car stereo problem, 1997 Ford Contour

I have a recent problem that has developed in the stereo of my 1997 Ford Contour. All of the stereo components have been replaced and consist of a sony cdx-L550X cd player, Infinity 973.2 cf 6x8 (2ohm)door speakers, and a MTX roadthunder 202 amp hooked up to a 15" (4ohm) sealed subwoofer.


These components have been installed for over a year and a half with no problems. The other week I started my car and noticed a crackling sound coming out of my speakers....then no sound out of the door speakers. However, I could hear the subwoofer working from the trunk. The head unit powers up fine...and nothing else seems wrong. Just no sound from my door speakers.

To investigate I pulled out the head unit to make sure all my connections were tight, and they were. It is interesting to note that every couple days the door speakers will magically start working again....but usually wont come back on if I start the car.

Given that the CD receiver was about 5 years old, I thought maybe the amplifier in the head unit was going bad. So this week I bought a new Pioneer 1900MP head unit. I rewired the harness....turned it on....and it worked great...and I thought "oh that must have been the problem".

Well, I turned my car off....came back an hour later...and I heard the same crackling sound...no door speaker sound...and the subwoofer was working in the trunk.

Any ideas as to what my problem is? The new Pioneer cd player says to only use speakers down to 4 ohms...and my Infinity speakers are 2 Ohm....is this causing the problem? If it is I dont undertand why, because I ran these speakers for 18 months with no problems.

The only think I have done to the car in the past few months is change the spark plugs.....could this be causing interference?

Thanks,
Greg

Running 2-ohm speakers off head unit power is never a good idea as almost all heads are only rated to 4-ohms.  The fact that your Sony lasted as long as it did is a miracle.  You could also have loose connections at the speakers.

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I think loose connections is unlikely...considering all 4 worked fine and then all stopped playing together....I could see 1 getting loose but all 4...probably not. I am thinking the 2-ohm speakers are the problem.

try using 4 ohm speakers or an amp that for the 2 ohm speakers

Well, I decided to swap out the Infinities for some 4-Ohm pioneers I had in the basement...and now all the speakers are working properly. I only ran my new head unit for about 5-10 minutes with the 2-ohm speakers....hopefully I didn't damage the amp in it.

Can someone explain to me why 2-ohm speakers wont work or can damage a amp only rated to 4-ohm? When you read the specs on an external amp it lists the RMS at different Ohm ratings...usually 8,4 and sometimes 2. I just figured if my head unit put out 20 RMS at 4-ohm, it would essentially run 40 RMS at 2-ohm.    

Lower impedance (ohms) rated speakers draw more current through an amplifier.  Most head unit amps cannot handle less than 4-ohms load because it will draw more current than the circuitry can handle, so they will shut down.

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