What is the ohm resistance in headphones? What does headphone impedance mean and how does it affect sound02/08/2015. Dynamic In-Ear Headphones

2014-02-16T01:32

2014-02-16T01:32

Audiophile's Software

Prologue

Headphones typically have impedances ranging from 16 to 600 ohms (and some higher). So what is the best headphone impedance value? The answer largely depends on where you are going to connect them.

Which is better?

Are low impedance headphones better than higher impedance ones? What is the optimal impedance value? Here are some important recommendations (albeit in a somewhat simplified form):

• If you are looking for headphones for use with a portable player or laptop, you should give preference to headphones with an impedance of 16 - 32 Ohms and a sensitivity of at least 100 dB/mW. There are also higher impedance headphones, up to 80 ohms, that are sensitive enough to work with some portable devices, especially if you don't need too much volume. But in fact, the lower the impedance, the better the compatibility with battery-powered devices.
• If you do not know the output impedance of the source device, it is better to refrain from using armature headphones, as they can interact in undesirable ways with high output impedance, resulting in downright bad sound.
• If your source meets European maximum volume regulations (many modern phones do, even those sold outside Europe), it is all the more important to choose headphones with an impedance of 16 ohms and a sensitivity of 100 dB/mW or more. European compliant devices have a lower output level than most other portable devices.
• If you're using a dedicated headphone amplifier or DAC, check its specifications or instructions for the recommended headphone impedance range.
• If you are looking towards headphones with a sensitivity of less than 100 dB/mW, read at least the first five paragraphs of this article.

Different headphone impedance

Impedance of almost all non-professional acoustic speakers lies in the range of 4 - 8 ohms. This simplifies the work of developers of amplifiers, receivers, etc., because they know almost exactly what the load impedance will be. But with headphones things are a little different. There are several standards, so impedance varies widely depending on the developer, and also depending on the devices for which these headphones are designed: portable devices, consumer, studio/professional equipment. Range - from 16 to 600 (40 times more) Ohm. This causes a significant number of compatibility issues.

Why impedance is important

Sources intended for headphones, for the most part, provide absolutely different meanings power with different headphone impedances. For example, portable player The Clip+ can deliver 16 mW into 16 ohms and only 0.8 mW into 300 ohms. The FiiO E7 can output more than 100 mW into 16 ohms, but only 2.8 mW into 600. Some sources - for example, Mini3, FiiO E9 - are not compatible with low-impedance loads at all.

Sufficient volume

Most sources provide at least 5 mW of power into 16 ohms. For headphones with a sensitivity of 100 dB/mW (the recommended minimum for a portable), this will give 107 dBSPL (sound pressure), which is in the range of 105 dBSPL - 115 dBSPL, which is a sufficient volume level for most people. See More Power.

What impedance is considered high?

I haven't heard of any hard limits, but in most cases 100 ohms and above is defined as "high impedance". These headphones are most often not intended for portable use. Also, 32 Ohms and below can be confidently called “low impedance”; such values ​​are suitable for use anywhere. This leaves an undefined region between 32 and 100 ohms, in which other factors determine the suitability of headphones for certain purposes.

In-ear headphones with balanced armature

Many high-end in-ear monitors use balanced armature technology. Examples include in-ear models from Shure, Etymotic, Ultimate Ears, etc. These headphones typically have an impedance between 16 and 32 ohms, but their actual impedance varies greatly with frequency. The 21-ohm Ultimate Ears SuperFi 5, for example, varies its impedance from 10 to 90 ohms. Such impedance deviations often result in undesirable interactions with the source output impedance.

Why does headphone impedance vary so much?

There are many reasons for this:

• Historical preferences- Before the advent of the first good-sounding portable devices, most high-quality headphones were connected to either a home stereo system or professional studio equipment. For reasons of simplicity and cheapness in the 60s - 80s, such devices had a high output impedance. They simply used large resistances to create a voltage drop from the outputs to the speakers (so headphones could be connected to these outputs).
• Outdated standard from 1996- In 1996, a standard for headphone output was introduced - 120 Ohms - obviously more than would be convenient for developers of the corresponding equipment. Subsequently, Stereophile expressed his opinion about this standard: “Whoever came up with this is clearly living in a dream world.”. Low output impedance offers many benefits, but the ill-conceived standard still continues to influence the design of high-impedance headphones.
• High impedance is welcome for high-end headphones- In this case, there may be several compelling arguments in favor of high impedance headphones. High impedance allows more turns to be used in the speaker's voice coil. This can improve the efficiency of the moving system and reduce the number of compromises required, improving the overall sound experience. Also, high-impedance headphones require less current to drive, which often leads to a reduction in various types of distortion. High impedance makes the sound of headphones less dependent on the output impedance of sources, including less sensitive to the length of a three-wire cable and the quality of the connector (jack, mini-jack, etc.). Amplifiers almost always produce less distortion on higher impedance headphones.
• The iPod Revolution Drives Impedance Reduction- As of 2009, more than 200 million iPods had been sold. Before the iPod, there were other portable devices. You could even say that taking into account music mobile phones we have more than one billion portable devices in use. This is important because battery-powered devices cannot work properly with high-impedance headphones. Thus, the development of suitable low-impedance headphones was accelerated. But this goes against the first three points; So we have the high-end advantages and relics of the past against the huge marketing potential of a billion portable devices.

What headphones can I use for my device?

This main question which most people ask. To answer this, you need to decide on three things:

• Power Requirements- Does the source have enough power to drive this pair of headphones to a sufficient volume level? The 100 dB/mW recommendations mentioned above will most likely help answer this question. In case the headphones have lower sensitivity (or it is not specified), see the article More Power.
• Device output impedance- Finding it out is problematic, since the output impedance of most devices is unknown. But the idea is to follow the 1/8 rule described in the article on output impedance. If you multiply the source impedance by eight, you will get the minimum load impedance that is recommended to be used with this device. The FiiO E9 amplifier, for example, has an output impedance of 10 ohms. Thus, if you want to be sure of maximum quality, it should be used with headphones with an impedance of 80 ohms or higher.
• Source Distortions- Some sources have problems with low-impedance loads. Tube amplifiers without output transformers, for example, produce significantly more distortion with low-impedance headphones.

Is it possible to damage something by mistake?

Use of inappropriate of this device headphones will usually not harm anything other than the sound. However, some sources are capable of producing very large output values ​​and therefore can actually damage highly sensitive headphones. But this will only happen if you increase the volume level far beyond reasonable limits, i.e., most likely this can only happen by accident. Some headphone amplifiers have a gain switch to prevent this from happening.

When do you need a headphone amplifier or DAC?

Finally

TECHNICAL PART

Voltage and current

To understand what impedance is, it is important to have at least general idea about voltage and current. Voltage is analogous to water pressure, while current is analogous to water flow (eg gallons/minute). If you run water from your garden hose without a nozzle, you will get a large flow of water and will be able to quickly fill a bucket with it, but the pressure at the end of the hose will be almost zero. If you use a small nozzle, the pressure (voltage) will be much greater, but the flow of water will be reduced (it will take longer to fill the same bucket). These two quantities are inversely related. High pressure usually corresponds to low flow, and vice versa. The same is true for voltage/current.

Hose attachments

Roughly speaking, impedance is similar to the size of a hose nozzle. High impedance headphones are like a narrow ear tip. To get more water, higher pressure (voltage) is needed. Low-impedance headphones are more likely to correspond to the case of filling a bucket without a nozzle, requiring more flow and not too high pressure. Most headphone outputs are good or for the first one, or for the second case, but not for both. That's why it's important to know what you're dealing with and choose your headphones accordingly.

Load impedance (headphones)

Headphone impedance describes the resistance of headphones as a function of frequency. Unlike a resistor, headphones can have a different impedance curve.

Headphone impedance and sensitivity

Impedance indirectly affects the sensitivity of the headphones (to voltage); the lower the resistance of the headphones, the more often the sensitivity (to voltage) is higher for headphones of a given form factor (based on the diameter of the speaker membrane). High impedance headphones tend to have lower sensitivity.

The dependence of voltage sensitivity is determined by the level of current flowing through the inductor; the lower the resistance, the higher the current. When focusing on “loudness” from a freely selected source, you should pay attention to higher sensitivity to voltage and lower resistance.

When expressing power sensitivity, resistance does not have any effect on the numerical value of sensitivity, and the value of power sensitivity between different headphones mainly demonstrates the overall efficiency of the system (the effect of the mass of the cone, the power of the magnetic system, etc.)

Low impedance headphones and portable sources

Low impedance headphones typically require high levels of current from the amplifier at low voltage, while high impedance headphones require high voltage at low current levels, which breaks some stereotypes that the lower the headphone impedance, the better for portable devices. In fact, low-impedance headphones tend to play louder, but on the contrary, they drain the device’s battery much faster due to increased current consumption. The second unpleasant feature for low-impedance headphones and high current consumption is a heavier mode for the amplifier, which, with a large current output, amplifies the signal with a high level of distortion.

Thus, if a portable source has a low output voltage, then high-impedance headphones will play quietly, but if the output voltage of the source is about 1 V or higher, then it is wiser to use headphones of 32 ohms and higher, this will give more quality and the device’s battery will be discharged slower.

If the resistance of the headphones is low, then when choosing an amplifier you need to pay attention to whether the amplifier is designed to work directly with a low-impedance load. Phones and inexpensive players usually operate with minimal distortion with loads of 100 ohms and above and do not have a high maximum output voltage, which is why low-impedance headphones sound distorted and high-impedance headphones are not loud enough.

Low-impedance headphones are usually the most highly sensitive and this sometimes leads to the problem of “background noise”, when all the source noise is clearly audible during pauses. When using an amplifier with a high signal level in its nominal operating mode, headphones with a higher impedance will be more successful.

Dependence of headphone frequency response on impedance

The higher the resistance of the headphones and the lower the total output impedance of the amplifier, the less the frequency response of the headphones will change. It is also true that the smaller the range of changes in the impedance curve over resistance, the smaller the changes in frequency response will also be.

In other words, if the amplifier has zero resistance and the headphones are high-impedance, then the frequency response will remain unchanged. If the amplifier impedance is high and the headphone impedance is low, the frequency response will change close to the proportions of the headphone impedance curve. If the headphone impedance and output impedance are straight lines, then the frequency response will not change.

Typical headphone impedance curves and their interaction with an amplifier

Recall that there are three types of typical amplifier impedance curves:

The interaction of specific headphones with amplifier types is shown in headphone reports

Dynamic In-Ear Headphones

As a rule, such headphones have a straight impedance curve and the frequency response of such headphones changes only when connected to amplifiers with zero resistance in the mid and high frequencies and increased in the area low frequencies. When connected to amplifiers with a constant output impedance or zero, the frequency response does not change. Common resistance values ​​are 16 and 32 Ohms.

Examples

Single-driver in-ear headphones

This type of headphone has a relatively flat impedance curve in the low-frequency region and has two rises, local in the region of 1-2 kHz and a gradual rise in the high-frequency region. Thanks to these boosts, many single-driver armature headphones sound comfortable in the upper midrange and high frequencies. Only when connected to an amplifier with zero resistance, the frequency response does not change; for the two remaining types (constant non-zero resistance and zero resistance in the mid and high frequencies and with an increase in the low frequencies), the frequency response changes in proportion to the impedance curves.

Examples

Multi-driver in-ear headphones

For this type of headphones, the headphone impedance curve can be anything, therefore, only when connected to an amplifier with zero resistance, the frequency response does not change, for the two remaining types (constant non-zero resistance and zero resistance in the mid and high frequencies and with an increase in the low frequencies ) – The frequency response changes in proportion to the impedance curves. This type of headphone is one of the most capricious and least predictable for matching with an amplifier if there is no measurement data.

Examples

Dynamic over-ear headphones

In most cases, the impedance curve has a local rise at low frequencies and a rise at the highest frequencies. When connected to an amplifier with zero resistance, the frequency response does not change; for the two remaining types (constant non-zero resistance and zero resistance in the mid and high frequencies and with an increase in the low frequencies), the frequency response changes in proportion to the impedance curves.

Examples

• You can often come across the statement that if the resistance of the headphones and the amplifier is equal, the best combination will be obtained, because in this case, the amplifier will be able to deliver the highest power level. From a mathematical point of view, in some cases this will be the case, but in practice this is nothing more than a myth, because:
  

  • very often in amplifiers with a resistance less than 100 Ohms there is a current limit for a load below 100 Ohms and, accordingly, with equal resistance there may not be a maximum power
  • sound quality has nothing to do with the same impedance of headphones and amplifier
  • lower amplifier impedance provides potentially greater damping
  • lower amplifier resistance has less effect on the final frequency response
  • higher resistance provides potentially lower distortion, due to less dependence on the temperature of the headphone inductor (the main advantage of current amplifiers)

  How is impedance measured?

  To measure impedance, a signal is supplied by a chain of one headphone channel and an additional resistor, where the signal level is assessed at two points in the circuit. Based on the difference in signal amplitudes with a known resistor resistance, the resistance of the headphones at a given frequency is determined.

  
  

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  With the rapid development of information and communication technologies More and more often you can see a person with headphones in the subway, on the street, at home. If initially they were used for radio communications, then later the audio device became a mass means of information consumption. To choose the most suitable headset for your smartphone or tablet, the user needs to understand the basic characteristics of the device. Before we look at what and how resistance in headphones affects, let’s understand what impedance is. Knowing this information, you can extend the service life of equipment.

  The impedance in the headphones gives input resistance. The operational and technical properties of portable devices for listening to sound depend on this characteristic. To find out how much energy the equipment requires to ensure good sound, this parameter is indicated in the passport of portable devices.

  The unit of measurement of electrical resistance of a conductive element is Ohm.

  For pocket audio players and modern smartphones, headphones with a nominal impedance of 16-40 Ohms are suitable. This value ensures high sound of the device at a low level of outgoing signals. When connected to a headset with standard sound cards using special amplifiers choose an audio device with high impedance parameters - 120-150 Ohms. Devices with high resistance electrical resistance suitable for professionals who work on special equipment with a high level of outgoing voltage.

  Types of equipment depending on resistance values

  In the multimedia equipment market, manufacturers offer a wide range of different devices with different technical characteristics: sensitivity, impedance, frequency range. Based on the resistance the headphones provide, two types of equipment are distinguished: high-impedance and low-impedance devices. For full-size and in-ear headsets, the separation boundary parameters are different.

  1. Low impedance headset– devices whose impedance for in-channel devices is no more than 32 Ohms, for full-size devices – no more than 100 Ohms.
  2. High resistance devices– impedance of which for in-channel devices is more than 32 Ohms. For full-size, the value should be more than 100 ohms.

  Impedance curve for different types of devices

  Let's consider what information a graph of frequency in the range from 20 to 20,000 Hz versus resistance provides for various types of devices.

  
  

  Based on the impedance curves, it is clear that the declared value in the headset is different from the real values.

  Optimal impedance values ​​for use with various devices

  To purchase devices with a good range of sound reproduction, it is necessary to take into account the impedance values. The sensitivity of devices with high resistance is less than that of low-resistance models. Therefore time battery life technical devices does not match when using headphones with different impedances.

  1. Let's consider the optimal values ​​of the level of consumed electrical voltage for various devices. Smartphone. The nominal impedance for better sounding headphones is low impedance (for example, 22 Ohms). In this case, the devices, in addition to, will consume more current. So that you can play music on your smartphone longer, choose a 32-ohm model. When using devices with iPhone, models with standard frequency audio ranges of 22-32 Ohms are suitable. Headphone monitors are not advisable to use without auxiliary accessories: a portable amplifier, an audio player with a powerful sound card.
  2. Player. The most optimal headphone impedance for a standard device is 16 Ohms. If audio players have a more powerful output (Hidisz or iHiFi), which provides an electrical voltage level of more than 200 mV, choose less sensitive devices with an impedance of 32 Ohms. Such devices reduce current consumption and increase battery life.

  

  When choosing listening equipment, consider the following points:

  • in reality, single-driver reinforcement devices (Grado GR10, various Klipsh, Etymotic models) have a higher average resistance, so audio players and smartphones work with them long time without recharging;
  • Multi-driver dynamic and reinforcement technology has a lower average resistance, so smartphones or players operate for a short time without recharging.

  Portable amplifier for optimal sound

  High-impedance headphones are used not only by professional musicians, but also by ordinary music lovers. In order to listen to music at a sufficient volume, you need to match the power of the speakers to the device. In this case, absolutely all frequencies are reproduced, and the sound is of high quality. Helps solve this problem portable amplifier

  for headphones - it provides high fidelity sound reproduction. The operating principle of the amplifier is as follows: due to the high impedance value in the headphones, the device delivers less current, which prevents frequency distortion

  separate cascades. The high-impedance headset has uniform amplitude and frequency characteristics due to the use of an amplifier.

  To avoid deterioration in the quality of headphones and their rapid wear, when purchasing equipment, pay attention to the impedance. Which one is better depends on the devices they will interact with. This parameter must correspond to the audio equipment model and listening device. The resistance of different types of headphones affects the sound quality and ensures stable operation of the audio device.

  

  Just a little theory audio frequency(ZCH).

  These voltage fluctuations cause the dynamic heads to emit sound waves. But the average output voltage level is far from the same for different classes of devices.

  The AF amplifier (AF) of a smartphone produces an average of 200 mV (milliVolt). Headphones connected to the ultrasonic frequency output have a specific value of active and reactive resistance for different frequencies of the applied voltage. The average value of the sums of these resistances is called impedance.

  For simplicity, and so as not to accidentally proceed to calculating your ultrasonic frequency with ideal parameters, and then not get bogged down in impedance matching, we will assume that the sum of the internal resistances of the headphones is a constant over the entire frequency range.

  In full accordance with Ohm's law, different devices they will sound differently, because different voltage values ​​will be applied to them, and we consider impedance to be a constant and unchanging value.

  This means that under such conditions, an unequal amount of current will flow through the driver or dynamic head, to which the headphones will respond by decreasing or increasing the volume level.

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  What is the sensitivity of headphones and which one is better?

  Problem of choice

  Among thousands of models different types It’s easy to get confused with a unique combination of characteristics, but let’s leave aside the totality of their advantages and disadvantages, dividing them into groups taking into account only one parameter - resistance.

  Its value for products ranges from 8 to 600 Ohms, but for example, let’s take the most popular and affordable ones - channel in-ear headphones with an impedance from 16 to 64 Ohms, because once you understand the main principle, you will be able to navigate the choice of these accessories for any device.

  Headphones for smartphone

  

  A mobile phone is a compact thing and the normal adequate solution is to choose earbuds that take up less space compared to older models. But in the context of the review, it is more correct to start not from their size.

  To compare parameters such as volume, power consumption (not the last argument for a gadget with a battery), sensitivity, it is important to know the range of resistance values ​​of the earbuds, as well as the voltage level at the output of the smartphone’s ultrasonic filter. Neither one nor the other group of characteristics is a secret:

  Technical characteristics of good headphones
  

  Volume and power

  

  To assess the degree of influence of impedance on the quality of the experience of listening to music, first, let’s calculate the current that will flow in the emitter. The volume of the sound, as well as the power consumption, depends on its value.

  Let's take the most common 16 Ohm models and see that:

  We calculate the power:

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  Sensitivity

  

  First of all, this characteristic indicates how the sound pressure level (volume) 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 natures to the music.

  Understanding the degree of influence of resistance on sensitivity is a little more difficult - the fact is that not all manufacturers inform the consumer about the value of sensitivity, and it depends on impedance.

  In the best case, the sensitivity is indicated on the box without any units of measurement at all, but sometimes dB/mW is indicated - in these units the ratio at all frequencies will be the same.

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  To confirm these words, perform a thought experiment - turn the volume control to maximum in an amplifier with connected acoustics. Has the power increased? Great.

  Now disconnect the speaker wires and turn the controls - how does the power change? No way.

  The resistance of the consumer circuit tends to infinity. No current flows. No power. Therefore, by connecting headphones with different impedances to the ultrasonic output, you are guaranteed to get divergent amplifier power values.

  How not to make a mistake

  

  But, if it is not possible to make a calculation, then you can remember a simple solution:

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  Just a little theory
  To answer the question briefly, the answer would be: The reason lies in the different output signal levels on different devices that are used to listen to music with the same headphones.

  A smartphone, a computer or a top-end cinema - each of them has an amplifier at the output, the task of which is to generate fluctuations in the audio frequency (AF) output voltage. These voltage fluctuations cause the dynamic heads to emit sound waves. But the average output voltage level is far from the same for different classes of devices. The AF amplifier of a smartphone produces an average of 200 mV (milliVolts), and the Hi-End class head unit can operate at units of Volts and even more! Headphones connected to the ultrasonic frequency output have a specific value of active and reactive resistance for different frequencies of the applied voltage. The average value of the sums of these resistances is called impedance.

  For simplicity, and so as not to accidentally proceed to calculating your ultrasonic frequency with ideal parameters, and then not get bogged down in impedance matching, we will assume that the sum of the internal resistances of the headphones is a constant over the entire frequency range. In full accordance with Ohm's law, they will sound differently on different devices, because different voltage values ​​will be applied to them, and we consider impedance to be a constant and unchanging value. This means that under such conditions, an unequal amount of current will flow through the driver or dynamic head, to which the headphones will respond by decreasing or increasing the volume level.
  Problem of choice
  Among thousands of models of different types with a unique combination of characteristics, it’s easy to get confused, but let’s leave aside the totality of their advantages and disadvantages, dividing them into groups taking into account only one parameter - resistance. Its value for products ranges from 8 to 600 Ohms, but for example, let’s take the most popular and affordable ones - channel in-ear headphones with an impedance from 16 to 64 Ohms, because once you understand the main principle, you will be able to navigate the choice of these accessories for any device.
  Headphones for smartphone
  A mobile phone is a compact thing and the normal adequate solution is to choose earbuds that take up less space compared to older models. But in the context of the review, it is more correct to start not from their size. To compare parameters such as volume, power consumption (not the last argument for a gadget with a battery), sensitivity, it is important to know the range of resistance values ​​of the earbuds, as well as the voltage level at the output of the smartphone’s ultrasonic filter. Neither one nor the other group of characteristics is a secret:
  The average impedance value for the selected group is from 16 to 32 Ohms, although models with a resistance of 64 Ohms are also produced;
  An ordinary smartphone rarely boasts an output voltage of more than 200 mV.

  Volume and power
  To assess the degree of influence of impedance on the quality of the experience of listening to music, first, let’s calculate the current that will flow in the emitter. The volume of the sound, as well as the power consumption, depends on its value. Let's take the most common 16 Ohm models and see that:
  If
  I(current)= U(voltage)/R(resistance)
  then for the most common models, at maximum volume on the smartphone (output 200 mV), 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, then the current will flow exactly half as much:

  I(A)= 0.2V/32Ohm = 0.00625 A or 6.25 mA

  This means that higher impedance headphones will be noticeably quieter.
  We calculate the power:
  W(power W)=I(current, A)*U(ex. V)

  With an impedance value of 16 Ohms, the maximum consumption will be 2.5 mW, and 32 Ohms - 1.25 mW. For the buyer, this means that high-impedance headphones will sound quieter, but use battery power more economically. Low-impedance ones, on the contrary, are much louder, while consuming more current; although not by much, they reduce the battery life of the smartphone.
  Sensitivity
  First of all, this characteristic indicates how the sound pressure level (volume) 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 natures to the music.

  Understanding the degree of influence of resistance on sensitivity is a little more difficult - the fact is that not all manufacturers inform the consumer about the value of sensitivity, and it depends on impedance. In the best case, the sensitivity is indicated on the box without any units of measurement at all, but sometimes dB/mW is indicated - in these units the ratio at all frequencies will be the same. Perhaps this is easier for the average buyer, but linking sensitivity to power will not help in the choice at all!

  By changing the volume using controls on your phone or amplifier, you do not change the power, but only the output voltage level. To be able to use the word “power” at all, you need a consumer.

  To confirm these words, perform a thought experiment - turn the volume control to maximum in an amplifier with connected acoustics. Has the power increased? Great. Now disconnect the speaker wires and turn the controls - how does the power change? No way. The resistance of the consumer circuit tends to infinity. No current flows. No power. Therefore, by connecting headphones with different impedances to the ultrasonic output, you are guaranteed to get divergent amplifier power values.
  This suggests that 16-Ohm headphones with a sensitivity of 97 dB/mW, which are required to produce 97 dB of sound for each mW spent, and the same 32-Ohm accessory with a similar sensitivity, when connected to the same source, will definitely work with different actual volume level, producing different power.

  Thus, 32-Ohm headphones sound noticeably quieter, because to provide the same current at different resistances, you need to apply different voltages, and it may not be enough at the ultrasonic output.
  How not to make a mistake
  Ideally, to select headphone impedance for a specific technique, you need to know maximum level voltage, which is possible at the output of the ultrasonic sounder without distortion. With this information in hand, it is fairly easy to calculate current values ​​and actual power for headphones with different impedances.
  But, if it is not possible to make a calculation, then you can remember a simple solution:
  lower impedance headphones will provide higher volume levels at higher sensitivity (noise and distortion are possible). An ideal solution for smartphones and players where the output voltage of the ultrasonic amplifier is limited.
  high-impedance - will be noticeably quieter at low sensitivity (interference simply cannot affect the sound, their amplitude is too small for this), but require an amplifier with a high output voltage level - good decision for stationary equipment.

  After the interview greatest number The issues were related to the characteristics of the headphone impedance. Let's consider what the characteristic affects and what it is eaten with. To better assimilate the material, we will consistently release materials, collect questions and comments, and move on.
  
  Before we figure out what and how the resistance of the headphones affects, let’s figure out what kind of overseas bird this is. And we are preparing for the fact that there will be as many as two formulas from a standard school physics course. Those. the material is complex and heavy.

  Resistance headphones are often called impedance or headphone impedance.

  From the point of view of terms, where resistance means only the active (resistive) part, impedance (impedance) means the combination of active and reactive resistance. Remembering the school physics course, we know that reactance includes capacitance and inductance.

  The final impedance of the headphones depends on the frequency at which the impedance is measured. On boxes, only the active resistance or occasionally the value obtained at a frequency of 1 kHz is often given. Unfortunately, the accompanying parameters are rarely indicated and one can only guess what the actual impedance value of the headphones is.

  
  

  If we are talking about dynamic headphones, then the values ​​​​are in the form of 16, 24, 32 Ohms, etc. mean only the resistance of the speaker inductor and do not take into account the resistance of the wire, soldered contacts and plug. In reality, headphone impedance is usually 1-3 ohms higher and varies slightly between the right and left channels. The most conscientious manufacturers honestly indicate that the accuracy of the indicated resistance is 20 or 30% and this is normal (only the marketer vigorously objects to this; no errors can be shown on the box - “truth” kills sales).

  Low and high impedance headphones

  Headphones are usually divided into low-impedance and high-impedance. For in-ear and full-size headphones the boundary of separation is different.

  For full-size ones: low-impedance headphones have an impedance of less than 100 ohms, and high-impedance ones have a resistance above 100 ohms.

  For in-channel: low-impedance not higher than 32 Ohms, higher than 32 Ohms – high-impedance.

  What type of impedance do different headphones have?

  In-ear headphones

  
  
  
  

  Majority in-ear dynamic headphones have a flat impedance curve and values ​​of 16, 24 or 32 ohms have no deviations for frequencies from 20 to 20 kHz.

  The graph shows frequencies horizontally, from 20 Hz to 20 kHz. Vertical - resistance (on a logarithmic scale).

  Over-ear dynamic headphones

  
  
  
  

  U full-size dynamic headphones It is quite common to find an uneven impedance curve, with local rises in the low-frequency region and a slight rise in the high-frequency region.

  The resistance can be equal to 32 Ohms without taking into account the reactive part (conventionally, this is 0 Hz, measured by any universal multimeter), but in practice it can be twice as high at certain frequencies.

  Unevenness (rises) can indicate both resonances and design features of the emitter in a given headphone housing. So, when measuring resistance, the frequency and magnitude of the rise can vary greatly depending on whether the headphones are lying freely on the table or are put on a mannequin (in this case, the internal space of the headphones is damped).

  
  
  
  

  Some dynamic headphones have no noticeable resonances or deviations. This line is conventionally ideal, but selecting headphones this way is not recommended. In pursuit of improving one characteristic, you have to sacrifice another.
  Among top-class headphones you can find impedance curves with both minimal deviations and significant ones. If the headphones show a narrow-band boost (in the graph above this is the Grado GS1000), then the amplifier should be selected with a low output impedance for better control low frequencies (as, by the way, it was done with the proprietary Grado RA1 amplifier).

  Isodynamic (orthodynamic) headphones

  
  
  
  

  In addition to dynamic emitters, isodynamic emitter type(and its similar type - orthodynamic). These headphones always have a straight impedance line. Isodynamic headphones are now produced by: Abyss, Audez"e, HiFiMan, Oppo, Fostex. In Soviet times there were TDS-5/m, TDS-7, TDS-15, TDS-16 and TDS-25 headphones. Today for TDS-7 models and TDS-15 are most often modded.

  Formally, this is an ideal load for an amplifier, but in the ultra-high frequency range (megahertz and gigahertz), the resistance of some models decreases and approaches zero. Such insidiousness cannot be seen on a standard chart, and with some amplifiers this can lead to poor-quality operation.

  In-ear reinforcement headphones

  
  
  
  

  The impedance looks hardly predictable in-ear headphones with reinforced radiator. Single-driver models have a common feature - there is always a local rise in the upper midrange (around 1-3 kHz) and in the highest frequencies. Thanks to the high-frequency boost, most single-driver armature models “sound clean” in the high-frequency region, because in this frequency range the amplifier produces less distortion.

  In the low-frequency region, the typical resistance is 8, 16, 24 or 32 ohms. Above 500 Hz rises begin.
  If a resistance of 100 Ohms at 1 kHz is indicated, this does not mean that the headphones are high-impedance; their resistance may be only 16 Ohms according to the readings of the multimeter (in the low frequency region).

  Hybrid and multi-driver headphones

  
  
  
  

  It is impossible to predict the impedance curve for multi-driver And hybrid in-ear headphones. The impedance curve can be anything above 500 Hz. The resistance drop can easily reach 4 ohms with the stated 100 ohms at 1 kHz.

  General conclusions

  • Resistance in reality it will be like on the box, if headphones: In-channel dynamic or isodynamic
  • Resistance in reality will be like on a box and have unknown lifts, if headphones: Dynamic invoices and p full-size
  • Resistance in reality It will NOT be like on the box, if headphones: reinforcing or hybrid

  Why actually know all this? Sometimes manufacturers of amplifiers and players indicate what headphone impedance will be compatible and it is useful to rely on this information.

  If you need to find out the real resistance of reinforcing or hybrid headphones, then you can try searching for measurement results on the Internet. Methods for measuring impedance usually give a single result and do not depend on the software with the stand or the measuring complex.

  What does headphone impedance affect?

  Headphone sensitivity

  The sensitivity of headphones is usually reduced to power, which takes into account two characteristics at once: the voltage and current supplied to the headphones. This is a convenient final characteristic for theorists and extremely confusing for practical application by end users.
  For the average consumer, it is logical to think of “sensitivity = volume.” This works with speakers, because... the value is always indicated by the speaker resistance in the form of 4 or 8 ohms, and the power of the amplifier is indicated similarly. It's hard to get confused.

  But if for speakers there are only two standard resistances of 4 and 8 Ohms and each amplifier has power for two types of resistance, then headphones have about 11 resistances: 8,16,24,32,64,128,256,320, 608, etc.

  As a result, the consumer picks up headphones with different impedances and naively believes that he can compare something in terms of sensitivity.

  For the sensitivity = loudness relationship to apply to headphones, sensitivity must be expressed in terms of voltage rather than power (as Sennheiser does). But most manufacturers don't indicate at all, in what units the sensitivity is given.

  This is why “everyone knows” - that high-impedance headphones are quiet, and low-impedance headphones are loud. And they naively believe that for high-impedance headphones you need “ powerful amplifier", and for low-impedance headphones, a lousy smartphone is enough. And although in reality everything is completely different, due to extremely unfortunate terms from the GOST and AES standards, separate “concepts” were formed that contradict the laws of physics, but in common language quite accurately describe the result, like: “High-impedance headphones need a powerful amplifier.” Physically illiterate, but “everything is clear to everyone.”

  Let's touch on this topic deeper (be careful, we're moving on to formulas from school, we're starting to strain our brains!)

  At the output of the amplifier, we do not directly regulate the power at all, but only the voltage level. Depending on the resistance of the headphones, the level of current consumed by the headphones is determined, which in turn determines the resulting power level.

  This is very important to understand, because... Without changing the voltage level at the output of the amplifier, we physically cannot separately increase the current level and thereby increase the power level.

  U=I*R, Where
  
  I – current strength, A
  R – headphone resistance, Ohm

  W=I*U, Where
  W – amplifier output power, W
  U – amplifier output voltage, V
  I – current strength, A