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what would happen using 500 watt amp with 125 watt 15in speakers? what would happen using 125 watt amp with 500 watt 15in speakers? I have been told to match amp wattage with speaker rating. Then I have been told the amp should have double the wattage rating of the speaker. Do larger wattage speakers have a better sound when matched with the proper amp?Or are they just louder. Thanks for any advice.

Often times the speaker's power rating is something the maker just pulled out of his donkey. In an ideal world the speaker and power amp ratings should match, that is to say the the program power (watts) should be equal to the output of the power amp. Too much power to the speakers and they distort and heat and then die. Too little power and the volume is low. Way too little power and a cheap speaker might heat and die too, although that is far less likely.

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Okay, who took my pants?

First, you have to understand that "500w amp" and "150w speaker" doesn't tell us much. There is no one number.

If it says 500w peak -- that is meaningless. The key rating is RMS output at a particular output impedance. So you need this number:
[pre] 500W RMS, 4 ohm load
275W RMS, 8 ohm load[/pre]
Then you need the numbers for a speaker. These usually take the form of:
[pre] 150w continuous
300w program
600w max[/pre]
And an output impedance:
[pre] 8 ohms[/pre]
You want to match the RMS output of the amp with the program rating of the speakers.

A QSC RMX2450 has 400W per channel RMS into an 8 ohm load. This makes it a close match with a pair of Yamaha S115V, which are 8 ohm speakers with a 500w program rating.

The rules change if you parallel two speakers into one amp output. The ohms are cut in half (two 8 ohm speakers become one 4 ohm load). And you need twice as much power, which is usually possible as amps that are capable of handling the load will usually put out twice as much power to 4 ohms as to 8 ohms.

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[color=#ffff55]Mickey J.[/color]
Alas for those who never sing, but die with all their music in them.
-- Oliver Wendell Holmes, Sr.

Like Mickey stated, those numbers are pretty much useless without knowing the actual models of the speakers & amps in question.

You basically want your amp to push twice the RMS power rating which most manufacturers today rate as the 'Program' rating. If you have an amp that doesn't push enough power, you are going to be more wanting to turn the volume up higher, and once the amp reaches it's maximum 'clean' output, everything over that is going to come in the form of distortion - a regular speaker killer.
If your pushes more than your speaker - yes you can still blow them, however, you will be running clean power, chances are the sound is going to be much fuller, and you will not need to turn the volume up as high to get the same loudness.
So while in essence, yes higher wattage amps are generally louder (although subject to actual wattage, it may not seem much louder), you won't have to turn them up as high to achieve the same volume level, it will sound cleaner, fuller over the lower wattaged amp at the same volume.

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The analogy i always like to use is that an amp is like a car engine. WATTS are like HORSEPOWER, which is not always directly proportional to SPEED/VOLUME, like most people think.

So, what would happpen if you put a 500 HP engine into a mini-cooper, assuming all fo the car's other machinery was built to handle 125HP? What would happen if you put a 125 HP engine into a Semi-Truck?

That's about what you are dealing with with speakers. If all of the major components of the speaker (crossover, high frequency driver, and low frequency driver) are designed to handle 125 total watts, and you put 500 watts into it, then there is just way too much sonic energy, and one of the components is going to fry from getting too much energy. If the speaker components are designed to handle 500 total watts, and you only feed it 125 watts, then the speakers are going to be sluggish and really strain and struggle for power to produce the frequencies they are meant to produce, which = distortion, which = unintelligible vibrations that can damage speakers if you keep jacking up the volume to where the speakers are asking for more power than they are receiving.

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C Mc
KJ, FL

Well, this part of your explanation / analogy is wrong.

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Jeff Wheeler, moonlight DJ/KJ