Originally Posted by OllieS
Just a question on speaker impedance. If I buy a speaker that has a nominal 4 ohm impedance, then I assume the impedance would dip below 4 ohms and above 4 ohms.
The assumption that the speaker's impedance would rise above 4 ohms is very good - you can take that to the bank.
The assumption that the speaker's impedance would dip below 4 ohms is more marginal - it may or may not be true.
But how would this affect amplifier power when listening to music?
As you probably know, music has component frequencies at various frequencies and their relative amplitudes and their frequencies are varying all of the time.
When the music contains energy that falls in a frequency range where the speaker's impedance is low, then the speaker will draw more power for that amplitude of energy than what happens when there is music with energy that falls in the frequency range where the speaker's impedance is high.
The source material must be low in impedance in order to for the speaker to draw more power?
The source material have components that are in a frequency range where the speaker's impedance is low and have a high amplitude to draw large amounts of current that might cause problems for the amplifier.
So the source must be in low in impedance and the speaker needs to be low in impedance?
If the source material has components that are mostly in a frequency range where the speaker's impedance is high or be of lewer amplitude then it is unlikely to draw large amounts of of current that might cause problems for the amplifier.
I think I'm getting confused here. Basically, speakers that have a low impedance like 4 ohms, please explain why it wouldn't pose problems for an av receiver.
If the source material has components in a frequency range where the speaker's impedance is low and has a high amplitude and has a low crest factor then the speaker might draw large amounts of current that could cause problems for the amplifier.
For example I've seen reports of people who have a particular make and range of models of speaker that have very low impedance (below 2 ohms) at high frequencies (greater than 10 KHz). They say that they sucessfully drive it with AVRs.
In order for them to do this:
(1) They don't use the full power capabilities of the AVR.
(2) They don't play music that has most of its power above 10 KHz.
(3) They are always playing music with a high crest fact - music that is dynamic and impulsive.
(4) They are tolerant of distortion.
IME (4) is far from being certain, but items(1)-(3) could be true much if not all of the time.
For example music that has lots of energy above 10 KHz is often produced by percussion instruments that are impulsive and peaky and have a high crest factor. The high crest factor reduces the possibility that the music has high average energy even though its peaks may be high.
The pedal tones of a pipe organ may have a high amplitude and a lower crest factor but its frequency components are largely at low frequencies where the same speakers have a far higher impedance.
Two common bullets were dodged!