Well, if the base system door speaker is designed to handle frequencies between 200Hz and 3khz with a peak of 5dB at 1000Hz, the base amp will pass these frequencies to that speaker with a 5dB cut at 1000Hz. If the door speaker in the ML handles frequencies of 300 to 2000 with no peak at 1000 Hz, you will have a 5dB dip at 1000hz from the base amp which will make the sound very dull and recessed. You will also have 2 drivers handling frequencies between 200 and 300 with odd interference and loudness characteristics and nothing handling frequencies in the 2000-3000Hz range.

A bit of an oversimplification, but you get the point. Not conducive to "good" sound.

 

Ok! lol. So what are the specs I should look for in a replacement speaker then

 

I'd leave the stock system alone. If you want to improve it, add a real sub/amp combo in the trunk. You'll be surprised how much it improves the entire sound spectrum.

 

Not trying to change the system. I'm getting some base info to help me choose some speakers just in case one of mine are broken. There are speakers out there that can substitute just fine for our stock speakers. I know there is.