Barn Owl Directional Noise MonitoringBarn Owl Directional Noise MonitoringNoise is an inevitable by-product of many industrial practices, and where industry is co-located with the general population it can impact the surrounding communities. If industrial sites are located near other noise sources such as road, rail and other industrial premises, determining what is causing noise can be problematic, but is critical to demonstrating compliance with planning conditions.

Directional Noise Monitoring accurately determines where noise is coming from, and if it is due to an industry or process or if it can be attributed to another source. This is essential in presenting an accurate assessment of the industry’s noise impact and their compliance with noise limits.

Directional monitoring has applications in:

  • Industrial plants
  • Mines
  • Waste recycling plants
  • Wind farms
  • Any facility in a mixed source noisy environment

Directional monitoring is accomplished by deploying one or more BarnOwl® directional noise monitors. BarnOwls may be deployed with traditional noise monitoring terminals to provide a comprehensive monitoring network. Operating as part of Noise Sentinel, Directional Noise Monitoring provides the usual real-time display, alerting and reporting capabilities but in a configurable angle of interest, separating the user’s noise from everyone else's. This product data describes Directional Noise Monitoring only. The full capabilities of Noise Sentinel are covered in a separate product data, BP 2389.

Features and Benefits


  • Determines the direction of noise
  • Ignores noise coming from other directions
  • Continuous unattended outdoor operation
  • Real-time display
  • Alerts on exceedance in specific directions so immediate action can be taken to reduce impact
  • Automatic notification via email or text message (SMS)
  • Automatic exclusion of wind and insect noise
  • Patented algorithm
  • Proven solution in operation for over 10 years


  • Ensures that the noise you are monitoring is actually yours
  • Improved assessment of noise impact
  • More accurate determination of compliance
  • Reduces false alerts, saving time
  • Maximises site operations while ensuring that you are within operating limits
  • Accurate, reliable and simplified compliance reporting makes it easier for you to do your job

The Benefits of Directional Noise Monitoring

Noisy industry located near population centres can cause significant noise nuisance and is often required by their operating permits to routinely monitor their noise impact. While processes and equipment have evolved to reduce noise levels and minimise disturbance, some noise remains. In order to manage this impact, local regulatory agencies establish operating noise limits that the industry must not exceed, with exceedance often being subject to a fine. Many industrial sites therefore establish continuous noise monitoring systems to demonstrate compliance with limits in order to protect their operating licence. While these go a long way to help in some situations, their efficacy may be limited.

Industrial sites are often co-located with other industry and while one may be subject to noise limits, another may not. There are also any number of other unrelated sources of noise, including road and rail traffic and noise from the local community itself. Fig.1A shows a familiar problem. Industry A might be producing a noise level of 47 dB, well within the operating limits of 50 dB. However, noise measured at the boundary of the facility includes noise levels from other surrounding sources such as rail at 48 dB, road traffic at 50 dB, community noise at 45 dB and noise from Industry B 52 dB. In this case, a standard noise monitor would measure all of the noise and record a value of 56 dB – well above the compliance limit.

In Fig. 1B, a directional noise monitoring terminal set to register only noise from the direction of Industry A would record the noise level of Industry A at 47 dB, not causing a noise alert. 

Directional noise monitoringDirectional noise monitoring

Other noise monitoring systems would register an alert, leaving the user to try and determine if they are responsible or not. With Directional Noise Monitoring, the user’s time is not wasted. Noise Sentinel effectively separates Industry A’s noise from other sources.

Another challenge exists with very large industrial sites such as mines. Noise restrictions are most often defined as noise limits at the boundary of the site with the community. For large sites, this may be far from the source of the noise, resulting in very low noise limits defined at the boundary, typically below 50 dB. The boundary is often closer to the community than the noise source and any noise activity such as road traffic, barking dogs or even bird song may trigger a threshold exceedance.

By separating noise coming from the direction of the user’s site while excluding noise from other directions, the user can reduce the number of false alerts from noise that have nothing to do them. This saves the user time, provides a more accurate assessment of their compliance with operating restrictions and helps them to put their noise impact in the context of everything else that is going on around. 

Compliance Reporting Made Easy

Directional Noise Monitor SetupsDirectional Noise Monitor SetupsThe Noise Sentinel Real-time Noise Control application shows all noise data in real time, updated every 1⁄2 second. The location of all noise monitoring terminals is identified on the map along with the current noise level. A BarnOwl directional noise monitor is shown alongside standard noise monitors, with a shaded area showing the angle of interest. The level displayed in the green circle may be defined as the noise level in the angle of interest only, or as the overall noise level, as required.

The angle of interest may be altered from within Noise Sentinel by the user as required. 

 A more comprehensive display of real-time noise is available within the Noise Sentinel client (see example in Fig. 4). Here the user can see, for a selected directional noise monitor, the overall noise, the noise due to detected sources, and the noise in the angle of interest only. This display, also updated in real time, very clearly shows the noise level of interest (in red) relative to the overall noise (in green).

Noise Sentinel Client Real Time DisplayNoise Sentinel Client Real Time DisplayThe BarnOwl directional monitor has been deployed at many Australian mines to address legislation compliance against low boundary noise limits in complex multi-source environments. With Noise Sentinel, it meets the requirements for real-time monitoring required by state planning authorities.

Noise Alerts

Noise Alert PanelNoise Alert PanelEquipped with directional monitoring, Noise Sentinel is able to provide normal alerting capabilities with the added benefit of knowing the direction of the noise. Noise is monitored in all directions, and when an exceedance is detected, the direction of the exceedance level is determined. If the direction is within the angle of interest, an alert will be generated. The alert is immediately displayed in the Noise Sentinel Real-time Control application and recorded in its reporting system. Depending on configuration, the alert may also be automatically transmitted via email or text message to designated persons. The alert will show the time of the exceedance, the level within the angle of interest as well as the overall level.

As with all Noise Sentinel alerts, the user can determine the outcome of the investigation and record the result in Noise Sentinel, which includes reporting.

Directional Noise Alert ReportDirectional Noise Alert ReportAlerts may be triggered by all noise, or just noise within the angle of interest. This may be appropriate when using Noise Sentinel for complaint investigation. The user can respond to the complainant, for example, by acknowledging that there was significant noise, and/or show that it did not relate to their premises.

Each noise alert is accompanied by a detailed report showing the levels measured overall, the levels measured in the angle of interest, and a radar plot. The radar plot shows data recorded during the alert period as a polar plot (angle versus level). Fig.6 shows that the loudest level was recorded to the southwest of the monitoring position.


Directional Noise summary reportDirectional Noise summary reportReporting directional noise, as with other data captured by Noise Sentinel, is seamlessly integrated with Microsoft® Excel®. By using the simple report setup wizard, the user can define a report to be produced regularly and automatically emailed to a distribution list. Users can choose from a wide range of broadband noise metrics and have Noise Sentinel present the data broken down by angle of interest and overall levels, as well as reporting on all sources which exclude wind noise and insect noise.

Reports are available within Noise Sentinel and displayed in tabular form. Data may be charted and exported to other applications in order to compile reports, and also for more detailed analysis/presentation.

The alert report will summarise all alerts for the reporting period. The detailed report with the radar plot is available by clicking the details link.

Data from the directional monitors may also form part of the presentation on the Noise Sentinel Stakeholder Website so that the noise data can be shared with external parties such as regulators, councils or communities.

Noise alert summaryNoise alert summary


Directional monitoring in Noise Sentinel is provided by BarnOwl instrumentation, in partnership with Australian company SoundScience. Over 50 BarnOwls have been deployed at mining sites throughout Australia since 2002. The directional monitoring algorithm is subject to patents in Australia, UK, USA, France, Germany, Spain, Italy and Denmark.


The BarnOwl Outdoor microphone arrayThe BarnOwl Outdoor microphone arrayThe BarnOwl directional noise monitor comprises three Brüel & Kjær outdoor microphones, positioned a precise distance apart in an array. Digital signal processes analyse the three signals in real-time to determine the level and directional component. Every 1⁄2 second, BarnOwl measures the level and the bearing of the dominant noise to a resolution of 5 degrees. As well as measuring the total noise, as with a standard noise monitor, BarnOwl employs further processing to determine all sources. These exclude noise from wind, anything at more than 15 degrees from the horizontal plane and anything very close to the monitor. It also excludes noise without any definite direction such as insect noise.

The data is further processed to provide the required noise metrics such as sound level, Leq and statistical levels.

Enclosure for the processing unit, power supply, communications device and other peripheralsEnclosure for the processing unit, power supply, communications device and other peripheralsThe three BarnOwl microphones are mounted on a plate that correctly positions the microphones. The plate is in turn mounted onto a small mast or tripod, typically 2 metres off the ground. Microphone cables run from each microphone down the mast to the processing unit, which is mounted nearby in an environmentally sealed enclosure. In addition to the processing unit, the enclosure contains a power supply, communications device and other equipment intended to ensure continuous operation and provide remote access.

For correct operation the unit is required to be more than 4 metres away from large reflecting surfaces. Setup is provided as part of the Noise Sentinel service, which includes commissioning, setup and everything to ensure correct operation.

Power is most commonly provided from wired mains with a battery backup that ensures continuous operation in the case of short-term power failure. Other power configurations are possible, including solar power where climate conditions permit.

Communications are provided either by 3G digital wireless communications or by a wired LAN connection to the Internet. The use of proprietary data communications networks is possible where these exist.

In addition to permanently sited units, BarnOwl may be provided within a trailer configuration to facilitate mobile monitoring for periods of up to several months at a time.


Full noise measurement and reporting specifications are covered in the Noise Sentinel Product Data BP 2389. The following specifications relate to Directional Noise Monitoring only. 


Measurement Range: 30 to 143 dB(A) 

Maximum Level: 143 dB(A) 

Noise Floor: 26 dB(A) 

Resolution: 0.1 dB 

Frequency Range: 1 Hz to 12.5 kHz 

Frequency Weighting: A or Lin Accuracy: IEC 61672 Type 1


Frequency Range: 100 Hz to 8 kHz 

Directional Range: 0 to 360° 

Directional Resolution: 5° 

Directional Accuracy: 10°


Trigger: Leq or Ln overall or in angle of interest 

Alert Recording: 15 seconds 

Alert Output: Overall Leq or Ln All sources Leq or Ln Directional Plot Audio Recording Time of Day


Recording Interval: 1 second to 24 hours 

Reporting Duration: 1 minute and beyond


Standard communication via Ethernet LAN connection. 

Optionally 3G wireless digital data communications router. Proprietary digital data networks may be utilised where these exist


Mains power: 110 to 240 V AC, 50 to 60 Hz 

External Power: 12 V DC 


PHYSICAL (Standard Configuration)

Dimensions: 25.4 × 11.75 × 10.80 cm (10 × 4.63 × 4.25′′)

Weight: 2.27 kg (5 lb)

Operating Temperature: –40 to +50°C (–40 to +122°F)


There are no international standards relating to directional noise measurement. However, measurement is according to IEC 61672 Type 1, except for directionality requirements


Calibration Interval: 12 months 


Electrical Standards: CE Class B (IEC 61000–4–2 to IEC 4–6 and IEC 4–11, 1994–1996)

Ordering Information

Noise Sentinel may be ordered by contacting your local Brüel & Kjaer representative


Download the Product Data Sheet 

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