Was just reading the thread about headphones deafening people etc and it got me thinking about db levels.
Mikeee mentioned that some of the ipods are pushing out 125db, what does this actually mean?...apart from the fact that it's bleedin loud!
How is a decibel rated?
Full Version: Can someone explain this whole db business?
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Until someone more knowledgable comes in and saves me from making an idiot of myself.....
A decibel is a measure of relative sound levels - it is not an absolute measure as, say, a mile would be. It depends on your distance from the sound source. It is best used to express ratios, although to say your weekly wages are 3dB up on mine would be incorrect useage of the term.
1 decibel is one tenth of a Bel. (there's a surprise!)
A difference in sound level of 1 decibel is generally regarded to be the smallest change in volume readily detectable by the human ear. Not a lot, then.
To increase the volume of sound detected by either an ear or a microphone by 3 decibels you need to double the power supplied to the speaker. This is why there is little actual difference between 200 watts and 300.
You could also increase the sound pressure level (decibels) by moving closer to the source - halve the distance and the level goes up by 4 times - 6 decibels. (I think)
So it might now be apparent that when someone says a jet airoplane makes 130 decibels when taking off, it is complete rubbish, as they have to say the distance from the aircraft at which that level was obtained. 4 miles distant it wouldn't sound too bad.
The decibel is a logarithmic measurement, meaning that for each numerical increase of ten, the power level is upped by ten times. Therefore, relating to speakers and wattage, 90 decibels may be produced by a given speaker at 1 metre with 1 watt input, so in theory 100 decibels would be produced with 10 watts. 110 decibels would be produced with 100 watts and 120 decibels would be produced with 1,000 watts input. PA speakers may be far more efficient than this though.
The reason why headphones can produce so many decibels is simply because they are so close to your ear.
A decibel is a measure of relative sound levels - it is not an absolute measure as, say, a mile would be. It depends on your distance from the sound source. It is best used to express ratios, although to say your weekly wages are 3dB up on mine would be incorrect useage of the term.
1 decibel is one tenth of a Bel. (there's a surprise!)
A difference in sound level of 1 decibel is generally regarded to be the smallest change in volume readily detectable by the human ear. Not a lot, then.
To increase the volume of sound detected by either an ear or a microphone by 3 decibels you need to double the power supplied to the speaker. This is why there is little actual difference between 200 watts and 300.
You could also increase the sound pressure level (decibels) by moving closer to the source - halve the distance and the level goes up by 4 times - 6 decibels. (I think)
So it might now be apparent that when someone says a jet airoplane makes 130 decibels when taking off, it is complete rubbish, as they have to say the distance from the aircraft at which that level was obtained. 4 miles distant it wouldn't sound too bad.
The decibel is a logarithmic measurement, meaning that for each numerical increase of ten, the power level is upped by ten times. Therefore, relating to speakers and wattage, 90 decibels may be produced by a given speaker at 1 metre with 1 watt input, so in theory 100 decibels would be produced with 10 watts. 110 decibels would be produced with 100 watts and 120 decibels would be produced with 1,000 watts input. PA speakers may be far more efficient than this though.
The reason why headphones can produce so many decibels is simply because they are so close to your ear.
So if a disco is set up in a hall that is 200ftx200ft and the gear is at one end of the hall, if there's say 100db being pushed out of the speakers, it would only be around 60db or 70db at the other end of the hall?
Also, is there an accepted db level/range of the human voice for talking & shouting?
For example I've played at venue's with sound limiters that were set at 90db, my actual volume levels were set so that the peaks were far below 90db and the lights were safely in the green area, but the crowd noise, clapping, cheering etc caused the limiter to cut power a few times, even though when seeing the levels go up into the red from the crowd noise I'd dropped the volume quite a bit, so it seemed that just the crowd noise alone had caused the volume to exceed 90db... that's IF the limiter was set correctly!
Also, is there an accepted db level/range of the human voice for talking & shouting?
For example I've played at venue's with sound limiters that were set at 90db, my actual volume levels were set so that the peaks were far below 90db and the lights were safely in the green area, but the crowd noise, clapping, cheering etc caused the limiter to cut power a few times, even though when seeing the levels go up into the red from the crowd noise I'd dropped the volume quite a bit, so it seemed that just the crowd noise alone had caused the volume to exceed 90db... that's IF the limiter was set correctly!
"if there's say 100db being pushed out of the speakers, it would only be around 60db or 70db at the other end of the hall?" I know what you mean, and the answer is yes, although the level wouldn't drop to as low as 70dB, but it would drop considerably.
At risk of confusing things (and myself), when you refer to the number of decibels a speaker pushes out, you should always state the distance at which it was measured.
A good illustration is 'miles per hour'. You wouldn't indicate your speed my stating that you were doing '80 miles' down the Motorway - that would be an incomplete and inaccurate statement. Likewise with decibels. You must always quote the distance it was measured at.
Now, on to your hall scenario:
If your speakers were pushing out 100 dB at 1 metre, that would easily amount to far less than 90 dB at the limiter sensor. But then, 100 dB isn't all that loud - at a guess it would be about the same as loud speach half a metre from your ear.
However, when you get several people shouting and cheering, the level can be surprisingly high and if this was ocurring near the sensor, then it would easily trip. You know this yourself I expect: You are doing a disco and it might be difficult to hear normal speach near you, but if the women start to squeal on the dance floor, you can most certainly hear it above the music!
Remember also that walls and ceilings reflect sound and can reduce the normal volume reduction with distance, so this adds to the complication.
To my mind, I think 90dB is a bit unreasonable for a function room, but that's their decision, not mine!
Are you now more confused than ever??!
At risk of confusing things (and myself), when you refer to the number of decibels a speaker pushes out, you should always state the distance at which it was measured.
A good illustration is 'miles per hour'. You wouldn't indicate your speed my stating that you were doing '80 miles' down the Motorway - that would be an incomplete and inaccurate statement. Likewise with decibels. You must always quote the distance it was measured at.
Now, on to your hall scenario:
If your speakers were pushing out 100 dB at 1 metre, that would easily amount to far less than 90 dB at the limiter sensor. But then, 100 dB isn't all that loud - at a guess it would be about the same as loud speach half a metre from your ear.
However, when you get several people shouting and cheering, the level can be surprisingly high and if this was ocurring near the sensor, then it would easily trip. You know this yourself I expect: You are doing a disco and it might be difficult to hear normal speach near you, but if the women start to squeal on the dance floor, you can most certainly hear it above the music!
Remember also that walls and ceilings reflect sound and can reduce the normal volume reduction with distance, so this adds to the complication.
To my mind, I think 90dB is a bit unreasonable for a function room, but that's their decision, not mine!
Are you now more confused than ever??!
| QUOTE (Andy Westcott @ Jan 6 2006, 09:10 PM) |
| To my mind, I think 90dB is a bit unreasonable for a function room, but that's their decision, not mine! Are you now more confused than ever??! |
Agreed 90db is too low, but it would seem that it's very easy to scare/baffle some venue managers and so some venue's have limiters at ridiculously low levels, although this is sometimes simply because the limiter has been set incorrectly by an unqualified/incompetent person and the venue didn't actually intend for the level to be so low!
Nope, I'm not confused... I always have this baffled look on my face
I had a rough understanding of it anyway; just didn't know any of the technical mumbo jumbo, but no worries, I'll have forgotten the technical explanation within a few weeks
I'm quite impressed that no-one has leaped out of the bushes to tell me I got it all wrong! 
Some of it might actually be correct then. Pleased to be of assistance, sir!
Some of it might actually be correct then. Pleased to be of assistance, sir!
Some of it is incorrect
I just don't know which bits
I just don't know which bits
If, and its a big IF, the Limiter has been set correctly, it would have been set using the approporiate measure equipment at the point of complaint or concern. NOT in the venue hall. (unless staff were complaining).
BUT.......the law is changing and the levels will be set in the venue to ensure a safe working environment for staff and guests. Forward looking management will be already implimenting this.
This could mean shorter gig times at a higher level or a lower level for a longer period of time.
The above is based on fact as laid out in health & safety law for factories and noise polluted environments.
The law will eventually catch up with entertainments at venues that are out in the sticks.
Jimbo
BUT.......the law is changing and the levels will be set in the venue to ensure a safe working environment for staff and guests. Forward looking management will be already implimenting this.
This could mean shorter gig times at a higher level or a lower level for a longer period of time.
The above is based on fact as laid out in health & safety law for factories and noise polluted environments.
The law will eventually catch up with entertainments at venues that are out in the sticks.
Jimbo
That's interesting.
I wonder if that will reduce even further the permitted sound levels, because the guidelines are quite a shocker when you see how un-loud (sorry!) a sound can be, but still be a hearing risk if the duration is long enough.
The customers have a choice as to whether to be present or not when sound levels are high, but yes, it is right that employees should be protected from it, but I'd rather see hearing protection offered rather than attacking the sound at source, as the requirement for fairly high sound levels is a necessity for the business, and unique in that respect.
Interested to hear other views on this.
I wonder if that will reduce even further the permitted sound levels, because the guidelines are quite a shocker when you see how un-loud (sorry!) a sound can be, but still be a hearing risk if the duration is long enough.
The customers have a choice as to whether to be present or not when sound levels are high, but yes, it is right that employees should be protected from it, but I'd rather see hearing protection offered rather than attacking the sound at source, as the requirement for fairly high sound levels is a necessity for the business, and unique in that respect.
Interested to hear other views on this.
Very very interesting read.
I think (I hope I'm heading in the right direction) that when the installed premises limiter mic is set, generally, the 'mic' is positioned in the room (usually overhead) but away from the entertainment area (not directly over the disco).
I can only guess that when the 'crowd' are excited or cheer in close proximity to the said mic, with additional 'background noise', it is likely to 'trip' even when the DJ is monitoring the speaker volume??!!
I don't dislike sound limiters that much..... but I hate it when a client has not been told about it when they book a venue, or when the client says that they don't believe one is installed in a venue.....only to 'find' one on the night!
I think (I hope I'm heading in the right direction) that when the installed premises limiter mic is set, generally, the 'mic' is positioned in the room (usually overhead) but away from the entertainment area (not directly over the disco).
I can only guess that when the 'crowd' are excited or cheer in close proximity to the said mic, with additional 'background noise', it is likely to 'trip' even when the DJ is monitoring the speaker volume??!!
I don't dislike sound limiters that much.....
but I hate it when a client has not been told about it when they book a venue, or when the client says that they don't believe one is installed in a venue.....only to 'find' one on the night!
I've yet to encounter one of these devices, but don't like the idea of having power completely cut, and then returned suddenly. I'd need to make a dash for the amps' power switches!
This discussion of limiters has been thrashed here before, but still an interesting discussion. I think the best all-round idea would be to have a warning system to simply indicate when the sound limit had been reached, but no physical action taken. Such systems exist, I believe.
Are mobile DJs generally sensible enough the take notice of such a system, I wonder?
This discussion of limiters has been thrashed here before, but still an interesting discussion. I think the best all-round idea would be to have a warning system to simply indicate when the sound limit had been reached, but no physical action taken. Such systems exist, I believe.
Are mobile DJs generally sensible enough the take notice of such a system, I wonder?
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