Posted by: whippersnapper

## Speaker Impedance vs Amplifier Power - 09/02/12 10:46 PM

Hey all you electrical engineer types:

In my feeble mind, I've always equated higher speaker impedance with higher efficiency. I tended to think of an 8-ohm speaker system as more efficient, requiring less amplifier power to reach a given sound pressure level. As the impedance drops, additional stable amplifier power is necessary to drive the "less efficient" speaker to an equivalent sound pressure level.

Not long ago, I was working on putting a custom stereo in my car. I bought a subwoofer with dual 4-ohm voice coils. The sub came with jumpers to wire the voice coils in series or in parallel, thus presenting either an 8-ohm or 2-ohm load. I bought a dedicated mono class-D amp to drive the sub. It was rated to deliver roughly 200 watts into 8 ohms or 500 watts into 2 ohms.

Now here's where I get confused: Everything I read made it sound desirable to use the 2-ohm setting for the sub (which is rated to handle up to 500 watts), in order to draw the full 500 watts from the amplifier. This would reportedly keep the sub "happier" by providing extra power.

I would have thought I'd be better to drive an 8-0hm load and not require the amplifier to work quite so hard. Can anyone help me understand the pluses and minuses of wiring and driving the sub one way versus the other?

Your puzzled Whippersnapper friend.

In my feeble mind, I've always equated higher speaker impedance with higher efficiency. I tended to think of an 8-ohm speaker system as more efficient, requiring less amplifier power to reach a given sound pressure level. As the impedance drops, additional stable amplifier power is necessary to drive the "less efficient" speaker to an equivalent sound pressure level.

Not long ago, I was working on putting a custom stereo in my car. I bought a subwoofer with dual 4-ohm voice coils. The sub came with jumpers to wire the voice coils in series or in parallel, thus presenting either an 8-ohm or 2-ohm load. I bought a dedicated mono class-D amp to drive the sub. It was rated to deliver roughly 200 watts into 8 ohms or 500 watts into 2 ohms.

Now here's where I get confused: Everything I read made it sound desirable to use the 2-ohm setting for the sub (which is rated to handle up to 500 watts), in order to draw the full 500 watts from the amplifier. This would reportedly keep the sub "happier" by providing extra power.

I would have thought I'd be better to drive an 8-0hm load and not require the amplifier to work quite so hard. Can anyone help me understand the pluses and minuses of wiring and driving the sub one way versus the other?

Your puzzled Whippersnapper friend.