Analysis with recommendations for Sendy Audio Apollo headphones based on the measured characteristics

 The table shows the most common "typical" audio sources and the field of application of headphones with an amplifier.

The compatibility rating is similar to car analysis by its clearance. When we know clearance we can estimate which type of road will optimally for that car 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.

To assess the compatibility of the sensitivity of the headphones and the power of the headphone amplifier, we assume that the user will listen to music at a comfortable volume level of 90 dB SPL

For final calculations, an additional 9 dB correction is added, because music is usually uneven in volume and louder short sections are often found, but we still perceive the overall volume as averaged. Thus, the final reference sound pressure is 99 dB SPL, perceived as 90 dB SPL.

Additionally, it is taken into account that sometimes the user may want to listen to music louder or, conversely, quiet recordings with a wide dynamic range (this gives an addition to the volume in calculations of 24 dB) and an estimated sound pressure of 123 dB SPL.

Depending on the external conditions, this volume varies, and we evaluate in which conditions the source will play in high-quality mode, and in which there will be a lack of volume, unnecessary distortion or other negative factors.

Detailed description formula of the table of headphones

In a professional way, the assessment of the compliance of the sensitivity of headphones to the characteristics of the amplifier is done through the comparison service voltage and sensitivity or the simpler service sound pressure in a bundle.

Thus, in order to assess the compatibility of audio sources with Sendy Audio Apollo in voltage and current, a calculation is made for the possibility of providing a maximum sound pressure level of 123 dB SPL for a quiet environment and 135 dB SPL for noisy, with subjective listening to music in conditionally ideal conditions of 90 dB SPL.

If we consider not a general case, but an individual one, where each listener has his own music and his own environment, then you can determine your reference level independently and already evaluate everything for him. You can set your own reference level in all relevant RAA tools.

Depending on the sensitivity of the headphones, a certain voltage is required from the amplifier to get the desired final volume.

At the same time, if the source is too "powerful", then there is a high probability of constantly hearing background noise, and if weak, then there will be insufficient volume. In relation to the concept of volume, it is customary to use the word "power", but in fact only voltage is responsible for the volume level. The rating in the form of stars depends on two conditions, the maximum and minimum voltage that the amplifier gives.

Since we perceive the difference in volume not linearly, but in multiples, not only the final sound pressure is expressed in dB SPL instead of Pa (Pascal), but similarly the voltage instead of V_RMS is expressed in dBV. A 6 dB change is a multiple of the voltage doubling. A person can subjectively distinguish a difference in volume of 1 dB.

In a quiet environment, to obtain a subjective 123 dB SPL with a voltage sensitivity of 100.206 dB/V SPL from an amplifier, a voltage of 22.79 dBV is required. For a noisy environment 34.79 dBV. These are the minimum voltages that the amplifier should provide in high-quality mode.

The list of suitable amplifiers according to the calculated data for 22.79 dBV can be viewed on the comparison page of the parameters of the amplifiers measured in RAA according to the parameters: the minimum voltage of 22.79 dBV for the impedance of the connected headphones is 17 ohms.

But an amplifier with excessive volume is undesirable, otherwise, with a small signal-to-noise ratio at the desired comfortable volume level, background noise will be heard during pauses, or it will be difficult to adjust the volume with the effect of channel imbalance. For each amplifier tested in RAA, a parameter such as the optimal volume control range is assigned. According to this condition, the amplifier will receive the maximum rating if its maximum level, minus the optimal volume control range, is lower than the calculated optimal sound pressure.

For example, for an amplifier with an optimal adjustment range of 50 dB for a sound pressure of 99 dB SPL in a quiet environment, its maximum voltage should not be higher than 48.79 dBV.

The list of suitable amplifiers according to the initial parameters can be viewed on the comparison page of the parameters of the amplifiers measured in RAA according to the parameters: gain quality class "No Current Limit", maximum voltage 48.79 dBV for the impedance of the connected headphones 17 Ohms.

The average impedance of Sendy Audio Apollo headphones is 17.40 ohms.

The impedance affects the amount of current that the amplifier should give to the headphones. If there is not enough current, then the sound quality will deteriorate, starting with sharpness in the sound and ending with a banal wheeze. In most cases, at low current values, the amplifiers operate in a linear mode comparable to Class A quality, and with an increase in current output, the quality decreases towards the nonlinear mode and the clipping zone.

Imagine that you have a tank that is gradually filling with water. The voltage at the amplifier is the pressure with which the pump pumps water out of the tank. If the water inflow in the tank is lower than the volume that the pump pumps out, then at the pump outlet we get "bubbles" along with the water. Similarly, with the sound from the headphones, which did not have enough current from the amplifier.

For the example above, to obtain a maximum sound pressure of 123 dB SPL for a quiet environment, an amplifier with an output current level of at least 3792.93 57.98 dB(mA) is desirable for the Apollo.

For a loud environment, a sound pressure of 135 dB SPL will require 3156.70 mA / 69.98 dB(mA).

Five stars in the recommendation table are given to those amplifiers that have a sufficient margin in terms of output current.

For an unbalanced connection, the amount of headphone impedance affects the antiphase mixing of channels.