noisetools.net/dbmap

Configure your model

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.

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

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

Using a ray receiver to inspect the calculated levels

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

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.

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.

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.

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

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

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

G = 0 (hard) G = 0.25 G = 0.5 G = 0.75 G = 1 (soft) Height = 1m Height = 2m Height = 4m Height = 10m

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.