##### Talking about the headphone impedance, impedance curve and sensitivity

This series of articles will make the product parameters, test methods, test results get a better combination of audio equipment, the subjective sense of hearing is not what metaphysics. Do not think that the objective test data, product parameters and subjective sense of hearing a far cry from that Because we test the method is not good enough, the test project is not accurate, the understanding of the product parameters are not deep enough.Today we talk about headset products, the two most common data "impedance" and "sensitivity." These two concepts explained Baidu Encyclopedia has, but the term is clearly not the purpose of this article.If you have enough experience with the headset will find that these two values ??in the purchase of headphones, to determine whether the headset is "push", not every And why are these two parameters in the end how much reference value? Why all headset products should list these two parameters? First, to briefly introduce the existing headset and industry test methods under the norms of the impedance of the impedance. : The rated impedance. This value cheap beats headphones generally represents the minimum impedance value in the ideal state when the maximum power is reached in the approved frequency range, since the margin should not be higher than the minimum impedance 20% .This set of definitions and related test methods to the dynamic headphones as a reference. Electrostatic headphones, moving iron headphone impedance curve will change with the frequency, test and definition methods may be different from the existing products Look, it may take 1kHz or a certain frequency impedance as the rated impedance.

First of all, we call it impedance, indicating that no matter what the principle of the speaker, it is not pure resistance circuit. In the circuit with resistance, capacitance and inductance, the circuit (circuit), the circuit, the circuit, the circuit, the circuit, the circuit, The current is called the impedance, the unit is ohm , where R is the resistance, L is the inductive reactance, 1 / is capacitive reactance. The inductance is the inductance in the AC circuit in the current obstruct function, Is the capacitor in the AC circuit in the role of the current impediment.As it is not a physics class, so the concept described here so far.

Although the industry test generally stipulates that the impedance should test a minimum [20% deviation] in the frequency range, whether the speaker is using a speaker or a headphone speaker, but it seems that the nominal impedance of the headset now comes from the 1kHz frequency. Perhaps the moving coil, flat headphone speaker impedance curve is relatively flat, many of them will be marked with the rated impedance is obtained at 1kHz, and in order not to bring too much trouble to ordinary users, it is estimated that moving coil headphones will not mark a Heap resistance value for your reference.

Impedance curve: for the headset products, we rarely refer to the impedance curve, the speaker impedance curve is the speaker in the input of different frequency signals show different impedance values ??of the "impedance / frequency" curve. As the moving headset speaker Impedance curve at 20Hz-20kHz or even higher frequencies are relatively beats headphones flat, so that the indicator is not much.While the speakers used in the speaker, the impedance curve is an important indicator, generally it will be in the low frequency near a large Raised, and then quickly dropped [with the first low as the rated impedance], followed by the frequency increases, the impedance may have different degrees of increase

Innerfidelity The frequency and impedance of the relationship, as well as the frequency and phase of the relationship between the two curves placed in a table.Phase is the phase / frequency curve, impedance is the impedance / frequency curve. The graph said 600 output impedance test, Is the source output level is 0dBu under the completion of [level concept, after the article talk].

What is the inspiration for us to play headphones?

First, the rated impedance of the headset is a number of ohms obtained by a test method such as a comparison method or a replacement method.

Second, the moving coil, plate, static, moving iron headphone unit will be in the effective frequency [can take 20Hz-20kHz, can also be higher, such as 50kHz] impedance changes, rather than immutable.

Third, moving coil headset, flat diaphragm headphones, dynamic ring earplugs impedance curve is relatively flat, but the moving coil large-size speaker [speaker use] impedance curve is far less than the headphones on the flat.

Fourth, the impedance curve of the moving iron unit is very exaggerated, a single moving iron unit covering the whole band when the high-frequency impedance will be steep.Multi-unit moving iron, in fact, is to improve this problem, but still very different.

Fifth, the impedance is a complex number, it is related to the signal frequency, phase.

Sixth, the impedance and the external resistance can not be the same, especially the impedance curve changes in the huge headphones, may bring a very strange sense of listening.

Then talk about the sensitivity of the headset.

Sensitivity of the headphones: After understanding the impedance, let's look at the other impedance-related values ??of the headphone sensitivity.

The sensitivity of the headphones refers to the sound pressure level that can be reached when the headset reaches 1mW of power using the 1kHz sine wave AC signal under the specified test conditions [IEC artificial ear and different coupling devices to simulate the human ear, or ear canal] DB / mW. As dB as the exponential unit, it must follow the test conditions, for many ordinary users to use inconvenience, we mentioned the sensitivity may be omitted mW units.But many headset products will be very complete write dB SPL / MW @ 1 kHz, or similar wording. The U power **beats solo** value can be obtained using the power formula P = U ^ {2} / Z, where the P power requirement is 1mW, ie 0.001W is known, ie the maximum sine power. Sinusoidal voltage, Z is the speaker rated impedance. Looks and DC power calculation method no difference.

For example, a headphone marked with a nominal impedance of 32 ohms, the required voltage is about 0.179V [0.032 square root]; 150 ohms corresponds to 0.387V. So different impedance values ??tell us a headset in reaching its nominal The sensitivity of the value of the sound pressure level, the required voltage difference between the supply voltage.

Here is an additional discussion of a topic, that is why more and more mobile phones can claim that they can drive 600 ohm headphones? According to the above formula can be obtained, if the headphone load is 600 ohms, then the need for power supply voltage is 0.775V, and according to Industry test standard Previous analog level digital standard 0dBu definition, that is 600 ohm load to 1mW analog voltage 0.775V is 0dBu [also 600 ohm 0dBm] .dBu, in fact, we usually measure sound cards, mobile phones, decoders, etc. The product speaks about the output level xxx dB. The next time you talk about this concept, the phone says it can drive 600 ohm headphones, which means that it can provide 0dBu, ie 0.775V output voltage, and achieve 1mW of output power.

Headset sensitivity parameters for us to use, what is the inspiration to buy headphones?

First, the current headset sensitivity is generally around 100dB, small earphone sensitivity is easy to more than 100dB. And we most people in a quiet environment to listen to music needs headphones to achieve the sound pressure level in the average 90dB-100dB or so now less than 90dB sensitivity The headset is not much, below this value, and then look at its rated impedance, basically know whether it is easy to drive.

Second, the sensitivity and the rated impedance is a set of related parameters, although it is a frequency point on the static indicators, but also need to be combined together. For example, with 100dB sensitivity, impedance is 32 ohms and 300 ohms, there are very Because the sound pressure is the exponential unit, the impedance should correspond to the voltage value in the open square [in order to get 1mW power index], so for the habit of linear relationship between the human brain, the feeling will not be so accurate.

Third, the above mentioned, the speaker impedance will change with the signal frequency changes, the sensitivity is only 1kHz to 1mW when the sound pressure level, it is only a quick, preliminary judgment indicators, so sometimes you will think that these two Parameters and hearing a good or bad judgment almost no reference value.For the headset is a good push the quantitative significance, low impedance, to achieve the sensitivity of the sound pressure voltage is lower; high sensitivity, naturally in the same input power, the sound pressure will But it is only a measure of the size of the sound, not to mention a single frequency of 1kHz.We have to consider its impedance curve and many factors.

Fourth, because of the contents of the third article, so we have to be vigilant can also understand why some sources that can drive 600 ohm or even 1000 ohm impedance headphones, this is a not strictly responsible for the argument.

As an introductory content, the information and knowledge points involved in this article seem to be somewhat complicated. As a loudspeaker with such a loudcomings, it is not enough to summarize its performance, frequency range, impedance and sensitivity, as headphone products The most common of the three related acoustic parameters, it plays a role need to take into account its definition and test conditions. Hope this article a few tips for everyone to understand these two parameters help.