RIGID113 Posted July 27, 2009 Share Posted July 27, 2009 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 about ±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 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 The sound level depends highly on the distance between the sound source and the place of measurement. The only given sound pressure level Lp in dB without the given distance r to the sound source is really useless. Unfortunately, that error happens quite often. The reference sound pressure level for 0 dBSPL is the sound pressure p0 = 20 µPa = 2 × 10-5 Pa. That is 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. 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: From this follows 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 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 at a distance of 50 cm (maximum level) 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 gives the impression of a doubling of loudness (volume). Your loudspeakers need 10 times more power. If you have 6 violins as source, then you have to tenfold the violins; so you need 60 violins to double the psycho-acoustic volume. 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 Chart 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 = v10 10 +6 dB 1.52 fold 2.0 = double 4.0 +3 dB 1.23 fold 1.414 fold = v2 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 Log. quantity Psycho quantity Field quantity Energy quantity dB change Loudness multipl. Voltage multiplier Power multiplier The psycho-acoustic volume or loudness is a subjective sensation size. 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. Quote Link to comment Share on other sites More sharing options...
wuzzzer Posted July 27, 2009 Share Posted July 27, 2009 Quote Link to comment Share on other sites More sharing options...
BerserkNitro Posted July 27, 2009 Share Posted July 27, 2009 .....LMAO!!!! thats what i was thinking Quote Link to comment Share on other sites More sharing options...
fini Posted July 27, 2009 Share Posted July 27, 2009 Hmm, I'll bet this is what he needs (if he's using Safari): Quote Link to comment Share on other sites More sharing options...
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