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| Date: |
March 11, 2008 at 21:52:28 |
| From: |
Oscar , [65.116.31.254] |
| Subject: |
Re: A Question of Vents |
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one thing that i have found after many many years of making vented reflex alignments, is that the closer you put the ports to an adjacent wall, the more it drops the actual tuning frequency compared to the theoretical...i first saw this when i started doing slot ports
i found that if you use a slot port that uses 3 walls of the enclosure for the port itself, the port only needs to be 60%-65% of the the theoretical length required....i came to the conclusion that the end-effect is greatly multiplied when using several walls
i then built some ported boxes with traditional circular vents....well obviously, with a round pipe you cant use any 'enclosure walls' as part of the port walls, but if you put it in a corner of the box (while still maintaining at least one-diameter's distance from the back wall), the tuning frequency is also shifted downwards a substantial amount
so what does do for us?....well, instead of just using shorter ports, you can increase the port area to effectively reduce mach vent air speed with no penalty to required length, because the required length will now be simply 60% of the original value [for slot ports], for circular flared ports i use 65% of the original calculated value
i hope this helps you all in your future box building endeavors :)
in fact before i end this message, look at this project:
http://www.diysubwoofers.org/projects/home/inf10bp/
notice how close those ports are to the sides and one of the othe walls?.....see how the tuning was dropped wayyyy lower than expected?.....that is what is happening here....i would be willing to bet money that if one were to keep trimming the ports down to get the original target Fb of 58 Hz, the final length of the ports would indeed be close to 65% the length of the original port length as dictated by most eq's and speaker design programs
oscar
musico79@msn.com
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