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Old 31st January 2011, 08:20 PM   #1
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Default Question about sensitivity specs

I can't get my head round the calculation to convert a Sennheiser spec of 113dB for 1 V rms for a 16 ohm earphone to convert to the more usual Sony type spec of 103 dB/mW also for 16 ohm unit.

1V rms for 16 ohm is 62.5 mW for 113dB?
Is it then 31mW for 110 dB?
15 mW for 107dB?
7mW for 104dB?
can't be right because the answer should be roughly equivalent, so I'm missing something?
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Old 1st February 2011, 12:52 AM   #2
Lukas87 is offline Lukas87  Czech Republic
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since the Z are the same, therefore:
62.5 mW = 17.96 dBm (cca 18 dBm).

then 113 - 18 = 95 dBm (and that equals Senn's SPL/mW).
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Old 1st February 2011, 01:12 AM   #3
jcx is online now jcx  United States
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its definitely a pain when the manufacturers own specs don't specify the reference for the sensitivity with some in dB re 1 mW and others refered to 1 V

different models of supra aural dynamic headphones vary over ~20 dB range of sensitivity so there's no necessity for the numbers to match even stated in the same units

iem can be ridiculusly high sensitivity - to the point that the only hiss free "amplification" is a step down transformer from line level source
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Old 1st February 2011, 02:30 PM   #4
Gordy is offline Gordy  United Kingdom
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Quote:
Originally Posted by audiolabtower View Post
I can't get my head round the calculation to convert a Sennheiser spec of 113dB for 1 V rms for a 16 ohm earphone to convert to the more usual Sony type spec of 103 dB/mW also for 16 ohm unit.

1V rms for 16 ohm is 62.5 mW for 113dB?
Is it then 31mW for 110 dB?
15 mW for 107dB?
7mW for 104dB?
can't be right because the answer should be roughly equivalent, so I'm missing something?
1V RMS into 16R is 62.5mW as you note.

Given 1V RMS is 62.5mW and your stated sensitivity of 113 dB, then working from the fact that loudness reduces by 3 dB for ever power division by 2, we can track back as follows…

Power in mW........dB

62.5........113
31.25......110
15.63......107
7.81........104
3.90........101
1.95........98
0.98........95


So 0.98 mW produces 95 dB.

0.98 is very close to 1, therefore we can say that the sensitivity for 1mW is approximately 95 dB.

This figure is for the specific headphone that you noted.

As jcx has pointed out, it does not necessarily apply to all 16R headphones. They will vary in sensitivity according to their physical design.

: )
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Old 1st February 2011, 06:57 PM   #5
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Thanks for all your help folks.

This is what mystifies me, the 113dB/1V is quoted for Sennheiser CX300 Mk2, which are 1dB more sensisitve than the Mk1.

The 103dB/mW is quoted for Sony MDR EX75 which are 3dB more sensitive than the older MDR EX71s.

I can hear the slight loudness difference between CX Mk 2 and Mk1, and can clearly hear the sensitivity gain of the 75 over the same sounding 71.

Yet the Sennheiser 300Mk2 and the Sony EX75 sound much the same switched between, so should work out around the same sensitivity within 1-2dB, which I cannot understand from these figures.

Though not in Shure territory for fine detail, both these earplugs are reasonably well balanced across the frequency spectrum, without obvious peaks or troughs to fool subjective evaluation, and good value first step up mid range buds, IMHO.
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Old 12th February 2011, 10:30 AM   #6
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You are right rather misleading spec(not intentionally) do trouble people with specific requirements. Anwways my favourite are Sennheiser HD 428 can find them on Testfreaks. Nice sealed headphones.
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