90 dB + 90 dB is not 180 dB. Decibels are not on linear scale, they are on a logarithmic scale, which better approximates how humans perceive loudness. You can get around the math by adding 3 decibels for every doubling of values, so 90 dB + 90 dB = 93 dB.
For example:
The sound pressure level of one person in conversational speech is 60dB.
The maximum sound pressure level achieved in an underground railway is 100dB.
If you have two people speaking, 60dB+60dB=63dB. So the achieved SpL is 63dB. It is not 120dB, which is significantly louder than an underground railway, in fact, it is about the SpL of a rock concert.
The maximum theoretical value of sound is 194dB (which probably cant be achieved since it requires a sound-wave to oscillate into negative pressures (in Pascals))
A: Most op amp feature a 90 Db noise ratio rejection. For a 741c it varies from 70 to 90 Db ideally the bigger the number the better.
The decibel scale is a logarithmic scale where each change in three dB represents a power factor change of two. (3 dB is power times two, 6 dB is power times four, 9 dB is power times 8, etc. Similarly, -3dB is power divided by two, -6 dB is power divided by four, etc.) Zero dB is assigned some arbitrary reference power. One example is 1 mV across 600 ohms. If you double the voltage into a constant resistance, the power quadruples, so 2 mV would be +6 dB, 4 mV would be +12 dB, etc. The letter after dB is the reference power. In the case of dBm, it means that 0 dB is 1 milliwatt, so 2 milliwatt is +3 dB, etc. There are many dB scales, such as dBa, used in sound measurements. Still, fundamentally, 3 dB is a doubling of power, -3 dB is a halving of power, so, for any arbitrary scale, say dBq, then saying +6dBq is saying a power four times higher than 0 dBq. In the end, dBm plus dBm is delta dB, with no scale.
If a + b + c + d + 80 + 90 = 100, then a + b + c + d = -70.
Decibels (db) is relative power, log base 2, times 3. Increasing power from 200 watts to 400 watts is doubling power, so the decibel change is +3 db.800 watts would be +6 db, 1600 watts would be +9 db, 100 watts would be -3 db, 50 watts would be -6 db, and so on.
60 dB sound pressure level is about conversational speech listened in 1 meter distance.
90 > 70
A sound at 90 dB measured at a distance of 100 meters will decrease by 60 dB due to the inverse square law. Therefore, at a distance of 100 meters, the sound will be around 30 dB.
60 dB: normal conversation 90 dB: lawnmower 120 dB: rock concert 150 dB: fireworks display
A 90 dB sound is 1,000 times more intense than a 60 dB sound. This is because the decibel scale is logarithmic, with every 10 dB increase representing a tenfold increase in intensity.
90 dB is considered very loud and can cause hearing damage with prolonged exposure. It is equivalent to the sound of a motorcycle or a lawnmower from a close distance. It is recommended to use ear protection in environments where the noise level reaches 90 dB or higher.
The loudness level at 90 dB for a 4000 Hz tone is 7 sones. Sones are a unit of perceived loudness.
385
480
Effectively, OSHA has two noise limits that apply simultaneously. First, employees may not be exposed to a full-shift (8-hour) time-weighted average noise level of 90 dB (deciBells) or more. This translates to a limit of: 90 dB averaged over an 8 hour day, or 95 dB for 4-hours as long as the rest of the day does not involve exposure to noise greater than 90 dB, or 100 dB for 2 hours, 105 dB for 1-hour, 110 dB for 30 minutes, 115 dB for 15 minutes, and no continuous noise louder than 115 dB In addition, employees who have 8-hour exposures of 85 dB or more must be placed in a Hearing Conservation Program and, in some cases must be provided with hearing protection. The table is a bit different because sounds from 80 dB and above are used in the assessment. This translates to a criterion level of: 85 dB averaged over an 8-hour day, or 90 dB for 4-hours for 4-hours as long as the rest of the day does not involve exposure to noise greater than 80 dB, or 95 dB for 2 hours, 100 dB for 1 hour, 105 dB for 30 minutes, 110 dB for 15 minutes
90
Sounds from 90 db and up can eventually damage hearing. but 95db is equivalent to a subway train from 200 feet.
The difference in sound intensity between the orchestra and the soloist is 20 dB. Since the decibel scale is logarithmic, a 10 dB increase represents a doubling of sound intensity. Therefore, the orchestra is 100 times louder than the soloist.