Clipping an amp??

[museav]

An amplifier clips when the input signal drives the amplifer beyond it's ability to deliver the signal to the speakers (at the specified amplified ratio). When the amplifer is driven to this point, and beyond, the output waveform distorts (specifically, clips at the top and bottom), and the speaker is now attempting to respond to this hard edged (clipped) waveform. Yes, some can call it a square wave, but the bottom line is the speaker is now being asked to move in a fashion which is non-musical, non-sinusoidal, and outside of the design specifications for the speaker.

From QSC

Clipping occurs in an amplifier circuit when the input signal, multiplied by the gain, results in a signal that exceeds the circuit.

From Rane

clipping Term used to describe the result of an amplifier running into power supply limitation. The maximum output voltage that any amplifier can produce is limited by its power supply. Attempting to output a voltage (or current) level that exceeds the power supply results in a flattoping effect on the signal, making it look cut off or "clipped." A clipped waveform exhibits extreme harmonic distortion, dominated by large amplitude odd-ordered harmonics making it sound harsh or dissonant. Hard clipping is the term used to describe extreme clipping of a signal, producing highly visible flattoped waveforms as viewed on an oscilloscope; soft clipping refers to moderate clipping that results in waveforms having softly-rounded edges, as opposed to the sharp edges of hard clipping.

I see the most signiifcant result of clipping as being delivering increased average power to the speaker. Say you have an amp whose peak output is 500W into a speaker whose peak power rating is 500W. Since the crest factor of a sine wave is 3dB that means the average power the speaker is seeing is 3dB below the peak or 250W. So peak power of 500W, no clipping and and average of 250W. If you increase the input level and start clipping the waveform the peak output power stays the same since it is already at the limit it, however the time at the peak level increases as does the average power, along with an increase in the high frequency harmonics generated by the clipping. The driver is still moving from the same full + value to full - value but as the signal level and clipping increase it stays at those extremes for more of the period of the signal. Keep increasing the level and clipping and the sine wave starts to resemble a square wave with the peak and average levels converging. Since the peak power rating of most speakers is calculated and intended to address short term peaks 6dB above the average level, at some point the speaker quits working.

As far as clipping and DC content in a square wave, please read this, http://www.excelsior-audio.com/Publications/Square_Waves_&_DC_Content.pdf.

 

[waynehoskins]

That's an excellent article, Brad. Thanks!

I tire of arguing with Mr. Ashton about things I learned in first-year Intro To EE.