I’ve wanted to build a line source array for quite a while. The barrier has always been cost – a single driver might be $15 – $30, but build a speaker with 40 or 50 of those drivers and the price gets a little insane.
Well, the tweeters were a no-brainer. Parts Express has had 3/8″ mylar dome tweeters made by Onkyo for quite a while at $0.25 each. The performance is pretty good, but they were designed for a specific automotive application so the construction makes them impossible to flush mount. But, at only $15 for sixty of them, I’d find a way to make them work.
Power Handling: 20 watts RMS/40 watts max
VCdia: 3/8″
Znom: 4 ohms
Re: 3.50 ohms
Frequency range: 6,000-20,000 Hz
Fs: 4,200 Hz
SPL: 87 dB 2.83V/1m
It wasn’t until very recently that I found a bargain on woofers to make these speakers a reality. Made by Hi-Vi Research, these 3″ shielded mid/woofers have a square frame which makes them easier to mount in an array.
Power Handling: 15 watts rms / 30 watts peak
Znom: 6 ohm
VCdia: 3/4″
Re: 5.2 ohms
Frequency range: 85-9000 Hz
SPL: 82db 1w/1m
Vas: 0.05 cu ft
Qms: 4.68
Qes: 0.43
Qts: 0.39
Fs: 85 hz
Xmax: 2.85mm
So here is the plan: 80 inches tall with 30 tweeters and 20 woofers in each speaker for a total of 100 drivers, each channel a mirror image of the other. The tweeters would have to be back-mounted, so a 3/4″ round-over makes for a nice pseudo-horn effect. The backs are to be open and the speakers equalized to flat response in the actual listening environment.
![Line Source Plan](http://marulla.com/wp-content/uploads/2007/07/line-source-3.jpg)
Line Source Plan
The early construction was nothing but lots and lots and lots of drilling. Sorry, no pics of that joy. First, mounting the tweeters.
![Mounting the Tweeters](http://marulla.com/wp-content/uploads/2007/07/igp3688small.jpg)
Mounting the Tweeters
Then, getting the woofers unpacked and ready for install.
![Woofers Ready for Mounting](http://marulla.com/wp-content/uploads/2007/07/igp3689small.jpg)
Woofers Ready for Mounting
The holes for the woofers were pretty tight, not leaving a lot of wiggle room to get all the spacing exact. By darkening the space between the woofers with a magic marker, a little misalignment goes unnoticed. You can see a nice detail of the rounded-over tweeter holes here too.
![Darkening the Intra-Woofer Spaces](http://marulla.com/wp-content/uploads/2007/07/igp3692small.jpg)
Darkening the Intra-Woofer Spaces
![A Handy Cheat!](http://marulla.com/wp-content/uploads/2007/07/igp3694small.jpg)
A Handy Cheat!
Mounting the woofers. The terminals do not fully clear the woofer holes, so I had to do “wire-as-you-go” while installing the woofers.
![Mounting the Woofers](http://marulla.com/wp-content/uploads/2007/07/igp3697small.jpg)
Mounting the Woofers
Everything finally mounted and wired. That’s only 100 driver holes, 400 mounting holes, and 200 soldered connections!
![Everything Mounted and Wired](http://marulla.com/wp-content/uploads/2007/07/igp3699small.jpg)
Everything Mounted and Wired
Here’s a shot of the crossover network (24db at 7500Hz), and the terminal panel.
![Crossover and Terminals](http://marulla.com/wp-content/uploads/2007/07/igp3701small.jpg)
Crossover and Terminals
The base took some special consideration. After everything was mounted, I was surprised at the weight. I guess 50 drivers add up! Also, since they were over six feet tall, I needed to make sure that tipping would be a non-issue. So I used a pair of machine screws and dowel nuts per leg, and an oversize base.
![Holes for Dowel Nuts](http://marulla.com/wp-content/uploads/2007/07/igp3704small.jpg)
Holes for Dowel Nuts
![Base Attached](http://marulla.com/wp-content/uploads/2007/07/igp3705small.jpg)
Base Attached
And that’s all, folks!
The sound was a little nasal at first, but I expected some equalization would be required. First a bass boost because the woofers, at 3″, were never designed to go very low. However, 20 of them together have almost as much area as a 15″ woofer. Handling the power of such a boost is easy since the input power is split 20 ways. Second, there was a little bump around the crossover point to tame. And finally, the tweeters were not exactly flat from the factory.
I used a pair of mono 1/3 octave equalizers from Audio Control, a TrueRTA spectrum analyzer and a Behringer calibrated microphone a to get things pretty flat, but after a few hours use it wandered from that goal by quite a bit. I let the drivers break in for about 200 hours and then re-equalized.
After getting dialed in, the sound is pretty amazing. Here are the finished speakers in my listening room.
![Line Source Speakers in Place](http://marulla.com/wp-content/uploads/2007/07/igp3712small.jpg)
Line Source Speakers in Place