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Decibel - Wikipedia, the free encyclopedia

A ratio in decibels is ten times the logarithm to base 10 of the ratio of two power .... To calculate the ratio of 1 mW (one milliwatt) to 10 W in decibels, ...

Sound level meter

Sound level meters measure sound pressure level and are commonly used in noise pollution studies for the quantification of almost any noise, but especially for industrial, environmental and aircraft noise. However, the reading given by a sound level meter does not correlate well to human-perceived loudness; for this a loudness meter is needed. The current International standard for sound level meter performance is IEC 61672:2003 and this mandates the inclusion of an A-frequency-weighting filter and also describes other frequency weightings of C and Z (zero) frequency weightings. The older B and D frequency-weightings are now obsolete and are no longer described in the standard.

A-frequency-weighting

In almost all countries, the use of A-frequency-weighting is mandated to be used for the protection of workers against noise-induced deafness. The A-frequency curve was based on the historical equal-loudness contours and while arguably A-frequency-weighting is no longer the ideal frequency weighting on purely scientific grounds, it is nonetheless the legally required standard for almost all such measurements and has the huge practical advantage that old data can be compared with new measurements. It is for these reasons that A-frequency-weighting is the only weighting mandated by the international standard, the frequency weightings 'C' and 'Z' being optional fitments.

Originally, the A-frequency-weighting was only meant for quiet sounds in the region of 40 dB sound pressure level (SPL), but is now mandated for all levels. C-frequency-weighting however is still used in the measurement of the peak value of a noise in some legislation, but B-frequency-weighting - a half way house between 'A' and 'C' has almost no practical use. D-frequency-weighting was designed for use in measuring aircraft noise, when non-bypass jets were being measured and after the demise of Concord, these are all military types. For all civil aircraft noise measurements A-frequency-weighting is used as is mandated by the ISO and ICAO standards.

Exponentially averaging sound level meter

The standard sound level meter is more correctly called an exponentially averaging sound level meter as the AC signal from the microphone is converted to DC by a root-mean-square (RMS) circuit and thus it must have a time-constant of integration; today referred to as time-weighting. Three of these time-weightings have been standardised, 'S' (1 s) originally called Slow, 'F' (125 ms) originally called Fast and 'I' (35 ms) originally called Impulse. Their names were changed in the 1980s to be the same in any language. I-time-weighting is no longer in the body of the standard because it has little real correlation with the impulsive character of noise events.

The output of the RMS circuit is linear in voltage and is passed through a logarithmic circuit to give a readout linear in decibels (dB). This is 20 times the base 10 logarithm of the ratio of a given root-mean-square sound pressure to the reference sound pressure. Root-mean-square sound pressure being obtained with a standard frequency weighting and standard time weighting. The reference pressure is set by International agreement to be 20 micropascals for airborne sound. It follows that the decibel is in a sense not a unit, it is simply a dimensionless ratio—in this case the ratio of two pressures.

An exponentially integrating sound level meter, giving as it does a snapshot of the current noise level, is of limited use for hearing damage risk measurements and an integrating or integrating-averaging meter is usually mandated. An integrating meter simply integrates—or in other words 'sums'—the frequency-weighted noise to give sound exposure and the metric used is pressure squared times time, often Pa²·s, but Pa²·h is also used. However, because sound was historically described in decibels, the exposure is most often described in terms of sound exposure level (SEL), the logarithmic conversion of sound exposure into decibels.

Note: in acoustics all 'levels' are in decibels.

''LAT'' or ''L''eq: Equivalent continuous sound level

Sound exposure level—in decibels—is not much used in industrial noise measurement. Instead, the time-averaged value is used. This is the time average sound level or as it is usually called the 'equivalent continuous sound level' has the formal symbol LATas described in paragraph 3,9 "Definitions" of IEC 61672-1 where many correct formal symbols and their common abbreviations are given. These mainly, follow the formal ISO acoustic definitions. However, for mainly historical reasons, LATis commonly referred to as Leq.

Formally, LATis 20 times the base 10 logarithm of the ratio of a root-mean-square A-weighted sound pressure during a stated time interval to the reference sound pressure and there is no time constant involved. To measure LATan integrating-averaging meter is needed; this in concept takes the sound exposure, divides it by time and then takes the logarithm of the result.

Short ''L''eq

An important variant of overall LATis "short Leq" where very short Leq values are taken in succession, say at 1/8 second intervals, each being stored in a digital memory. These data elements can either be transmitted to another unit or be recovered from the memory and re-constituted into almost any conventional metric long after the data has been acquired. This can be done using either dedicated programs or standard spreadsheets. Short Leq has the advantage that as regulations change, old data can be re-processed to check if a new regulation is met. It also permits data to be converted from one metric to another in some cases. Today almost all fixed airport noise monitoring systems, which are in concept just complex sound level meters, use short Leq as their metric, as a steady stream of the digital one second Leq values can be transmitted via telephone lines or the Internet to a central display and processing unit. Short Leq is a feature of most commercial integrating sound level meters—although some manufacturers give it many different names.

Short Leq is a very valuable method for acoustic data storage; initially, a concept of the French Government's Laboratoire National d'Essais (ref 1), it has now become the most common method of storing and displaying a true time history of the noise in professional commercial sound level meters. The alternative method which is to generate a time history by storing and displaying samples of exponential sound level has too many artifacts of the sound level meter to be as valuable and such sampled data cannot be readily combined to form an overall set of data.

Until 2003 there were separate standards for exponential and linear integrating sound level meters, (IEC 60651 and IEC 60804—both now withdrawn), but since then the combined standard IEC 61672 has described both types of meter. For short Leq to be

Free time (music)

Free time is a type of musical meter free from musical time and time signature. It is used when a piece of music has no discernible beat. Instead, the rhythm is intuitive and free-flowing. There are five ways in which a piece is indicated to be in free time:

  1. There is simply no time signature displayed. This is common in old vocal music such as Gaelicpsalms.
  2. There is no time signature but the direction 'Free time' is written above the stave.
  3. There is a time signature (usually 4/4) and the direction 'Free time' written above.
  4. The word FREE is written downwards across the stave. This is mostly used when the piece changes to free time after having had a time signature.
  5. Instead of a time signature, a large X is written on the stave.

Examples of musical genres based around free time include free improvisation, free jazz and noise music. Examples of music written in free time include Erik Satie'sGnossienne No. 1,Charles Ives'Concord Sonata, andKaikhosru Sorabji'sOpus Clavicembalisticum. Examples of contemporary songs in free time include "Hunting Bears" by Radiohead and "Lover, You Should've Come Over" by Jeff Buckley.

The usage of free time is almost absent in popular music. The Allman Brothers Band was known for occasionally dropping into free time segments on their lengthy live jams. The most famous example can be found on "Whipping Post" on the live album At Fillmore East. The band drops into a lengthy free time at the 10 minute mark, before coming back into 12/8 time about 5 and half minutes later. They drop into free time again at the 17:15 mark and continue to the end of the song at about 23:00.

Another famous example is in the nearly 10 minute psychedelic Pink Floyd composition "Interstellar Overdrive", The opening hook of the piece is a distorted, descending guitar riff played in unison by the band. This riff eventually turns into improvisation, including modal improvisations, percussive flourishes on the Farfisa organ, and quiet interludes. The song gradually becomes almost structureless and in free-form tempo, punctuated only by strange guitar noises. Eventually, however, the entire band restates the main theme, which is repeated with decreasing tempo and more deliberate intensity. The novel use of stereo (in the second mix of the album, the original being monophonic) makes the sound oscillate between speakers towards the composition's conclusion. Live version of the song often exceeded 20 minutes.


Electricity meter - Wikipedia, the free encyclopedia

Three-phase electromechanical induction meter, metering 100 A 230/400 V supply. ..... Electricity Meter - Interactive Java Tutorial National High Magnetic ...


From Digg

PicoBrothers Decibel Meter v1.00 S60v5/S^3

[SYMBIAN] PicoBrothers Decibel Meter v1.00 S60v5/S^3 SymbianOS9.x SignedSymbian S60 v5 [i8910HD/5800/N97/Mini/X6] AppsSymbian^3Here is an decibel meter for S60 5th and Symbian^3 devices. It uses to phones microphone to measure the sound level i dB and is quite accurate.Enjoy!Note:Must have installed NOKIA QT v4.7.1 to run this application.Download to PC ClickshereAlternatehere


From Yahoo Answers

Question:How can I measure volume of headphone in db?? on the specifications of headphone following mentioned sensitivity-105 db/mw impedance-32 ohz power export - 1000 mw frequency-20hz-20000 hz Does it say anything about db? I am asking this because I am using headphone for voice chat and voip...and I want to make sure I am not damaging my ears

Answers:It looks to me that these headphones are capable of producing 105db. You could get an SPL meter (Radio Shack used to sell them.) and place the microphone directly onto the headphone and measure the SPL. Yes, with some headphones, you could damage your ears. SPL for speakers is measured in db at a certain distance from the speaker, typically at one meter. The closer to the speaker, the louder it is. Headphones are placed very closely to your ears. But 105db doesn't sound that loud to me. As a sound man for rock bands, I normally ran the system at 117db for most of the room. I think most hearing damage comes with impulse sounds that far exceed the levels we are accustomed. Jack Hammers and other such loud noises produce such sounds. Loud music is compressed, and as such, represents a sustained pressure level. Unless you listen to it at extreme levels, for long periods of time, it's generally not going to harm you.

Question:I can't seem to find one. I want to hear what 20, 30, and 40 decibels sound like. I have found charts that tell you a whisper is such and such and a vacuum cleaner is such and such, but I want to HEAR it. Thanks for any sites!!

Answers:Here is one: The exact decibel will depend of course on your starting level of your speakers or earphones, and so isn't given. The chart shows how much louder, by decibel, each tone is relative to the others. http://www.phys.unsw.edu.au/jw/hearing.html

Question:The loudness L of a sound measured in decibels (dB) is given by the formula: L = 10 log , where I represents the intensity of the sound measured in watts per square meter (), and I0 = 10-12 . A certain noise has an intensity of 6.2 10-4 . What is the decibel level (dB) of this noise?

Answers:see the Pearson's chi square test

Question:I am wondering how a sound level meter works. I am no scientist so I do not fully understand the technical details. My Logitech Z2300 speakers claim to have a response bandwith of 35 - 20,000 hertz while the sound level meter has a frequency range of 31.5 - 8KHz. Does this mean that the sound level meter will not be able to measure accurately? Also how does room temparature affect such things and does it matter if the time weighing is FAST or SLOW? Thanks a lot. Thanks a lot. Could you also answer this question for me. It is reccomended that you only listen to 90 decibels for 2 hours. Does this mean that if I was to listen to 90 decibels for two hours, would I be able to listen to 87 decibels for a further four hours? Or would the two hours of 90 decibels be the required listening hours when playing music to ensure the safety of my ears? recommended*

Answers:sound level meter has a frequency range of 31.5 - 8KHz. Does this mean that the sound level meter will not be able to measure accurately? Not at all, there are 8 octave bands that are generally used in noise control. 63,125, 250, 500, 1000, 2000, 4000, 8000 Hz octave bands, below 125 & above 6 K are considered inaccurate, but however 63 & 8000 are kept in the equation. Also how does room temparature affect such things? ( It doesn't!!) does it matter if the time weighing is FAST or SLOW? depends on what model you are using and for for what purpose, read the instruction manual?

From Youtube

WRX exhaust decibel meter :This is to show how loud the TXS exhaust is in decibels for the people that are interested in how loud it is. Sounds ALOT louder in person. Just audible 10 dB Whisper Quiet Library 30dB Normal conversation (3-5') 60-70dB Vacuum cleaner 70dB Food blender 85dB Train whistle at 500', Truck Traffic 90dB Subway train at 200' 95dB Level at which sustained exposure may result in hearing loss 90 - 95dB Snowmobile, Motorcycle 100dB Power saw at 3' 110dB Gets up to 112+ at WOT from outside

2400 Watt Power Acoustik Amp w/ Kenwood Head Unit and Ebay Decibel Meter. :CAMERA BATTERY DIED!! I got most of the video but when I was gonna let ya hear the system my camera died RIGHT BEFORE. Very sorry that u don't get to hear any bass but it was dark anyway so you wouldn't have been able to see my subs at all like you see (well don't see) in the video. You do get to see a decent amp (well so far) thats pretty cheap and a decent cheap little decibel meter. Thanks so much for watching and check out my later videos to hear the subs and amp and see my decibel meter work. ALSO NOT SURE THE AMP IS REALLY 2400 WATTS thats just what the guy said when I bought it. Of course on these subs I have it hooked to now I have the amp turned down. THE SYSTEM (1) Power Acoustik Sapphire MRP 2400 - Class D Monoblock Amplifier (2) 12 inch Kenwood Tsunami Subs - 400 Watts @ 4 ohms (1) Old School Kenwood Head Unit (2) Infinity Kappa Mids (rear deck) 330W peak power (110W RMS) Cheap 8 gauge power and ground wire (Stupid for this amp) Had a Kenwood KAC 744 watt 4 channel amp running the mids nicely but blew it by hooking things up without a fuse block and not disconnecting the battery. DON'T HOOK THINGS UP WITHOUT A FUSE BLOCK. Also have the Infinity Kappas for the front door but to cold to put in right now and I gotta get my mid amp fixed.THANKS FOR WATCHING!!!!!!