About background noise levels

Introduction

Audio experts will give different recommendations regarding background noise levels. Due to the differences in the recommendations, it’s important to understand the basis of them, how to interpret them and what actions to take.

The sound pressure level (SPL) is measured at a known distance from the source and reported in decibels (dB). If the measurement were to be taken at a different distance from the source, the level would change. For instance, conversational speech is typically considered to be 60 dB at a 1 m distance from the talker. If the distance increased from 1 m to 2 m, the level would decrease by 6 dB to 54 dB.

Measuring background noise involves capturing the average level of ambient noise in a space. Ambient noise includes the noise generally heard from the following sources:

• HVAC systems

• Fans in computers, displays, projectors and other devices

• Any other sources of sound heard when the space is free of people

Most often, background noise measurements are taken from several distinct positions in a room and averaged.

Frequency weighting

When using a sound meter to determine the background noise level in a room, different weightings can be used depending on the situation. This article references A-weighting, which is the sound meter weighting that focuses on the frequency range to which the human ear is most sensitive. This is dB SPL A-weighted measurement. For easier reference, A-weighted decibels are abbreviated as dBA.

Signal-to-noise ratio

The ratio of speech compared to the background noise is a key factor in ensuring signal (or speech) comprehension. This is the signal-to-noise ratio (SNR). Industry guidelines describe the minimum signal-to-noise ratio for conference room spaces to be at 20 dB. So, if a person spoke at a 60 dBA level, then the room should ideally have a background noise level of no more than 40 dBA.

Room size

Vocal effort is related to distance, noise and room properties. With all noise levels being equal, people in smaller rooms are closer together and will need to exert less vocal effort. In larger rooms, people are farther away, so more vocal effort (a higher level) will be required to maintain an adequate SNR for distant listeners.

In a smaller room, people can have softer conversations than in a larger room. In a smaller space, the conversation decibel level is often lower than the referenced 60 dB. Due to this, smaller spaces should have an appropriate SNR to support these quieter conversations. An example is that if a person is speaking at 54 dBA, then the room would ideally be no more than 34 dBA.

In larger rooms, people are farther apart and tend to speak louder. This does not mean the background noise level can be higher. The amplitude of the speech — the signal — decreases as it travels through the room while the background noise remains the same. To maintain an adequate SNR, the background noise level still needs to be approximately 20 dB lower than the signal. If a person were to be speaking at a level of 65 dBA, measured at 1 m in free space, the measured level at 4 m away would be 53 dBA. In this case, an ideal background noise level would be 33 dB to support easy listening and to prevent the person speaking from having to raise their voice even more.

Measuring background noise levels

Nureva^® audio systems measure background noise differently than that of a single measurement capture used by generic sound level meters.

Our audio devices use Microphone Mist™ technology and take the quietest reading found in a 1-minute period from continuous 500-millisecond captures. This is done over 5 minutes and then the values are averaged. For every minute moving forward, the average is based on the last 5 minutes. This captures the essence of the background noise. It attempts to omit speech events or sounds that are not consistently there.

Similar values can be obtained with a data-logging sound level meter as follows:

1. Set the sound level meter to capture values over a 1-minute period.

2. Log the slow response, A-weighted minimum value.

3. Repeat and average the results for 5 minutes.

Acceptable background noise levels

Nureva advises a maximum background noise level of around 40 dBA. If Nureva Console is reporting a background noise level beyond 45 dBA for a sustained period, steps should be taken to review the room and improve the noise level.

Improving background noise levels

If excessive background noise is reported from within the room, the following causes should be investigated.

• Ensure the microphone and speaker bar is not installed too close to equipment with a fan or fans.

• Check the HVAC system and/or ventilation fans to see whether the noise can be reduced through system maintenance or settings changes.

• Check other electronics in the room for fan noises and move them into cabinets.

• Check neighboring spaces for equipment that generates loud noise.

If excessive background noise is coming from outside the room, sound dampening might be required.