Quick answer
If you get thin bass and a collapsed centre image after a rewire, one driver is usually polarity-swapped, or your amp sees too low a net load. Check +/− against your diagram at every speaker. Then make sure the impedance on each channel stays within the amp's rated minimum.
Problem
- Your speaker polarity or impedance is wrong after a swap or rewire.
Symptoms
- You hear thin bass and the stage sits inside the dash.
- Your amp trips protect on certain tracks.
Cause
- One driver runs opposite polarity to another driver, or against the crossover reference. In mono blends you lose the low end.
- Net impedance on a channel sits below the minimum your amplifier or factory mini-amp is rated for.
Fix Step-by-step
- Open your reference diagram: factory, aftermarket or amp manual. Mark which terminal is + at the speaker, at the crossover (component sets) and at the amp output.
- Pick one convention for the whole car: stripe = + end to end. Common mistake: assuming your old and new cable reels share jacket colours.
- Quick phase check (coax / full-range): play mono content, then swap +/− on one door only. If bass fills in and the stage moves forward, you know that side was opposite the other.
- Component sets: the woofer and tweeter have to follow the crossover's polarity marks. Common mistake: flipping only the tweeter to soften the highs. You break the intended phase through the crossover.
- Do the impedance maths before power-on: two 4 Ω voice coils in parallel give 2 Ω on that channel. Make sure the amp (or the retained factory mini-amp) allows that net load.
- DCR with a meter: voice-coil resistance is a rough sanity check only, so plan from the manufacturer nominal. If you get an odd reading, there's often a hidden parallel at the box terminal.
Typical 4WD / ute scenarios
- One of your doors ends up inverted after a beach-trip speaker swap: you only hear the thin bass when road noise drowns the other channel.
- A dual voice coil sub wired for the wrong Ω: the amp hits protect only when you play heavy bass tracks.