8ohm speakers for 4ohm car audio question

[ducklets]

I have fitted two 8 ohm hi fi speakers in the boot of my car, replacing the pair of small 4 ohm speakers that were mounted either side of the rear parcel shelf. These work fine and have improved the sound in the car immensely, however because they're 8 ohm, I understand they are possibly not being used to their full potential. I currently have the front/back fade adjusted to favour the back, to balance out the difference in power to the front & back.

I have read that 2 8 ohm speakers in parallel will give the equivalence of 4 ohms, so I was wondering whether it might give me more volume out of the rear speakers if I connect both rear speakers in parallel to just one of the channels.

I'm not concerned at all about losing the stereo picture from the rear speakers, as they are in the boot compartment and are mostly providing the bass anyway. However I am concerned about blowing my amp!

I'm wondering which would be best out of the following:

1) Connect both rear speakers in parallel to one channel, leave the other rear channel wire unconnected to anything.

2) Connect both rear speakers in parallel to one channel, leave the other rear channel connected to its old 4 ohm small speaker.

3) Connect both rear speakers in parallel to *both* channels...? I have no idea of the implications of this but my intuition says this is the most likely option to case smoke to come out of my stereo

4) do nothing, keep each rear hi fi speaker connected to separate channels as-is.

 

[americanaudiophile]

1 and 2 will not gain you any additional volume as you will be doubling the power of one channel and not using the other,
3 will damage your amp
4 Is the right answer. With an 8 ohm speaker you are getting half the power to each speaker than with 4 ohm speakers so maybe your max volume is less (maybe because the 8 ohm speakers may be more efficient than the old 4 ohm speakers). If you don't have enough volume out of the subs then get a bigger amp or add two more 8ohms speakers in parallel on both channels to the ones you already have. 2 ohm speakers might hurt your amp but 8 ohm speakers can't.