Ohmic Audio

6.6 Measurement Procedures and Standards

Tiny version

Use this page when you want the same measurement to mean the same thing tomorrow, not just today.

Beginner field version

Get the mic in a repeatable place, keep the noise floor down, run the same sweep every time, and write down what changed.

Standards version

The deeper sections below are for when you need formal repeatability, competition-style comparison, or lab-grade verification instead of a quick tuning pass.

A practical measurement does not need to be perfect to be useful. It does need to be repeatable. The first goal is to create a setup you can come back to, so the next graph reflects the system change instead of a random mic move.

Translation box

  • Repeatable means you can do it again and get meaningfully similar results.
  • Noise floor means the background noise level before the test starts.
  • Reference means the baseline result you compare the next change against.

Common mistake

People often move the mic, seat, or volume between tests and then think the new graph proves the change worked. Keep the setup fixed first, then compare.

Checklist card

  • Place the mic at the listening position.
  • Use the same sweep level each run.
  • Write down DSP and volume settings.
  • Change one variable at a time.
Front stage Right side Mic at driver head position Keep this point repeatable for before/after comparisons

When Standards Matter

If you are comparing your own system before and after a change, a consistent in-car setup is often enough. If you are comparing products, publishing claims, or judging maximum output against formal references, that is when the standards language matters much more.

Measuring Frequency Response

Use this for: checking target-curve drift, seeing bass humps or crossover dips, and verifying whether EQ or placement changes helped.

  1. Check that background noise is comfortably below the test signal.
  2. Place the calibrated microphone at the listening position.
  3. Run the same sweep range and level each time.
  4. Average multiple runs if the environment is noisy.
  5. Label the graph so you know what changed.

Relevant standards: IEC 60268-5 for loudspeaker measurement language and repeatability expectations.

Measuring SPL (Maximum Output)

Use this for: output testing, competition-style checks, and confirming the system can get loud without immediately falling apart.

For everyday tuning, the useful question is often simpler: did the system get louder cleanly, and under the same conditions as last time?

Measuring Amplifier Gain

Use this for: gain setting, clipping checks, and confirming the amp reaches rated output cleanly.

  1. Use an oscilloscope or true-RMS meter.
  2. Feed a known test tone at a known source level.
  3. Measure output voltage across the amplifier output.
  4. Stop when the target voltage is reached without visible clipping.

Impedance Measurement Procedure

Circuit diagram showing a reference resistor, speaker under test, and measurement taps for impedance measurement.
This is the repeatable bench version: reference resistor in series, measured voltages at known points, then solve the speaker impedance from the ratio.

Use impedance measurement when you need resonance, enclosure tuning clues, or confirmation that the load behaves the way you think it does.

Distortion Measurement Procedure

Use distortion testing when output level alone is not enough. The clean question is not just "how loud?" but "how loud before the signal gets ugly?"

Power Measurement

For most practical amplifier checks, measure supply voltage, supply current, and speaker output voltage with repeatable conditions. That is usually more useful than pretending the load is simple when it is not.

Worked example: if your before/after graph changes by 4 dB at 70 Hz, but the mic position or sweep level also changed, the measurement is not good enough to prove the tuning move helped. Repeatable setup beats a dramatic screenshot.