Quick answer
Thin bass and a collapsed centre image after a rewire usually mean one driver is polarity-swapped or the amp sees too low a net load. Check +/− against the diagram at every speaker and confirm channel impedance stays within the amp’s rated minimum.
Problem
- Speaker polarity or impedance is wrong after a swap or rewire.
Symptoms
- Thin bass; stage sounds “inside the dash.”
- Amp protect trips on certain tracks.
Cause
- Opposite polarity between drivers or against crossover reference collapses low-end summing in mono blends.
- Net impedance per channel is below the minimum the 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 - e.g. stripe = + end-to-end. Common mistake: assuming jacket colours match between old and new cable reels.
- Quick phase check (coax / full-range) - Play mono content; swap +/− on one door only. If bass fills in and the stage moves forward, that side was opposite the other.
- Component sets - Woofer and tweeter must follow the crossover’s polarity marks. Common mistake: flipping only the tweeter to “soften highs” - that breaks intended phase through the crossover.
- Do the impedance maths before power-on - Two 4 Ω voice coils in parallel = 2 Ω on that channel. Confirm the amp (or retained factory mini-amp) allows that net load.
- DCR with a meter - Voice-coil resistance is a rough sanity check only; plan from manufacturer nominal. Weird readings often mean a hidden parallel at the box terminal.
Typical 4WD / ute scenarios
- One door inverted after a beach-trip speaker swap: thin bass only shows up when the other channel is drowned by road noise.
- Dual voice coil sub wired for the wrong Ω - the amp hits protect only on heavy bass tracks.