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So periodically the community puts together a wish-list of drivers we wish we could buy but none of the distributors seem to want to stock/build/etc.
One of the most common I have seen is a small for factor, high sensitivity, dedicated midrange that doesn't cost $100 or more (looking at you, Scan Speak). I personally do not think it asking too much to have Dayton rework the RS100/125 to have an underhung coil and overall lighter moving parts to drive sensitivity up.
One of the biggest obstacles to DIY being able to crank out large, multiple woofer 3-ways is the sensitivity gap in available mids. I really think a 93+db 8 ohm 5" mid would be very popular. The pro audio world has demonstrated this technology is neither difficult nor necessarily expensive. More of us would use pro drivers in this application, but I am almost certain the looks turn us off.
What prompted this is my search for a good looking, high performance 4-5" midrange that will keep up with a pair of 8" woofers. They are pretty rare outside of the pro audio world, and the typical pro audio driver (regardless of performance) will look like shit sandwiched between those beautiful carbon fiber cone Rival woofers and the Viawave SRT tweeters. Let's face it - that matters.
I also wish yellow woven kevlar would make a comeback. I know the material is difficult to work with, but many manufacturers have created cone treatments that yield a smooth response over the years. It looks cool, but is largely relegated to cheap shit drivers or very expensive studio monitors these days.