Interdyn

Most sound level meters are equipped with two filter settings: A and C. These filters ‘weight’ or bias the response of the SPL meter when measuring sound pressure in various types of environments. For low frequency measurements in the home, the C setting should be used.

Even though the C setting is appropriate for low frequency measurements, starting below about 80 Hz, the SPL reading displayed by the meter is lower than the actual SPL - and this error grows progressively larger at increasingly deeper frequencies. In order to obtain the most accurate data possible during your frequency response measurements, this error needs to be corrected – hence the term ‘correction factors’.

For enthusiasts who want to manually measure the subwoofer frequency response using test tones, SVS offers a spreadsheet which contains the C-weighted correction factors. The reading from the sound level meter is input into the spreadsheet, and it automatically adds the appropriate correction factor for that test tone frequency. When all test tone SPLs have been entered, the spreadsheet automatically plots the subwoofer frequency response. For a free copy of this spreadsheet, please contact Customer Service.

For enthusiasts who are using a software program to measure the subwoofer frequency response, the correction factors need to be entered into the software as a microphone correction file. Some software programs such as Room EQ Wizard already contain a microphone correction file for C-weighted sound level meters.

For software programs which do not contain a pre-loaded C-weighted microphone correction file, the C-weighted correction factors are provided below. Note, these are the theoretical correction factors for the C-weighted filter, but they cannot account for any additional error an individual sound level meter may exhibit due to reasons other than the C-weighted filter. These correction factors are presented in 1/12 octave resolution, which is generally sufficient for plotting the subwoofer frequency response. Note, a negative value means the sound level meter reads lower than actual at that frequency.