The impedance of the headphone

On the road of looking for a separate headset for ourselves, surely you’ve ever researched and heard a familiar concept, it is “The impedance of the headphones”. So what is it? How it affects the sound quality soles? The issue will be answered through this article.

Before going into details, we need to understand a few concepts follows:
dB: Decibel, unit of the intensity of the sound, is the log of the ratio of 2 order of 10 units. 1B = 10dB
Impedance (R) calculated by Ohm: resistance, used to measure the resistance of the circuit with the first alternating current, similar to the concept of the line resistors 1 pm, still obey Ohm’s law (Ohm).
Sensitivity: Sensitivity, with each sonorous V increases will be added as many dB (dB / V).
Efficiency: performance / power / performance, with per mW increase will make great voice headset discovered how much more dB (dB / mW).
Note: Sensitivity and performance quite similar but actually different, one based on the voltage, 1 based on the capacity, which must count on the line.

I. The object relationship between the concepts above:

Perhaps everyone is familiar with the line of Ohm’s law: R = U / I and P = U2 / R
Inside :
U is the voltage, or called voltage, in Volt (V)
I is amperage, in Ampere (A)
P is the power, in Watts (W)
Capacity is determined by the pressure and flow, using the formula above we can see the U unchanged (volume unchanged), R increases, I will decrease and vice versa. Impedance means higher headset earphones that will draw as little lines and vice versa.

However, one must take into account the sensitivity and performance here, one thing to note: the sound quality to the sound completely different. Many amplifier could make a sound like headphones but sound is cut í othe details. With a highly sensitive headset (> 110dB / V), then certainly with the public sources it will sound quite loud because of the increased volume means increased pressure.

In contrast at low sensitivity (<90dB / V) will have to increase the volume up to achieve the same level of hearing 1. A typical example from the last century is the AKG K1000 headphones, 120ohm impedance only, however with very low efficiency (74dB / mW). In short, impedance headphones only tells us which will require more U or I.

II. Contact between the quantities:

For example 2 headphones with impedance 32 ohm and 600 ohm, performance and 100dB / mW. Under the current formula P = U2 / R, supercharged to 1V, we have 0.03125W P = 1/32 = = 31.25mW => ratio is 31.25 times => dB increase = 10 x log31.25 = 14.9dB => sensitivity = 100 + 14.9 = 114.9 dB / V

With R = 500 ohm, P = 1.67mW => sensitivity = 100 + log1.22 = 89.52 dB / V.

From there we can see the same power level of one power line, headphones with high impedance will have to turn over larger volumes, which is why many people think impedance or bigger hard pull, but the truth is not the case, it is only true in the case of the performance.

Now we try to take into account the AKG K701 headphones, impedance 62 ohm low average, sensitivity 105dB / V, change to the performance will be 93dB / mW, quite low. So it’s not just more lines but also need high powered amp.

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