Sound Pressure Level Determination of Household Appliance Noise: Standards, Methods and Applications

Sound pressure level determination is the core procedure for quantifying and controlling the noise emitted by household electrical appliances such as refrigerators, washing machines, dishwashers and range hoods. This article explains the measurement principles, applicable international standards (IEC 60704, ISO 3744, GB/T 4214), test procedures, and typical applications in compliance testing and product development, providing a practical reference for manufacturers and accredited third-party laboratories.

Technical Overview

Noise performance has become one of the most important quality attributes of household electrical appliances, directly affecting user comfort, product competitiveness and market access. Sound pressure level determination is the standardized procedure used to quantify the airborne noise radiated by an appliance under defined operating conditions, expressed in decibels (dB) with A-frequency weighting, written as dB(A).

Sound pressure level (Lp) is defined as twenty times the logarithm to the base ten of the ratio of the measured RMS sound pressure to the reference sound pressure of 20 µPa, corresponding to the threshold of human hearing. The A-weighting network approximates the frequency response of the human ear, which is less sensitive to low-frequency sound, making dB(A) the universal metric for appliance noise declaration.

In practice, sound pressure measurements are performed on a defined measurement surface surrounding the appliance, and the results are used to derive the A-weighted sound power level (LWA), an intrinsic property of the noise source that is independent of the measurement distance and environment. Together, the emission sound pressure level and the sound power level form the technical basis for noise labelling, limit compliance and benchmarking of household appliances.

Testing Samples

Virtually every category of household and similar electrical appliance can be subjected to noise sound pressure level determination. Typical sample categories include:

Laundry and Dishwashing Appliances

Drum and impeller washing machines, spin extractors, clothes dryers, washer-dryers and dishwashers, which are tested in normal washing, rinsing and spinning or drying programs.

Refrigeration Appliances

Refrigerators, freezers, fridge-freezers and wine storage cabinets, evaluated in steady-state compressor operation and during defrost cycles.

Kitchen Appliances

Range hoods, microwave ovens, blenders, food mixers, electric kettles, coffee machines, rice cookers and range cooking appliances, measured at the operating speeds or power settings specified in the relevant product standard.

Climate Control and Air Treatment Appliances

Room air conditioners (indoor and outdoor units), electric fans, dehumidifiers, humidifiers and air purifiers, typically tested at maximum and rated fan speeds.

Floor Care and Personal Care Appliances

Vacuum cleaners (cylinder, upright and cordless), hair dryers, electric shavers, hair stylers and similar handheld appliances, for which emission sound pressure at the operator position is particularly relevant.

Testing Items

A complete noise evaluation of a household appliance generally comprises the following measured and derived quantities:

• A-weighted sound pressure level at specified measurement positions, in dB(A)
• Time-averaged (equivalent continuous) sound pressure level, LAeq, measured over the stabilized operating period
• Surface-averaged sound pressure level on the hemispherical or enveloping measurement surface
• A-weighted sound power level, LWA, in dB(A) re 1 pW, derived from the pressure measurements
• Octave-band or third-octave-band sound pressure spectra for frequency analysis
• Emission sound pressure level at the operator or bystander position, where applicable
• Identification of prominent discrete tones and other noise quality characteristics
• Declared single-number noise emission values, LWA and LpA, prepared in accordance with ISO 4871 for labelling purposes

Testing Methods

Applicable Standards

The primary international test code for appliance noise is the IEC 60704 series:

• IEC 60704-1 specifies the general requirements for the determination of airborne acoustical noise from household and similar electrical appliances, based on the engineering-grade methods of ISO 3744
• The IEC 60704-2 series defines particular operating, mounting and installation conditions for individual appliance categories, for example dishwashers (Part 2-3) and washing machines and spin extractors (Part 2-4)
• GB/T 4214.1 is the Chinese national equivalent of IEC 60704-1 and is widely used for testing on the Chinese market, alongside the mandatory noise limit standard GB 19606
• ISO 3744 (engineering method over a reflecting plane), ISO 3745 (precision method in anechoic rooms) and ISO 3741 / ISO 3743 (reverberation room methods) provide the underlying acoustic measurement methodology
• ISO 11201 and related parts govern the determination of emission sound pressure levels at the operator position
• ISO 4871 specifies the rules for declaring and verifying noise emission values of machinery and equipment, including appliances

Test Environment and Instrumentation

Measurements are performed in an acoustically controlled environment, most commonly a hemi-anechoic chamber with a hard reflecting floor, or in a reverberation room when the comparison method with a reference sound source is applied. The instrumentation chain must satisfy the following requirements:

• Class 1 integrating sound level meter or analyzer compliant with IEC 61672
• Measurement microphones with known free-field frequency response, mounted on the standard microphone array
• Octave and third-octave band filters compliant with IEC 61260 when spectral analysis is required
• Acoustic calibrator compliant with IEC 60942, applied before and after each measurement sequence to verify calibration
• Ambient condition monitoring (temperature, humidity, barometric pressure) within the tolerance ranges of the standards

Measurement Procedure

The appliance is installed in the test room in accordance with the mounting and installation provisions of the applicable IEC 60704-2 part, simulating normal domestic use. It is then operated under the specified loading and program conditions until a stable noise state is reached. Sound pressure levels are sampled at the microphone positions distributed over a hemispherical measurement surface centered on the acoustic center of the appliance, typically at a radius of 1.5 m for standard-size appliances, with a larger radius for bulky appliances. The measured values are energy-averaged over the microphone positions and over the observation time to obtain the mean surface sound pressure level.

Data Processing and Corrections

Two principal corrections are applied before calculating the final results:

• Background noise correction K1: the sound pressure level of the test environment without the appliance operating is measured, and K1 is applied when the difference between the total noise and background noise falls within the range specified in ISO 3744; if the difference is too small, the environment is unsuitable for the measurement
• Environmental correction K2: accounts for reflections from room boundaries and obstacles, and must not exceed 2 dB for the engineering grade of accuracy

The A-weighted sound power level is then calculated as the sum of the mean surface sound pressure level, the area term 10 log10(S/S0) with S = 2πr² for a hemisphere and S0 = 1 m², minus the applicable corrections. The expanded measurement uncertainty, typically of the order of 1.5 dB for A-weighted levels under engineering-grade conditions, is documented in the test report together with all operating conditions and instrumentation details.

Applications

Noise sound pressure level determination serves multiple purposes throughout the product life cycle:

• Regulatory compliance: demonstrating conformity with mandatory noise limit standards such as GB 19606 and with ecodesign requirements, for example the cap placed on the declared sound power level of domestic vacuum cleaners sold in the European Union
• Energy labelling: providing the airborne acoustic noise emission figures required on EU energy labels for refrigerators, washing machines, dishwashers and related appliances
• Product development: comparing noise contributions of motors, compressors, fans, pumps and vibration paths during design optimization and pre-certification evaluation
• Market surveillance and claims verification: validating declared values declared in catalogues, e-commerce listings and advertising through verification testing by accredited third-party laboratories
• Quality control: monitoring production consistency and detecting assembly defects such as imbalanced rotors, loose components or degraded bearings
• Benchmarking: comparing the acoustic performance of competing products under identical standardized conditions to support product positioning and consumer information

FAQ

What is the difference between sound pressure level and sound power level?

Sound pressure level describes the noise perceived at a specific location and decreases with distance from the source, whereas sound power level characterizes the total acoustic energy radiated by the appliance and is independent of the measurement position. Appliance test standards measure sound pressure on a defined surface and use it to calculate the sound power level, which is the quantity declared on energy labels and in product documentation.

Why is A-weighting used for appliance noise?

A-weighting adjusts the measured spectrum to match the sensitivity of the human ear across frequency, attenuating low-frequency components to which hearing is less responsive. It therefore provides a single-number indicator, expressed in dB(A), that correlates well with subjective loudness and is accepted worldwide for noise declaration.

Under what operating conditions is the appliance tested?

The appliance is operated under the conditions specified in the relevant part of the IEC 60704-2 series, which define the program, load, water and power supply conditions, installation geometry and stabilization period. Where no dedicated part exists, the appliance is tested under normal rated operation, typically including the noisiest functional mode.

How is background noise controlled?

The ambient noise of the test room is measured with the appliance switched off. If the difference between the combined level and the background level is greater than 15 dB, no correction is needed; if it is between 6 dB and 15 dB, the K1 correction from ISO 3744 is applied; if it is below 6 dB, the measurement cannot yield a valid engineering-grade result.

What are typical noise levels for household appliances?

As an indication, modern refrigerators commonly emit 35 to 45 dB(A), washing machines around 50 to 75 dB(A) depending on the program phase, dishwashers approximately 40 to 55 dB(A), range hoods 55 to 75 dB(A) and vacuum cleaners up to the 80 dB(A) ecodesign ceiling. Values vary with capacity, technology and operating mode, which is why standardized measurement is essential for fair comparison.

How are noise values declared on labels and in manuals?

Declared noise emission values are rounded and documented in accordance with ISO 4871, which specifies how the measured sound power and sound pressure levels, together with their uncertainty, are converted into the single declared figures used for labelling, and which also defines the verification rules applied during market surveillance.