How does the conversion affect efficiency? I'm kind of happy running high efficiency speakers on what these days is considered a low powered tube amp, albeit I think 30-watts is just fine.
Since I'm the Originator of the Super Heresy, I thought I should chime in.
The
reason I did the Modification to Paul Klipsch's Original (Pre 1982) was to improve the marriage of the Midrange (PWK said that is where it's most important) to where it "hands off gently to the Horns."
I knew that using a high bl product (large magnet) woofer designed for Guitar Amplifiers, would do well in the Female Vocal range, "in concert" with the horns, by adding an extra 3 db of sensitivity, tipping the curve towards 700 Hz rather than 70 Hz.
I also knew that in a sealed box, I would be making the bass "thinner" that it already was with the K22 woofer, so I initially used a K42, which was, originally, an EVM 12 L from Electro-Voice (PWK got all his K77 tweeters from them originally also).
Electro Voice still makes the EVM 12 L but it's ridiculously expensive versus other options from Eminence and Celestion, who also make guitar speakers.
Knowing all this I knew I would have to port the box in the rear, since there was no room in the front, to try and get back, some of the bass I would lose. The wall/corner proximity and the room gain were definitely responsible for elevating the bass curve lower than the simulations.
Much to my surprise, not only did I get much greater midrange micro detail, I also got Incredible bass
Down to 30 Hz!!! in my Indianapolis bedroom's main listening position, when I lived and worked in that city.
This further proved to me that the ROOM is the most important component for bass response below 200 Hz., and having a rear port allow for many more great options for bass loading vs. front porting which was not possible in my Walnut Heresy cabinets.
Eminence created an exact copy of the EVM-12L called the Delta Pro 12 A, which is was I had in my first build. If you find woofers with similar Thiele/Small Parameters, known as TSP (not the floor cleaner), you can use it if you find them cheaper. My version 2.0 uses a more expensive NeoDymium magnet which saves 10 lbs and provides more air in the box for a slightly lower and slightly more sensitive response, if your budget allows. Keep in mind that Heresy IV's from Klipsch cost north of $3,000 a pair new, and are somewhat compromised by using a 4 ohm woofer to get more bass (all my picks are 8 ohms) in a different way at a lower manufacturing cost (bean counters have higher priority than engineers). You can pretty much determine all that by just looking at the size of the magnet in the back of the driver, as a visual indicator.
