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F.A.Q. / Headphones and Amps - interplay

Analytical table and recommendation for using headphones with different types of amplifiers based on the measured characteristics

About

For whom RAA made this: for those who is hard to understand graphs or/and for who want to see brief graph analysis in common words. RAA developed an algorithm to calculate the compatibility of sources and headphones. This table is the first step to create a simplified general report. We want to make two reports: first short simplified report for simple user and second report for a pro.

Such the algorithm became possible due to:

Measuring the sensitivity of headphones and power characteristics of sources.
Determination of the average statistical data for different headphones and sources (amplifiers).
Direct comparison of headphones live and comparison of the received data after measurements.

From the idea of the table to the final implementation took about three years. And gradually the algorithm is being improved for modern products.

In this general table, we show the most common variations of sound sources and the field of headphones application.

The compatibility rating is similar to car analysis based on its ground clearance - on which road the car will move optimal without evaluating the class of the car. On a race car of Formula 1 is difficult to drive on a ground road. The same foolish idea to use caterpillar all-terrain vehicle on a highway.

The table allows to estimate the most complete opening of the potential of headphones while use with amplifiers of a similar class, but with different power parameters.

Analysis and recommendations for ASTRO Gaming A40 based on the measured characteristics
Sources (to which the headphones will be connected)	Areas of using headphones	Sensitivity	Impedance	The type of acoustic design	Total
Sources (to which the headphones will be connected)	Areas of using headphones	113.30 dB/V SPL	62.22 ohm	Semi-open
Low-power sources -6dBV/15dB(mA): a smartphone a player a tablet Examples	Home or studio, where sound from the headphones does not bother anyone	5 ★★★★★	5 ★★★★★	3 ★★★☆☆	4.3 ★★★★☆
	Office and home, where people should not hear the sound from the headphones	5 ★★★★★	5 ★★★★★	3 ★★★☆☆	4.3 ★★★★☆
	Street with active traffic	5 ★★★★★	4 ★★★★☆	3 ★★★☆☆	4.0 ★★★★☆
	Metro (subway), public transport	4 ★★★★☆	3 ★★★☆☆	3 ★★★☆☆	3.3 ★★★☆☆
Mid-power sources 6dBV/27dB(mA): a computer with sound card a Hi-Fi player a portable amplifier a mixer console Examples	Home or studio, where sound from the headphones does not bother anyone	5 ★★★★★	5 ★★★★★	3 ★★★☆☆	4.3 ★★★★☆
	Metro (subway), public transport	5 ★★★★★	5 ★★★★★	3 ★★★☆☆	4.3 ★★★★☆
	Recording a voice or instrument in the studio	5 ★★★★★	5 ★★★★★	3 ★★★☆☆	4.3 ★★★★☆
Hi-power sources 18dBV: a home system with a headphone amplifier Examples	Home or studio, where sound from the headphones does not bother anyone	5 ★★★★★	5 ★★★★★	3 ★★★☆☆	4.3 ★★★★☆
	Office and home, where people should not hear the sound from the headphones	5 ★★★★★	5 ★★★★★	3 ★★★☆☆	4.3 ★★★★☆

In the example below, the conditions for a low power source with an output level of -6.00 dBV, 15 dB(mA) (5.62 mA) under conditions of high ambient noise and the necessary noise insulation will be considered.

Optimum volume level

The combination of headphones and a source is ideal if it is possible to get the optimum volume level for listening to music.

The sensitivity parameters of the headphones and the power of the amplifier are not indicated to the musical signal. It is common that parameters are indicated to the sine. This gives distorted data while we calculate the sound pressure for music by the power of the amplifier and the sensitivity of the headphones.

In RAA we set a comfortable volume level and after determined, with which level it corresponds to the characteristics of headphones and amplifiers. At fixed values of the sound level meter, an average of 85-90 dB SPL resulted in the equivalent of 110 dB SPL, if we summarize the output voltage at the amplifier output with the sensitivity of the headphones.

Analysis of the sensitivity of headphones

The optimal volume level we determined for ideal conditions, when there is no outside noise. In reality, the situation is different and an amendment is made for each specific situation.

If the headphones is with noise cancellation, the level is reduced by 6 dB, and with a partial noise cancellation by 3 dB.

The surrounding situation is estimated by a factor from 0 to 2. Then it is added to the optimal level by multiplying the coefficient by 6 dB.

Optimal = SPL_Optimal + Environment•6 - Noise cancellation

where

SPL_Optimal = Optimal baseline 110 dB SPL
Environment – noise environment factor
Noise cancellation – amendment noise isolation headphones

Having received the value of the optimal level, we make an estimate of the capabilities of the source, based on its power parameters.

We can have two variants of poor compatibility: the source is too quiet or too loud.

For example, for headphones with partial noise insulation (semi-open type) in a noisy subway train environment, the optimal volume level will be:

Optimal = 110 dB SPL + 2•6 дБ – dB = 122 dB SPL

A source is too quiet

A source is too quiet and can not provide the required volume with specific headphones.

Calculate the difference between the source and the optimal level.

Delta = Sensitivity + Amp Voltage - Optimal

where

Sensitivity - Headphone sensitivity of voltage
Amp Voltage – Maximum voltage level in dBV
Optimal – Previously calculated optimum required level

Mark = 5 +[Delta/6]

For example, for headphones with a sensitivity of 113.30 dB/V SPL and a player with a level of -6 dBV will be:

Delta = 113.30 dB/V SPL + -6 dBV - 122 dB SPL = -14.70 dB

Thus, the maximum volume level differs from the desirable by -14.70 дБ.

Mark = 5-[ 14.70/6] = 5-[2.45] =5 -2 = 3

On a five-point scale, the difference by 6 dB decreases by one.

The source is too loud

Многие современные устройства используют цифровую регулировку громкости, и при выставлении малого уровня фоновый шум на выходе не убавляется и становится заметным на фоне воспроизводимой музыки. У устройств с аналоговым регулятором часто наблюдается разбалансировка громкости между правым и левым каналом из-за несовершенства типовых переменных резисторов, управляющий уровнем громкости.

Если полученная ранее Delta является положительной и не более 20 дБ, то оценка 5 по пятибалльной шкале. Свыше 20 дБ оценка уменьшается на единицу на каждые 6 дБ.

Оценка = 5-[(Delta – 20)/6]

К примеру, если бы Delta была равна 30 дБ, то оценка была бы равной 4.

Оценка = 5- [(30-20)/6] = 5- [10/6] = 5-[1.67] = 5-1 = 4

Analysis of the headphones impedance

When analyzing the headphones impedance, we take optimum volume level (Optimal, see above) and estimate the source according to the maximum current, without considering the voltage. If source give enough current or have reserve by current, the mark is 5 on a five-point scale. If the current is not sufficient, the estimate is reduced. In those cases where the current level is insufficient, the sound of the source becomes less quality.

First consider the required voltage level at the source.
dBV = Optimal - Sensitivity

where

Sensitivity - Headphone sensitivity of voltage
Optimal – Previously calculated optimum required level

In our example, this will be: 113.30 dB/V SPL - 122 dB SPL = 8.70 dBV

Convert voltage from dBV to V.

V = 10^8.70dBV/20 = 2.72 V rms (You can use on-line calculator)

Now consider the current
I_Optimal = 1000•V/R

where

R – Resistance of headphones, in our example the resistance is 62.22 Ohm
V - Voltage in volts

I_Optimal =1000* 2.72 В/ 62.22 Ом = 43.77 mA

We compare the current with the maximum for the source in dB. Suppose that we have a low-power smartphone with an output current of not more than 5.62 mA (when working is equivalent to class A)

The ratio of the currents will be:
Delta_I = 20•Log₁₀(I_Sours/I_Optimal) = 20•Log₁₀(5.62 мА/43.77 mA) = -17.82 дБ

By analogy with voltage, we calculate the mark, where a decrease by 6 dB decreases mark by 1 star.

Mark = 5 -[Delta/6] = 5+[-17.82/6] = 5-[-2.97] = 5 - 2 = 3

Mark of noise isolation headphones

The mark of headphones noise isolation depends from external conditions and requirements to noise isolation. For example, for a cyclist on the street among machines, noise insulation is contraindicated. In the subway in a noisy environment, noise insulation is a must.

If the headphones have noise isolation and it is needed, then the mark is 5.
If there is noise isolation and it is not needed or vice versa, there is no noise isolation and it is needed, then a mark is 1.
For headphones with a partial noise isolation mark is 3.

In our example, headphones is semi-open and noise isolation is needed, thus the mark is 3

The final mark is the arithmetic mean of the three marks:
The final mark = (3 + 3 +3)/3 = 3.00

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