dBmap.net Noise Mapping Tool

Introduction

What is this noise mapping tool?

For modelling sound levels using sources of noise and screening from 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.

Software that runs in the browser

All settings are stored in the URL. This is updated every time you make a change.

Save your model by bookmarking the page or share the link. Click here for more information

The browser back button will "undo" changes.

Computer requirements

Any up-to-date web browser. Calculation times will depend on the processing power of your device.

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

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by MAS Environmental Ltd

Get started

Configure your model

The top right button is where you can access the Global Settings sidebar panel. Here you will find all the options for your model including configuration settings based on the calculation parameters of ISO 9613.

In there you will also find the button to open up this guide.

Tools for editing

Select
Pan
Zoom
Edit Objects
Draw Grid

Normal mode
Draw Section *

Cross Section mode
Height Point *

Ground Levels mode
Add Objects

Objects

Point Source
Line Source *
Barrier
Building
Receiver
Ray-Receiver
Accessory Line
Image

* Subscription only

Calculating levels

Calculations are automatically run whenever a change is made to the model. You can temporarily pause this process by clicking the top left button.

To stop these calculations permanently, under Global Settings change Display to "Grid off".

Multi-thread calculations Subscription only

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

Display Modes

Normal mode - map calculated noise levels (grid)

Referred to as the "grid", this sound level map displays an adjustable area that maps the calculated levels using colours and values. The settings for this map are found within the Global Settings.

Cross section - vertical noise map (vertical grid) Subscription only

Map sound levels and inspect sound paths and objects on the vertical plane

Ground level mode Subscription only

Modify the ground level topography. The grid area will change to display a map of calculated ground levels and you can add or edit height points.

3D View mode Subscription only

Navigate your model in 3D space

Saving and sharing

How to save the model

All the settings for the model are stored in the URL in the location bar which means you can simply bookmark the web page and it will save your model exactly as it is.

Remember to create a new bookmark or update the old one whenever you make any further changes.

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.

What about Subscription-only objects? Subscription only

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.

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 Subscription only

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

Stored in your browser history

Each change you make creates a new entry in your browser history, which means you can undo your changes simply by hitting the back button or going back through the history.

Inspecting the model

Using a ray-receiver to inspect the calculated levels

The ray-receiver illustrates the sound paths considered.

These include:

Example A Direct paths are drawn from all sources
Example B Black dots mark barrier intersections (up to two)
Example C Red dots indicate the ISO barrier attenuation limit has been reached on some or all of the frequency bands (when the limit is enabled)
Example D Grey dots indicate that the barrier does not shadow the receiver and is below the line of sight
Example E 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
Example F 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
Example G Paths considered around vertical edges of screens are illustrated in blue (when enabled in settings)

Ray-receiver examples

Cross section inspection Subscription only

Mapping the vertical plane

Cross Section mode allows you to slice through your model and see the vertical location of objects.

Example of the cross section line

Control object display

Lines that intersect the section line and points within the capture area (1 metre) will appear.

Click the eye icon to view the projection of all objects and sound rays upon the vertical plane.

The grid icon will toggle displaying the horizontal grid height.

Inspecting ground height topography Subscription only

Ground levels are calculated by triangulating between groups of three height points or slopes where only two height points are available.

This triangulation is illustrated in Ground Level mode. Make use of this mode to inspect how ground topography is triangulated and what screening is created by this.

Screening ground is highlighted in white

Ground level and barrier heights Subscription only

Barriers and buildings are modelled as flat with no sloping roof. When a building is placed on sloping ground, the model considers one end of the barrier or one corner of a building as the reference point for the height.

When in Ground Level 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 level mode

Modify the reference point: from where the height is taken. Hover over the object and Click the centre point to move it to the next available location.

3D model inspection Subscription only

View your model in 3D space

The Compass indicates the direction of view. Click to reset the view orientation.

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 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 grids.

Note: The vertical grid must be calculated in Cross Section mode before it will be available to the 3D view.

See calculations in detail

Within the Export / Import options, export the Receiver calculations in detail (CSV).

Here you will be able to view a detailed breakdown of the calculated values for each receiver. Best viewed in spreadsheet software.

Insert receivers for each location where you want to inspect. Add Object names to better correlate the exported data with the original diagram.

Sound levels for sources

What is a sound power level?

Receivers (e.g. sound level meters) measure the "sound pressure level" (Lp), a decibel value of the sound by a source at a distance.

The source of sound itself is calculated with a "sound power level" (Lw). This is a decibel value that represents the total acoustic output radiated.

They both contain frequency and amplitude information, but the difference is that a sound power level does not include distance information.

Calculating a sound power level

If you have a distance included with your decibel level, the decibel figure may represent a sound pressure level. You can use this to calculate the sound power level using the following calculator.

Sound pressure to sound power calculator

Sound pressure level (Lp)

dB

Distance

m

Directivity (Q)

Type

Sound power level (Lw)

dB

Frequency information

If you have only a single decibel figure for your sound power and it is for a broadband source, put it in at 500Hz as instructed in ISO9613-2.

The scope of ISO9613-2 only covers the octave bands 63 Hz to 8 kHz. The 31.5 Hz and 16 kHz octave bands are not officially supported by ISO9613-2 but are made available in the model for use, utilising the equation parameters of the adjacent octave band where necessary.

Leq or Lmax?

Useful for modelling sound sources that are not consistent, the Leq or "equivalent continuous sound level" is a single value that represents the equivalent amount of energy in a given period for a fluctuating source as if it were a steady continuous noise level. For this reason the Leq is always accompanied with a reference to the length of time that it represents.

The Lmax is a maximum level (based on the standard time-weightings: fast, slow or impulse) and is useful for situations such as a vehicle pass-by when you wish to model the peak of the noise.

Sound energy from line sources Subscription only

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 (note: lateral paths are considered but not shown).

Reflections are not yet supported for line sources.

Limitations and assumptions

Assumptions used in calculations

Noise sources behave as a point/line and are far-field, where inherent directivity is minimal.
The ground is of a continuous type (a single ground factor)
Screens are flat with no transmission of sound through or under the screen. i.e. not floating off the ground or with empty sections or perforations.
Meteorological conditions are for moderate downwind propagation. Strong winds or temperature inversion that could affect the propagation path are not accounted for.

For more information about the calculations and their limitations, refer to ISO9613 parts 1 and 2.

Accuracy

It is essential to consider that modelling is only ever an estimate and real-world measurements may differ greatly.

The following table of accuracy is taken from ISO9613-2 based on tests without screening or reflections

Average height of source and receiver	Distance between source and receiver
Average height of source and receiver	0 - 100m	100m - 1km
0 - 5m	+-3dB	+-3dB
5 - 30m	+-1dB	+-3dB

Degree of error

Computer modelling requires a simplification of real-world conditions into basic components. For each simplification there will be a degree of error added to the model. It is recommended that you highlight where these simplifications have taken place.

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

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 find these situations and decide yourself the importance of these diffracted levels. Read here for more information on using the ray-receiver

Parameters in detail

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.

Plot the ground factor results

Barrier Attenuation

ISO 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 two screens. ISO9613 only considers up to two screens, the two that are most effective, and all others are ignored.

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

ISO check barrier perpendicular dimension > wavelength

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 reflections

In the equations 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.

Reflections

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.

Reflections from line sources are currently not supported

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 one 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.

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 barrier surface size check

For a barrier screen 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 barrier, to test out and better understand this relationship.

Terms of use and your privacy

Rights over using the model

The model is free to use for both private and commercial use but without any warranty.

This is an approximate calculation tool to assist in understanding acoustics and noise mapping (sound level modelling).

It should not replace your own calculations and real life measurements.

Full Terms of Service for Users
Privacy - what information is online?

The settings of the model are stored in the URL. This is transmitted to our server when you or someone else first loads the model from the URL and each time the URL shortening service is used.

We also use Google Analytics to track page visits.

We may sometimes use information about the general activity of the model to improve the service but we treat your settings as confidential and will not pass this information on to third parties.

The User Subscription service also stores your account settings, and library (snapshots, colour schemes, sound levels and images) in our database. This data is never made available to other parties or used for any purpose outside the use of this tool by the registered account. You control this data and can remove it from within your account at any time.

Full Privacy Policy for Users
What information is stored locally? i.e. Cookies

Browser cookies are used for accessing your User Account and to store certain user interface settings such as when you have seen the side tips and want them hidden. We do not use them for anything else.
Calculations

The calculations are done client side, this means that they are not stored anywhere online but are generated by your computer each time you access the page.

All the objects and settings are saved in the URL.
Images

Images are referenced by their URL or filename. They are not automatically stored on our servers and are only temporarily cached on your computer when generating the model.

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.

If you use a local image file in the model you can choose to upload the image to your User Account to make it accessible to others when you share the URL. Subscription only
Getting help

This tool is made freely available for you to use but unfortunately we cannot offer free technical support if you get stuck.

Please sign up to our subscription service to access technical support.

We are keen to hear feedback such as your thoughts on how to improve it or any bugs you have encountered. Please let us know using the contact form.
References and libraries
- Calculations are based on
  - ISO 9613-1:1993 — Attenuation of sound during propagation outdoors — Part 1: Calculation of the absorption of sound by the atmosphere
  - ISO 9613-2:1996 — Attenuation of sound during propagation outdoors — Part 2: General method of calculation
  - ISO/TR 17534-3:2015 — Acoustics — Software for the calculation of sound outdoors — Part 3: Recommendations for quality assured implementation of ISO 9613-2 in software according to ISO 17534-1
- Colour scheme from
  - Coloring Noise
- Javascript libraries:
  - JQuery (Programming)
  - SnapSVG (Object drawing)
  - THREEjs (3D View)
  - Delaunator (Topography triangulation)
  - MarchingSquares.js (Contour calculation)

Noise Mapping Tool

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