MAS Environmental Tools - www.masenv.co.uk/dbmap

Noise Mapping / Sound Level Modelling - Guide

Introduction

This is a web page for basic sound level modelling using sources of noise and screening from barriers. It 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. It can be accessed at any time from within the Global Settings sidebar.

This tool is still under development and is likely to have bugs! We're keen to hear your feedback

Disclaimer - please note:

It is important to read through this guide before using this tool or its calculations. By using the model you are accepting our terms of use.

Computer Requirements

Any modern web browser which supports HTML5 features. Calculation times will depend on the processing power of your device.

Built into the browser

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

Example of the browser location bar

This means you can easily save your model by bookmarking the page or copying the URL for other people to access and look at. Click here for more information

The browser back button will "Undo" any modifications.

Try out some layouts

Once you have read through the guide, use these pre-built layouts to see it in action

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

  • Add Objects

Objects available

  • Point Source

  • Barrier

  • Building

  • Receiver

  • Ray Receiver

  • Accessory Line

  • Image

Noise Map / Sound Level Map (Grid)

Referred to here as "the grid", this is an adjustable area that maps the calculated sound levels using colours. The settings for this map including its ground height and design are found within the Global Settings.

Example of the sound level map

To move or resize the grid, click and drag the white border or black corner nodes.

Alternatively, there is the option to Fit to objects under Global Settings. With this ticked, the grid automatically resizes to fit the model.

Calculating levels

The sound level map is automatically updated whenever a change is made to the model. You can temporarily pause this process by clicking the top left button.

To turn off the sound level map and stop these calculations permanently, under Global Settings change Display to "Grid off".

Inspecting the model

Using a ray receiver to inspect the calculated levels

The ray receiver draws dotted lines (rays) or waves to illustrate the considered sound paths.

These include:

  • Direct paths from all sources to the ray receiver A
  • Paths attenuated by up to two screens:
    • Dots mark screen intersections B
    • Red dots are used to indicate the ISO barrier attenuation limit has been reached on some or all of the frequency bands (if the limit is enabled) C
  • Reflected paths (when reflections are enabled and screens are considered as reflecting) D
  • Paths considered around vertical edges of screens.
    • These paths are included in the barrier attenuation calculation along with the direct path
    • The paths and intersection dots are drawn in blue E
    • Vertical paths are often not considered in complex situations. See Limits and Assumptions for more information.

Ray receiver examples

Picture of ray receiver with A-F indicators

In the "rays" mode with broadband sources, each dash represents a single frequency band

See calculations in detail

In the Global Settings you will find the Export / Import options where you can choose to export the Receiver calculations in detail (CSV). Here you will be able to view a breakdown of the calculated values for each receiver and frequency band in your spreadsheet software of choice. Make sure you insert receivers where you want to inspect and enable Object labels to better correlate the exported data with the original diagram.

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.

Example of the browser location bar

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

Sharing the model

As with saving, all you need is to copy the URL exactly as it is and anyone else can view the model exactly as you have set it up. Their browser may be different and may recalculate from the configuration at a different speed but the results will be the same.

The URL is too long!

There is an option to use a Shorter URL under Global Settings. When ticked, this will use our server database to store your configuration and automatically convert it to a short URL.

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.

Keeping your browser clean

If you are modelling a lot, your browser history records may become uneccessarily filled up with these entries. To prevent this, either clear your browser history after you have finishing editing or alternatively run your browser in a "Private" or "Guest" mode and it will be cleared automatically.

Limitations and Assumptions

Assumptions used in calculations

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

For more information about the calculations and their limitations, refer to ISO9613 parts I and II.

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 receiverDistance between source and receiver
0 - 100m100m - 1km
0 - 5m+-3dB+-3dB
5 - 30m+-1dB+-3dB

Screens and vertical edge diffraction

Complex screens and multiple vertical edges

One large difficulty in noise mapping / sound modelling is vertical edge diffraction which can create a very complex situation.

As complex ray tracing is beyond the scope of this model, vertical edge diffraction is only considered for simple situations where the screen intersects the direct path and there is an unobscured path around it.

This means that the diffraction around screens with a degree of complexity, such as multi-faceted buildings with an unusual shape, will not always be properly represented in the model.

Vertical edges must be shadowing

ISO9613-2 considers the effect of screens that are along the source to receiver path even when the source is still in sight of the receiver, for example an observer looking over the top of a wall.

This model only accounts for such a situation along the top edges. For vertical edges, the attenuating effect of a screen is only considered when you are in the shadow of the barrier.

Therefore, a tall vertical screen that stands to one side of the source to observer eye-line would have an attenuating effect, however this would not represented in the model until the observer has moved behind the screen.

Inspect the sound paths

We recommend you 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.

See the effect with the following graph

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.

Reflections

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

  1. 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 modelling.

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

  2. Privacy - what infomation is online?

    Your settings are transmitted to our servers when you or someone else first accesses the page from the URL and each time the URL shortening service is used. For example when you click on your bookmark and load up the model, when you use an online bitmap image including the Google Map import, or each change made while Shorter URL is ticked.

    When these settings are transmitted to our servers they will be captured by the site statistics tracker, which is currently Google Analytics. We may use information about the use of the model to improve the service but we treat your settings as confidential and will not pass this information on to third parties.

  3. What information is stored locally? i.e. Cookies

    We use cookies 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.

  4. 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, this is what makes it possible to bookmark your model and use the browser back button as an undo button.

  5. Images

    Images are only ever referenced by their URL or filename, they are never directly stored on our servers and are only temporarily cached on your computer when generating the model.

    Therefore it is recommended that you do not reference images that are not yours and that you understand that if the image is removed then the model will no longer have access to it.

  6. Getting help

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

    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.

Calcs On Calcs Paused Calculate Grid
  • Settings Settings
  • Select Tool Select Objects

    Select tool

    Use this tool to select and move objects.

    Using your touchscreen

    • Touch and drag objects to move or reshape.
    • Single tap objects to toggle their various states.

    Using a mouse

    • Click and drag objects to move or reshape.
    • Hold Shift to keep movement at right angles.
    • Single Click objects to toggle their various states.
    • Right Click objects to edit their options (same as using the Edit tool).

    Got it!

  • Pan Tool Pan

    Pan tool

    Using your touchscreen

    • Touch and drag to move around the model

    Using a mouse

    • Click and drag to move around the model
    • Right Click to return to Select mode

    Got it!

  • Zoom Tool Zoom

    Zoom tool

    Using your touchscreen

    • Tap to zoom in
    • Two finger tap to zoom out
    • Touch and drag to draw a box to zoom in on

    Using a mouse

    • Click to zoom in
    • Right click or Shift + Click to zoom out
    • Click and drag to draw a box to zoom in on
    • Ctrl + Click to fit all objects in the browser window

    Note: You can also zoom using the scale-bar on the left, your mouse-wheel if you have one or by setting the Scale in Global Settings.

    Got it!

  • Edit Objects Edit Objects

    Edit objects

    Using your touchscreen

    • Tap on an object to load its settings for editing.

    Using a mouse

    • Click on an object to load its settings for editing.
    • Right Click to return to Select mode

    Got it!

  • Add Objects Add Objects
    • Point Add point
    • Receiver Add Receiver
    • Barrier Add Barrier
    • Building Add Building
    • Ray Receiver Add Ray Receiver
    • Line Add Accessory Line
    • Image / Map Add Image

    Add a point source

    • Tap/Click anywhere to insert a point source

    What is a point source?

    This is a source of noise that emits from a single point and in all directions.

    Using the select tool

    • Tap/Click on a source once to disable it
    • Touch/Click and drag to move it around.

    Got it!

    Add a barrier

    1. Touch/Click and drag to draw a single barrier
    2. Tap/Click successively to draw a barrier with multiple sections.
      • Right click or Double click to end the barrier.
      • Alternatively Tap/ Click the start point to make it a building.

    What is a barrier?

    This is a screen that both breaks sound paths and potentially reflects them, such as walls and fences. It is assumed to be connected to the ground, to be perfectly built without gaps or significant uneven texture.

    Using the select tool

    • Single Tap/Click on the middle of a barrier to disable it.
    • Touch/Click and drag to move it around.

    Got it!

    Add a building

    • Touch/Click and drag to draw the dimensions of a four sided building
    • Use Shift to keep it at right angles

    To draw buildings with more than four sides, use the Add Barrier tool.

    What is special about buildings?

    These are the same as barriers except that the model ignores internal walls, roof reflections and potential sound transmission from inside to out. Any point sources inside the building are deactivated.

    Buildings that overlap themselves are not valid and will be deactivated.

    Got it!

    Add a receiver

    • Single Tap/Click anywhere to insert a decibel level receiver

    What is a receiver?

    This is a marker where the total decibel noise level is calculated at the specified height along with an optional frequency spectrum graph. To see a breakdown of the calculations steps for all receivers, under Global Settings, Export / Import choose Receiver calculations in detail (CSV)

    Using the select tool

    • Tap/Click on a receiver to toggle the frequency graph display
    • Touch/Click and drag to move it around.

    Got it!

    Add a ray receiver

    • Single Tap/Click to insert a ray receiver

    What is a ray receiver?

    All sources of noise will have lines drawn directly to these receivers to indicate sound propagation paths or "rays".

    When showing waves, the wavelength is drawn to scale.

    When showing lines the dashes represent different frequency bands.

    More information can be found in the guide

    Using the select tool

    • Tap/Click on a ray receiver to toggle the ray type (lines, waves or disabled)
    • Touch/Click and drag to move it around.

    Got it!

    Add an accessory line

    1. Touch/Click and drag to draw a single line
    2. Tap/Click successively to draw a line with multiple sections.
      • Right click or Double click to end the line.

    What is an accessory line?

    These lines can be used for measuring distances or simply for illustration.

    You can also convert between accessory lines and barriers / buildings.

    Using the select tool

    • Tap/Click on the middle of a line to toggle measurement.
    • Touch/Click and drag to move it around.

    Got it!

    Add bitmap images

    1. Tap/Click to insert an image or Google Map. The image is only linked to, not copied or stored anywhere.
    2. Drag and drop images to insert them from your computer. When you do this the file location will not be available to the model and you will be prompted to reload the image into the browser each time you visit the page.

    Using the select tool

    • Maps will be inserted to scale. Touch/Click and drag outline to reposition
    • Images will need to be scaled manually - there are extra handles for resizing and rotating:
    Example of image handles

    When rotating, hold the Shift key to constrain to right angles

    Got it!

Global Settings

Object labels

Grid settings

Values:
Lines:

Viewpoint

Calculation settings

Barrier attenuation

Reflections