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|The sensitivity rating is usually for 1 milliwatt POWER input to the phones and a corresponding sound pressure level (SPL) output (USUALLY 102 to 106 dB SPL output for moderate to high sensitivity rated phones).
However, connecting different sets of phones with the same 1 milliwatt to SPL output sensitivity rating to the same headphones amplifier output may, or may not give corresponding equal or loud enough SPL operation!
The impedance (the ohms rating of the phones voice coil) determines how much audio 'voltage' needs be applied to get that '1 milliwatt' or more power into the phone's motor circuit.
For example: A low 16 to 45 ohm headphone (low ohms impedance that's typical for Sony headphones) will easily get to operate for many milliwatts for providing close to live loudness on battery powered portable equipment that typically output only .5-1.5 volts RMS volts output.
A 65 to 600 ohms phones set impedance (higher ohms typical of Sennheiser, Beyer, & AKG headphones). will require a higher headphones amplifier output voltage signal to get the same milliwatts into the phones voice coil for providing equal loudness.
Most of these higher impedance phones require connection to a headphone amp circuit that has ability to drive at least 2-6 Volts RMS to get reasonable loudness for phones listening. Not the type of headphone to use on most portable powered deck's with low voltage phones outputs. These high ohms phones really need a an AC powered amplifier's headphone jack or even direct connection to 10 watt or more power amp's speaker outputs for realistic (loud) listening. There are headphone amps available for this purpose and some are battery powered with at least (1 or 2) 9 volt batteries, the minimum supply needed for higher impedance phones to work at reasonable loudness.
Bottom line: Phones sensitivity is only a measure of the ability to play loud enough only if comparing phones with about the same ohms impedance that are being driven by the same headphone amplifier.
Best before buying is to try out the phones on the exact equipment you to use while playing typical sounds of interest.
|Why are some headphone louder than others?
Loudness is directly related to the impedance and sensitivity of the headphones. Impedance determines how much power the headphones will draw, while sensitivity indicates how much of the electrical signal delivered to the headphones is converted into sound. Because low impedance headphones draw more power from the amplifier they will sound louder, at the same control settings, than high impedance headphones. Also, headphones of higher sensitivity will sound louder than those of lower sensitivity. Check the manufacturer's spec sheet for impedance and sensitivity information.
|More than likely, those who inquire about "efficiency" are actually concerned with the speaker's sensitivity. It is important to remember that sensitivity and efficiency are two very different things, though they are intuitively related. Most people do not realize that it is entirely possible to produce a speaker which has an extremely low sensitivity figure, yet is highly efficient (at least one electrostatic model, no longer made, fit this description many years ago). People are generally concerned with sensitivity because that tells us how loudly a speaker will play when presented with a standard voltage. It does not, however, take into account the impedance of the speaker, and therefore really tells us nothing about the efficiency, because we don't know how much current is being drawn from the amplifier...|
getting the impression that for portables ,you want low impedance and high sensitivity ;but A benefit to a higher sensitivity rating is your drivers will respond very well to a wide range of power output and do not require peak power for good performance. A draw back to high sensitivity is the drivers will not take a lot of abuse (listening at high levels of distortion, etc) . Lower sensitive drivers are more power hungry and force you to give them the full power to receive the full performance. The benefit to low sensitivity is that their simply harder to damage
So, by this measure of sensitivity (sound dB / mW) you double your mW of power, and you double your sound dB. For example, if your sound dB is 0, and you apply 100 times the power, you still have 0 dB. Yeah, that makes sense.
How might one measure the dB of sound output by the headphone?
(scroll down just slightly)