# Technical specifications

Impedance
Impedance is opposition to the flow of current. The higher the impedance, the less current will flow. Impedance is measured in Ohms, indicated by the Greek sign Omega (Ω). Earphones and headphones impedance usually range from 8 Ohms to 600 Ohms or higher. The audio source (the headphone output) also has an impedance rating. To obtain maximum power transfer (all usable power from the source reaches the earphones) impedances should match. However, that’s rarely the case. When impedances don’t match, there is either a loss of voltage or of current, in other words, a loss of power. This power loss can be calculated with the following formula:

Where
- RS: Source impedance (the impedance of the audio system’s headphone output)

Let’s assume we want to use a typical over ear headphones. Its impedance is 110 Ohms. If connected to a source that matches this impedance, the above formula shows a loss of -6.0 dB. Even though there is maximum power transfer, there is a loss. This is called load loss and there’s no way to avoid it. For example, using a higher source impedance, say 600 Ohms, the power loss becomes -8.8 dB. This is nearly 3 dB lower than before; -3 dB represents half the power. Using a lower source impedance, say16 Ohms, the power loss is –9.5 dB. Note that the load loss increases if the source impedance is higher or is lower than the exact earphone impedance. A headphone amplifier typically can deliver far more power than needed, thus overcoming the effect of unmatched impedances.

Sensitivity
Sensitivity is how effectively an earphone converts an electrical signal into an sound signal. Sensitivity indicates how loud the earphones will be for a given level from the source. This measurement is given in decibels of Sound Pressure Level per mill watt, or dB SPL/mW. In some cases it might be shown as dB/mW and is based on a 1 mW input signal. One mW is one thousandths of a Watt, or 0.001 Watts. The sensitivity of earphones is usually in the range of 80 to 125 dB SPL/mW.

In-ear monitors frequency response
Do you wonder why so many people tell you that custom in-ear monitors are very reveling and full of detail, yet most IEM don't seem to go pass 20 kHz when you look at their frequency response? Here is the reason:

Although the human hearing range is listed at 20 Hz to 20000 Hz, most adults can't actually (or at least have difficulty) hear sound above 16kHz, especially once a person passes his/her twenties. Don't worry about losing treble/detail over 16kHz, as humans tend to interpret sound between 5kHz to 16kHz as 'high' and most details are actually on the lower region.

Some of you might have read elsewhere that although humans can't hear sound beyond 20KHz, they can still feel the presence of ultrasound (and the harmonic distortion caused by ultrasound) and it does have a positive effect on sound quality (*the studies involved are controversial, but let’s assume the conclusion is real).

However, given that almost all CD, lossy and lossless music produced these days have a cap of 20 KHz in recording / encoding, we can safely conclude that most music we listen to these days doesn't come with any meaningful sound beyond 20KHz that can be reproduced by your headphones or IEMs. If you want to listen to a recording that does include sound beyond 20KHz, you'll have to go back to analog record (LP) or get SACD, but mind you, you'll still need equipment that is capable of playing those sounds back.

16.Custom in-ear monitors and Health
Custom in-ear monitors (CIEM) are often mistaken as a kind of health hazard responsible for hearing loss and ear infection. The fact is, CIEMs are very safe when properly used.

Firstly, you need to understand that listening to music at loud volumes over time can damage your hearing, regardless of what kind of headphones (or speakers) were used. The advantage of using an IEM is that you can turn your volume down since you do not need excess volume to cover the ambient noise.

Do not think that IEM will cause damage to your hearing as it is closer to your eardrum.

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