Noise Mapping Tool

What is this noise mapping tool?

The dBmap.net Noise Mapping Tool is used for modelling external sound propagation and calculating sound levels using sources of environmental and industrial noise and screening from buildings and barriers.

This is intended to be a tool for understanding and implementing the calculations of ISO-9613 and creating interactive models that are freely accessible.

Please read through this guide. You can print this page and you can access it again at any time from within the Global Settings sidebar.

Video tutorials on Youtube

This tool is free to use. Some features are only available when you are logged into a user account with a valid subscription.

Multi-thread calculations

You can speed up calculations by enabling multi-thread calculations. This will utilise more cores of your CPU for faster processing.

Sharing the model

As with saving, you can share the link and other users can view your model exactly as you have set it up at that moment. Their browser may be different and may recalculate at a different speed but the results will be the same.

The URL is too long!

Click the Short URL button in Global Settings. This will use our server database to store your configuration and automatically convert it to a short URL.

Snapshots feature

Subscribers can take Snapshots that saves the short URL to their account with a thumbnail of their model.

What about sharing to non-subscribers?

Users who are not logged-in or do not have a valid subscription will not be able to access the subscription-only features, however any line sources and ground heights that you have added to the model will still be included.

Export results

In the Global Settings sidebar there are various Export options:

• Report (PDF)

  Generate a PDF of the noise model based on the active mode and current view. Includes tables and charts of receiver levels, spectrums and breakdown of sources.

• Image (PNG)

  Download an image of the noise map. Subscribers export higher resolution images. To download the Cross Section, Ground Heights or 3D view, activate this mode first.

• Receiver calculations in detail

  Create a comma-separated file to load into spreadsheet software. All objects are detailed in full and each receiver has a detailed list of sources including calculation breakdown.

Inspecting the sound path

• 1 Direct paths from all sources
• 2 Black dots mark barrier intersections
• 3 Red dots indicate the ISO barrier attenuation limit has been reached on some or all of the frequency bands (when the limit is enabled)
• 4 Grey dots indicate that the barrier does not shadow the receiver and is below the line of sight
• 5 When set to "waves" the rays will illustrate the wavelength of the source.  When set to "rays" for broadband sources, each dash represents one single frequency band
• 6 Reflected paths when reflections are enabled and screens are considered as reflecting. In the example, not all frequency bands are reflected causing gaps in the dashed line
• 7 Paths considered around vertical edges of screens are illustrated in blue (when enabled in settings)

Compare two scenarios

Calculate the difference in level between two configurations of your model. When activated the following options will appear:

The configuration of the following objects can be compared:

• Point and line sources
• Barriers and buildings
• Global settings (environmental settings, barrier attenuation and reflections)

Object positioning and ground height topography is fixed and cannot be compared.

View all the differences in a table

Ground height topography

Triangulation and screening ground

Ground height is triangulated using the height points and lines. The ground is sloped in locations where only two height points are available.

When "Draw ground height triangulation and screening" is selected in the Global Settings, the resulting ground height triangles are drawn onto the noise map and the edges that can cause screening are highlighted in white.

Screening ground is highlighted in white

Barrier heights over sloping ground

When placed on sloping ground, the model considers one end of a flat barrier or one corner of a building as the reference point for the height.

When in Ground Height mode each building and barrier has a basic wireframe of the 3D shape to illustrate the difference in height at each point.

Example of the building wireframe in Ground Height mode

Change the height reference point 1

Hover over the object and Click the centre point to shift the reference point to the next available location.

Cross section

Mapping the vertical plane

Example of the cross section line

Points within the 1m capture area 1 and objects that intersect the section line 2 will be shown.

Click the line to reverse the direction 3

Pop-up window

Control the cross section height by dragging the top edge of the pop-up window.

Dragging either side of the window will rescale the cross section noise map.

Control object display

The eye icon will show the projection of all objects and sound rays.

The noise map icon will toggle displaying the horizontal noise map height.

Quick-select a cross section

Click on the following to quickly set the cross section to fit:

• Barrier/Building face or 1m facade (depending on settings). This also sets the cross section height to match
• Sound ray drawn by a ray-receiver
• Accessory line

3D view

Example of the 3D view

Rotate the view either with the set direction buttons or Click and drag the window using your mouse.

Navigate from the main area using the Pan tool or by repositioning the 3D view centre point. Alternatively, use the right button or arrow keys in the pop-up window.

Centre point shown in the main window

Toggle displaying the horizontal and vertical noise maps.

Sound energy from line sources

For a point source, sound radiates in a sphere and the "sound power level" represents the total sound energy. A line source radiates as a cylinder along the section lengths and the sound power level is usually considered by the sound energy per metre of length. Therefore, the sound power values are different to a point source and are not directly interchangeable.

When the model calculates a line source, it breaks the line into segments with a point source at the centre with a level proportional to the length of this segment. Use a ray-receiver to inspect this behaviour.

Vertical edge diffraction

When enabled, lateral paths around vertical edges are found within a flat plane inclined along the direct source-to-receiver line.

Illustration of the inclined source-to-receiver plane

Convex path option

The lateral path method can be configured to only consider "convex" paths that curve in a single direction and do not zig-zag.

Convex path illustration

Limit distance (ISO recommendation)

ISO17534-3 recommends that lateral paths are limited to vertical edges within the range of the most distant horizontal edge multiplied by 8, with respect to distances from the direct source-to-receiver line. In complex models, applying this recommendation will improve calculation times considerably.

Vertical edges must be shadowing

ISO9613-2 considers the effect of edges that are not screening, for example an observer looking over the top of a wall. This model only accounts for such a situation along the top edges. Vertical edges are only considered when you are in the shadow of the barrier.

Inspect the sound paths

It is recommended to use a ray-receiver to inspect vertical paths and decide yourself the importance of these diffracted levels. Read here for more information on using the ray-receiver

Ground Factor

Sound waves will be reflected or absorbed by the ground depending upon the frequency of the sound wave and how porous the ground is (indicated by the "Ground factor" value G). The barrier attenuation formula also accounts for ground effects.

• For "Hard Ground" G = 0. Hard ground reflects sound waves. Examples include roads and paved areas.
• For "Soft Ground" G = 1. Soft ground is porous and absorbs sound waves. Examples include grass, trees and other vegetation.
• For "Mixed Ground" use a value for G between 0 and 1 that represents the fraction of the ground that is soft.

Apply barrier attenuation limit (20/25dB)

Insertion of a screening barrier will reduce the level of a source using the formulae of ISO9613-2. The guidance states that this reduction in any octave band is limited to 20dB in the case of a single screen or 25dB for multiple screens.

You may want to disable this limit to see what effect it has on the final levels.

Barrier perpendicular dimension > wavelength

Following the method in ISO9613-2, a barrier is only considered to be screening if the horizontal dimension perpendicular to the source-to-receiver line is greater than the wavelength.

You may want to disable this check to explore the unusual effect it causes. For example, as you move around a barrier its apparent width in your field of vision decreases. There will be a point where this width drops below the wavelength of the source and the barrier will no longer be considered to be screening.

Screening Ground

Screening ground reflections

In the formulae of ISO9613-2 (1996) ground effects are removed by the insertion of a barrier. However, ISO17534-3 (2015) recommends that only negative ground effects are removed - i.e. attenuation due to ground absorption.

When "Do not screen ground reflections" is selected, any increase in level due to ground effects will not be affected by barrier insertion, as is recommended.

Ground as a barrier

Raised ground levels will behave as a barrier when breaking the line-of-sight between source and receiver. Read here for more information about inspecting ground level screening

Reflections

Reflecting surfaces

Screens with a reflection coefficient above 0.2 are considered to be reflecting and the model will include these reflected sources in up to two screens when First and Second reflections are enabled in the settings. Barrier attenuation along the reflected path is also considered up to the height of the reflecting screen.

Only barrier and building sides make up the reflecting surfaces considered. Reflections from the roof of a building are not considered. Ground reflections are part of the ground effect calculation (ground factor).

Reflection coefficient (⍴)

ISO9613-2 provides the following estimates of the sound reflection coefficient:

• 1 - Flat hard walls
• 0.8 - Walls with windows
  
• 0.4 - Factory walls with 50 % openings / installations
  
• 0 - No reflections. Open installations
  

Reflected level in dB

This is the reduction in level applied to the original sound level based on the chosen reflection coefficient.

Facade level (1m)

A "facade level" measurement is one taken at 1 metre perpendicular distance from a large reflecting surface. It is an industry practice for measurements that can be later adjusted to a free-field measurement, one that is outside of the range of influence of reflecting surfaces. The behaviour of reflections at less than 1m from the facade are not accounted for.

By enabling this all buildings and barriers will show a dashed line illustrating the 1m facade location. Reflections are only considered at distances beyond this line. Additionally, receiver points will be kept outside of this area when being positioned.

ISO reflector surface size check

For a surface to be considered as reflecting, the size of the surface is compared to the wavelength of the sound using a formula that also considers the angle of incidence and sound path length. This formula can be found in the guidance.

You may want to disable this check to see the result when reflections are always considered for a vertical surface regardless of its size.

Images

Images are referenced by their URL or filename.

It is important that you do not reference images that breach license, copyright or legal restrictions and that you understand that the model will no longer have access to the image if it is removed.

They are not automatically stored on our servers and are only temporarily cached on your computer when generating the model.

Upload Image

Local image files can be uploaded to your User Account to become accessible to others when you share the URL.