I picked up a pair of the great Heil AMT tweeters a while ago, and have been working on building a set of DIYs around these amazing tweeters. I started out by measuring the frequency response and impedance, and then trying to figure out how best to mate a woofer to these. Since they are a pleated ribbon construction, they would require a pretty fast woofer to keep up, and probably no more than 8 inches in diameter. The impedance looks pretty good, and the frequency response is simply amazing.
Initially, it looks like I would want to cross over no lower than 1000 Hz. I looked at quite a few woofers, and there were many that would fit the bill. But I couldn't find any that would give good sensitivity and frequency response at a price that I wanted to pay. I decided to go with 2 8 inch woofers instead, and this opened up a lot more possibilies. I finally settled on the Dayton RS225 woofers wired in parallel. This would give me about 90db sensitivity, and the 4 ohm load would match the Heil tweeters. These woofers look spectaculare up to about 1400 Hz, and then they exhibit some pretty severe breakup modes due to the aluminum cones. Still, they looked like a good match for the tweeters.
One of the design criteria for the speakers is they will have to be comfortable in the corners of my listening room. Because of this, I decided to go with a fairly large cabinet, and tune it lower than normal. This will roll off the bass from about 200 Hz down, which should help compensate for the 8 Pi room gain. I also wanted to avoid having to put any baffle compensation in the crossover. Since the crossover point at 1000 Hz, I made the baffles 12 inches wide. This will make the speakers effectively monopole from 1000 Hz down. Hopefully this will simplify my crossover a bit.
The cabinets are coming along nicely. I decided to go with baltic birch for the sides, MDf for the top, bottom, and braces, and 1 inch particle board for the baffles. Everything is rabbeted and glued together. The fronts get walnut and zebrawood veneer, and the trim pieces are mahogany. I'm using water based poly and dye to finish them. So far, I like what I'm seeing.
I plan to use 4th order Linkowicz-Riley crossovers for both the woofers and tweeters. From using simulations using my measured data, it looks like this will provide a good match, as well as taming the breakup modes in the woofers. I hope to get around to building the crossovers in the next week. Thanks to Kegger and PakProtector for the finals bits I need to build them.
Stay tuned for further updates!
Mark
Initially, it looks like I would want to cross over no lower than 1000 Hz. I looked at quite a few woofers, and there were many that would fit the bill. But I couldn't find any that would give good sensitivity and frequency response at a price that I wanted to pay. I decided to go with 2 8 inch woofers instead, and this opened up a lot more possibilies. I finally settled on the Dayton RS225 woofers wired in parallel. This would give me about 90db sensitivity, and the 4 ohm load would match the Heil tweeters. These woofers look spectaculare up to about 1400 Hz, and then they exhibit some pretty severe breakup modes due to the aluminum cones. Still, they looked like a good match for the tweeters.
One of the design criteria for the speakers is they will have to be comfortable in the corners of my listening room. Because of this, I decided to go with a fairly large cabinet, and tune it lower than normal. This will roll off the bass from about 200 Hz down, which should help compensate for the 8 Pi room gain. I also wanted to avoid having to put any baffle compensation in the crossover. Since the crossover point at 1000 Hz, I made the baffles 12 inches wide. This will make the speakers effectively monopole from 1000 Hz down. Hopefully this will simplify my crossover a bit.
The cabinets are coming along nicely. I decided to go with baltic birch for the sides, MDf for the top, bottom, and braces, and 1 inch particle board for the baffles. Everything is rabbeted and glued together. The fronts get walnut and zebrawood veneer, and the trim pieces are mahogany. I'm using water based poly and dye to finish them. So far, I like what I'm seeing.
I plan to use 4th order Linkowicz-Riley crossovers for both the woofers and tweeters. From using simulations using my measured data, it looks like this will provide a good match, as well as taming the breakup modes in the woofers. I hope to get around to building the crossovers in the next week. Thanks to Kegger and PakProtector for the finals bits I need to build them.
Stay tuned for further updates!
Mark