dB

1. BEL=10 dB

2. dBu is referenced to 0.775 volts RMS

3. dB SPL (sound pressure level) – for sound in air and other gases, relative to 20 micropascals (μPa) = 2×10−5 Pa, approximately the quietest sound a human can hear

4. ECHO vs reverberation         reverberation is perceived when the reflected sound wave reaches your ear in less than 0.1 second                   if reflected sound wave reaches your ear in more than 0.1 second this is called ECHO

5. Sensitivity of Human Ear

6. Frequency: 20 Hz - 20,000 Hz (corresponds with pitch) Intensity: 10-12 - 10 watts/m2 (0 to 130 decibels) Pressure: 2 x 10-5 - 60 Newtons/m2 2 x 10-10 - .0006 atmospheres

7. A system consists of 3 amplifiers in series, with gains (ratio of power out to in) of 10 dB, 8 dB, and 7 dB respectively, for a total gain of 25 dB. Broken into combinations of 10, 3, and 1 dB, this is: 25 dB = 10 dB + 10 dB + 3 dB + 1 dB + 1 dB With an input of 1 watt, the output is approximately 1 W x 10 x 10 x 2 x 1.26 x 1.26 = ~317.5 W

8. dBw

8.1. The decibel watt or dBW is a unit for the measurement of the strength of a signal expressed in decibels relative to one watt.

9. dB mw

9.1. Compare dBW to dBm, which is referenced to one milliwatt (0.001 W).

10. dBa  A typical question: "What does the "a" behind the dB mean?" Since human hearing feels different frequencies as different loud, the sound signals are filtered by a sound pressure level meter so that the properties of human hearing are mimicked. We then speak of a so-called A weighting of the sound level, short dB (A). The decibel scale is logarithmic. Zero dBA corresponds to the threshold of hearing (auditory threshold). 130 dBA is about the threshold of pain.