How to wire a powerful amp with two speakers to avoid damage

Most amplifiers supply voltage to the load (speakers) and the impedance of the speakers at the frequency being reproduced determines the amount of current flowing. A battery is also a supplier of voltage to a load. The bulb of a flashlight uses less current than a headlight of a car. An amplifier is like a battery and is happy to deliver whatever current is needed up to the point of its max output current.

The only other factor that effects both the battery and an amplifier is heat. Automotive batteries can supply much more current at 25 deg C than at 0. An audio amplifier usually sounds better after it is warmed up and is probably the main concern in an over powered "class AB" amp. A high bias amplifier should not have any problems driving even a pair of headphones because the high bias will keep the amp warm even with no signal applied.

The analogy of an amplifier and a car is not correct because an audio amplifiers voltage and current are a linear relationship while the RPM and torque curve of an engine is not.

Angela touches upon an interesting point, although the issue, I believe, is not the danger of the amps working really hard at not delivering the current, but rather, the amps not being allowed to work hard enough to be in a confortable, never mind ideal operating range.

Every component has an ideal operating range, and while I agree with everything that has been said already as concerns the issue of potential damage, the matching of components with concern to this issue is IMHO one of the keys to really musical sound from a system. It's kind of like my SAAB Turbo; at 25 mph it's great, but at 50 mph+ you just sense that the motor is happier and performing at closer to full potential.

Thank you, 1439bhr, for the excellent explnation as to the damage caused by under powered amps. I like to see posts that explain why things happen so that everyone can better understand what is happening inside their 'black' boxes. I hope to see many more posts from you. Chris

Just one more tidbit: why do underpowered amps potentially damage speakers? The reason, as previous posters pointed out, is that they are more likely to go into clipping in the listener's quest for louder sound. Nearly all of the power in a music signal is in the bass and low midrange. When the signal is clipped, this distortion generates an abnormally high proportion of power at high frequencies. So even though the total signal power can't increase (the amp is clipping because it's reached maximum output power), more and more of the power is appearing in the high end of the frequency spectrum. That's part of why it sounds so bad. Plus, it's this abnormally high power in the upper midrange and treble pouring into the tweeter that burns it out. The voice coil in the tweeter is sized for "normal" amounts of power in the treble range. Clipping causes abnormally high levels of power in the treble range, overheating the tweeter voice coil and causing it to fail. Next to go is the midrange speaker's voice coil. It's beefier than the tweeter, but still relatively wimpy compared to a woofer voice coil.

Bottom line: I agree with previous posters and would not worry about hooking up 75 W amps to speakers with a labeled rating of 25 W. I would be cautious, though, and start with the volume turned ALL the way down, and cautiously raise it, listening to see how the speakers react. At the first hint of distortion, back the volume down IMMEDIATELY.

Thanks, Chris and Bob. Good knowledge to tuck away. AJ

I have never had a problem running a very efficient speaker with high wattage as long as the volume is kept low to be certain it does not clip! (as mentioned above)

Sean is correct. More speakers get damaged from underpowered amps than from overpowered ones. The amount of power delivered to the speakers is dependant upon the voltage delivered to the speaker, which is dependant upon the volume control. If you play the speakers at a comfortable level the big amp will not harm them in any way.

The heat generated by an amp is mostly caused by the current in the output stage. In a pure 'Class A' design the output current is at a very high level all the time and thus the amp is hot all the time. In a 'Class AB' design the output current is at a low level unless a lot of current is being delivered to the load. Under low listening levels or with very efficient speakers the output current is small and the heat being generated is also small.
Chris

Paul (& Angela) the amp would barely be working hard at all & probably wouldn't get much warmer than it runs at idle dissipation. You can in fact operate very high powered amps into low-wattage speakers without doing any harm at all, provided that you exercise reasonable restraint. We once drove some 100-watt-rated B&W speakers with a Mac2500 amp (500 w/ch. conservative) with no problems. In fact since the Mac never went into clipping, we were able to drive the B&W's at about 300 watts before they were audibly straining to handle that amount of power. At any higher power level we would have gotten in trouble burning up a voice coil, but as long as you're even reasonably careful then there is no problem in doing this.

Sean, would the amp be working really hard at NOT feeding the current? Would it then be running really hot? If so, you may want to pack ice around the amp (kidding) and don't allow small kids or animals near it(not kidding).
Or just the opposite and barely be breaking a sweat?

Speakers or their internal components are typically damaged from either being WAY underpowered or WAY overpowered. As such, using them under normal listening conditions will probably not harm them in the least. Even though the amps are capable of WAY more power than what the speakers are rated for, the speakers will only play ( absorb or dissipate ) as much power as you feed them. So long as you don't crank the volume up on a continuous basis, i would NOT worry about it. Besides, speakers that are rated for 25 watts are either EXTREMELY conservatively rated or not designed for real world operating conditions. Sean
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PS... i understand that the drivers may be operating full range with no internal crossovers to protect them. As such, that is still NO excuse.