PLANNING FOUNDATIONS
2.4.3 Definitions of further terms

The equivalent continuous sound level

The average sound level L_m calculated in the previous section is also called "energy-equivalent sound level" or "equivalent continuous sound level" due to the obligatory energetic averaging. It is commonly abbreviated as L_m or L_eq.

The energy-equivalent continuous sound level is equivalent to an A-weighted noise level with a constant amplitude, which transmits the same ("equivalent") sound energy within the same period of exposure as the sound level with a fluctuating amplitude on the basis of which it was created.

Figure 2/9 illustrates the problems associated with the indication of average sound levels. You can see that uniform traffic with 2,000 cars per hour has about the same average sound level as a single train in one hour. So we could conclude that an adequate assessment of certain sound situations is not possible on the basis of average sound levels. And this is absolutely true in regard to the disturbing effect. Nighttime peace can be perfectly respected at a relatively uniform outdoor noise level of about 65 dB(A) caused by traffic when the windows are closed (from a building hygienic point of view, sound-insulated ventilation appliances would be required here). A peak level of more than 90 dB(A) caused by a passing train, however, can wake the occupants even when the windows are closed. Such sleep disturbances may cause cardiovascular diseases if they occur over many years. This is why a peak level criterion should be introduced for traffic noise as well, similar to the assessment regulations for industrial noise and noise from sports and leisure facilities.

What can be countered here is that single values, which can only be compared with a limit, guide or orientation value, are frequently used due to their simple application (yes/no criterion, adherence/no adherence). From the administrative point of view, this procedure has therefore proved itself.

The impulse-weighted average sound level

The impulse-weighted average sound level L_AIm differs from the strictly physical energy definition of the equivalent continuous sound level as it weights impulse noises more (e.g. shooting noises, striking mechanisms etc.) due to a short rising time constant and a slow falling one.

The takt maximal sound level procedure

A special way to evaluate impulse sound is the takt maximal sound level procedure. The particular peak levels are determined in precise intervals (usually five seconds) and used to create the average sound level L_AFTEq. The takt maximal average sound level is generally higher than the average sound level L_m and increases further with the impulsiveness of the sound. The difference between the average sound level L_m and the takt maximal average sound level is known as impulse addition. A further impulse addition is therefore not necessary.

The takt maximal sound level procedure is mainly used in cases with highly variable noises, like at container transshipment points, tennis courts, skating or shooting facilities. A number of regulations and ordinances prescribe the takt maximal sound level procedure for noise measurements, like the Technical Instructions on Noise (TA Lärm) or the Ordinance on the Prevention of Noise from Sports Facilities.

The exceedance level

Exceedance levels are based on the frequency distribution of measured sound levels. They allow for a more detailed description of the basic structure of an existing noise situation than the simple indication of the average sound level could.

L₉₅ is the sound level which is attained or exceeded during 95 % of the measurement period. This means that only during 5 % of the measurement period, it is more silent than the L₉₅ level. It is therefore called the "background noise level" and used for the analysis of constantly dominating extraneous sounds.

L₁ is the sound level which is attained or exceeded during only 1 % of the measurement period and is therefore regarded as the "average maximum level".

The rating level

Finally, the rating level L_r of a measured or calculated situation is the result of evaluating sound level additions or deductions, which are determined according to the agreements prescribed in the various sets of regulations. Level additions are applied for example in the context of more disturbing noises during specified resting periods, of sounds with impulsive characteristics or discrete components, or as a result of meteorological corrections. The rating level serves for a comparison with immission values (limit, guide and reference values). Just like the average sound level, it refers to limited periods of time, e.g. an eight-hour working shift, the time from 6 am to 10 pm (16 hours) or the nighttime from 10 pm to 6 am (8 hours or the loudest hour).

As for road traffic noise, a level addition is considered which takes into account the increased disturbing effect of nearby signal-controlled crossings. Rail traffic, on the other hand, is considered with a sound level deduction (the so-called “railway bonus”, see also section 3.1.2.5).