Introduction

When selecting a sound level meter, specifications often refer to “Class 1” or “Class 2.” These classifications are closely related to the instrument's measurement performance and are an important consideration when determining whether a meter is suitable for professional noise measurements.

Under the IEC 61672 series of standards, sound level meters are classified according to defined performance requirements. Both Class 1 and Class 2 instruments can measure sound pressure level, but they differ in permissible tolerances, frequency response, and performance under certain environmental conditions.

It is important not to interpret Class 1 and Class 2 simply as “high accuracy” and “low accuracy.” Nor can the class of an instrument be determined solely from a manufacturer's stated ±dB accuracy. The classification covers a comprehensive set of electroacoustic performance requirements.

Key Points

● Class 1 and Class 2 are performance classes for sound level meters defined by the IEC 61672 series;
● Class 1 generally has tighter tolerances and a wider applicable frequency range;
● Class 2 is suitable for many general industrial, environmental survey, and routine noise measurement applications;
● Class 1 is commonly used for professional measurements, engineering analysis, and regulatory applications where measurement uncertainty requirements are more stringent;
● Whether a sound level meter qualifies as Class 1 or Class 2 depends on compliance with the relevant standard requirements, not on a single manufacturer-stated accuracy specification;
● Selection should be based on the measurement objective, applicable standard, frequency range, and reporting requirements.

What Are Class 1 and Class 2 Sound Level Meters?

Class 1 and Class 2 generally refer to sound level meters that meet the corresponding performance requirements of the IEC 61672 series.

IEC 61672 specifies multiple aspects of sound level meter performance, including frequency weighting, time weighting, level linearity, frequency response, and the effects of environmental conditions. The class therefore represents the overall performance of the instrument rather than a single accuracy figure.

In general:

● Class 1: Tighter allowable tolerances and intended for higher-level professional acoustic measurements;
● Class 2: Wider allowable tolerances and suitable for general noise surveys, industrial inspections, and routine sound level measurements.

Provided that the instrument meets the requirements of the intended application, both classes have valid uses. Class 1 is not necessary for every measurement task.

What Is the Main Difference Between Class 1 and Class 2?

The most important difference is the performance tolerance permitted by the standard. Class 1 has tighter allowable limits than Class 2 and is therefore designed to meet more stringent performance requirements across a wider range of measurement conditions.

These differences are not limited to an error value at one fixed sound pressure level. They apply to the instrument's overall performance across different frequencies, sound levels, and environmental conditions.

For this reason, it is not technically correct to state that “Class 1 is always exactly a certain number of decibels more accurate than Class 2.” The actual allowable deviation depends on the specific IEC 61672 test requirement, frequency, and test condition.

How Does Frequency Response Differ?

Frequency response is one of the important differences between Class 1 and Class 2 instruments.

Real-world sound contains energy across a range of frequencies. A sound level meter must maintain a response within specified tolerances over the relevant frequency range, and these tolerances differ between the two classes.

Class 1 generally has tighter frequency-response requirements and can satisfy specified tolerances over a wider frequency range. It is therefore better suited to professional measurements involving significant low-frequency, high-frequency, or complex spectral content.

Class 2 is generally sufficient for common environmental noise, machinery noise, and routine industrial measurements. However, where stricter frequency analysis or standards compliance is required, the applicable test method should be checked to determine whether Class 1 is mandatory.

How Does Measurement Accuracy Differ?

Describing Class 1 as “more accurate” than Class 2 is useful as a general explanation, but technically it is incomplete.

The class designation does not simply require an instrument to achieve a single specification such as ±0.5 dB or ±1.0 dB. Instead, it defines a comprehensive set of performance requirements under different test conditions.

Because Class 1 has tighter allowable tolerances, it generally provides a higher level of measurement performance under equivalent conditions. However, actual measurement accuracy can still be affected by:

● Instrument performance;
● Measurement microphone characteristics;
● Acoustic calibrator and calibration status;
● Measurement position and distance;
● Wind speed and windshield use;
● Temperature, humidity, and atmospheric pressure;
● Background noise;
● Reflective surfaces and the acoustic environment;
● Measurement procedure and operator technique.

Therefore, even a Class 1 sound level meter cannot guarantee reliable results if the measurement method is incorrect.

How Does Environmental Performance Differ?

IEC 61672 considers not only performance under ideal laboratory conditions but also the effects of specified environmental conditions on the instrument.

Class 1 and Class 2 have different permissible deviations under certain environmental conditions, with Class 1 generally subject to more stringent performance requirements.

For routine indoor measurements or general equipment checks, the practical difference may be limited. However, environmental performance becomes more important in professional environmental noise monitoring, outdoor measurements, long-term monitoring, and applications requiring formal measurement reports.

Regardless of class, the instrument should always be operated within the temperature, humidity, and other environmental limits specified by the manufacturer.

Where Are Class 1 Sound Level Meters Used?

Class 1 sound level meters are primarily used where measurement performance, uncertainty, or standards compliance is particularly important, including:

● Professional environmental noise monitoring;
● Building acoustics measurements;
● Acoustic laboratory testing;
● Product noise testing and research and development;
● Machinery acoustic analysis;
● Professional measurements requiring frequency-spectrum analysis;
● Tests where regulations, certification schemes, or standards specifically require a Class 1 instrument;
● Formal acoustic measurement reports with stringent technical requirements.

Whether Class 1 is mandatory for a particular project should always be determined by the applicable regulation, test standard, contract, or technical specification.

Where Are Class 2 Sound Level Meters Used?

Class 2 sound level meters can meet the requirements of a wide range of routine noise measurements and often provide a practical balance between performance and cost.

Typical applications include:

● Routine machinery noise checks in factories;
● Preliminary workplace noise surveys;
● HVAC equipment noise checks;
● Construction site noise inspections;
● General acoustic surveys in offices, schools, and commercial spaces;
● Comparative noise testing of appliances and machinery;
● Educational laboratory work;
● Equipment maintenance and troubleshooting;
● General environmental noise trend surveys.

Where measurements are intended primarily for on-site assessment, equipment comparison, trend monitoring, or internal quality control, and no applicable standard requires Class 1, Class 2 is often the more cost-effective choice.

Class 1 vs Class 2: Main Differences

This table provides a quick comparison, but final selection should always be based on the applicable test standard and project requirements.

Is Class 1 Always the Better Choice?

Not necessarily.

If the applicable test standard explicitly requires Class 1, then a compliant Class 1 sound level meter should be used. However, for equipment maintenance, routine field noise checks, or general environmental surveys, Class 2 may fully meet the measurement requirements.

For example, a maintenance technician may only need to determine whether the noise from a motor has increased noticeably compared with the previous month. For this type of trend measurement, maintaining consistent measurement position, distance, instrument settings, and environmental conditions may be more important than simply selecting the highest instrument class.

The correct principle is therefore to select a sound level meter that meets the measurement objective and applicable standard requirements, rather than automatically choosing the highest class.

How Can You Verify Whether a Sound Level Meter Is Class 1 or Class 2?

When purchasing a sound level meter, it is not advisable to determine the class solely from terms such as “high accuracy,” “professional grade,” or a single ±dB specification.

Check the following information:

● Whether the product explicitly states compliance with the relevant IEC 61672 requirements;
● Whether the manufacturer declares the instrument as Class 1 or Class 2;
● Whether the technical documentation identifies the applicable standard;
● Whether type-evaluation, calibration, or other technical documentation required by the project is available;
● Whether the measurement requires an acoustic calibrator that meets the relevant requirements;
● For regulatory, certification, or third-party reporting applications, whether the documentation is accepted by the applicable authority or project requirements.

A display resolution of “0.1 dB” does not mean that the instrument is Class 1. Display resolution and IEC 61672 performance class are different specifications.

Should You Choose Class 1 or Class 2?

The first step is to define the measurement objective rather than compare prices.

For equipment inspections, general industrial noise measurements, educational applications, or basic environmental surveys, Class 2 is often sufficient.

For professional environmental noise monitoring, acoustic engineering, product R&D, laboratory testing, or applications requiring lower measurement uncertainty, Class 1 is generally the preferred choice.

If the results will be used for regulatory compliance, certification, dispute resolution, or formal test reports, the applicable regulation or test standard should be checked first. It may specify the required sound level meter class, calibration procedure, measurement position, time weighting, frequency weighting, and data-processing method.

FAQ

Is a Class 1 sound level meter always more accurate than a Class 2 meter?
In terms of standardized performance requirements, Class 1 has tighter allowable tolerances and therefore generally offers a higher performance level. However, actual measurement accuracy also depends on calibration, measurement position, environmental conditions, and measurement procedure.

Can a Class 2 sound level meter be used for factory noise measurements?
Yes. Class 2 meters are widely used for machinery inspections, general industrial surveys, and routine noise measurements. For occupational noise compliance assessments, the required instrument specifications should be confirmed against the applicable local regulations and test standards.

Does 0.1 dB resolution mean that a sound level meter is Class 1?
No. A 0.1 dB specification normally refers only to display resolution. It does not demonstrate compliance with Class 1 requirements. The IEC 61672 class is determined by a comprehensive set of performance criteria.

Do Class 1 and Class 2 sound level meters have different measurement ranges?
Not necessarily. Measurement range is a product-specific specification and is not the sole criterion distinguishing Class 1 from Class 2. Two instruments may have similar nominal measurement ranges while belonging to different performance classes.

Do both Class 1 and Class 2 sound level meters require calibration?
Yes. Where reliable and traceable measurements are required, acoustic calibration and periodic calibration should be performed according to the instrument instructions, applicable standard, and project requirements.

Should I always choose a Class 1 sound level meter when purchasing an instrument?
No. The appropriate class depends on the application. Class 2 is usually sufficient for general industrial inspections and basic noise surveys, while Class 1 should be selected for professional acoustic measurements or where the applicable standard specifically requires it.

Summary

The main difference between Class 1 and Class 2 lies in the performance requirements and permissible tolerances defined by the IEC 61672 series. Class 1 has tighter requirements and is generally more suitable for professional acoustic measurements, engineering analysis, laboratory testing, and applications requiring lower measurement uncertainty. Class 2 is suitable for a wide range of industrial inspections, basic environmental surveys, and routine noise measurements.

When selecting a sound level meter, do not focus solely on a stated ±dB accuracy or display resolution. Consider the applicable standard, measurement objective, frequency range, calibration requirements, and intended use of the data.

For regulatory, certification, or formal testing applications, confirm the required sound level meter class in the applicable standard before selecting a Class 1 or Class 2 instrument.