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Question about using a decibel meter

crouse

crouse

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I have an American Recorder sound level meter. I has A and C frequency weighting. The readings on C are 5 to 10 decibels higher than the readings on A. It also has hi (60-130dB) and lo (30-100dB) settings. The readings on hi are always greater than the readings on lo. So, the question is: which settings are a more accurate reading of the actual listening levels?:confused:
 
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I believe the A weighted scale "averages" the sound pressure level, giving the user a better idea of the sound level over a period of time. The C weighted shows peaks in the sound level (not averaged) and while may read louder, do not show the long term average of a sound event.
 
Thanks Wayner. Can anybody explain the differences between the hi and lo readings?
 
Different weightings tend to come into play depending on exactly what you are trying to measure:

666px-Acoustic_weighting_curves.svg.png

A-weighting tends to be used for safety / potential hearing-damage related measurements. Human hearing is more sensitive to certain frequencies, and more susceptible to hearing damage via those frequencies. A-weighting places the most value on those frequencies. For comparison, these curves approximately represent the sensitivity of human hearing:

714px-FletcherMunson_ELC.svg.png

A-weighting is old, and D-weighting is a more modern attempt to do what A-weighting is supposed to do, but A-weighting is so established that it persists (most meters only do A and C, or sometimes only A).

C-weighting is much more flat, representing most frequencies equally regardless of human hearing sensitivity to those frequencies. The biggest noticeable difference is that bass frequencies are represented much more. For a bass-heavy song, it's common for C-weighting measurements to be higher, sometimes much higher.
 
Chris Brown said:
Different weightings tend to come into play depending on exactly what you are trying to measure:


C-weighting is much more flat, representing most frequencies equally regardless of human hearing sensitivity to those frequencies. The biggest noticeable difference is that bass frequencies are represented much more. For a bass-heavy song, it's common for C-weighting measurements to be higher, sometimes much higher.
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Actually, linear weighting represents all frequencies flat. C-weighting is commonly used in proximity to military installations to better simulate the noise/disturbance from artillery.
 
crouse said:
It also has hi (60-130dB) and lo (30-100dB) settings. The readings on hi are always greater than the readings on lo. So, the question is: which settings are a more accurate reading of the actual listening levels?:confused:
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If the actual sound is less than 60 dB, the higher scale will read higher, because it "bottoms out" at 60 dB, so may not read any lower than that. My Quest 2900 (professional unit used for work) will read/report to about 3 dB below the lower limit of the scale with a span of 60 dB (e.g., 20-80, 30-90, 40-100, 50-110, and 60 - 120).

OTOH, if the actual sound is above 100, the higher scale will again read higher because the lower scale has "topped out" at 100 and won't go higher.

In the range from 60 - 100, both scales should read identical if the meter is a quality piece.
 
Its a shame that when speaking about Sound level meters some terms clash with each other. Weighting to me corresponds to the response time of the meter. There is fast, slow, and impulse for instance. As the name suggests the impulse measures the peaks and most of the time is about 10 db above the average or slow reading. The A, B C, And D curves filter the frequency response try to correspond with the ears sensitivity and its potential to be damaged. So with the C scale being more sensitive to bass the readings will be higher. Possibly 20 db or more using impulse C versus average or slow A. There are national standards meters must follow, so we can compare readings. A preciscion sound level as the name suggests is much more accurate and faithful when taking readings. The maner or technique you use in obtaining the measurements can greatly influence the readings, too. So place the meter on a stand in the accumulate mode and stand away from the meter to take accurate readings is one recommended way. A reflection of a nearby object such as your body can influence the reading in many ways and make the readings in consistent.
 
twiiii said:
Its a shame that when speaking about Sound level meters some terms clash with each other. Weighting to me corresponds to the response time of the meter.
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They don't really clash. In basic terms there are two seperate weighting protocols. The term weighting can apply to more than one measurement protocol.

One lives in the time domain (fast, slow, peak, impulse) and one lives in the frequency domain (A, B, C, D, Z).

In this technical sense, weighting means to give precedence to certain characteristics of the measurement be they in the time domain, frequency domain or both.

In the case of an SPL meter either one or both may be applied to the measurement depending on the required protocol and the application. Some but not all SPL meters may combine time domain weighting and frequency domain weighting setting in a single switch position if that is what the required measurement protocol calls for.

It is not unusual to see posts where a particular sound pressure is indicated by just XX dB. Without an indication of the weighing protocols applied to the measured value (time domain or/and frequency domain) the measurement is somewhat meaningless.

This is especially true when comparing measurement made be different people.

As you can see some people believe that the letter weighting applies to ballistics of the measurement, ( amplitude versus time-not correct) or that the term weighting only applies to one measurement protocol (again not correct).

I took just a quick look at the link that toddalin posted and it seems to give some good information.
 
According to the manual of my SPL meter, The fast setting is analogous to a peak setting while the slow setting is damped and reads a more average sound level. The C reading measures sound in the 32-8000 Hz range and the A setting measures in the 500-10,000 Hz range.

Edited to correct
 
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HTHMAN said:
The A reading measures sound in the 32-8000 Hz range and the C setting measures in the 500-10,000 Hz range.
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That can't be correct. C weighting should go lower in frequency than A weighting because A weighting filters these lower frequencies out.
 
Not sure the hi/lo thing was addressed, but if the ranges overlap, and they almost always do, they should agree if you're reading it correctly. Might need to be calibrated. If it's really old it can suffer from the same component issues as old hifi gear.
 
toddalin said:
That can't be correct. C weighting should go lower in frequency than A weighting because A weighting filters these lower frequencies out.
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You are absolutely right. I wrote it down backwards. Proofreading, who needs proofreading? I have spellcheck.

I corrected the post.

Thanks
 
The IH techs tend to use the higher energy scale first, and then bump down to the 30-100 db scale. Keep in mind that any continuous energy/sound >85 db will cause damage to your hearing over an 8 hr time period.
 
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