A friend of mine, Dennis Murphy, likes to design hifi speakers, especially their crossovers. Occasionally he buys something on sale for a ridiculously low price, tests them, and designs a new crossover that is inexpensive, but improves their response. He recently did this for some Polk R-300s available for a special price of $50 a pair. First read this introductory thread. He then posts a number of frequency response curves. The first 3 are with the original Polk crossover, and the rest are with his new crossover. He says the new crossover parts cost about $23 for each speaker. Not too bad - what a difference a good crossover can make .