18ms. The measured length is the portion of the port that doesn't change in diameter. For example; Precision Ports are made with flared ends but the calculated length is only the center pipe, not the flared ends. At least, that's my understanding.
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Old 5th February 2004, 10:39 PM   #4
Ron E is offline Ron E  United States
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All that matters in a port is its diameter and how much the air inside weighs. The air in the port acts like a rigid piston - hard to believe perhaps, but it's essentially true.

A ported box is really two systems - The woofer-box system and the port-box system. If you imagine the slug of air as a piston and imagine the amount of force it would take to compress the air in the box. If you have a large piston and a small piston, both mounted in a box of the same size, which will resist motion more? The larger one would, because for the same inward motion, the larger piston is displacing (compressing) more air.

The resonant system of the port-box consists of the mass of the port and the springiness caused by the port compressing the air in the box. The stiffer that springiness is, the larger the mass has to be (IOW, the larger the port diameter- the longer the port).

That is all that matters, it does not matter if the port is in the box or out of the box. I think the reason that people say the driver needs to "see" the port is just to stress that you shouldn't really put fill material in a ported box unless you want to reduce the action of the port.
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Old 5th February 2004, 10:46 PM   #5
Guss is offline Guss  Canada
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Quote:
Originally posted by Ron E
All that matters in a port is its diameter and how much the air inside weighs. The air in the port acts like a rigid piston - hard to believe perhaps, but it's essentially true.

A ported box is really two systems - The woofer-box system and the port-box system. If you imagine the slug of air as a piston and imagine the amount of force it would take to compress the air in the box. If you have a large piston and a small piston, both mounted in a box of the same size, which will resist motion more? The larger one would, because for the same inward motion, the larger piston is displacing (compressing) more air.

The resonant system of the port-box consists of the mass of the port and the springiness caused by the port compressing the air in the box. The stiffer that springiness is, the larger the mass has to be (IOW, the larger the port diameter- the longer the port).

That is all that matters, it does not matter if the port is in the box or out of the box. I think the reason that people say the driver needs to "see" the port is just to stress that you shouldn't really put fill material in a ported box unless you want to reduce the action of the port.
As sweet as I expected ! Nice so thats what I meant by diam and lenght relation, yeah thing appears clear to me this way, thanks Ron
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