I guess I have to ask "what is 'critical listening'"? You hook up some
Radio Shack speakers. You know they're cheap. So what are you
critiquing?
Radio Shack made some surprisingly good speakers and some other ones too :)
They are most noted for having purchased Linaeum so they could use the Linaeum tweeter. The Optimus Pro LX5 got some good comments in the high end audio press. These days they need new woofers and there are good replacements. I picked up a set for $50.00 and replaced the woofers. So when I play them, I'm listening for imaging and depth. However they don't work well in my bedroom system because of the rear0firing information from the tweeters, and I have to have the speakers very near the wall behind them.
I've also been playing with the Radio Shack Minimus 7 speakers for my desktop. They made a variety of versions of this speaker and apparently the early ones are considered the best. However all of them tend to have a brightness due to superposition effects since the woofer isn't rolled off. In addition the capacitor in the tweeter crossover is a non-polar electrolytic. So what people do with this speaker is install a film cap for the tweeter and a choke (about 2.1mH) in series with the woofer, plus a few other parts to smooth out the response. Measured on-axis response is quite flat once this is done, and off-axis response is smooth. So they image quite well and are nicely detailed; if I am doing critical listening, I'm not really thinking about the speakers, although I never play them very loud.
I am using a sub crossed at about 60Hz.