Line Array BR and/or TL advice please

[mpmarino]

Guys, if what I am asking is posted somewhere else..sorry..I seeked and did not find.

I am going to build a mini line array (5-6' tall)(WAF). The drivers I am using are vifa 4.5 buyouts from pe. The parameters of the drivers:
Specifications: *Power handling: 40 watts RMS/80 watts max *VCdia: 1" *L1k: .60 mH *Impedance: 6 ohms *Re: 4.00 ohms *Frequency range: 60-5,000 Hz *Fs: 58 Hz *SPL: 89 dB 2.83V/1m *Vas: .20 cu. ft. *Qms: 3.95 *Qes: .33 *Qts: .30 *Xmax: 3.5 mm *Dimensions: Overall Diameter: 4-7/8", Cutout Diameter: 3-7/8", Mounting Depth: 2-3/8".

It seems to me that with a Qts of .3, I am best using a vented or maybe a sealed enclosure. I will be using 9 per side with series/parallel for 6 ohms.

I am leaning towards the vented as I prob will not be adding a sub till funds allow and also would like them to extend as far down as I can get them anyway.

Using winisd It seems that I can get them (vented) to below 45Hz no prob...however....FB is less than FS. Is that a prob.? I am thinking they will overextend very quickly...True?? What's the lowest I should tune these things?
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If I were to do a TL..The same questions apply, PLUS..Where would the pipe start? Would it start at the centerpoint of the drivers, or at the driver further or closer to the mouth? Is this a practical use of TL? How low can this app be tuned??

Looking at my post I notice a LOT of question marks..Sorry!

Any advice at all is greatly appreciated..

[BillFitzmaurice]

With a low Q driver Fb is usually going to be lower than Fs. WinISD automatically gives you the flattest possible alignment, so go with it. With an F3 of 45 Hz you'd usually be concerned with excursion, but I wouldn't sweat it with 9 drivers per side.

A TL is not the best bet with a .3 Qts; you would not get the F3 that the vented alignment allows.

Your array height seems a bit high. If you're going that high for the volume that's fine, but make sure the woofers are spaced tight frame to frame or they won't integrate.

In a TL/LA you can expect that the line frequency will be at least a half octave higher than the quarter-wavelength measurement would suggest due to the line being excited so far down its length. I doubt if you could get below 120Hz with those drivers.

[mpmarino]

Thanks Bill,
I appreciate your insight. I'll ditch the TL idea on this one. The box would probably be too big for me anyway.

Actually, winisd gives an alignment with a F3 of 78hz if I remember correctly. I was trying to stretch it as far as possible by stretching the vent and increasing encl. size a bit. (lower FB and increase volume of box) I would like to do this however I am afraid the system will be way 'underdamped'. Am I getting in trouble if I push it too far? Every vented system I have built in the past has has a FS very near FB and things have worked nicely. Am I going to get myself into trouble stretching fb too low here? Whadya guys think?

I saw another thread relating to standing waves in narrow enclosures which I think may relate to my application nicely. This board is great! I am thinking maybe creating a 'pyrimid' shaped top and bottom in the interior may break up standing waves nicely.

Regarding the height..I don't have to go that high. I actually would like to make it shorter. I was trying to 'center' the array floor to ceiling. Any advantage?

Bill, I am impressed with your site and hope ypu have good luck with your product. By the way, I see you are in NH, I'm in MA..10 min. from the Nashua border. Howdy neighbor!

Thanks,'
Marc

[BillFitzmaurice]

You can push the alignment a lot, but what you gain in extension you lose in flatness of response. Use WinISD with different box volumes and tunings to see what is possible. A dip of up to 6dB in response above the Fb isn't all that bad, especially since you'll likely get some room reinforcement there to fill in the hole, as it were.

Standing waves are really no issue until you get a single dimension of at least 3 feet from a single point source, which doesn't occur in an array with multiple sources.

You can certainly shorten the height; all that matters is that the listening position is on a horizontal plane within the field of the drivers, and you can do so with either a stand or wall mount. I wouldn't center the box vertically, though, as sound waves hate symmetry- offset it about 20% one way or the other.