This may be because your speakers are wired out-of-phase ("+" to "+" on one speaker, and "+" to "-" on another. When this happens, the sound "cancels each other out" to some extent.

To test this, adjust the fader and balance to isolate a single speaker (say, the front-left speaker) and see if the apparent volume increases.

This may be because your speakers are wired out-of-phase ("+" to "+" on one speaker, and "+" to "-" on another. When this happens, the sound "cancels each other out" to some extent.

To test this, adjust the fader and balance to isolate a single speaker (say, the front-left speaker). Then bring in a second speaker. It they are wired out of phase, the volume and sound quality will decrease. Do this a few times, using different combinations of speakers (front-right and front-left, then front-right and back-right, etc), to make sure they all sound good together.

This may be because your speakers are wired out-of-phase ("+" to "+" on one speaker, and "+" to "-" on another. When this happens, the sound "cancels each other out" to some extent.

To test this, adjust the fader and balance to isolate a single speaker (say, the front-left speaker) and see if the apparent volume increases.

Good luck!

This may be because your speakers are wired out-of-phase ("+" to "+" on one speaker, and "+" to "-" on another. When this happens, the sound "cancels each other out" to some extent.

To test this, adjust the fader and balance to isolate a single speaker (say, the front-left speaker) and see if the apparent volume increases.