Summary of How to think in dB
The article explains the origin and fundamental concept of the decibel (dB) unit, established by The Bell System in 1928 as a measure of sound power levels. It clarifies that the dB scale is based on the logarithmic ratio of power levels, initially for sound but now generalized to all power types. The article illustrates the immense range of sound power from the threshold of hearing to extreme levels like rocket launches, highlighting the necessity of sound suppression systems such as the water system used at the Saturn V launch pad to protect equipment.
Parts used in the Sound Suppression System at Saturn V Launch Pad:
- 900,000 gallon per minute water sound suppression system
The dB (decibel) is one of the most common units in engineering, yet also one of the most confusing, especially when it comes to manipulating S-parameters. Here is how not to be confused.
The Bel is a fundamentally new unit, which was originally established in 1928 by The Bell System to describe sound levels. This scale has since been generalized to relate to the log of the ratio of any two power levels.
The most important principle of the Bel scale to keep in mind is that it is, without exception, by definition, the ratio of powers. It originally related to sound level powers, but has since been generalized to all types of powers.
Sound level power has a huge range. It starts at the threshold of hearing (TOH) with a sound level of about 10-12 W/m². The onset of pain is about 10W/m², and the power level to rupture an eardrum is 1000W/m².
The loudest recorded man-made sound is from rocket launches. The Saturn V produced 100W/m² of sound level power about 1 mile from the launch pad. It only got larger closer to the launch pad.
This amount of sound power reflecting off the launch pad could have easily damaged the Space Shuttle. This is why a 900,000 gallon per minute of water sound suppression system was installed on the launch pad (Figure 1). Even with this system, the sound level power at the position of the Orbiter was about 100W/m².
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