A question about decibels

VicS

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If something is marked 99dB ... see picture... what does it mean and what are the implications for the user.

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grumpy_o_g

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L-WA is the old abbreviation for "Level Weighted according to the A filter". In other words it's decibels Absolute to a scale adjusted to approximate the human ear's sensitivity where` 0dB is the threshold of human hearing.

According to that weighting, typical volumes of noise result in the table Twister Ken has posted. 99 dBA would be uncomfortable after a short while probably, depending on a whole range of variables of course.

These days most people just abbreviate to dBA.
 

MOTORBÅD

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SPL

A dB number without knowing the messurement distance is meaningless. If you double the distance the dB number will decrease by 6 dB.
 

VicS

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Yes I appreciate the decibel scale in relation to noise intensity and the meaning of the A weighting but but does the figure mean in relation to the item it is marked on.
My wheelie bin
th_DSCF0718.jpg
 

VicS

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Are you telling us that your wheelie bin emits 99 dB?
No. I am asking why it's labelled 99dB. There's no one in it, just abit of garden rubbish. Does not even produce 99dB when used for flushing the outboard.

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savageseadog

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It could be the sound level generated generated at a certain distance when the bin is dropped from a standard height?

The 6db reduction when doubling distance is a result of the square law reduction in sound pressure level with respect to distance. This only applies in a free field situation, the ground and other reflecting surfaces and atmospheric effects will always increase the level.
 

Billjratt

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dBs always attract the techies, don't they?
Once we've all agreed what they are, (which we knew already) Vic is asking WHY his bin should be rated at 99.......
Could it be related to the noise it makes as you roll it down the drive at 0500 in time to catch the collection lorry?
Does a bin with delux rubber tyres get a different rating? and, if so, is the moulded number altered to suit?
Does it take into account the worst case scenario vis-a-vis rough surface?
What about bin resonance under various different load conditions?
These questions, and many more, (no doubt) need to be answered before we come to a reasonably acceptable answer.
Or, maybe we should ask the guy who made it.
 

RIB_imposter

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It is indeed the noise that the bin is capable of producing in certain circumstances (I'm not sure of the exact test criteria) but essentially the Dustmen should (according to the relevant HSE/EU directive) be wearing ear defenders if they are exposed to > 85 dBA for significant periods of the day. I guess that empty wheelie bins resonate nicely and are a bit like a big speaker cone.
 

VicS

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I was wondering about the significance of the symbol top left. Seems to be a loudspeaker inside an enclosure.
Any chance that the 99db figure is the maximum sound level to which the bin should be subjected?

According to Twisted Ken an iPod at max volume is 115dB. Any body care to turn their ipod up to full blast and pop it into a wheelie bin to see what happens.
 

misterg

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I was wondering about the significance of the symbol top left...

It's a marking that indicates that your wheelie bin is in compliance with EC Directive 2000/14/EC relating to the noise emission in the environment by equipment for use outdoors.

Unfortunately I'm not joking :(

(See here for example)

Jesus, indeed, wept.

Andy
 

misterg

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As you're undoubtedly wondering what aspect of wheelie bin operation the dB figure refers to, I can refer you to Statutory instrument 2001 1701


39. Mobile waste containers
{..}

Measurement surface/number of microphone positions/measuring distance
Hemisphere/six microphone positions according to Part A item five/r = 3 m

Operating conditions during test
All the measurements shall be carried out with an empty container.

Test No. 1: Free shutting down of the lid along the container body

To minimise his influence on the measurements, the operator shall stand at the back side of the container (hinge side). The lid shall be released by its middle, to prevent warping during its fall.

The measurement is carried out during the following cycle, repeated 20 times:

- initially, the lid is raised vertically

- the lid is released forward, if possible without giving an impulse, with the operator at the back of the container, unmoving until the lid is shut

- after complete shutting, the lid is raised to its initial position.

Note: If necessary the operator can move temporarily to raise the lid.

Test No. 2 Complete opening of the lid

To minimise his influence on the measurements, the operator shall stand at the back side of the container (hinge side) for the four-wheel containers, or on the right side of the container (between microphone position 10 and microphone position 12) for the two-wheel containers. The lid shall be released by its middle or as near as possible to its middle.

To prevent any moving of the container, wheels shall be locked during the test. For the two-wheel containers, and to prevent any bounce of the container, the operator can maintain it by placing his hand on the top rim.

The measurement is carried out during the following cycle:

- initially, the lid is opened horizontally

- the lid is released without giving an impulse

- after complete opening, and before a possible rebound, the lid is raised to its initial position.

Test No. 3: Rolling of the container over an artificial irregular track

For this test, an artificial test track, simulating an irregular ground is used. This test track consists of two parallel strips of steel mesh (6 m long and 400 mm wide), fastened in the reflecting plane approximately every 20 cm. The distance between the two strips is adapted according to the type of container, in order to allow the wheels to roll all over the whole length of the track. The mounting conditions shall ensure a flat surface. If necessary, the track is fastened on the ground with resilient material to avoid emission of parasitic noise.

Note: Every strip can be composed of several 400 mm wide elements fitted together.

An example of adequate track is given in Figures 39.1 and 39.2

The operator is situated at the lid hinge side.

The measurement is carried out while the operator draws the container along the artificial track, with a constant speed of approximately 1 m/s, between point A and B (4.24 m distance - see Figure 39.3) when the wheel axle, for a 2-wheel container, or the first wheel axle for a 4-wheel container, reaches point A and B. This procedure is repeated three times in each direction.

During the test, for a 2-wheel container, the angle between the container and the track shall be 45°. For a 4-wheel container, the operator shall ensure an appropriate contact of all the wheels with the track.

Period(s) of observation/determination of resulting sound power level if more than one operating condition is used

Test Nos 1 and 2: Free shutting down of the lid along the container body and complete opening of the lid

If possible, the measurements are carried out simultaneously at the six microphone positions. Otherwise, the sound levels measured at each microphone position will be classified in increasing order and the sound power levels are calculated by associating the values at each microphone position according to their row.

The A-weighted single-event sound pressure level is measured for each of the 20 shuttings and the 20 openings of the lid at each measurement point. The sound power levels LWAshutting and LWAopening are calculated from the quadratic mean of the five highest values among those obtained.

Test No. 3: Rolling the container over an artificial irregular track

The period of observation T shall be equal to the duration necessary to cover the distance between point A and B on the track.

The sound power level LWArolling is equal to the mean of six values differing by less than 2 dB. If this criterion is not fulfilled with six measurements, the cycle is repeated as far as necessary.

The resulting sound power level is calculated by:

LWA = 10 log 1/3 (100.1LWAshutting + 100.1LWAopening + 100.1LWArolling)


People are starving in the world while we fart about passing laws about empty wheelie bins. It really beggars belief! :mad:

Andy
 
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