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Class D Switching Power Amplifiers and Power D/A conversion

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Old 4th June 2014, 06:16 PM   #1
moldo2 is offline moldo2  Denmark
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Default Busting speakers

Hey there. I was wondering, since class D amplifiers are basically just pulsing a signal to the speakers(the MOSFETs either fully on or off), do they have the same tendency to burn out speakers that are rated for a higher power handling as other amps do? For instance, if you drive a 400W driver with a 200W rated amp it will clip and bust the speaker. Does this also apply to class D? I would assume it does, but I'm curious ;-)
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Old 4th June 2014, 06:40 PM   #2
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Usually it is not the amp, but certain people who have tendency to fry the speakers.
This applied to the analogue guys in the 70s as well as it applies to the digital natives of the 2ks. The only thing which can keep ignorant people from frying/busting/bottomingtodeath speakers is a correctly adjusted limiter, which is locked against unauthorized changes.
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Old 5th June 2014, 02:28 AM   #3
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Class d amplifies square waves as well as class ab.
So it will destroy speakers just as easy.
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Old 5th June 2014, 04:06 AM   #4
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the pope is muslim, bears use lavatories and clipping kills speakers

BillFitzmaurice.info - View topic - Can I underpower my speakers?Will clipping hurt them?
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Old 5th June 2014, 06:55 PM   #5
moldo2 is offline moldo2  Denmark
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Quote:
Originally Posted by horst303 View Post
the pope is muslim, bears use lavatories and clipping kills speakers
hahahahaha lol, but thanks for the link. very informal!
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Old 6th June 2014, 04:15 AM   #6
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Horst I think it is very important to make the distiction between underpowering and clipping. Sure if you have an amp that even outputing a square wave will not produce more average power than your speakers can handle then that clipping will not damage the speakers.

However if you have an amp that whilst not clipping is a bit below the speakers power handling ability, but you drive it into clipping, then you almost certainly Will damage your speakers!

This is an extract from Bill's post. Bolding is mine.

Quote:
Most widely available recordings have a crest factor of approximately 10dB. Looking at this in terms of power, the peak power is 10 times greater than the average power. If we were to play one of these recordings with our 50 watt amplifier when not clipping, the speaker needs to dissipate a mere 5 watts of average power over time. When the amplifier begins clipping, the peak level/power does not increase. BUT, the average power DOES increase. If we were to turn the volume up 6dB higher than the clipping level of our recording, we have reduced our crest factor to 4dB. Guess what? We are now needing the speaker to dissipate 20watts. This is four times the average power and four times the heat when measured over time. As you can see here, it is not the distortion or the waveform or anything along those lines that is killing your speaker; there is simply more average power over time. However, if the average power of time is still below what your speaker can handle, it doesn't matter if it's clipping or not. At higher power levels, the fact that a clipped signal carries more average power over time can result in damage.
as to whether or not having a more powerful amp which will not clip if turned up that extra bit, will result in overpowering the speakers is another matter. What is apparent (from my experience of drunk people at parties) is that the demise of tweeters comes quickly after the volume level is advanced that little bit past clipping. I guess the safest option is to have an amp that when clipping can only deliver slightly less power than the continuous rated power of the speakers (or prevent clipping in the first place, or use speaker protection)

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Last edited by wintermute; 6th June 2014 at 04:21 AM. Reason: add final comment.
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Old 6th June 2014, 04:35 AM   #7
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yes you're absolutely right, I should have said killing a speaker by under-powering it is a myth.
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Old 6th June 2014, 01:38 PM   #8
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There are two worlds regarding clipping: a) full-range amp and passive X-over: The additional harmonics when lower or mid frequencies are clipped go through the X-over and can overload the tweeter (and sound ugly too).
b) active X-over and one amp for each driver: clipped signals do not reach the tweeter as long as the tweeter channel itself is not clipped. Clipping e. g. of the bass amp will sound less ugly too - due to the mechanical lowpass of the subwoofer almost no high frequencies are reproduced AND the low frequencies in case of LF amp overload do NOT modulate mid and high - this makes quite a bit of difference. (Intermodulation is what sounds really ugly - pure THD is much more "pleasant".)
In this b)-case I almost go along the line of Bill Fitzmaurice. Some minor errors though:
"If we were to play a sine wave on our 50 watt amplifier, just below its clipping level, the average power over time the speaker would need to dissipate is 25 watts" -> Wrong, it is 50Watts. (with peak power at the sinewave crest being up to 100W or double the average power).
"Our same 50 watt amplifier playing a square wave into our speaker requires the speaker to dissipate 50 watts." Wrong -> (If the amps power supply does not sag) it can actually deliver up to 100W average in square mode. But no more than 100W peak.
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Old 6th June 2014, 01:51 PM   #9
speaker is offline speaker  United States
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Quote:
Originally Posted by moldo2 View Post
Hey there. I was wondering, since class D amplifiers are basically just pulsing a signal to the speakers(the MOSFETs either fully on or off), do they have the same tendency to burn out speakers that are rated for a higher power handling as other amps do? For instance, if you drive a 400W driver with a 200W rated amp it will clip and bust the speaker. Does this also apply to class D? I would assume it does, but I'm curious ;-)
Clipping or clean, if it exceeds the ability of the speaker assembly to shed the heat that results, it will fail.
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Old 6th June 2014, 02:53 PM   #10
gmarsh is offline gmarsh  Canada
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A clipping amp can create high frequency harmonics at high power, and cause tweeter damage in a multi-way speaker.

Spent a summer repairing speakers/amps/etc for a pro audio rental shop. Second to mechanical damage, tweeter death was the most common failure mode of a speaker.
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