FOH / Mons Mixing / Loudspeaker Failure Diagnosis
Loudspeaker Failure Diagnosis
Reference: SRH-SPKR-FAIL-01. When a driver dies, the failure itself is usually the best evidence you've got. A charred coil, a torn suspension, a pulverised diaphragm — each points toward a fairly specific cause, whether that's a factory defect, plain misuse, or a fault sitting upstream in the signal chain that never showed up as an audible symptom. Work through the two habits below first, since they prevent a chunk of these failures outright, then use the reference tables to match what you're looking at on the bench to a probable cause.
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Key facts: manufacturing defects are almost always mechanical (a loose glue joint, a cold solder joint, a bad weld) and show up as buzzing or an out-of-spec coil resistance reading — handle these through the maker's warranty channel, not a repair bench. Misuse failures are usually down to excessive continuous or peak amplifier power, or physical mishandling, and are generally identifiable on sight. A driver can also fail from something happening upstream of it — a DC offset at an amp's output, or an inaudible high-frequency oscillation — with no obvious symptom until the coil is already cooked. Sequence your amps on last and off first, always.
Two Habits That Prevent Driver Damage
Diagnosing a DC Offset From an Upstream Component
A DC offset riding on the amplifier's output is a classic hidden killer, and it almost always shows up in low-frequency drivers rather than high-frequency ones, since HF drivers are typically capacitively coupled and end up shielded from it. A large offset of the wrong polarity can drive the coil straight out of the gap and burn it — a failure that looks a lot like straightforward excessive peak power damage. A smaller offset won't necessarily kill the driver outright, but it holds the cone off-center continuously; over time the suspension takes a set in that position, so the cone still looks pushed in or out even with the driver unplugged, and along the way it generates noticeably more distortion than normal.
To track down where the offset is coming from: if the amplifier is AC-coupled (meaning it shouldn't pass DC at all) and DC still shows up at its output, treat the amp itself as faulty. If the amplifier is DC-coupled instead, the offset could be arriving from whatever's feeding it — so test the amplifier and the stage in front of it separately rather than assuming either one is the culprit.
Manufacturing Defects
These are mostly mechanical assembly issues that slip past spot-check quality control. A sine wave sweep or a simple DC resistance check on the voice coil is usually enough to confirm one. Once you suspect a factory defect rather than misuse, work it through the manufacturer's published warranty and service process rather than opening the driver up yourself.
| Defect | Test | Result |
|---|---|---|
| Insufficient gluing of suspension components | Sine wave sweep | Buzzing sounds; surround or spider separating from the cone or diaphragm |
| Incomplete bonding of the voice coil to the diaphragm | Sine wave sweep | Buzzing sounds; coil rubbing; coil separating from the diaphragm |
| Cold solder joints at the coil lead-in wires | DC resistance check of the voice coil | Resistance reads higher than the driver's rated impedance, or infinite |
| Faulty welds at the voice coil terminations on the former | DC resistance check of the voice coil | Resistance reads infinite or intermittent; sound drops out or turns to static |
| Poorly assembled driver frame or casing | Visual check; sine wave sweep | Cracks, breaks, or loose parts; buzzing sounds; coil rubbing |
LF Driver Failure — Misuse Symptoms
Failures caused by improper operation, rather than a factory defect, are usually catastrophic and easy to spot on visual inspection. Note that disassembling a driver to confirm one of these will likely void any remaining warranty, so if there's a chance the failure is actually covered, check with the manufacturer before pulling it apart.
| Symptom | Probable Cause |
|---|---|
| Voice coil looks charred | Excessive continuous amplifier power |
| Fused or blackened coil lead-in wires | Excessive continuous amplifier power |
| Voice coil out of the gap | Excessive peak amplifier power |
| Torn suspension | Excessive peak amplifier power; possibly an out-of-phase connection if used in a cluster |
| Coil rubbing | Frame deformation from improper mounting; coil separated from the former by excessive continuous power; frame deformation from a dropped cabinet/driver or rough shipping; a shifted pole piece |
| Burned cone | Grossly excessive continuous amplifier power |
| Torn or punctured cone | Excessive peak amplifier power; careless transport; vandalism |
| Broken basket or misaligned magnet assembly | Dropped cabinet or driver |
HF Driver Failure — Misuse Symptoms
| Symptom | Probable Cause |
|---|---|
| Voice coil looks charred | Excessive continuous amplifier power; amplifier failure putting DC at its output |
| Fused or blackened coil lead-in wires | Excessive continuous amplifier power |
| Diaphragm forced out of the gap or crushed against the pole piece | Excessive peak amplifier power; HF driver wired to a low-frequency amp channel in a biamplified system |
| Diaphragm cracked or pulverized | Excessive continuous amplifier power (often frequency-related); excessive peak amplifier power; HF driver wired to a low-frequency amp channel in a biamplified system |
| Diaphragm dimpled or torn | Careless tool use during an attempted repair or disassembly |
| Coil rubbing | Dropped cabinet or driver; diaphragm assembly reinstalled incorrectly; coil separated from the former by excessive continuous power |
| Magnet assembly or pole piece misaligned | Dropped cabinet or driver |
Source: Davis, Gary D. & Jones, Ralph. The Sound Reinforcement Handbook, 2nd ed. (Hal Leonard/Yamaha). Section 13.11.1–13.11.3, pp.238–241. Rewritten in Ryan's own words from the source material.