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    subboxmaker's Avatar
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    homemade bandpass.. design suggestions?

    i finally bought the plexiglass and ports for it. When i installed the box and turned it up there is like a loud air noise coming thru the ports. does anyone have any idea why it is doing that? would it help if i installed more ports? because when i plug up a port it gets worse.. Any ideas or suggestions will be greatly appreciated. Thanks

    if i can figure out how to post pics i will.







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    I'm not an expert, but from what an audiophile friend of mine told me many years ago is, your ports are too small (diameter wise).. you are trying to push air through them faster than they can easily flow.. if you increase the diameter, more air can flow in the same amount of time.. This should reduce the 'air noise' significantly..

    I'd immagine you would have to make the ports shorter when you open the diameter.. not sure if your box will allow that or not.. And, I'm not sure if you would have to change the volume of the box on a bandpass for different porting.. but I'd immagine that math says you can keep all other things constant (box volume/tuned freq. etc) and get new values for just ports (increase diameter, see what you get for length).. the problem there is, you could physically pass limits (get a length of say, -2 inces for the port, but increasing/decreasing the volume of the box would bring it to the right side again)..

    I'd say re-calc your port length on a bigger diameter and see what you come up with for numbers.. if it's doable, that should clear up your noise problem..

    Hope that helps (and is right)




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    That's why I like calculators

    Thanks for the clarification..

    (OH, and make sure the ports don't get too close to the bottom/inside of the box.. if there isn't enough room for the air to flow behind the port to get out, you might get noise again, or the tuning will probably go out the window..)
    Last edited by Savant; 12-07-2002 at 05:15 PM.




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    well i have 3 ports they are each 1 7/8" wide by 4 inches long. the top of my box looks like this kinda lO O Ol so there isnt anymore room on the top for another one. could i possibly put two more ports of the same size on the sides. one on each side? do u think that would work? also does anyone know how to make picture files smaller so u can post them? i took some with my digital camera and there too big.... well thanks for the help guys




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    Just one quick thing...

    The box might not sound good because of the plexi. It will make a thudding noise, and sound like crap...and it will almost sound like the subs are locking up....the quick fix to this is to have the plexi facing into the floor of your vehicle.

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    Savant's Avatar
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    Originally posted by subboxmaker
    well i have 3 ports they are each 1 7/8" wide by 4 inches long. the top of my box looks like this kinda lO O Ol so there isnt anymore room on the top for another one. could i possibly put two more ports of the same size on the sides. one on each side? do u think that would work? also does anyone know how to make picture files smaller so u can post them? i took some with my digital camera and there too big.... well thanks for the help guys
    To get the files smaller, open them in some app (like Paint Shop Pro, or what ever you have) and reduce the size.. Make it something like 300x240 (or what ever ratio you would get, most apps let you keep the current aspect.. you set one value and it calculates the other).. Also, it's probably a .bmp, change the type to .jpg (that's compressed compared to .bmp).. and you can try to reduce the number of colors.. if it's at 16 Mil, set it to 32K for example..


    As far as other port locations, I have no idea.. You really should see how much space you have between ports and see if you can make them larger.. If you have the room, you might only make the outer two bigger.. like this
    | O o O |
    Ideally, you would keep them all the same size I think (and I'm not sure you can properly tune with different port sizes, but I don't see why not as long as the lengths match the diameters for the note).. You don't need 'more' ports, you need bigger ports (if you can swing it).. more ports could help, but the idea isn't to make as many holes as you can, it's get rid of the wind noise... If you can do that on 3 by making them bigger... Also, if you can 'easily' change the piece that has the ports in it, you could put in new wood and make 2 ports instead of 3, each would be much bigger.. Depending on size of woofers and power into them, you might want 3" or bigger diameters for each port (on 2).. If you can't replace the top easily, you might still try making the existing ports bigger..

    Hope that helps..
    Last edited by Savant; 12-07-2002 at 06:01 PM.




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    well i bought some real thick plexiglass and i sealed it real good and it doesnt make any noise so im good there. and i cant make the ports any bigger than what they are.. can i maybe just put one more on each side???




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    Did you round/smooth over the edges of the ports? If not try this first as it may be the problem. If after this you still get noise your going to have to do a redesign with more port area.



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    i think ill hafta redesign my ports...will adding more ports be the same as making the originals bigger? how many more do u guys think i should add? Thanks




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    i dont have enough room to put 3 inch ports




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    o allright i caught myself after i replied to that..thanks man ill try that




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