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Measuring noise levels

One of the first and most important steps in reducing noise and/or adjusting the acoustics of a room or area is the proper and accurate measurement of noise levels. To do this, you’ll need a quality sound level meter such as those described in this manual. For accurately and consistently recording your sound level readings, we recommend using the ASI “Octave Band Analysis Worksheet”. Following are recommended procedures for taking sound level readings and using the worksheet.

Taking sound level readings:

1. First and foremost: read, understand and follow the operating instructions for the noise level meter you
    are using.

2. Do not get too close to the noise source. Take reading where the nearest employee stands.

3. If you are measuring the loudness of a specific machine, stand as far away from the machine as the
    longest dimension of that machine. For example, if the machine is 6 feet long, take sound level readings
    from 6 feet away from any part of that machine.

4. Also, when measuring the sound level of a specific machine, make sure the background noise is at least
    10 dB lower than the noise you are trying to measure.

5. When taking readings, hold the meter upright at shoulder level, facing away from plane surfaces that can
    reflect noise and adversely influence your readings.

Using the Octave Band Analysis Worksheet

1. This worksheet, shown on the right, is located in the “forms” section of this manual. Use it as a master for
    photocopying your own supply of worksheets.

2. Not that the worksheet is set up to allow you to take sound level readings from up to 5 different locations.
    This could be 5 locations within or around a single, open area or machine, or sound level readings in up
    to 5 different rooms.

3. Start by filling in the top of the worksheet with the client’s company name, the client contact name and the
    date the readings were taken. If the time of day is important to record, include that along with the date.

4. At the bottom of your form, write in a brief description of the location(s) you are going to test. Use clear
    descriptions so that both you and your client will easily be able to go back to that exact location if required
    later on.

5. For each location, the worksheet contains 3 columns. The first column, headed “dB(L)” is where you’ll
    write in the actual un-weighted (flat) sound level reading for each of the 10 frequencies listed. (See note on
    automatic weighting sound level meters)

6. The center column, headed “+ or dB(A) Weight” is a government standard weighting figure for each of the
    10 frequencies that must be applied to the flat reading. This adjusts the readings in relationship to
    established thresholds for determining harmful sound levels. (See note on automatic weighting sound
    level meters).

7. The third column, headed “Adjusted dB(A)” is where you’ll write in the sum of column 1 and column 2. For
    example, at 31.4 Hz, if your flat reading is 77 dB, your adjusted dB(A) figure will be 37.6 (77.0 minus 37.4 =
    37.6). If your flat reading at 2000 Hz is 77dB, the Adjusted dB(A) figure will be 78.2 (77 plus 1.2 = 78.2). In
    the interest of saving time at the client’s site, you may want to take flat readings, than do the weighting
    calculations later at your office. (See note on automatic weighting sound level meters).


Many sound level meters, including those Quest models in this manual, can automatically perform the dB(A) Weighing calculation when you take the reading. In that case, all you’ll need to do is take the reading and enter it directly into the “Adjusted db(A)” column. See your sound level meter’s operating instructions for further information.