I have a PAM8403 based amplifier module and going to build a small portable speaker, mostly to listen to lectures and audio books. The module looks like this:
First I attached two 4 ohms 3 watts speakers and it worked fine. But I've read that it would make a clearer sound with 8 ohms speakers. And in the module properties it is said it can work with 4-8 ohms speakers.
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A clear sound would be a benefit for me, but will I loose power (loudness) with higher resistance speakers?
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How is the sound quality related to the speaker resistance? What is the theory behind it?
All the speakers I am going to use would be the same diameters.
Here is the efficiency chart from the PAM8403 datasheet:
As far as I know, efficiency is about delivered power, not quality of the sound. Please correct me if I am wrong.
Best Answer
With the higher impedance (8 ohm) speaker, you will deliver 3dB less power to the speaker than you would with a 4 ohm speaker. However, the efficiency of the speaker will likely have a much larger effect on the volume. In general, speakers with lower efficiency will have less distortion. Note that typical efficiency for speakers ranges from about 4% for loud, cheap ones to 0.2% for reasonably good audio equipment. (Of course, it's easy to make a speaker that's both distorted and inefficient, so it's not a hard rule.)
Amplifiers will show higher distortion for lower impedance speakers because the higher currents required to drive them stress the drivers more, introducing higher levels of nonlinearity.
If you're looking to reproduce legible voice, you can easily handle the levels of distortion that you're looking at in this example; you probably wouldn't even notice it if you weren't listening for it. If you were looking to listen to music, my advice would be different.