Along with all my other interests in life, audio and speaker building is near the top. The first set of speakers I ever built had drivers that came from Radio Shack in 1978. The tweeters had a 10uF capacitor on the + lead and at the time, I thought that was all you needed for a crossover... Over the next 30 years I learned a quite a bit more. I was also very interested in line arrays as the concept always seemed like a good idea. A line array is a group of audio drivers (speakers) mounted in a row. It does a couple things for you. First, it allows each individual driver to use less power thus, in theory minimizing distortion as the driver does not have to work as hard. Second, all the acoustic energy couples together to provide a sound field that does not drop off at the same rate as single driver, which acts as a point source. For more information see this and this. This project started out like a lot of mine. Parts Express had a sale on 3inch audio drivers and I said “I always wanted to build a line array, let me order 16 of them!” three years later I actually got around to building them. I am actually glad I waited because there was more information I needed to learn before I built them.
There is a lot of debate around how good they are and what there issues are. On the down side, multiple drivers can cause interference and acoustic artifacts. Interestingly, the same argument is the same for why an orchestra sounds so good live. Next time you go to a concert look at the PA speakers... They are most likely set up as a line array. If you really want to hear how they sound lets build one!
Step 1: The Design
I found a speaker building buddy who happened to live in my neighborhood. The first time I went to his house he had a line array using 9 three inch drivers per side and 9 small tweeters. This reminded me about the 16 I had in my garage. After listening to his I knew I needed to put my drivers to good use. Dave suggested I pair them up with a different tweeter than he used. He used a ¾ inch dome tweeter and recommended the same driver that had a 5/8 inch dome. He had used this tweeter in a couple other projects and really liked them.
I had 16 of these:
and ordered 16 of these for use as my tweeter:
Dave had substantial experience with speaker design, after measuring my little woofers designed a great crossover. With 8 drivers I chose to wire them 4 in Parallel and then the two sets of paralleled drivers in series giving me roughly a 4 ohm load. This was taken into account for the crossover design. See the theoretical frequency response graph.
Crossover parts (for two speakers:)
(2) 2.4 Ohm Resistor
(2) 3.3 uF Capacitor
(2) 7.5 uF Capacitor
(2) 10 uF Capacitor
(2) .70 mH Inductor
(2).15 mH Inductor
Cabinet/Enclosure Parts (for two speakers:)
½ ” Birch plywood
(2) Front Panel 7” X 34”
(2) Rear Panel 7” X 34”
¾ ” Birch Plywood
(4) Top and Bottom 3” X 5.5”
(4) Side panels 3” X 34”
20 feet of Black 18 gauge wire
20 feet of Red 18 gauge wire
Semi Gloss Polyurethane
Mounting Screws for the 3” drivers
One bag of Poly Stuffing to act as acoustic insulation in the cabinet
Mounting screws for the rear panel.
Electrical Tape or Heat Shrink Tubing
Hot Glue Gun (with a bunch of glue sticks!)
For the cabinet I chose 13 ply birch plywood. In the Dallas area you can get it here. I wanted the line array to be small and compact. And, easy to build with the tools I have. I drew the front panel in inkscape (Great Open Source drawing program!) Because the tweeters were so small I decided to just drill the right size hole and then glue the driver in flush to the front panel. I experimented with a 1 ¼” hole and a 1 3/8” hole and ended ordering a 1 5/16” forstner bit from here that was just right.