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### Topic: Having difficulty understanding power when dealing with speakers/amps. (Read 3017 times)previous topic - next topic

#### scswift

#15
##### Mar 12, 2012, 07:45 pm
And thanks again for your help; you've gotten me to where I'm 99% sure this will work.  It's just that 1% that nags at me. :-)

#### Grumpy_Mike

#16
##### Mar 12, 2012, 07:53 pm
Quote
but how does one "decide" to operate at a specific level of distrotion?

You don't it is a function of what signal you put into it. You put in a signal that has a 1% total harmonic distortion then that is the power curve you get. If you put in one with 10% then you get the other curve. If you put in a signal with 20% THD then they are not saying what power you will get.

Just because a speaker is running at less than its rated power does not mean it will not distort. The same goes for amplifiers.
To find out the cause of the distortion look at the signal with an oscilloscope, if the signal is not distorted but the sound is then it is your speaker.
Remember those circuits in the data sheets are just starting points for a practical design not a finished design. Supply decoupling is important as well as filtering and correct capacitor type selection.

#### retrolefty

#17
##### Mar 12, 2012, 10:12 pmLast Edit: Mar 12, 2012, 10:15 pm by retrolefty Reason: 1

Quote
but how does one "decide" to operate at a specific level of distrotion?

You don't it is a function of what signal you put into it. You put in a signal that has a 1% total harmonic distortion then that is the power curve you get. If you put in one with 10% then you get the other curve. If you put in a signal with 20% THD then they are not saying what power you will get.

I don't think that is correct. It is stating two operating conditions that would allow the amplifier itself to ADD
up to that amount of distortion to the signal. Amplifier stages do add distortion, how much is a function of the device linearity and how they are operating on their load lines. Overdrive an amplifier and the amp itself will be the source/creator of the distortion. An amplifiers distortion specification has nothing to do with how much or little distortion is on the input signal. An amps distortion spec is based on only the distortion added by the amplifier.

Lefty

#### Grumpy_Mike

#18
##### Mar 12, 2012, 11:17 pm
Quote
An amplifiers distortion specification has nothing to do with how much or little distortion is on the input signal. An amps distortion spec is based on only the distortion added by the amplifier.
Yes I don't disagree with that.
But the point is that the more distortion is on a signal, however it got there, changes the power output of the system.

#### retrolefty

#19
##### Mar 12, 2012, 11:24 pm

Quote
An amplifiers distortion specification has nothing to do with how much or little distortion is on the input signal. An amps distortion spec is based on only the distortion added by the amplifier.
Yes I don't disagree with that.
But the point is that the more distortion is on a signal, however it got there, changes the power output of the system.

No I don't see that either. Power output and distortion output are two separate measurements dealing with different attributes of a audio output signal. Distortion is simply the deviation of output signal relative to input signal (minus gain). Power output is simply the product of voltage and current of the output signal. Specifying power at a maximum allowed distortion value is just a truth in advertisement method so one can make sure they are comparing apples to apples for two different manufactures power claims.

Lefty

#### scswift

#20
##### Mar 13, 2012, 01:07 am
Apparently I don't need to be concerned about someone blowing the amp by using a speaker with too low of an impedance:
http://e2e.ti.com/support/amplifiers/audio_amplifiers/f/6/t/112003.aspx#396690

Of course there is still the possibility of the amp blowing a small speaker, but I have to assume most small speakers you'll find can handle at least 5v at whatever their impedance is.

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