port location on linearrays

[justinc]

I need to place the port on the front of the line arrays I am going to build because they will have a curved back. Does the port need to be inline with the woofer line. or can it be inline with the tweeter line/parallel to the woofer line without causing any problems. Also will it be more beneficial to place one at the top and one at the bottom to spread it out some instead of having just one. thanks

[VDOSC]

Based on what criteria?

FYI http://www.l-acoustics.fr/

worlds leader in line-array design. Everyone just started to copy after their long lasting success on line arrays. ProSound News was always full of events with them and still...

might be a good source of idea...

The technology behind the idea is pretty heavy. Check out their own basic criterias on WST.

A real line array just works awesome.

[RJ]

What drivers are you using for the mid-bass???
I've used 5 1/4" drivers with an fs of 55 hz and was able to get an F3 of 40 hz. in room with a sealed enclosure.
Room gain took over from there.
I've tryed ported and passive radiators on mine before settling on a closed enclosure. There was just too much midrange noise coming from the ports and the passive radiators.

[justinc]

I was going to use 12 dayton rs125 and 8 pt2B's In about a 2.8cft enclosure tuned to about 50hz getting and F3 of 52... in the same size enslosure sealed it looks like I would get an F3 of 80hz and qts around .5

[johninCR]

I would put at least 3 or 4 ports. You want the port output to have array dispersion to the extent possible. Also with such a long narrow cab I'd question whether 1 or 2 ports would behave the same as with a more traditionally shaped box.

[justinc]

well I coule put two at the top of the tweeter line and two at the bottom would be the most reasonable locations for them. Is it important if they are in an array really since most of what you hear coming from them will be less than 100hz anyways? In a previous line array I built a square port into the back and this worked out fine. But like I said these will have a rounded back so the port will have to go in the front.

[johninCR]

The difference is a 6db reduction in spl per doubling of distance vs 3db if you can get them to act like an array. For bass you need one as close to the bottom and the top as possible because bass needs as long an array length as possible. Spacing isn't important since the wavelengths are so long. I don't know if just 2 will get array dispersion or not. 4 should though. 1 top and bottom and 1 at each end of the tweeter array.

[justinc]

would putting them inline with the tweeter array parallel to the woofer array cause cancellation problems similar to if if you put two woofers next to each other in an array? thanks

[johninCR]

Originally posted by justinc
would putting them inline with the tweeter array parallel to the woofer array cause cancellation problems similar to if if you put two woofers next to each other in an array? thanks

No, the ports will be a source of lower frequencies, but even if they were playing the same frequencies, comb filtering only comes into play when the wavelengths are in direct relation to the source spacing and you're talking about wavelengths in excess of 6 meters.

[cmckasty]

Have you thought of a narrow slot loading the length of the array. It may be a challenge to build but if your building rounded backs, your probably up for a challenge. If the length of the slot is possible it may behave more like a line source. I am a beginning builder so pardon me if this is an ignorant question.

either way good luck, Chris M