Laptop Speakers Drawing a Lot of Power

Question

My laptop broke a while back, so I opened it up. I took the speakers out today, and hooked them up to one of those cheap 3 watt PAM amplifier modules. To my surprise, it didn't work that well. Above 70% or so volume on my phone, the speakers would stop working intermittently, and the current draw would spike. It would crackle as well.

When I had a look at the power draw of the module, it had peaks of about 500mA. I instead connected a much bigger 10w speaker to the module, at full volume, it worked perfectly. It was much louder that the two laptop speakers combined. The current draw had maximum peaks of just over 100mA.

So what's going on? How is it that those tiny laptop speakers are drawing so much more current than the big 10w speaker? Has it got something to do with the resistance?

Answer 1

Look on the datasheet for the PAM8302A IC. It is designed for 4 ohm or 8 ohm speakers and usually a 5V supply. Then its output with fairly low distortion is 2.2W into 4 ohms or 1.4W into 8 ohms. It is class-D so it has high efficiency. The datasheet shows a supply current of 550mA at 2.2W into 4 ohms with a 5V supply. Maybe your current meter is too slow to measure peak current.

But you connected TWO speakers instead of one speaker so maybe you overloaded the amplifier module.

A large speaker is usually much louder than a small speaker so maybe the large speaker power was less and maybe it was 8 ohms that uses half the power of a 4 ohm speaker.