To briefly answer the question posed, the answer would be: The reason lies in the unequal output levels on different devices that are used to listen to music with the same headphones.
Content:
Quite a bit of theory
Whether it's a smartphone, a computer or a top-of-the-line cinema, each has an amplifier on its output whose job it is to generate oscillating sound frequency (VF) output voltage.
These voltage fluctuations are what make the dynamic heads emit sound waves. But the average output voltage level is far from the same for different classes of devices.
A smartphone's power amplifier (PA) outputs an average of 200 mV (milliVolts). The headphones connected to the output of the sonic converter have a specific value of active and reactive impedance for the different frequencies of the applied voltage. The average value of the sum of these resistances is called impedance.
For simplicity, and in order not to accidentally go to the calculation of his sonic with perfect parameters, and then do not get bogged down in impedance matching, we will assume that the sum of the internal impedances of the headphones is a constant over the entire frequency range.
In full accordance with Ohm's law, they will sound different on different devices, because they will have different voltages applied to them, while the impedance is considered a constant and unchanging value.
This means that under these conditions, an unequal amount of current will flow through the transducer or the dynamic head, to which the headphones will respond by decreasing or increasing the volume level.
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The problem of choice
Among thousands of models of different types with a unique combination of characteristics it is easy to get confused, but let's leave aside the totality of their advantages and disadvantages, dividing into groups according to only one parameter - resistance.
Its value for the products ranges from 8 to 600 ohms, but for example, let's take the most popular and affordable - channel earbuds with impedance from 16 to 64 ohms, because understanding the main principle, you can navigate the choice of these accessories for any device.
Headphones for your smartphone
Cell phone - a thing compact and the normal adequate solution is to choose earmuffs, which take up less space in comparison with older models. But in the context of the review, it is more correct to start not from their size.
To compare such parameters as volume, power consumption (not the last argument for a gadget with a battery), sensitivity - it is important to know the resistance range of the earmolds, as well as the voltage level at the output of the UHF smartphone. Neither one nor the other group of characteristics is a mystery:
- The average impedance value for the selected group is from 16 to 32 ohms, although models with an impedance of 64 ohms are also produced;
- The average smartphone rarely boasts an output voltage of more than 200 mV.
Specifications for good headphones
Volume and Power
To assess the degree to which impedance affects the quality of listening to music, to begin with, let's calculate the current that will flow in the transducer. Its value determines the loudness of the sound, as well as the power consumption.
Let's take the most common 16 ohm models and see that:
If
I(current)=U(current)/R(resistance)
then for the most ordinary models, at maximum volume mode on the smartphone (200 mV output) the current value will be:
I(A)= 0.2V /16Ohm = 0.0125 A or 12.5 mA
But if you connect a 32 ohm model, the current will flow exactly half as much:
I(A)=0.2V /32Ohm = 0.00625A or 6.25mA
This means that headphones with a higher impedance will be noticeably quieter.
Let's calculate the power:
W(wattage)=I(amperage, A)*U(impedance V)
At an impedance value of 16 ohms, the maximum power consumption will be 2.5 mW, and 32 ohms will be 1.25 mW. For the customer, this means that high impedance headphones will sound quieter, but they will consume battery power more economically. Low-ohm headphones, on the contrary, are much louder, while consuming more current, they reduce the battery life of the smartphone, albeit slightly.
Sensitivity
First of all, it is a characteristic that indicates how the sound pressure level (volume) changes when the input signal changes by a certain amount.
The higher the sensitivity characteristic, the louder the headphones sound. However, too much sensitivity will add the amplifier's own noise and electrical interference of various kinds to the music.
To understand the degree of influence of impedance on sensitivity is a little more difficult - the fact is that not all manufacturers make the consumer aware of the value of sensitivity, and it depends on impedance.
In the best case, the box indicates the sensitivity without any units, but sometimes they indicate dB/mW - in these units, the ratio at all frequencies will be the same.
By changing the volume with the volume control on your phone or amplifier, you do not change the power, but only the output voltage level. To be able to operate with the word "power" at all, you need a consumer.
To confirm these words, set up a mental experiment - turn the sound control to maximum in the amplifier with the speakers connected. Increased power? Perfect.
Now unplug the speaker wires and twist the adjustments - how does the power change? It doesn't.
The resistance of the consumer circuit tends to infinity. No current is flowing. There is no power. So by plugging headphones with different impedances into the output of the UHF, you are guaranteed to get mismatched amplifier power values.
This means that 16 ohm headphones with 97 dB/mW sensitivity, which should deliver 97 dB of sound for every mW spent, and the same 32 ohm accessory with similar sensitivity when connected to the same source will absolutely work with different actual volume level, producing different power.
Thus, 32-ohm headphones sound noticeably quieter, because to provide the same current with different impedance you need to apply different voltage, and it may not be enough at the output of the sonic converter.
How not to make a mistake
Ideally for the selection of headphone impedance for the specific equipment you need to know the maximum voltage level that is possible at the SPL output without distortion. With this information in hand, it is easy enough to calculate current and actual power for headphones with different impedances.
But, if there is no way to do the calculation, you can remember a simple solution:
- Lower impedance headphones will provide more volume at high sensitivity (noise and distortion are possible). An ideal solution for smartphones and players, where the output voltage of the UHF is limited.
- high impedance - will be noticeably quieter at low sensitivity (the noise simply can not affect the sound, their amplitude is too small for this), but require an amplifier with a high level of output voltage - a good solution for stationary equipment.
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Just a little bit of theory
If a brief answer to the question posed, the answer would be: The reason lies in the differences in output levels on different devices, which are used to listen to music with the same headphones.
Whether it's a smartphone, computer or top-of-the-line theater, each has an amplifier on its output whose job it is to generate oscillating sound frequency (VF) output voltages. These voltage fluctuations are what cause the speaker heads to emit sound waves. But the average output voltage level is far from the same for different classes of devices. A smartphone's VF amplifier (VFI) averages 200 mV (milliVolts), while a Hi-End class head unit can operate at units of volts or even more! Headphones, connected to the output of the UHF, have a specific value of active and reactive impedance for different frequencies of the applied voltage. The average value of the sum of these resistances is called impedance.
For simplicity, and in order not to accidentally go to the calculation of his sonic with perfect parameters, and then do not get bogged down in impedance matching, we will assume that the sum of the internal resistance of the headphones is a constant over the entire frequency range. In full accordance with Ohm's law, they will sound different on different devices, because they will have different voltages applied to them, while the impedance is considered a constant and unchanging value. This means that under these conditions, an unequal amount of current will flow through the transducer or the dynamic head and the headphones will respond by increasing or decreasing the volume level.
The problem with selection
Among thousands of models of different types with a unique combination of characteristics, it is easy to get confused, but let's leave aside the totality of their advantages and disadvantages, dividing into groups taking into account only one parameter - resistance. Its value for the products ranges from 8 to 600 ohms, but for example, let's take the most popular and affordable - channel earbuds with impedance from 16 to 64 ohms, because understanding the main principle, you can navigate the choice of these accessories for any device.
Headphones for your smartphone
A cell phone is a compact thing, and it is normal to choose earmolds, which take up less space compared to the older models. But in the context of the review, it is more correct to start not from their size. To compare such parameters as volume, power consumption (not the last argument for a gadget with a battery), sensitivity - it is important to know the resistance range of the earmolds, as well as the voltage level at the output of the smartphone UHF. Neither one nor the other group of characteristics is a mystery:
The average impedance value for the selected group is from 16 to 32 ohms, although models with an impedance of 64 ohms are also produced;
The average smartphone rarely boasts an output voltage of more than 200 mV.
Volume and Power
To assess the degree to which impedance affects the quality of music listening experience, to begin with, let's calculate the current that will flow in the radiator. Its value determines the volume of the sound, as well as the power consumption. Let's take the most common 16 ohm models and see that:
If
I(current) = U(volts)/R(resistance)
then for the most common models, at maximum volume mode on the smartphone (200 mV output) the current value will be:
I(A)= 0.2V /16Ohm = 0.0125 A or 12.5 mA
But if you connect a 32 ohm model, the current will flow exactly half as much:
I(A)=0.2V /32Ohm = 0.00625A or 6.25mA
This means that headphones with a higher impedance will be noticeably quieter.
Let's calculate the power:
W(wattage)=I(amperage, A)*U(impedance V)
At an impedance value of 16 ohms, the maximum power consumption will be 2.5 mW, and 32 ohms will be 1.25 mW. For the customer this means that high impedance headphones will sound quieter, but will consume battery power more economically. Low-impedance ones, on the contrary, are much louder, while consuming more current, they reduce the battery life of the smartphone, albeit slightly.
Sensitivity
First of all, this is a characteristic which indicates how the sound pressure level (loudness) will change when the input signal changes by a certain amount. The higher the sensitivity characteristic, the louder the headphones sound. However, too much sensitivity will add the amplifier's own noise and electrical interference of various kinds to the music.
To understand the degree of influence of impedance on sensitivity is a little more difficult - the fact is that not all manufacturers make the consumer aware of the value of sensitivity, and it depends on impedance. In the best case, the box indicates the sensitivity without any units, but sometimes they indicate dB/mW - in these units the ratio at all frequencies will be the same. It may be easier for the average buyer, but linking sensitivity to power does not help at all in the choice!
By changing the volume on the phone or amplifier, you do not change the power, but only the level of the output voltage. To be able to operate with the word "power" at all, you need a consumer.
To confirm these words, make a mental experiment - turn sound control to maximum in the amplifier with the connected acoustics. More power? Great. Now unplug the speaker wires and twist the controls - how does the power change? It doesn't. The resistance of the consumer circuit tends to infinity. No current is flowing. There is no power. Therefore, when you connect headphones with different impedances to the output of the UHF, you are guaranteed to get mismatched amplifier power values.
This means that 16 ohm headphones with 97 dB/mW sensitivity, which should deliver 97 dB of sound for every mW spent, and the same 32 ohm accessory with the same sensitivity, when connected to the same source will definitely work with different actual volume level, giving different power.
Thus, 32-ohm headphones sound noticeably quieter, because to provide the same current at different impedance you need to apply different voltage, and there may not be enough of it at the output of the SPD.
How not to make a mistake
Ideally for the selection of headphone impedance for the specific equipment you need to know the maximum voltage level that is possible at the SPL output without distortion. With this information in hand, it is easy enough to calculate current and actual power for headphones with different impedances.
But, if there is no way to do the calculation, a simple solution can be memorized:
lower impedance headphones will provide more volume at high sensitivity (noise and distortion are possible). The ideal solution for smartphones and players where the output voltage of the UHF is limited.
High impedance - will be noticeably quieter at low sensitivity (noise simply can not affect the sound, their amplitude is too small for that), but require an amplifier with a high output voltage - a good solution for stationary equipment.
