What is the Difference between Class 1 and Class 2 Sound Level Meters?
In a previous article, we’ve compared and contrasted the relative efficiencies of Apps and professional sound level meters, highlighting the inherent weaknesses of smartphone platforms for detecting noise levels. However, this is only part of the story. Sound level meters themselves are produced in two distinct classes – Class 1 and Class 2. But how do they differ, and which do you need to use? We’ve compiled a guide to help you understand the differences between the two classes, and how each is typically used to monitor sound.
What do Class 1 and Class 2 Sound Level Meters look like?
First of all, it’s important to understand that sound level meters in both of these classes will all look incredibly similar. Sound level meters are usually portable, hand-held devices with a microphone pointing out of one end. The microphone detects changes in air pressure caused by a sound source, feeding them into the body of the meter. The air pressure level is then converted into an electrical signal, which is calibrated back to a sound pressure level and displayed as decibels (dB) on a digital screen. Depending on the sophistication of the meter, as well as specific weighted frequencies, varying parameters such as data logging and octave band analysis will also be provided.
What Standards Need to be Met?
All Class 1 and Class 2 meters must comply with performance and functionality standards set out by the international standards and conformity assessment body, the IEC (International Electrotechnical Commission). In line with technological development and advances, these standards are regularly reviewed and updated. The standard that sound level meters need to meet today is IEC 61672-1:2013. In the UK, it’s also commonly referred to as the British Standards equivalent, BS EN 61672-1:2013. Both classes of meter will be manufactured to adhere to the strict guidelines set out in this piece of legislation, and by doing so will meet minimum sound measurement requirements.
What’s the Difference between the Two Classes?
In an ideal world, all sound level meters would be equal – they would all be similarly efficient and measure sound in an identically. However, they are complex pieces of equipment, and the sum of all the parts can result in varying abilities to detect noise fluctuations and levels. Because of this, the IEC standard sets out two allowable tolerance ranges, known as Class 1 and Class 2. A Class 1 meter will meet the Class 1 requirements; a Class 2 meter meets the Class 2 requirements.
In general terms, a Class 1 meter is more accurate than a Class 2 meter, it is also able to measure sound over a wider range of frequencies. Indeed, a Class 1 sound level meter is known as being ‘precision’ grade while the Class 2 meter is known as ‘general’ grade.
What are the Different Tolerances?
As explained above, the lower the class, the higher the accuracy of monitoring, particularly at the upper and lower range of frequencies. Class 1 meters achieve this by having tighter tolerances at these extremities.
The latest IEC standard sets the following tolerance limits for Class 1 and Class 2, from high to low frequency reference points:
· At 16 kHz: +3.5 dB, -17dB for Class 1 and +6.0 dB, -∞dB for Class 2.
· At 10 kHz: +2.6 dB, -3.6 dB for Class 1 and +5.6 dB, -∞dB for Class 2.
· At 1 kHz, which is used as a reference frequency for audio recording: +/- 1.1dB for Class 1 and +/-1.4 dB for Class 2.
· At 20 Hz: +/-2.5 dB for Class 1 and +/- 3.5 dB for Class 2.
· At 16 Hz: +2.5 dB, -4.5 dB for Class 1 and +5.5 dB, - ∞dB for Class 2.
So to achieve Class 1 status, a sound level meter must meet far narrower tolerances and perform with far greater accuracy at all frequencies, but particularly at these low- and high-end frequencies.
When should Each Class be used?
When deciding which class of instrument to use, it’s essential to think about what you need to measure, and then look at the regulations you need to meet. For example, the 2005 Noise at Work Regulations Act requires as a minimum that LAeq (equivalent continuous A-weighted sound levels) and LCpeak (maximum C-weighted pressure levels) are measured according to at least a Class 2 standard. However, when assessing environmental noise, for example, noise levels around an airport, a Class 1 instrument will need to be used.
As a general rule, the following applies:
· Class 1 – this precision grade meter is ideal for environmental noise, building acoustics, traffic assessments and in a laboratory testing environment.
· Class 2 – the general grade meter is ideally suited to monitoring noise at work, construction and vehicle noise, and noise emitting from an entertainment source.
Class 1 and Class 2: a cost comparison
Given the difference in accuracy, it’s hardly surprising that there’s a vast difference in pricing between the two classes of sound level meter. However, unless you’re a professional, such as an Acoustic Consultant, for basic noise assessments a Class 2 sound level meter will suffice. Any Google search will uncover a wide variety of options, ranging upwards from £100 for a decent model. However, a meter that complies with Class 1 and Class 2 will generally be in the thousands, so this is prohibitive for anyone using it outside their work remit.
If you need to assess or monitor noise levels and want to make sure the most accurate measurements are taken, then you’ll need to contact an Acoustic Consultant. Here at Auricl, we specialise in providing clear and precise acoustic advice to those working in the construction industry. Contact us today at firstname.lastname@example.org or you can call us on 020 7859 4530 for the London office; for the Reading office call 0118 207 7324. We provide advice across the full lifecycle of a project – from surveys and planning applications to site inspections and acoustic testing on completion. We make sure you stay compliant with legislative guidelines and will help you reach your goals in a warm and approachable manner, so contact us today and let our team of experts help you meet the standard.