Question 1

Can I use my iPhone as a calibrated sound level meter?

Accepted Answer

iPhones have reasonably consistent microphones, but they are not calibrated out of the box. The built-in MEMS microphone typically has a frequency response within ±3 dB from 100 Hz to 8 kHz, but absolute SPL accuracy can be off by 5-10 dB without calibration. To get usable results, calibrate against a known reference source such as a 94 dB pistonphone or a Class 1 sound level meter. SonaVyx supports single-point calibration at 94 dB or 114 dB, which corrects the absolute level offset. After calibration, phone-based measurements can approach Class 2 accuracy (±1.4 dB) within the usable frequency range. For legal compliance work, a dedicated measurement microphone with traceable calibration certificate is still recommended.

Question 2

How accurate are Android phone microphones for SPL measurement?

Accepted Answer

Android phone microphone accuracy varies significantly between manufacturers and models. Most flagship phones (Samsung Galaxy, Google Pixel) have MEMS microphones with sensitivity within ±4 dB from 200 Hz to 6 kHz. Budget phones may have larger deviations, especially below 200 Hz and above 8 kHz. The key limitation is the AGC (Automatic Gain Control) that some Android audio stacks apply, which can compress dynamic range and give incorrect readings. SonaVyx requests raw, unprocessed audio via the Web Audio API to minimize AGC interference. After calibration with a known reference, most Android phones can achieve ±2 dB accuracy for A-weighted measurements in the 40-100 dBA range. Always verify linearity across the expected SPL range before trusting readings for critical work.

Question 3

What is the difference between Class 1 and Class 2 sound level meters?

Accepted Answer

IEC 61672-1 defines two accuracy classes for sound level meters. Class 1 instruments have tighter tolerances: ±1.1 dB for the reference frequency (1 kHz) and ±1.4 dB across the operating frequency range (typically 20 Hz to 16 kHz). Class 2 allows ±1.4 dB at 1 kHz and ±2.3 dB across a narrower range (typically 100 Hz to 8 kHz). Class 1 meters are required for environmental noise surveys, building acoustics compliance, and legal evidence. Class 2 meters are acceptable for occupational noise assessment, general surveys, and preliminary investigations. SonaVyx targets Class 2 equivalent accuracy when used with a calibrated microphone, making it suitable for system tuning, venue checks, and preliminary compliance screening.

Question 4

How often should I calibrate my SPL measurement setup?

Accepted Answer

Best practice is to calibrate before and after every measurement session. This bracketing approach lets you verify that the calibration did not drift during the session, which is especially important for long-duration monitoring. For quick checks during live events, calibrating once at the start of the day is usually sufficient. If your microphone or phone is exposed to temperature extremes, physical impact, or moisture, recalibrate immediately. SonaVyx stores your calibration offset and applies it to all subsequent measurements until you recalibrate. A 94 dB pistonphone calibrator (about $150-300) is the most practical reference source. Alternatively, you can cross-calibrate against a known-accurate meter by measuring the same steady-state source simultaneously.

Question 5

Does wind affect SPL meter readings outdoors?

Accepted Answer

Yes, wind is one of the biggest sources of error in outdoor SPL measurements. Wind turbulence across the microphone diaphragm creates broadband low-frequency noise that can add 10-30 dB to readings below 500 Hz. Even a light breeze of 3-5 m/s can inflate A-weighted readings by 5-10 dB. A foam windscreen reduces wind noise by 5-15 dB depending on wind speed. For outdoor measurements per ISO 1996, use a foam windscreen and avoid measuring in winds above 5 m/s. If you must measure in windy conditions, consider using C-weighting (less affected than A-weighting) or apply post-measurement corrections. SonaVyx displays real-time octave band data so you can visually identify wind contamination as elevated low-frequency energy.

Question 6

What is the noise floor of a phone microphone and why does it matter?

Accepted Answer

The noise floor of a typical phone MEMS microphone is around 30-35 dBA, meaning it cannot accurately measure sounds below this level. Professional measurement microphones have noise floors of 15-20 dBA. This matters because if you are measuring a quiet room (e.g., NC-25 target = 36 dBA), the phone microphone self-noise will contaminate your reading. For accurate measurement, the signal being measured should be at least 10 dB above the microphone noise floor. So a phone microphone is reliable from about 45 dBA upward. SonaVyx displays a noise floor indicator so you know when readings may be unreliable. For quiet room measurements (studios, theaters), an external USB measurement microphone with a lower noise floor is recommended.

Question 7

Can I use SonaVyx SPL readings as legal evidence for noise complaints?

Accepted Answer

SPL readings from SonaVyx can support a noise complaint, but their admissibility as legal evidence depends on jurisdiction. Most noise ordinances and occupational safety regulations require measurements from a calibrated instrument with a traceable calibration certificate. A phone-based meter typically does not meet this standard. However, SonaVyx readings are valuable for: documenting patterns over time, identifying the noisiest periods, screening whether a formal measurement is warranted, and negotiating with noise sources informally. If you need legally defensible data, use a Class 1 or Class 2 certified meter with current calibration. SonaVyx can still serve as your primary analysis and reporting tool, with the calibrated hardware providing the raw input signal.

Question 8

What external microphones work best with SonaVyx for accurate SPL measurement?

Accepted Answer

For best results with SonaVyx, use a measurement-grade USB microphone or an audio interface with a calibrated condenser microphone. Popular affordable options include the miniDSP UMIK-1 (USB, comes with individual calibration file, ~$100), Dayton Audio UMM-6 (~$80), or Behringer ECM8000 with a USB audio interface (~$100 total). These offer flat frequency response from 20 Hz to 20 kHz, low self-noise (15-20 dBA), and wide dynamic range. SonaVyx accepts FRD calibration files to compensate for any microphone frequency response deviations. Load the calibration file provided by the manufacturer or generate one using a calibration service. With a proper measurement microphone, SonaVyx achieves accuracy comparable to dedicated hardware analyzers costing thousands of dollars.

Phone SPL Meter Accuracy: Calibration, Class 2, and Measurement Reliability

Frequently Asked Questions