Porting a fiberglass enclosure

[gr3nade 10+ year member]

When building a ported fiberglass box, how do you calculate the port length? You have to build the box first to get the displacement, so how do you add a port without changing the box volume that you used in the equation? Kinda hard to explain what I mean so sorry if I'm not very clear.

Thanks

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[bcarpenterfhl 10+ year member]

you make the box first, calculate the volume with water or packing peanuts, then design your port. you will have to use a sort of trial and error process when determining port length. ie start out with a port length, calculate the port displacement, then see what its tuned to. it'll probably be easiest to use round ports. once you make your enclosure and figure out its volume, people at this forum (ie me) would be more than happy to help you figure out what your port length should be.

 

[gr3nade 10+ year member]

Thank you for the reply. The problem with that would be that if you put the volume of the box into the equation, then got the port length and put a port in, that takes away from the volume in the box, which you used to get that port length. The formula is for volume after port displacement, right?

Thanks again

 

[bcarpenterfhl 10+ year member]

right, thats why you have to use trial and error.

 

[gr3nade 10+ year member]

Oh, I think I see what you mean. So just keep making the port a little bit shorter until the equation matches up with the correct volume and length, right?

Thanks a lot for the help //content.invisioncic.com/y282845/emoticons/thumbsupwink.gif.129404938effda6ad9cca39e7f4b58a3.gif

 

[bcarpenterfhl 10+ year member]

Oh, I think I see what you mean. So just keep making the port a little bit shorter until the equation matches up with the correct volume and length, right?
Thanks a lot for the help //content.invisioncic.com/y282845/emoticons/thumbsupwink.gif.129404938effda6ad9cca39e7f4b58a3.gif

yea. every time you make it a little bit longer/shorter, recalculate the displacement, subtract the displacement from the volume, and find out your tuning. if you have a graphing calc, the program listed in my sig will calculate your port displacement and everything else for you.

 

[jellyfish420 10+ year member]

pm req...he just did a ported fiberglass for 1 re10