Since humans detect frequencies differently, sound criteria are measured with curves across a range of frequencies. For instance, a 40 dB sound at 1000 Hz frequency would seem louder than a 50 dB sound at 80 Hz frequency – even though the sound pressure is higher in the 80Hz sound, our ears are not as sensitive to it as they are to the 1000 Hz frequency. Outside of that general range, we aren’t concerned about whether the sound levels are very high or low (for architecture, at least).īefore you can begin to understand the various rating criteria, it is important to understand that humans detect varying frequencies differently because the human ear is less sensitive to very high and very low frequencies. They can easily detect a 5 dB change in sound level under most conditions.ĭecibel A : dB(A) is simply a filter that adjusts decibels for the frequency range that the human ear is capable of hearing, which is in the range of 1 kHz to 4 kHz. Humans can just barely detect a 3 dB sound level difference. As a general rule of thumb, an increase of 10 dB means the sound is perceived to be twice as loud – however this can vary based on the type of sound and the listening conditions. Keep in mind that sound pressure increases on a logarithmic scale. There are different measurements for different conditions, so let’s take a look at them.ĭecibels : The decibel is used in acoustics as the standard unit of sound pressure level, or the loudness of a sound. Unfortunately, it isn’t as simple as saying the sound in a bedroom should be 30 dB or lower. Measuring Sound Levelsīefore you can determine the appropriate sound level for your space, we need to discuss the various ways of measuring sound. Be sure to check our article Architectural Acoustics - Controlling Sound, which talks about design methods for controlling sound. Part of that is to control sound sources. This article discusses acceptable sound levels within a room. Table of Acceptable Room / Space Sound Levels.So Which Noise Criteria Should be Used?.It is recommended to use a ray-receiver to inspect vertical paths and decide yourself the importance of these diffracted levels. Vertical edges are only considered when you are in the shadow of the barrier.

This model only accounts for such a situation along the top edges. ISO9613-2 considers the effect of edges that are not screening, for example an observer looking over the top of a wall. In complex models, applying this recommendation will improve calculation times considerably. 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. The lateral path method can be configured to only consider 'convex' paths that curve in a single direction and do not zig-zag.Ĭonvex path illustration Limit distance (ISO recommendation) Illustration of the inclined source-to-receiver plane Convex path option When enabled, lateral paths around vertical edges are found within a flat plane inclined along the direct source-to-receiver line. It is recommended that you highlight where these simplifications have taken place. For each simplification there will be a degree of error added to the model. The following table of accuracy is taken from ISO9613-2 based on tests without screening or reflections Average height of source and receiverĬomputer modelling requires a simplification of real-world conditions into basic components. It is essential to consider that modelling is only ever an estimate and real-world measurements may differ greatly. Alternatively, the average of varying meteorological conditions over months or years.įor more information about the calculations and their limitations, refer to ISO9613 parts 1 and 2.A moderate ground-based temperature inversion, such as is common on clear, calm nights should not significantly affect accuracy.Wind speed between approximately 1-5 m/s, measured 3-11 m above the ground.This is defined as a wind direction within an arc of 90 degrees with the wind blowing from source to receiver. Below are suitable conditions taken from ISO9613-2. Sound propagation is affected by variations in meteorological conditions. not floating above the ground or with empty sections / perforations. Screens are flat with no significant transmission of sound through or under the screen.The ground is of a continuous type (a single ground factor).Noise sources behave as a point (or line for line sources) and are far-field, where inherent directivity is minimal.

Db sound control