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| To get a feeling for decibels, look at the table below which gives values for the sound pressure levels of common sounds in our environment. Also shown are the corresponding sound pressures and sound intensities. From these you can see that the decibel scale gives numbers in a much more manageable range. Sound pressure levels are measured without weighting filters. The values are averaged and can differ ±10 dB. With sound pressure is always meant the effective value (RMS) of the sound pressure, without extra announcement. The amplitude of the sound pressure means the peak value. The ear is a sound pressure receiver, or a sound pressure sensor, i.e. the ear-drums are moved by the sound pressure, a sound field quantity. When listening, forget the sound intensity as energy quantity. The perceived sound consists of periodic pressure fluctuations around a stationary mean (equal atmospheric pressure). This is the change of sound pressure, which is measured in pascal (Pa) ≡ 1 N/m2 ≡ 1 J / m3 ≡ 1 kg / (m·s2), usually as RMS value. |
| Table of sound levels L and corresponding sound pressure and sound intensity |
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| Examples | Sound Pressure Level Lp dBSPL |
Sound Pressure p N/m2 = Pa |
Sound Intensity I W/m2 |
| Jet aircraft, 50 m away | 140 | 200 | 100 |
| Threshold of pain | 130 | 63.2 | 10 |
| Threshold of discomfort | 120 | 20 | 1 |
| Chainsaw, 1 m distance | 110 | 6.3 | 0.1 |
| Disco, 1 m from speaker | 100 | 2 | 0.01 |
| Diesel truck, 10 m away | 90 | 0.63 | 0.001 |
| Kerbside of busy road, 5 m | 80 | 0.2 | 0.0001 |
| Vacuum cleaner, distance 1 m | 70 | 0.063 | 0.00001 |
| Conversational speech, 1 m | 60 | 0.02 | 0.000001 |
| Average home | 50 | 0.0063 | 0.0000001 |
| Quiet library | 40 | 0.002 | 0.00000001 |
| Quiet bedroom at night | 30 | 0.00063 | 0.000000001 |
Background in TV studio |
20 | 0.0002 | 0.0000000001 |
| Rustling leaf | 10 | 0.000063 | 0.00000000001 |
| Threshold of hearing | 0 | 0.00002 | 0.000000000001 |
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The level is highly dependent on the distance of the sound source to the measuring point.
A given sound pressure level Lp in dBSPL without the measurement of the distance to the specific sound source is useless. The reference sound for 0 dBSPLpressure is p0 = 20 µPa = 2 × 10−5 Pa, the threshold of hearing. (The reference sound intensity is I0 = 10−12 W/m2.) These values are not given as dBA, but as dBSPL, that means without any weighting filter.  |
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Differentiate between sound pressure p as a "sound field quantity" and sound intensity I as a "sound energy quantity". I ≈ p2 for progressive plane waves. When it comes to our ears and the hearing, it is recommended that the inappropriate expression of the sound energy parameters, such as sound power and sound intensity to leave aside. So we are just listening to the sound pressure as sound field quantity, or the sound pressure level SPL. The sound pressure level decreases in the free field with 6 dB per distance doubling. That is the 1/r law. Often it is argued the sound pressure would decrease after the 1/r2 law (inverse square law). That's wrong. The sound pressure in a free field is inversely proportional to the distance from the microphone to the source. p ~ 1/r. |
Relation of sound intensity, sound pressure and distance law:
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Note: The often used term "intensity of sound pressure" is not correct. Use "magnitude", "strength", "amplitude", or "level" instead. "Sound intensity" is sound power per unit area, while "pressure" is a measure of force per unit area. Intensity (sound energy quantity) is not equivalent to pressure (sound field quantity). |
dB scale for field quantities, like volts and sound pressures
ratio
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The sound pressure is the force F in newtons N of a sound on a surface area A in m2 perpendicular to the direction of the sound. The SI-unit for the sound pressure p is N/m2 = Pa. p ~ 1/r. |
| Note - Comparing dB and dBA: There is no conversion formula for measured dBA values to sound pressure level dBSPL or vice versa. |
How loud is dangerous?
| 190 dBA | Heavy weapons, 10 m behind the weapon (maximum level) |
| 180 dBA | Toy pistol fired close to ear (maximum level) |
| 170 dBA | Slap on the ear, fire cracker explodes on shoulder, small arms |
| 160 dBA | Hammer stroke on brass tubing or steel plate at 1 m distance, airbag deployment very close at a distance of 30 cm (maximum level) |
| 150 dBA | Hammer stroke in a smithy at 5 m distance (maximum level) |
| 130 dBA | Loud hand clapping at 1 m distance (maximum level) |
| 120 dBA | Whistle at 1 m distance, test run of a jet at 15 m distance |
| Threshold of pain, above this fast-acting hearing damage in short action is possible | |
| 115 dBA | Take-off sound of planes at 10 m distance |
| 110 dBA | Siren at 10 m distance, frequent sound level in discotheques and close to loudspeakers at rock concerts, violin close to the ear of an orchestra musicians (maximum level) |
| 105 dBA | Chain saw at 1 m distance, banging car door at 1 m distance (maximum level), racing car at 40 m distance, possible level with music head phones |
| 100 dBA | Frequent level with music via head phones, jack hammer at 10 m distance |
| 95 dBA | Loud crying, hand circular saw at 1 m distance |
| 90 dBA | Angle grinder outside at 1 m distance |
| Over a duration of 40 hours a week hearing damage is possible | |
| 85 dBA | 2-stroke chain-saw at 10 m distance, loud WC flush at 1 m distance |
| 80 dBA | Very loud traffic noise of passing lorries at 7.5 m distance, high traffic on an expressway at 25 m distance |
| 75 dBA | Passing car at 7.5 m distance, un-silenced wood shredder at 10 m distance |
| 70 dBA | Level close to a main road by day, quiet hair dryer at 1 m distance to ear |
| 65 dBA | Bad risk of heart circulation disease at constant impact is possible |
| 60 dBA | Noisy lawn mower at 10 m distance |
| 55 dBA | Low volume of radio or TV at 1 m distance, noisy vacuum cleaner at 10 m distance |
| 50 dBA | Refrigerator at 1 m distance, bird twitter outside at 15 m distance |
| 45 dBA | Noise of normal living; talking, or radio in the background |
| 40 dBA | Distraction when learning or concentration is possible |
| 35 dBA | Very quiet room fan at low speed at 1 m distance |
| 25 dBA | Sound of breathing at 1 m distance |
| 0 dBA | Auditory threshold |
Threshold of pain
What is the threshold of pain?
You can find the following rounded values in various articles:
| Sound pressure level Lp | Sound pressurep |
| 140 dB | 200 Pa |
| 137.5 dB | 150 Pa |
| 134 dB | 100 Pa |
| 120 dB | 20 Pa |
Notice: Psychoacousticians say that a level increase of 10 dB |
| Half loudness - level: –10 dB | Double loudness - level: +10 dB |
| Half sound pressure - level: –6 dB | Double sound pressure - level: +6 dB |
| Half power - level: –3 dB | Double power: - level +3 dB |
| fourfold power - level: +6 dB | Tenfould power - level: +10 dB |
| Double distance: –6 dB | Double sources (Double power) +3 dB |
Sound Level Comparison Table and the Factors
Table of sound level dependence and the change of the respective factor to subjective
volume (loudness), objective sound pressure (voltage), and sound intensity (acoustic power)
How many decibels (dB) change is double, half, or four times as loud?
How many dB to appear twice as loud (twofold)? Here are all the different factors.
Factor means "how many times" or "how much" ... Doubling of loudness.
| Level Change |
Volume Loudness |
Voltage Sound pressure |
Acoustic Power Sound Intensity |
| +40 dB | 16 | 100 | 10000 |
| +30 dB | 8 | 31.6 | 1000 |
| +20 dB | 4 | 10 | 100 |
| +10 dB | 2.0 = double | 3.16 = √10 | 10 |
| +6 dB | 1.52 fold | 2.0 = double | 4.0 |
| +3 dB | 1.23 fold | 1.414 fold = √2 | 2.0 = double |
| - - - - ±0 dB - - - - | - - - - 1.0 fold - - - - | - - - - 1.0 fold - - - - | - - - - 1.0 fold - - - - |
| −3 dB | 0.816 fold | 0.707 fold | 0.5 = half |
| −6 dB | 0.660 fold | 0.5 = half | 0.25 |
| −10 dB | 0.5 = half | 0.316 | 0.01 |
| −20 dB | 0.25 | 0.100 | 0.01 |
| −30 dB | 0.125 | 0.0316 | 0.001 |
| −40 dB | 0.0625 | 0.0100 | 0.0001 |
| dB Change | Loudness multipl. | Voltage multiplier | Power multiplier |
The psycho-acoustic volume or loudness is a subjective sensation size.
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Is 10 dB or 6 dB sound level change for a doubling or halving of the loudness (volume) correct? About the connection between sound level and loudness, there are various theories. Far spread is still the theory of psycho-acoustic pioneer Stanley Smith Stevens, indicating that the doubling or halving the sensation of loudness corresponds to a level difference of 10 dB. Recent research by Richard M. Warren, on the other hand leads to a level difference of only 6 dB. *) This means that a double sound pressure corresponds to a double loudness. The psychologist John G. Neuhoff found out that for the rising level our hearing is more sensitive than for the declining level. For the same sound level difference the change of loudness from quiet to loud is stronger than from loud to quiet. It is suggested that the sone scale of loudness reflects the influence of known experimental biases and hence does not represent a fundamental relation between stimulus and sensation. *) Richard M. Warren, "Elimination of Biases in Loudness Judgments for Tones" |
Realm of Psychoacoustic - Relationship between phon and sone
Conversion of sound units (levels)
Calculations of Sound Values and their Levels
Conversion of voltage V to dBm, dBu, and dBV
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