Getting ready to buy my speakers tonight...

[mazeroth]

Going to be building line arrays using the Infinity speakers made by Vifa from Parts Express. I am 100% sure buying 16-24 (some for backup) of the 7" Infinity drivers. I can still get them for $8 each...

http://www.partsexpress.com/pe/showd...number=299-493

What I'd like to know is should I just use all 7" drivers, covering 40hz up to the tweeter, or would it be better to use some matching 4.5" Infinity speakers as well ($4 each), for the mids? If I went that route I'd have to use a 3-way crossover. Here are the 4.5" speakers:

http://www.partsexpress.com/pe/showd...number=299-492

I was thinking of doing 8 7" drivers per side, and if I went with the 4"s then maybe doing 6 7" drivers and 2-4 4" drivers. I could put the 7" on the bottom, the 4.5" on top to the left or right (depending which speaker it is) and put the tweeters next to the 4.5" speakers. That would look pretty good, I'd imagine. You guys know best!

Again, I'm a total newbie to this stuff so any info is GREATLY appreciated! THANKS!

[Andrew S-]

Wanna share where you are still getting them cheap?

[TheoM]

The approximation of an infinite line source depends on the near perfect coupling of a long line of drivers. Use as many identical drivers as you can afford. If you need to extend the low end get a sub. The 7"'s will be fine in the mids. Also, as they are 7's you want to cross over to the tweeter fairly low-ish - like 1500 to accomodate the rule of cone centers no more than one wavelength apart.

Also - use ribbbon tweeters, or if you can't afford then, get tweeters that are extremely small. They should be as close together as possible and the same length as the woofer line.

[joe carrow]

I'm sorry, I haven't been following your project closely enough to remember these details.

1) did you decide on a crossover point? A quick search seems to say that a 2.5khz crossover is what you're going for.

2) did you decide on a tweeter? 2.5 khz can be a little low for a tweeter to go, depending on the tweeter and the crossover.

If you've got a tweeter that goes there without trouble, I would say that those 7" speakers should go to 2.5 khz with no problem. My personal preference is to push crossovers as high or as low as possible (out of the critical range)- but if I were to use those 7's, I would cross them at 2 khz, a whole octave below 4 khz, where the funny stuff starts to happen... 2 khz also happens to be a frequency where they shouldn't have trouble with beaming.

Paired with the right tweeters, I think you're in good shape. Oh, and it looks like those 7"s don't go very low... 50 hz would be a stretch. Did you have plans for a subwoofer?

[TheoM]

Jim Griffin's guideline is pretty well researched. The wavelength of 1600 hz is 8 and 7/16th inches. Your woofers centers will be about 8" apart (being 7's). They way I read the formula if you try to go higher than that with the woofer you will be violating the rule, and get all sorts of nasty comb filtering in that zone.

see this:http://www.audiodiycentral.com/resource/pdf/nflawp.pdf

At 2500 hz the wavelength is 5 /38 inches, so your woofers centers would be further apart than the wavelength you are trying to couple. 1800 should be as far as you go. Note also, there's a big band of crossover in which the rule will be violated anyway even if you crossover much lower, depending on the order of the crossover. You might consider a 3rd order crossover.

If are going to go to all that trouble to build a line array (and it IS a lot of work) you might as well follow the best advice out there.

[joe carrow]

Originally posted by TheoM
Jim Griffin's guideline is pretty well researched. The wavelength of 1600 hz is 8 and 7/16th inches. Your woofers centers will be about 8" apart (being 7's). They way I read the formula if you try to go higher than that with the woofer you will be violating the rule, and get all sorts of nasty comb filtering in that zone.

see this:http://www.audiodiycentral.com/resource/pdf/nflawp.pdf

At 2500 hz the wavelength is 5 /38 inches, so your woofers centers would be further apart than the wavelength you are trying to couple. 1800 should be as far as you go. Note also, there's a big band of crossover in which the rule will be violated anyway even if you crossover much lower, depending on the order of the crossover. You might consider a 3rd order crossover.

If are going to go to all that trouble to build a line array (and it IS a lot of work) you might as well follow the best advice out there.

I'm sorry, I completely spaced out on the "line array" part. I was talking about using just one, although I definitely should have noticed that he's buying at least 16! Thanks for the informative link, and for correcting me on that.

[mazeroth]

Thanks for all the replies.

I think due to size contraints I will be going with an 8 woofer array, MAYBE 10. I think 8 is a good number, especially for my first speaker project.

This was taken off Parts Express:

*Frequency range: 40-4,000 Hz *Fs: 41 Hz *SPL: 86dB 2.83V/1m *Vas: 1.03 cu. ft.

By those specs, shouldn't these drivers be able to hit 40hz, or is that the EXTREME? I still don't know what all those numbers mean. The Vas 1.03 cu. ft, does that mean optomially these drivers should have a cubic feet of airspace each? I've been reading about open baffles and such and it just gets more confusing LoL!

Also, I'd like for these to look nice, so if YOU were building them, which tweeters would you go with?

SO sorry for being such a newbie, but I am. Thanks a million, guys!

[paulspencer]

Mazeroth,

A big part of a line array is that you make it tall enough to be in the "near field" and thus get less room coloration and more output, and less SPL falloff due to distance. If you don't make it tall enough, you lose the nearfield advantage.

Looking at those drivers, the crossover might be a bit tricky. The 7" has a nasty peak at 4kHz. Also before 1.4k the response steps up suddenly by 3db. This all suggests an xo point a bit lower than you might otherwise want. The off axis response looks much better (30D). The 4.5" looks a bit more manageable but looks like it won't go happily below 200 Hz. The 7" has a high Q and rolls off early. Not much bass at all. It might be a good candidate for trying open baffle!

In fact, an open baffle array with the 7" driver could be an interesting project!

It looks like a choice between using the 4.5" and having to add a woofer to cover up to 200 Hz (or 120 Hz at the lowest) or the 7" (with a bit more work on the xo to deal with the response over 1.4k and a subwoofer as even with this driver you won't get much bass.

[BillFitzmaurice]

Jim Griffin's guideline is pretty well researched. The wavelength of 1600 hz is 8 and 7/16th inches. Your woofers centers will be about 8" apart (being 7's). They way I read the formula if you try to go higher than that with the woofer you will be violating the rule, and get all sorts of nasty comb filtering in that zone

Actually this is not quite correct. The Journal of the AES has published from a number of sources the fact that proper spacing of line array elements depends on the distance between their radiating planes, not acoustic centers. In other words it is the space taken up by the cone surrounds and driver frames, and the enclosure edges in multiple box arrays, that must be held to less than a wavelength at the highest frequency. Therefore at 2.5kHz the amount of space taken up by the woofer frames and surrounds must be no more than 5.4 inches, which is a fairly easy target.

Things get problematic in the higher frequencies; you can't use dome tweeters that have wide frames, for instance. Ribbons work well here due to their higher radiating plane to frame width ratio. Frameless domes also work well, aa do horn-loaded tweeters, since on a horn the radiating area is the entire horn mouth.

[Hybrid fourdoor]

Originally posted by BillFitzmaurice


Actually this is not quite correct. The Journal of the AES has published from a number of sources the fact that proper spacing of line array elements depends on the distance between their radiating planes, not acoustic centers. In other words it is the space taken up by the cone surrounds and driver frames.....

Although I find what you say to be logical....I think your gonna start up some commotion with the "smarties" around here