Define the Intended Stress Without Creating Abuse

Start from the actual use case: background playback, karaoke with microphones, outdoor promotion, or high-level party use. Define the signal, volume, lights, wireless receivers, input source, environmental condition, and duty time. A torture test with no relationship to intended use may destroy hardware without answering a purchasing question.

Set stop conditions for smoke, odor, unstable battery voltage, repeated restart, excessive accessible temperature, severe distortion, or mechanical distress. Product safety evaluation remains a separate controlled activity under the applicable market standard; this performance test does not replace it.

Establish a Cold Reference

Condition the sample to the agreed starting state. Record room temperature, battery charge or supply voltage, enclosure condition, firmware, DSP mode, and sample history. Measure acoustic output at several fixed reference levels before the sustained run, not only at maximum volume.

The reference points let the team distinguish a hot-state loss from sample-to-sample variation. They also reveal whether protection changes bass, midrange, and high-frequency output differently. A broad overall level can mask a substantial tonal shift.

Build a Cold-to-Hot Test Sequence

Use a documented playback file or signal and log time. Step the input until the agreed operating level is reached, then hold it for the defined period while recording acoustic output, battery or supply behavior, temperatures, and protection events. Repeat the cold reference checks immediately after the sustained segment and again during recovery.

The maximum-SPL measurement guide explains why a headline power value cannot substitute for this time-dependent result.

Read Compression as a Curve, Not a Verdict

Power compression is observed when acoustic output increases less than expected as input rises or after the system heats. The buyer does not need to label every reduction as a defect. Some controlled limiting protects the product. The acceptance issue is whether the amount, onset, tonal effect, and recovery match the approved use and customer expectation.

Plot acoustic level against input step for cold and hot states. Add frequency-band or response data when possible. If bass is reduced first, the overall number may remain acceptable while the perceived product character changes. If high-frequency output falls, vocal clarity and microphone use can suffer.

Classify the Protection Behavior

Document whether limiting is gradual, audible as pumping, limited to a frequency band, accompanied by clipping, followed by mute, or followed by a restart. Record if the user must cycle power. A protection design that avoids damage may still cause returns when its behavior is abrupt or unexplained.

Connect the Result to Components and Cost

Corrective action may involve driver selection, amplifier efficiency, heatsinking, ventilation, battery resistance, power-supply margin, limiter tuning, enclosure airflow, or assembly contact. Do not ask the supplier to “make it louder” without preserving the thermal boundary. Moving a limiter can shift risk into the voice coil, battery, semiconductor, connector, or plastic structure.

When a fix changes the BOM, tooling, firmware, quotation, sample cost, lead time, packaging, or certification file, route it through the project change process. The mass-production approval guide helps keep the corrected configuration attached to the order.

Sustained-Output Approval File

• Intended use, signal, level, duty time, environment, and stop conditions are approved.
• Cold references include acoustic, electrical, thermal, hardware, and firmware records.
• The ramp, sustained load, hot reference, and recovery sequence can be repeated.
• Compression is reviewed by input step and frequency behavior, not one headline value.
• Limiting, mute, restart, clipping, odor, rattle, shutdown, and recovery are logged with time.
• Corrective changes are evaluated for cost, lead time, tooling, certification, warranty, and retail impact.
• Production samples repeat the approved sequence at an agreed sampling level.
• Raw logs, plots, media, and the final release decision remain traceable.

References

• International Electrotechnical Commission, IEC 60268-21:2018 — small- and large-signal acoustical measurements.
• International Electrotechnical Commission, IEC 62368-1:2023 — audio/video equipment safety requirements; applicable national or regional editions and certification routes require qualified review.