How to use a sound level meter?
When using a sound level meter for evaluation or classification of let´s say environmental and traffic noise, it is not only important to have precise equipment. For sure, the sound level meter used should be minimum class II and in calibrated condition, but mainly important is to avoid influences from the surrounding to receive repeatable and trustable results.
What does that mean?
The sound measurement can be influenced by some factors:
1. The Operator
2. Wind and Humidity
3. Temperature and Pressure
Why is the Operator influencing the sound measurement?
By touching the housing of the sound level meter, noise can be caused, which influences the measurement results. As well as clothes worn by the operator. Sometimes the body of the operator works as a reflecting surface. To minimize nosie reflections, a sound level meter housing is made in a conic form where the microphone is located. In addition, the sound level meter should be mounted on a tripod so that the operator can be in the background while measuring. Also extension microphone cables can be used to have really remote measurements. Modern sound level meter are equipped with a datalogging function. That makes it more easy to not have the operator to be present during the measurement. It is possible to preset all necessary parameters at the sound level meter.
What is the Influence of Wind and Humidity?
To avoid or minimize the sound measurement error caused by wind or airflow, a modern sound level meter ever is equipped with a foam ball (sponge around the microphone). This foam ball additionally protects the microphone against dust and small moisture particles. This is very important by doing noise measurements in areas with high relative humidity (>80 %). High humidity rates have influences on the quality of the microphone. For doing sound measurements in very humid or dusty areas, BDMETER Instruments offer outdoor kits. The sound level meter and the microphone are especially protected for outside measurements.
Why is it important to watch Temperature and Pressure?
Every sound level meter has got a technical specification where you can find the maximal temperature the instrument can be used with. As any test instrument high temperature can damage the circuits. But the main point to avoid is sharply changing temperatures, because condensation can be caused and this is a fact to negative influence on the microphone. A smaller cause for sound measurement errors is the ambient pressure. It influences the microphones sensitivity. But the pressure changes taking place must be large(±200 mbar).
What is the Influence of Vibration on sound measurements?
When you want to use a sound level meter next to vibration sources, it is recommended to protect the meter or the tripod feed by using anti vibration materials for having more reliable results.
When considering the above mentioned facts, you are able to receive much more stable results by using a sound level meter. For very special sound measurements like peoples sound dose or measurements on protective walls or so, you have to follow the ISO normatives, made for certain measurements:
– General standards IEC 651 and ANSI S1.4
– Sound effecting humans ISO 2204
– Noise at working places ISO 9612
The traditional unit for sound level is decibel. And one thing about evaluating the level of noise at the workplace or any other situation, is to remember that the conventional rule of doubling (x 2) does not work here. A certain threshold of the human hearing ability is 0. How to double it, if 0 cannot be doubled? In case of decibels, there is a rule to remember that an increase of only a few dB means the loudness / power getting 2-times higher. Thus, if the rule says that the 50dB limit should not be exceeded, and the increase of 10-15 dB seems to be harmless, since it is far from usual double value (100), it is not true and the change of 15 dB is a significant change in reality, which should be taken into consideration. If to speak about acoustics, then each additional 10 dB mean the double loudness/volume (power is doubled at each 3dB, and amplitude – each 6dB)
Class 1 and Class 2 Sound Level Meter Calibration
A sound level meter used for highly accurate measurements, such as reference standards, is referred to as class 1. A class 2 sound level meter primarily is used for testing and inspection to ensure compliance with workplace safety regulations.
Calibration is the control of measurement magnitudes correction for a measuring instrument without intervention in the measurement system, or the determination of the systematic display deviation in relation to the real value of the measuring magnitude.BDMETER Instruments Calibrated Sound Meter A calibration certificate is a document that confirms that the technical properties of test instruments comply with a recognized standard of measurement.
Since the dawn of measurement, there has been a need to verify accuracy or calibrate. The introduction of International Standards Organization (ISO) 9000 brought about new standards for quality control. As a result, many companies and laboratories must obtain ISO calibration certificates for their measuring instruments. An ISO calibration certificate is a controlled document that confirms that the specific test instruments meet the minimum requirements of the appropriate ISO standard. An ISO calibration certificate can be acquired for most sound level meters offered by BDMETER Instruments.
As a rule for recalibration, only the results of measurements over time may show when it is appropriate to recalibrate a sound level meter. Very important points to consider also are how and how often the noise level meter is used. If a sound level meter has been used frequently during a short time interval, it may make sense to recalibrate it to make sure that all the functions are correct and the accuracy corresponds. Depending on the environment the sound level meter is used in, the calibration time intervals may also be changed. Laboratory conditions can differ greatly from conditions in the field. Humidity, temperature and contaminants can have a negative influence on the device and recalibration may be desirable.
In reality, many modern devices remain in peak calibration condition. In the past, all instruments required calibration. Nowadays, instruments like sound level meters are very precise and stable. Of course, in the process of operation, damage is possible, especially with fragile and vulnerable components like microphones. In which case, calibration is applied to restore or verify the accuracy of a sound level meter.
Class I calibration is the most accurate, with a very small uncertainty (or tolerance). Class II allows a bigger deviation. Depending on the sound level meter class, different kinds of calibration can be applied.
For example, for sound:
– Class I should give +/-0.3 dB tolerance
– Class II should give +/- 0.5 dB tolerance
The period between calibrations of a sound level meter is called a calibration interval. It is the responsibility of each sound level meter user to determine and check the interval between calibrations. BDMETER Instruments’ friendly and knowledgeable technical experts are available to answer any questions related to the process of establishing a calibration interval.
BDMETER Instruments is a trusted manufacturer and supplier of accurate, reliable sound level meter products. Each test instrument is calibrated and adjusted according to the highest possible quality standards by BDMETER Instruments itself, or by a first-class calibration laboratory partner.
Handheld acoustic calibrators commonly are available for class 1 and class 2 sound level meters. To calibrate the meter, the microphone of the measuring instrument is inserted into the calibrator’s chamber. For calibration of class 2 meters, a sound pressure of 94 dB 1000 Hz is generated in the chamber. The class 2 sound level meter is then calibrated based on this value. With class 1 calibrators, the sound level meter is calibrated on two volume levels of 94 dB and 114 dB. An acoustic calibrator is often, but not always, paired with a sound level meter and sold as a set.
DAkkS or ISO certified calibration is possible for almost all sound level meters.
Outdoor sound noise measurement
Today it is nearly impossible to find a place in a town or city where there is absolute and total silence. There is simply too much traffic, too many people, factories, plants, railway stations, airports and so on. And yet noise pollution is proven to be detrimental to human health and safety. That is why permissible levels of sound emissions are under permanent control by various regulatory agencies. Any equipment used outside (vehicles, devices, machinery) should meet the requirements of the directives concerning noise and outdoor equipment. Especially in residential neighborhoods, there are particular time periods when work by means of drills and other noisy equipment can be carried out. Even though these sounds are fleeting, their levels are extremely high for unprotected human ears and must be measured by a sound level meter to assess risk and prevent damaging exposure. Problems with noise levels also are experienced by those living in close proximity to railway stations, airports, busy streets, hospitals and fire and police stations. Excessive long-term exposure to high-level noise negatively impacts human health, resulting in hearing damage, raised nervousness, irritability and unstable psychological conditions. Thus, in some areas noise monitoring and control by use of a sound level meter is an essential and mandated task. Noise levels between 120 dB and 150 dB (e.g., airplanes taking off and landing, drilling and sawing of roadways) are dangerous to human hearing and their continuous presence has dire consequences. Perfect noise levels are between 30 dB and 50 dB, though these pleasant levels are sometimes unreachable in today’s society.Sound level meter construction noise measurement
Physical perception alone cannot determine the severity of noise exposure. You must use a sound level meter to obtain physical measurements. Different people perceive noise in different ways. What is tolerable for some people is unbearable for others. Therefore, the limits of noise exposure are not based on opinion, but on scientific fact. These limits apply to all people exposed to noise, without regard to personal preference. These limits have resulted in many positive changes. For example, workers operating drills are required to wear protective equipment. Whenever possible, airports are built a safe distance away from residential homes. Sirens have been adjusted to alarming yet safe noise levels.
To accommodate diverse sound level measuring needs, BDMETER Instruments offers a vast array of sound level meters. Our datalogging sound level meters allow for long-term monitoring of noise pollution. Several sound level meters feature impressive ingress protection ratings (IP classes) and can be used in harsh conditions for uninterrupted measuring. For measurements carried out outside, near airports or construction sites, a long-lasting battery pack is ideal so there is no need to search for a power source when measuring in the field. The possibility of mounting a sound level meter on a tripod also exists. The readings collected after a certain period of time may be processed (calculation of LEQ data) and an absolutely clear picture of the noise level in a particular area is received.
It is important to remember that there are limits for noise levels and their duration. If the measurements received with the help of a sound level meter / Leq sound level meter show a discrepancy between the desirable and real values, any problem connected with the noise emission should be solved in a timely manner, so that all requirements for health and safety are met posthaste.