How to use a dB meter?

I am learning about dB and I don't know how to use a dB meter. When I'm testing volumes, should I put the dB meter right where the noise is coming from, or hold it away at the distance I would hear it from? Even if it's not much of a difference, I just want to be as accurate as possible.

6 Answers

  • 7 years ago
    Favourite answer

    Depends on what you want to know. The meter will measure the sound pressure level at the location of its microphone, and the accuracy of that measurement won't vary with the location (basic principle of physics). Cheap SPL meters are crap anyway and won't tell you much more than what you'd guess anyway.

    If you want to do 'accurate' measurements in the sense that you want to compare different audio sources, you'll need a more complicated setup. Those setups are (usually) described (quite detailed) in the corresponding measurement standard and might include:

    - shape of the audio source

    - position and distance of the microphone with respect to the audio source

    - drive signal shape, frequency and level

    and will usually include the requirement of a deadened room or free field, i.e. no reflections from adjacent walls/ceilings/floors/engineers - or alternatively describe the environment, down to the number of potato sacks (i.e. listeners, but you can't get enough people keeping absolutely quiet during the measurement, so potato sacks are a cheap and still fairly good alternative) in the listening room.

    Source(s): Not a sound engineer myself - those guys sit on the next floor - but interested in audio and building speakers since ~20 years.
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  • 7 years ago

    It depends on how you want to baseline the measurements that you are making. It would not be helpful to say "stand 2 metres away" because that may not be possible or appropriate. Your desire to be accurate is excellent so you must be prepared to be precise and understand some of the problems.

    It can often be difficult or dangerous to hold a dB meter right up to noise source, for example a motorway, airport or railway line. If you are measuring the noise output from a stationary device such as machine or loudspeaker then it may be very easy to hold the meter close, but you must not touch the source.

    In practice people who do noise measurements professionally will always state exactly what was being measured and the relevant conditions that were existing at the time of the measurement.

    For example:

    "Electric motor serial number 'MMMM'; motor running at 30 rpm; meter serial number 'NNNN'; distance from noise source 2 metres; duration of measurement 5 minutes; measured noise level 30dBA"

    The meaning of each of these terms is:-

    1) The serial number or identity of the noise source is important if you are comparing the noise

    from various sources. If it's a HiFi, radio or a tv then note the make and model.

    2) If it is a motor then the running speed is important because the noise level can vary at different speeds.

    If you are measuring a loudspeaker then state the music that is playing (or male/female voice) and the make, model and volume knob setting of the amplifier. Then the experiment can be accurately reproduced.

    3) The make, model and serial number, or identity, of the dB meter is important because the calibration accuracy of meters can vary according to how they're kept and maintained.

    4) The distance from the noise source is important for consistency. The noise level changes according to the "Inverse Square Law" so it is VERY important that all measurements of similar devices are taken at the same distance or they cannot be compared with each other in any meaningful way at all.

    The actual distance itself can be chosen for safety and convenience (you may not be able to get close and the meter must never touch the machine).

    5) The duration of the measurement is important to note because not all noise is constant (like an electric motor), noise levels can vary over periods. Road noise, speech and music all vary. So you must record the highest and lowest readings (peak and trough) that you get in your five minute (or whatever) period.

    6) The measurement itself must be written down properly including the exact scale that is used. There is a big difference between "dBA" and "dB", and "DB" which matters a great deal to scientists and engineers.

    If you are writing a report on your findings on comparing noise levels from various sources then try and keep as many things constant as you can. For example:-

    - Distance from noise source. If you are comparing road noise with domestic tv at normal volume or a vacuum cleaner, then hold the meter at a safe distance from the road kerb (eg 2 metres), and use the same distance at home from the telly or vacuum cleaner.

    - Spelling. Note the difference in spelling between "meter" (device for taking measurements) and "metre" (a measure of distance). This is important if you're writing a report and want to get the English correct so it's a proper job and not just lazy jottings. Beware of american spelling checkers and dictionaries (like Yahoo Answers). Unless you're American you should not use American spelling - it's wrong and Naff.

    - Structure. List the results in a table (headings as in the example above ) so that they can be easily compared with each other.

    Noise measuring is a fascinating subject and can produce some surprising results, especially when you understand how it's done and what the "weightings" mean (ask your teacher to explain these). You will discover that a noise measuring (eg) 89dBA actually sounds twice as loud to you as a noise measuring 86dBA. Most people don't know that.

    Source(s): I've done this professionaly. It's really fascinating.
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  • 4 years ago

    You have not stated what grade of meter you have,there are about 4or5 grades starting from the meter that can via bought from a well known element retailer which could have an accuracy of about 15% which would give you a studying that you've, peculiarly for those who change meter settings and would best be used as an indication that there's a output in all probability be within the range required. Then there's the variety of instrument use in commercial industry about 5% accuracy and switching tiers there will have to be give identical readings and nearing a right db reading. Sooner or later there's the substandard precision instrument utilized in laboratories and other places the place very correct measurements are required.(substandard instruments there calibration will also be traced back to N.P.L.) and require calibration each three to 6 months relying on there stability

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  • 7 years ago

    It's all relative, and therefore rather indefinite.

    If you want to know the loudness of a sound at its source,

    the meter's mic has to be right next to the source of the sound.

    Otherwise, the reading will indicate the loudness of the sound at the meter's position.

    >> The standard measurement distance for sensitivity testing of speakers is 1 meter.

    Of course, for the results to be comparable to those obtained by others,

    you need to drive the speaker with a 2.83-volt 1kHz sine wave.

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  • 7 years ago

    The dB meter comes with a microphone is used to measure audio level at the location where you stand. Other type dB meter comes with two test probes is used to measure amplifier output terminals where has a 600 ohm load.

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  • Anonymous
    7 years ago

    Think of it like listening to a speaker. The closer you get, the louder it will be. If you were to measure something like the DB of a car you would hold it close to the exhaust pipe. If you wanted to measure noise in a club you would hold it in the middle of the club.

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