decibel measurements

[nicklaus08]

I am looking at the maximum volume levels of music devices and want to know what this is in decibels. This is for my dissertation and the main aim is to find the maximum volume in decibels and if this is in excess of the EU guideline which should not exceed 100dB. 

I have used the spectral measurements to give results for power spectrum in decibels which produces a waveform chart of amplitude against frequency. Is this correct and if so how would I convert the amplitude figures to decibels as I cannot find the reference figure? Also when I record my music file I get minus figures would this be expected?

[johnsold]

The decibel is a measure of ratios.  Sound pressure levels, when expressed in decibels, are measured with respect to some reference level.  I am not familiar with the EU standards so do not have any idea what reference level is used by those standards.  Further, some audio standards are weighted by frequency in an attempt to correlate with human perception.

So, first you need to look at the relevant standard to see what reference level and frequency weighting is used.

Second, you need to calibrate against that reference. Third, you need to calibrate your recoeding system and the playback/analysis system.

A very unscientific and poorly reproducible measurement system: If you cannot talk to the person sitting next to you without shouting or raising your voice, then the music is too loud.

Lynn