When selecting acoustic warning signals, such as reversing alarms or Sirens and Speakers, "decibel" is the most commonly used term. However, there is often confusion about what this unit actually implies. Is 100 dB twice as loud as 50 dB? (Spoiler: No).

In this article, we explain the basic principles of sound and what you need to know about the dB(A) scale and distance regulations.

What is a Decibel (dB)?

The decibel (abbreviated dB) is not an absolute measure like a meter or a kilogram. It is a logarithmic ratio describing sound pressure intensity relative to the threshold of silence for the human ear.

The scale is named after Alexander Graham Bell. Since the human ear has a vast range (from a dropping pin to a jet fighter), a linear scale is impractical. The logarithmic dB scale makes these massive differences comprehensible.

The "Logarithmic Trap": 1 + 1 does not equal 2

• Logarithmic Scale: An increase of 10 dB represents approximately a 10-fold increase in sound intensity.
• The most important thing to remember is that decibels do not add up linearly.​
• If you have two machines each producing 80 dB, the total sound is not 160 dB; the result is 83 dB.
• The Rules of Thumb:
• • +3 dB: A doubling of sound energy (Technically measurable).
  • +10 dB: A doubling of perceived loudness (What the human ear experiences).
    Example: A siren at 110 dB sounds twice as loud to the human ear as a siren at 100 dB, even though the sound pressure is ten times higher.

Measuring Sound Levels

Sound levels are measured using a sound level meter. These devices register sound pressure and display the value in dB(A). The "A-weighting" is a correction filter that mimics how the human ear perceives different frequencies, weighting frequencies to which the ear is less sensitive lower.

Some practical measurement conditions for our sector include:Some practical measurement conditions for our sector include:

• Measurements at the rear of a vehicle or machine: To guarantee that a reversing alarm is sufficiently audible.
• Distances and ambient noise: Measurements are often taken at a specific distance from the vehicle, factoring in ambient noise, to assess whether the alarm stands out clearly without causing unnecessary nuisance.

The Inverse Square Law

For Sirens and Speakers, distance is crucial. A manufacturer often specifies a siren at 1 meter or 7 meters distance. How does that translate?

Every time you double the distance from the sound source, the sound pressure decreases by 6 dB.

• Source at 1 meter: 112 dB(A)
• At 2 meters: 106 dB(A)
• At 4 meters: 100 dB(A)
• At 8 meters: 94 dB(A)

This explains why a siren must be painfully loud up close to be an effective warning at 100 meters.

Application of dB in Reversing Alarms

1. Safety Standards and Regulations
   Specific guidelines for sound levels of safety alarm systems, such as reversing alarms, often apply in the industrial and transport sectors. These regulations ensure the alarm is loud enough to warn, but not so loud that it damages hearing or disturbs the environment. A typical target range may lie between 87 and 112 dB(A), depending on the location, vehicle type, and application environment.
2. Adaptive Sound Levels
   Modern reversing alarms can adapt to ambient noise. In busier, louder environments, the alarm level will increase, while in quieter areas, the level is reduced to prevent unnecessary noise pollution. This ensures an optimal balance between regulatory compliance and minimizing noise nuisance.
3. Frequency and Tonality
   It is not just the volume (dB) that matters, but also the frequency and tonality. Reversing alarms are often designed to operate within a frequency range that is easily perceptible to most people, even in noisy conditions. A clear and recognizable signal is essential for rapid hazard detection.

Benefits of the Correct Decibel Level for Reversing Alarms

• Improved Safety: Sufficiently audible signals prevent collisions, especially in busy logistics and industrial environments.
• Optimal Communication: A well-balanced alarm stands out without being perceived as 'noise pollution'.
• Regulatory Compliance: Correctly adjusting sound levels helps meet national and international regulations.

Conclusion

The decibel level plays a crucial role in the effectiveness and acceptance of reversing alarms in our sector. A well-understood and correctly applied sound level ensures an optimal balance between audibility and comfort, directly contributing to a safe and efficient working environment. By carefully selecting, measuring, and tuning dB values, we can ensure that reversing alarms fulfill their task optimally: safeguarding everyone in the vicinity of moving vehicles.

Do you have questions about decibel values or reversing alarms? Contact our team for professional advice!