Normal equal-loudness-level contours - Examples in practice
The black line shows the original frequency response of headphones MPH-1
, which is taken as reference sound pressure level of 72 dB SPL. If we add or lower the volume level in the amplifier in steps of 12 dB, then subjectively the frequency response will change as in the graph above.
The relatively flat frequency response is closest to the -12 dB line, but with a deviation of -24 dB.
Are these data accurate? For verification, the "natural volume level" was set, and on Windows PC in the Foobar2000 player the volume was reduced blindly until the frequency response became felt relatively flat. The result for the set volume level is -17 dB, quite close to the calculated data. Depending on the musical material, the data for each will differ slightly, because the frequency response in the low-frequency range of the MPH-1 is not a straight line for all possible loudness deviations. Someone will not take into account the lowest frequencies (at volume levels below 20 dB). Another one as a compromise will leave the slightly rise in the region of 60 Hz for frequencies below 50 Hz.
, the most flat line is the graph at level of -24 dB for the all frequency range. While the frequency response in the low frequency range is not exactly flat, there is a slight rise in the region of 200 Hz. Alternative line is the graph at level -12 with a more or less uniform low-frequency range with a slight dominance of low-frequencies.
On different musical material, subjectively, the headphones sounded linear at levels from -12 to -20 dB. Sometimes priority was of the evenness of the entire low-frequency range, and sometimes linearity in comparison with the middle and high frequencies. Thus the subjective perception was not far from the graphs.
In the examples above it is clearly shown that if you take into account the level of volume at which the listening will be performed, the headphones will be perceived more evenly, or vice versa. And at the same time when selecting a different level of volume, the earphones will not play music perfectly smoothly, there will still be some compromise.
has a rise in the low frequency range. But if you will list to them at 12 ~ 24 dB quieter, then the AFC will be "flat". Thus M50x will be smooth headphones for listening to music at levels of 48 ~ 60 dB SPL with a soundtrack with a natural volume level of 72 dB SPL. Or "terribly groovy bass" "at loudnesses above 80-90 dB SPL.If the original music is heavy metal rock with a natural level above 100 dB - then an amendment is made with respect to 100 dB.
Where connected to low power amplifiers M50x does not have a large volume level. But due to the fact that the headphones had flat frequency responce at a low volume, they are a good choice and "play well from any source", where the main bulk of everything is smartphones, tablets or low-budget players.
For example we take non-bass headphones AKG K701
The headphones are "linear" only at level only at + 6 to + 18 dB relative to 72 dB. Thus K701 is optimally to listen at a loudness from 85 to 90 dB SPL. Accordingly, the amplifier needs to be louder (more powerful). K701 will rock only at high volume. The best option for a person with low sensivity of hearing from the age (sarcasm, but with a share of truth).