Lehmannaudio Manual Black Cube Linear - page 5 -
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If the power is doubled then the resulting sound pressure level is 3dB higher. If this
is calculated the other way round it means that only half of the power is needed
when using a headphone with 3dB more effectivity to reach the same sound
pressure level. The 3dB formula is valid for headphones and for loudspeakers.
From the given effectivity the power needed for a certain sound pressure level can
be derived. The power for the same sound pressure level can differ up to a factor of
500 for the different headphones on the market. In the end what counts when
selecting a headphone or a headphone amplifier is if the desired volume can be
reached without distortion. At least equally important is to avoid damage for the
headphone and – most important – to avoid damage for your hearing. The
maximum power rating is a figure that can be found in the data sheet of the
headphone. From this power rating the maximum voltage can be derived. If the
voltage will be higher then the voice coils of the headphones will be destroyed.
Today most headphones allow hearing levels well above a secure level for the
listener. This means that a standard pair of cans might survive extremely high
levels without any degradation of long term performance but the hearing of the
listener might be seriously damaged. Especially interesting are the standards of
different regions. Taking a look at laws in the US and in Europe reveals tremendous
differences in what is thought to be suitable for the listener:
Taking a look at laws in the US and in Europe reveals substantial differences in
what is thought to be suitable sound pressure levels for the listener:
Permissible noise exposures in Germany (dBA)
1
SPL /dBA
Duration
85 88 91 94 97 100 103 106 109 112 115 118 121
hours per day 8 4 2 1
minutes per day 30 15 7,5
seconds per day 225 112 56 28 14 7
Permissible noise exposures in the USA (dBA)
2
SPL /dBA
Duration
90 92 95 97 100 102 105 110 115
hours per day 8 6 4 3 2 1,5 1
minutes per day 30 15
1
Roughly harmonized throughout Europe
2
Figures taken from US department of labour noise regulations
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