#### F1308

##### Addicted to Fun and Learning

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- May 24, 2020

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Thank you very much.When looking at efficiency numbers (dB/mW) the impedance is involved.

When looking at sensitivity (dB/V) it is not.... that is ... IF we have a source with near 0 ohm output resistance*and assuming the source in question is not current limited#and assuming the FR is the same~or very, very similar.

*When the output resistance is above say... 1 ohm or so (many interfaces and music instruments are, phones etc are not) then there is voltage division at play.

Say we have a 10 ohm output R and 2 headphones with the exact same sensitivity (dB/V) but one is 10 ohm and the other one is 32 ohm.

On a low output R source they will play equally loud (assuming FR is the same as well).

On a 10 ohm output R the 10ohm headphone will be playing 6dB softer and the 32 ohm headphone will play 2.4dB softer.

So in the end, not only sensitivity matters but also impedance combined with output resistance of the source.

#When a source is current limited (most are) there can be a difference in max SPL that can be reached.

When 2 headphones have the same sensitivity (dB/V) and the same FR but one is say... 12 ohm and the other one 300 ohm and the source is used that can supply 10V (in 300 ohm) but only 30mA then the 300 ohm headphone can reach 10V but the 16 ohm headphone can only reach 0.5V that is a whopping 26dB difference in max output level as the dB/V would be the same.

So... max output power in specific impedances also plays a role when looking for max. SPL

~When a headphone is listed as having say 105dB/V then this is only valid at a specific frequency or frequency band. This depends on the measurement method.

It could be at 400Hz, at 1kHz or even averaged over a narrow band noise. Usually this is not specified.

A headphone with 105dB/V could well have 120dB/V in the bass (very bassy headphone) or be 95dB at 30Hz (bass-light headphone).

Of course with the right EQ you can effectively change the FR to flat or a specific target. When done digital and applying a boost you will need negative pre-amp.

It therefore goes without saying that one cannot compute much, since there is not enough data provided to we the users. Just plug and see as I did, finding what I explained before, exactly the opposite of what thought to be obvious.

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