Testing a subwoofer with a multimeter takes about two minutes and gives you a clear answer. You’re measuring the DC resistance of the voice coil, the wire coil that converts electrical signals into sound. A healthy subwoofer will show a resistance reading roughly 60% to 90% of its nominal impedance rating. A blown one will read either zero (a short circuit), infinity/no reading (an open circuit), or a value wildly outside the expected range.
What You Need Before Testing
You’ll need a digital multimeter with an ohms setting (the Ω symbol) and your subwoofer disconnected from its amplifier. This second part matters. If the sub is still wired to your amp, the multimeter will pick up resistance from other components in the circuit and give you a false reading. Disconnect the speaker wire or RCA cables from the amplifier side. If the subwoofer is in an enclosure, you can test it right at the terminals on the back of the box without removing the driver.
Step-by-Step Multimeter Test
Turn your multimeter dial to the ohms (Ω) setting. If your meter has multiple ohm ranges, select the lowest one, typically 200 ohms. Touch the red (positive) probe to the positive terminal on the subwoofer and the black (negative) probe to the negative terminal. Hold them steady for a couple of seconds and let the reading stabilize.
Here’s what you’re looking for:
- A steady resistance reading in the expected range means the voice coil is intact. The sub is not blown, at least electrically.
- A reading of 0.0 ohms (or very close) means the voice coil wiring has shorted against itself. The coil is damaged.
- “OL” or infinity on the display means the voice coil wire has broken completely. No electrical path exists. This is the most common reading from a burned-out subwoofer.
- A reading that jumps erratically suggests an intermittent break in the coil. The wire is damaged but hasn’t fully separated yet. This subwoofer will cut in and out during use and is on its way to failure.
What a Healthy Reading Looks Like
Your multimeter measures DC resistance (DCR), which is always lower than the nominal impedance printed on the subwoofer’s label. That label number (2 ohms, 4 ohms, 8 ohms) describes the speaker’s impedance across a range of frequencies, not at DC. The actual DC resistance runs about 60% to 90% of the nominal value.
For a 4-ohm subwoofer, expect a reading between roughly 2.4 and 3.7 ohms. For an 8-ohm sub, you’ll see somewhere around 5 to 7.7 ohms. A 2-ohm sub will read around 1.2 to 1.8 ohms. If your reading falls in this range, the voice coil is electrically healthy. If it’s significantly higher than 90% of the nominal value but not at infinity, the coil may be partially damaged or corroded at the terminals. Clean the terminals and retest before concluding anything.
Testing a Dual Voice Coil Subwoofer
Many car audio subwoofers have two separate voice coils, each with its own pair of terminals (four terminals total). You need to test each coil independently. Put your probes on the positive and negative terminals of the first coil, note the reading, then do the same for the second coil. Both readings should be nearly identical. If one coil reads normally and the other reads “OL” or zero, that coil is blown.
You can also verify the readings by wiring the two coils in series: connect the positive terminal of one coil to the negative terminal of the other, then place your multimeter probes across the two remaining terminals. The resistance should roughly double. If you measured about 3 ohms per coil, the series reading should be around 6 ohms. A reading that doesn’t add up confirms damage in one of the coils.
The Physical Check You Should Do Too
A multimeter only tests the electrical path through the voice coil. A subwoofer can pass the resistance test and still be partially blown. The voice coil can be deformed, the cone can be torn, or the suspension (the flexible ring holding the cone) can be damaged, all without breaking the wire itself.
After the multimeter test, gently press the cone inward with even pressure from both hands. It should move smoothly in and out without any scraping, grinding, or scratching sounds. If you hear or feel the voice coil rubbing against the magnet assembly, the coil has warped from overheating. This subwoofer will distort badly even though your meter showed a normal resistance value.
Look at the cone itself. Tears, cracks, or separations where the cone meets the surround (the outer rubber edge) all cause rattling and loss of bass output. A subwoofer with these symptoms is mechanically blown regardless of what the multimeter says.
Common Symptoms That Led You Here
If your subwoofer is producing distorted sound at volumes that used to be clean, making a rattling or buzzing noise, or producing no bass at all, those symptoms line up with a blown driver. No sound at all typically corresponds to an open circuit on the multimeter (the “OL” reading). Distortion and rattling at moderate volumes usually point to a partially damaged coil or torn cone, where the multimeter might still show a normal reading but the physical inspection reveals the problem.
If the multimeter reads normal and the cone moves freely with no scraping, your subwoofer is probably fine. The issue is more likely upstream: a blown fuse in the amplifier, a bad signal cable, or a failed amplifier output. Test those next before replacing a working sub.