Measuring Loudness in Sone (DIN 45631 / ISO 532): The Better Decibel for Human Hearing Perception
In this domain, we examine the most critical psychoacoustic parameter: loudness, measured in sone. For decades, high-precision sound level meters have captured physical sound levels, typically displayed in dB(A). However, such measurements are strictly physics-oriented, offering only a rudimentary approximation of human hearing valid for single sine tones at steady state. To objectively determine whether sound source A sounds louder or quieter to human ears than source B, loudness in sone (based on the Zwicker model) represents human auditory perception far more accurately than conventional decibels.
Crucial note for measurement practice: Conventional handheld sound level meters (such as NTi XL2 or Bedrock SM50) measure dB(A) levels and 1/3-octave spectra, but cannot calculate loudness in sone – neither stationary according to ISO 532B nor time-variant according to DIN 45631/A1! In our PC-based measurement system Akulap, these standardized algorithms are fully integrated: from the economical standalone package (30005) for stationary signals, to our modular Akulap platform (with integrated-dongle USB microphone 6533 and optional 1/2" Class 1 upgrade), to our dedicated suite for the Audio Precision APx555 framework.
Stationary vs. Time-Variant Signals, A/C Weighting & the Secret of the Hi-Fi 'Loudness' Button
Play the 4 reference signals directly in your browser (including customizable synthesis parameters via the 'Advanced' toggle). Experience with your own ears which measurement standard (ISO 532B vs. DIN 45631/A1) fits which sound – and how loudness in sone closes the loop between level, frequency, and human hearing:
For Stationary Signals at a Fixed Level, dB(A) Is Meaningful – But Once the Level Changes, the Ear's Response Shifts!
For a purely stationary signal at a fixed, low-to-moderate level, a conventional sound level meter in dB(A) provides a useful indication. However, as soon as the sound level changes, the A-weighting curve is no longer valid – which is precisely why the C-weighting curve exists (for high levels, where our ears perceive bass much more strongly)! With conventional decibels, you would have to constantly switch weighting curves depending on the level.
Classic Hi-Fi amplifiers featured a dedicated button for this exact reason: boosting bass and treble at low listening volumes so music would sound balanced and 'ear-appropriate' again. And what was that button called? 'Loudness'! Loudness in sone (DIN 45631 / ISO 532) automatically computes this exact level- and frequency-dependent adaptation of human hearing – plus masking effects across all 24 Bark bands and temporal dynamics for fluctuating or impulsive sounds – in a single, ear-appropriate metric!
1. Constant Pink Noise (e.g. HVAC, Ventilation, Server Fan in Steady State)
Steady broadband noise without temporal level or pitch fluctuations. Use the 'Advanced' button to adjust the spectral cutoff and test a live Hi-Fi 'Loudness' bass/treble contour.
2. Pink Noise Modulated at 1 Hz (e.g. Slow Level Fluctuation at Listener Chair)
Pink noise swelling up and down at a 1-second rate (1 Hz). Open 'Advanced' to adjust the modulation frequency (0.2–5 Hz) and modulation depth (10–95%) in real time.
3. Wobbling Pump Noise & Cyclic Machine Pulsation
Low-frequency wobbling hydraulic or vacuum pump with rhythmic RPM, level, and spectral shifts. Adjust wobble rate and pump fundamental live under 'Advanced'.
4. Sharp Impulses, Switch Clicks, Relays & Mechanical Clacking
Transient impacts, latching clicks, relay clacks, or stamping impulses in the millisecond range. Use 'Advanced' to vary impulse interval (ms) and impact hardness/resonance live.
Find Your Optimal Sone Measurement System
Select your application – the matching turnkey package is preconfigured in the configurator with one click:
PATH A: Stationary Signals – Standalone Basic Package (ISO 532B)
For steady noise with arbitrary spectrum (fans, HVAC systems, steady-state motors): Our standalone package (30005) including precision calibrator Center 326 (7002). An economical solution for stationary sone tests (fixed system, not upgradeable to Class 1 or further Akulap modules).
PATH B: Stationary Loudness on Modular Akulap Platform
If you want to measure stationary sone loudness while retaining full Akulap modularity: Akulap Sound Base Module (3303016) + Psychoacoustics I Plug-in (3303025) + calibrated USB microphone with integrated dongle (6533) + calibrator Center 326 (7002). Upgradeable anytime to prepolarized 1/2" Class 1 capsule (30006 / 7050) or time-variant analysis!
PATH C: Time-Variant Loudness for Dynamic Signals & Impulses
When sound levels fluctuate rapidly (impulses, relay clicks, run-up cycles), ISO 532B falls short. Our Akulap Time-Variant bundle couples the Sound Base Module (3303016), Psychoacoustics II Plug-in (3303026, DIN 45631/A1 & ISO 532-1), calibrated USB microphone with dongle (6533), and calibrator Center 326 (7002) – directly upgradeable to 1/2" Class 1 prepolarized capsule!
3 Turnkey Sone Measurement Packages
All packages strictly include the precision active calibrator Center 326 (7002), as human hearing operates non-linearly with level and valid Sone values require a 94.0 dB reference.
Set 1: Standalone Basic Package Loudness in Sone (ISO 532B)
Turnkey standalone entry bundle for stationary sources (fans, HVAC, continuous operation) including calibrator Center 326. (Note: Self-contained kit – not upgradeable to Class 1 or further Akulap modules).
Set 2: Akulap Stationary Loudness Package (DIN 45631 / ISO 532B)
The modular Akulap workstation for stationary sone tests (DIN 45631 / ISO 532B): Includes Sound Base Module, Sone Plug-in I, USB microphone with integrated license dongle, and calibrator Center 326. (Upgradeable to Class 1 with 1/2" prepolarized capsule!).
Set 3: Akulap Pro Package Time-Variant Loudness (DIN 45631/A1 & ISO 532-1)
Our premier industrial solution for time-varying sounds, transient impulses, and product acoustics: Sound Base Module + Psychoacoustics II Plug-in (DIN 45631/A1, ISO 532-1, specific loudness & sharpness) + USB microphone with dongle + calibrator Center 326. (Optionally combinable with Class 1 1/2" prepolarized capsule in the configurator!).
B2B System Configurator: Tailored Loudness in Sone
Select your base system on the left and desired Sone plug-ins, microphones, and calibrators on the right. Pricing and quote update in real time:
1. Select Base System
Sound level calibrator Center 326
Sound level calibrator class 2
94.0 dB @ 1 kHz
USB measurement Microphone for Akulap / Option Sone low-noise microphone class 1 noise floor below 20dB
Your System Configuration
Is Source A Louder than Source B? Direct Comparison dB(A) vs. Sone
Experience why physical dB(A) falls short for human auditory perception and how the Zwicker model calculates perceived loudness accurately:
1 kHz Sine Tone vs. Broadband Fan at Exactly 60.0 dB(A)
Although both sources read identical physical values of 60.0 dB(A) on a sound level meter, the human ear perceives the fan at 11.8 sone as almost three times louder than the single tone (4.0 sone). The Zwicker model (ISO 532B) integrates specific loudness N' across all 24 critical auditory bands, uncovering this discrepancy objectively.
Switching Events, Relay Clicks & Impulses (DIN 45631/A1 & ISO 532-1)
For dynamic signals (switches, start-up curves, cycle noise), ISO 532B fails because hearing masks sound immediately before and after an impulse. Only the time-variant model (DIN 45631/A1 & ISO 532-1 in Akulap Plug-in II 3303026) produces the time curve N(t), maximum loudness N_max, and percentile N₅ mandated in engineering standards.
Level-Dependence of Hearing: Why Center 326 Calibrator Is Mandatory
Unlike relative frequency response measurements, human hearing is strictly level-dependent: auditory curves at 40 dB differ fundamentally from those at 80 dB. An offset of just 6 dB can halve or double the calculated sone value! Therefore, the actively regulated calibrator Center 326 (7002) is mandatory in every single one of our packages.
Fundamentals of Loudness Measurement by Dr.-Ing. Frank Jordan
From physical pressure fluctuations (Pa) to ear-appropriate loudness curves (Sone):
Physical Sound Pressure (Pa) – The Input Variable
Every acoustic evaluation begins with sound pressure in Pascals (Pa). However, psychoacoustic analysis seeks not merely physical quantification, but the fundamental answer: Does sound A sound louder or quieter to human ears than sound B?
The Decibel (dB) – Logarithmic Perception
Human hearing covers an immense pressure range from hearing threshold (20 µPa) to threshold of pain (>60 Pa) – a ratio exceeding 1 to 3,000,000. The logarithmic decibel scale compresses this into manageable numbers from 0 to 130 dB, but does not yet reflect human loudness perception.
Frequency Weighting (A, C, Z) – Historical Compromise
Human hearing is far more sensitive to mid frequencies (1–5 kHz) than to deep bass or ultra-high frequencies. However, the A-weighting curve was modeled strictly on pure sine tones at steady state. For complex broadband noise (fans, engines), dB(A) discards low frequencies and produces demonstrably flawed loudness ratings.
Stationary Loudness (ISO 532B) vs. Time-Variant (DIN 45631/A1)
The Zwicker model partitions hearing into 24 critical frequency bands (Bark) to calculate specific loudness N'. ISO 532B handles steady-state noise (fans, HVAC). DIN 45631/A1 (ISO 532-1) is the modern standard for dynamic sounds, incorporating millisecond-scale temporal pre- and post-masking.
Model Boundaries – Annoyance & Psychology
A sone value quantifies perceived loudness (1 sone = 40 phon), but does not equate to annoyance. Assessing annoyance requires sharpness, roughness, and tonality. Furthermore, psychological factors impose hard limits: a quiet dental drill or human scream triggers distress that no technical algorithm can encompass.
Further Psychoacoustic Parameters for Annoyance Rating
Loudness in sone quantifies perceived loudness. For comprehensive annoyance rating, Akulap offers these standardized modules:
Tonality & Tonal Penalty per DIN 45681:2006 & IEC 61400-11
Objective detection of discrete spectral tones for tonal penalty assessment (0–6 dB) per noise regulations and wind turbine standards.
Prominent Discrete Tones per ECMA-418-1 Annex B
Accredited testing for IT and office equipment: Tone-to-Noise Ratio (TTNR) and Prominence Ratio (PR) calculation per international standards.
Psychoacoustic Switch & Haptics Rating per GMW18141 & GMW14155
Specialized automotive module: Automated segmentation and psychoacoustic quality rating of switch and button actuation acoustics.
Sharpness (DIN 45692), Roughness & Specific Loudness
Included in Psychoacoustics II (3303026): Sharpness in acum, roughness in asper, and 24-Bark frequency band progression over time.
AM/FM Modulation Analysis for Gearboxes & Rotating Machinery
Detection of amplitude and frequency modulations for diagnostic troubleshooting in bearings, gears, and electric drives.
3-Part Video Course: Loudness in Sone with Akulap on PC
Hands-on workflows, hardware setup, and audio import direct from the acoustic laboratory of Dr.-Ing. Frank Jordan:
Measuring Time-Variant Loudness in Sone with Akulap (DIN 45631 & ISO 532)
Dr.-Ing. Frank Jordan demonstrates the complete workflow in 5 steps: 1. Required hardware & why the 94 dB calibrator is mandatory, 2. Calibration at 1 kHz / 94 dB, 3. Enabling raw WAV recording, 4. Selecting time intervals with mouse, and 5. Generating HTML report (Sone vs. dB(A) comparison) and CSV export.
A-Weighting vs. C-Weighting Explained – And Why Loudness in Sone Is Superior
What happens with a 50 Hz bass tone on a sound level meter? Why the A-curve filters low frequencies and why loudness in sone is the superior psychoacoustic model.
Importing Handheld Audio Recordings (e.g. NTi XL2 WAV) into Akulap for Post-Processing
Since handheld sound level meters cannot compute loudness in sone, this tutorial shows how to import audio WAV files recorded on handheld meters (with automatic NTi XL2 calibration header parsing) into Akulap for PC analysis.
Loudness & Psychoacoustics in Audio Precision APx555 Framework
For R&D labs and audio test benches with APx555, APx525, or APx515: Integrate standardized Sone and psychoacoustic tests into your automated APx test sequences:
Time-Variant Loudness in Sone (DIN 45631/A1) for APx
Direct software module for the Audio Precision APx framework: Time-variant loudness according to DIN 45631/A1 and ISO 532-1, specific loudness N', N_max, and percentiles in automated sequences.
Complete Multichannel Psychoacoustics Suite for APx Framework
Comprehensive industrial suite for APx: Multichannel time-variant loudness (DIN 45631/A1, ISO 532-1), stationary loudness (ISO 532B), sharpness (DIN 45692), tonality (DIN 45681), roughness (Daniel & Weber), impulsiveness & 1/3-octave spectrogram.
Rent Measurement Systems with 100% Purchase Credit
Test Akulap and measurement microphones flexibly on a weekly basis in your own lab. When purchasing afterwards, 100% of rental fees are credited:
FAQ on Loudness Measurement in Sone (DIN 45631 / ISO 532)
Why does loudness in sone (DIN 45631 / ISO 532) reflect hearing perception better than dB(A)? ↓
Conventional A-weighted sound level in dB(A) relies on a purely physical measurement with an oversimplified filter that severely attenuates low frequencies, valid only for quiet stationary sine tones. Human hearing operates non-linearly: it decomposes sound into 24 critical frequency bands (Bark) and exhibits spectral and level-dependent masking. Loudness in sone (Zwicker model) computes specific loudness N' across all bands and provides a linear scale: 2 sone sounds exactly twice as loud to human ears as 1 sone.
When is stationary loudness (ISO 532B) sufficient, and when is the time-variant model (DIN 45631/A1) required? ↓
ISO 532B is suitable exclusively for steady-state continuous noise with unvarying spectra (fans, refrigeration units, pumps, or motors at steady RPM). When acoustic events fluctuate in time, containing transients, clicks, or run-up curves (switches, appliances, machinery cycles), ISO 532B falls short. Here, the time-variant model per DIN 45631/A1 (ISO 532-1) is mandatory to compute temporal pre- and post-masking down to millisecond intervals.
Why can conventional handheld sound meters (such as NTi XL2 or Bedrock SM50) not calculate loudness in sone? ↓
Handheld sound level meters are engineered to IEC 61672 for physical metrics (Leq, Lmax, 1/3-octaves). Calculating Zwicker loudness (DIN 45631/A1) requires a complex 24-Bark digital filter bank with concurrent modeling of pre- and post-masking, non-linearities, and specific loudness integration. This exceeds the DSP architecture of handheld instruments. Akulap computes this in real time on PC, or via post-processing of WAV audio captured on handheld devices.
How do the Standalone Package (30005) and modular Akulap system differ regarding Class 1 upgrade? ↓
The Standalone Basic Package (30005) is a self-contained, economical solution strictly for stationary measurements (ISO 532B). It is hardcoded in hardware and software and cannot be upgraded to Class 1 or time-variant modules. In contrast, the modular Akulap platform (3303016 + 3303025/3303026 + 6533) is fully expandable: it can be upgraded at any time with the Class 1 package (30006) featuring a prepolarized 1/2" capsule (7050) for low-noise tests from 20 dB upwards, or extended with further Akulap modules.
Why is the Center 326 calibrator (7002) mandatory for every Sone test – and what are the model limits? ↓
Because human hearing is fundamentally non-linear: equal-loudness contours shift dramatically with absolute level. Without precise on-site calibration at 94.0 dB, an offset of just a few decibels disproportionately distorts the calculated sone value. The model boundary lies in psychology: sone measures perceived volume, but cannot evaluate emotional annoyance. A dental drill or crying baby sounds intensely annoying even when its physical sone level is modest.