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Old 26th April 2005, 12:36 AM   #11
GM is online now GM  United States
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Greets!

You're right on track! Many moons ago when I was experimenting with LAs I learned that a ~aperiodic slot vent worked the best since drivers nearest a standard vent or vents would unload quicker. In a way this was good since it creates a broader/flatter BW vent output, which unfortunately is also its downside, mass quantities of group delay (GD).

If the cab is tuned low enough and at frequency between the first fundamentals or harmonics, it's a great way to do it and is used in some better prosound cab designs, but tuned higher up it's better to match the vent to the app, which means to keep the vent length reasonable/GD low requires that it be ~aperiodic.

What I wound up with was a slot down the length of both sides of the LA, and when critically damped you get more gain than sealed, though less than vented, but the GD of a ~0.6 Qtc sealed alignment. With the rounded back though, sounds like it would be a natural for a full length slot.

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Old 26th April 2005, 12:38 AM   #12
justinc is offline justinc  United States
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thanks for the help. Great idea about the slot port but im limited to 10 inch with for the baffle and the 3/4 inch roundovers are going to come directly up to the edge of the woofer and tweeter line. the tweeter line will be about 12 inches or so shorter than the woofer line which is another reason i would like to place the ports above and below the tweeter line making the two about the same length.
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Old 26th April 2005, 01:29 AM   #13
dhenryp is offline dhenryp  United States
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I'm building a line array with 14 mid/woofs and I'm actually building seven seperate compartments, each with it's own port. I was concerned about pipe resonances if I built it with one long narrow box. I'm sending my ports out the back to reduce the possibility of hearing any port noise.
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Old 26th April 2005, 01:44 AM   #14
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I don't really understand why either of you are going to all the trouble of porting the arrays, since you're both still going to need a sub for the bottom anyway. I find it's more difficult to integrate a sub if you have ported bass above it making the extra construction complexity counterproductive.
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Old 26th April 2005, 09:01 AM   #15
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I'm with John on this, just go sealed.
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Old 26th April 2005, 02:22 PM   #16
justinc is offline justinc  United States
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The F3 sealed will be around 90hz. I would like to cross over to the sub around 60hz though, which is why I wanted to go ported. Do you think room gain will be sufficient enough to bring it down near that? Also sealed because it will be easier to build, or do you feel that the sound quality will be much better. thanks
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Old 26th April 2005, 03:18 PM   #17
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If you have a sub with variable XO points slopes, then integrating with ported array may not be too difficult. If you are using a typical 12db/oct fixed subwoofer XO, then matching the more gentle rolloff of a sealed array is likely to be much easier and it may even end up that the 60hz XO point works.

Also, if you go sealed and leave the back panel for last, then you can try it as my favorite, an OB line array.

If you do go ported, then you do have the option of adding some resistance in the ports like GM suggested. That will give you more extension than sealed and improves the group delay over ported, which is likely to help with sub integration. Plus you can always plug the ports later.

Personally, I like to take the easy route. Plus I think the 60-90hz range is very important for bass SQ, so I'd avoid causing group delay in that range if at all possible. GM is one of the very experienced people here who gives really sound advice, so if you do go ported, plan on going aperiodic for best results.
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