line array xover question

[johninCR]

You don't have to worry about air leaks too much. OB isn't like a box. There's no pressure buildup trying to escape through a leak. The baffle just acts as a wave guide to keep the front and back waves separated.

The holes are the hardest part of the whole job. With all those drivers, make sure you have a screw driver bit for your drill, as a screwdriver would destroy your hands and take forever. Another hint is to solder wires to all the drivers before mounting.

 

[johninCR]

The tweeter array needs to have the tweets as close together as possible because the wavelengths they are playing are much shorter. Assuming their diameter is smaller, the tweeter array will be shorter. I would put the centers of the 2 arrays at the same height and have them reasonably close together.

You definitely don't want to alternate MTMTMTMTM.... At a lower XO it wouldn't impact the mids, but it would affect the tweets.

 

[BillFitzmaurice]

Assuming their diameter is smaller, the tweeter array will be shorter. I would put the centers of the 2 arrays at the same height and have them reasonably close together.

So that the arrays have similar response. especially where nearfield and farfield transition is concerned, it's best to have them close in hieght, meaning you need far more tweeters than woofers unless the tweeters are large planars. The two line should be mounted as tight to each other as is practical to minimize the horizontal pathway differential.

 

[johninCR]

Bill,

Yes and no. The near field / far field transition point is dependant on both line length and frequency with the distance being farther for higher frequencies, so for a home application the tweeter array can be much shorter. We discussed this as it relates to Dr Griffin's work at http://www.diyaudio.com/forums/showthread.php?s=&threadid=33399&perpage=10&highlight=&pagenumber=6 .
With Dr Griffin's white paper here: http://www.audiodiycentral.com/resource/pdf/nflawp.pdf

In a typical room anything greater than 3ft for a tweeter array would be fine to stay in its nearfield response. You'd just want a longer array so you can be withing the plain of the tweeter array whether you are standing up or sitting down. Long array lengths are much more important for the lower frequencies.

 

[tomcat9]

Hey AJ,

How did your line arrays turn out? I am mainly interested in the PT2 tweeter you used. If you were to do the same project again, would you use the PT2 again?

I am ready to buy drivers for line arrays. I may also use the Dayton PT2. I am looking f or a very high end sound from the tweeters.

Thanks,
Tom

 

[AJ]

Hi Tom

The arrays ended up alot better than they should have.

If you were to do the same project again, would you use the PT2 again?

Probably not, but only because I'd just like to hear something different. I am going to rebuild the exact same line in a different enclosure (sealed this time) because I want to hear the differences. The dipole didn't work well at all in my room due to the fact that I just don't have enough of it and couldn't get them far enough away from back walls. I ended up closing up the backs with 1 inch insulation foam and layering the inside with fiberglass to create a quasi-sealed box. Not exactly air-tight, but the backwave was pretty well attenuated and they ended up sounding pretty decent. Some aspects of them (imaging, lack of distortion, dynamics) are pretty astounding considering the low cost.

I am looking f or a very high end sound from the tweeters.

I'm not the best judge of high end tweeters, but personally, I think you could do better than the PT2. Of course you'll probably end up paying alot more for it too. These are 25 dollar tweeters when you buy them by the dozen, so don't expect miracles. They're not bad, but to me, they can be a bit scratchy and harsh. I just bought a pair of Fountek JP3 ribbon tweeters and I'll be comparing them soon - I may find that the PT2's are a better value than I think.