AudioStudies
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Initial post will address very basic headphone info, with the hope that subsequent posts can add additional relevant info. Many thanks to those who helped me on the Objective and Subjective thread to better understand headphones, which I didn't get into until this year. Initial post revisions will be on-going for now, as more info comes in from the experts, to whom I am very grateful.
Introduction
Headphones are electroacoustic transducers (speakers) that convert electrical energy to acoustic energy; designed for a single person to listen, rather than a group. In the colloquial, headphones are known as cans. Historically, headphones originated from the telephone receiver earpiece, and were the only way to listen to electrical audio signals prior to the advent of amplifiers that could power speakers to produce sound. In 1958, John C. Koss, an audiophile and jazz musician, produced the first stereo headphones. Previously, headphones had monophonic sound directed to both ears, and were used only by the US navy, telephone and radio operators, and those in similar industries.
Mass market headphones are often marketed with features that can include noise-cancelling, built-in FM radios, waterproofing, and smart technology. High end headphones are luxury products often constructed with high quality components, and are designed to show the state of the art of headphone technology. Even with with high end headphones though, there are some misses and not all of them end up sounding good. Many of the higher end headphones are designed to be used with accessories such as external amplifiers called headphone amplifiers and combination headphone amplifier / digital-to-analog converters (DACs). Some high end headphones are designed specifically to be used with mobile phones. Mass market headphones typically work fine with mobile phones or other low powered devices.
Headphones designed to cover the ears are often characterized as either open-back (with an open grill on the back side of the ear cups) or closed-back, with no openings. Traditionally, open-back designs have allowed for easier production of high quality headphones; however many excellent products are of closed-back design.
The open-back / closed-back distinction, though colloquially common, is not ideal for characterizing all modern headphones. There are arguably two principle volumes from the standpoint of a headphone, the space in front of the driver (between the driver and the ear), and the space behind the driver (typically the cup, open air for some designs). Both of these volumes may be sealed or conversely have some degree of leak relative to the outside air. The connection of these two volumes to each other is of great significance with respect to headphone acoustic performance. Some headphones have a closed back to each cup but isolate noise poorly because both the rear volume and the front volume are not isolated from the exterior air. An open back is found on some headphones that have completely sealed ear chambers.
In most cases, with open-back use, sound will emanate into the nearby environment; and in most cases with closed-back use there is not nearly as much leakage. In general, closed-back has the advantage that they can be used when others are around, such as on airplanes. A more limited number of headphones are designed as semi-open, and the back is only partially open.
Some headphones are designed to fit directly into the ear (not cover the ear); and these are called in-ear monitors (IEMs); and they have become increasingly popular. The better IEMs have excellent sound quality, but may not feel as comfortable as over-ear headphones, especially for long listening sessions. IEMs are lighter, smaller and easier to store and transport than over-ear headphones.
Some of the companies that manufacture headphones include: Focal, Audeze, ZMF, HiFiMan, Sennheiser, Stax, Fostex, Grado, DCA, Denon, Final, AKG and Shure.
Earbuds are small ear pieces that unlike IEM's do not go into the ear canal and do not sit on the ear but are tucked into the concha of the ear.
The sound quality is often lacking as it is very difficult to get a good seal. These types of ear phones are often included as freebies with portable gear; and consequently are not recommended for high quality sound. They have the advantages of low cost (or no cost) and portability; as for example the Apple Earpod.
Another type of headphone is called an on-ear headphone, that doesn’t completely go over the ear, nor does it fit directly in the ear. On-ear headphones sit on the pinnae where over-ear sits around the pinnae onto the skull. Depending on the size of one's pinnae and the available room within the pads some over-ear headphones are partially on-ears for certain people. This usually leads to a poor seal and poor performance. On-ear headphones are not as popular as the other types; and not noted for sound quality. They may not feel as comfortable as over-ear; however they can feel less hot (or warm) for extended use and are more suited for on the go use.
The reason for the many different types of headphones is due to historical reasons and advances in technology that have led to better manufacturing techniques, smaller and more efficient transducers, and marketing for specific types of uses; gaming for example. The invention of many things such as mobile phones and laptop computers have influenced the headphone market, and subsequently the technology, considerably.
Impedance
Impedance is a measure of the opposition to current that a circuit exhibits when a voltage is applied to the circuit. Impedance is similar to resistance; however typically includes other aspects that oppose current, beyond just resistance, such as capacitance and inductance. Most headphones have significant inductance and small amounts of capacitance, in addition to resistance. Therefore, when headphones are connected to a power source, there is a reactive load, and impedance is present; and the magnitude of this impedance is a measure of opposition to current that a particular set of headphones exhibit. Headphone impedance is typically measured at frequencies of 500 Hz or 1 KHz and specified in units of Ohms (Ω).
Knowledge a headphone's impedance can help determine how much voltage headphones will need to produce a reasonable listening volume. High impedance headphones require the use of a headphone amplifier to perform properly. High impedance headphones cannot be powered well from the output jack of a smartphone or other low powered device.
Mobile phones and other low powered devices can typically power headphones up to 32 Ohms (32 Ω). When headphone impedance is between 33 Ω and 100 Ω it may (or may not) be possible to generate enough volume from a low powered device; however it is likely that an improved performance will be attained with the use of a headphone amplifier. Many headphones have impedance specifications in the range from 100 Ω to 300 Ω and these will definitely require a headphone amplifier.
In general, high impedance headphones require more voltage. Although high impedance headphones produce less volume for a given amplifier output level they are coveted because of their ability to handle electrical signals quite well; enabling more accurate and vivid sound. Typically high impedance headphones cost more than low impedance headphones. However, there are some excellent designs of headphones with relatively low impedance.
An amplifier used to power headphones, including headphone amplifiers and amplifiers within a low powered device, has an output impedance specification. The amplifier should have an output impedance less than of the impedance rating of the headphones; and the lower the better with respect to amplifier output impedance. An arbitrary statement that appears on many web sites is that an amplifier should have an output impedance less than 1/8th of the impedance rating of the headphones. Some experts believe 1/10th is a more appropriate ratio. Following the 1/10th guideline will help to ensure a flat frequency response when listening to the headphones.
Headphone impedance can vary with the frequency of the incoming signal; thus in these cases, the actual impedance can vary from the specified impedance when the headphones are in use. However, some headphone designs have little to no impedance change over the audible frequency range.
Sensitivity
Sensitivity is a measure of how effectively headphones (or other loudspeakers) convert electrical signals into sound; thus indicating how loud the headphones will be for a given electrical drive level. Sound pressure level (SPL) is typically measured in units of decibels (dB). There are two methods of measuring and specifying sensitivity:
Often voltage sensitivity specs from manufacturers depict only a number and leave out the units of measure (dB/mW or dB/V) for proper interpretation. Some manufacturers show dB/mW whereas others (who like to show high numbers) depict dB/V values. Yet other manufacturers do not even specify voltage sensitivity; rather they post maximum sound pressure levels (SPLs), based on their maximum power rating. All this corresponds to an un-standardized chaotic mess. The end user should be aware that the most convenient efficiency number that can be used to directly compare headphone efficiency numbers is the dB/V number (which if unknown can be calculated from dB/mW rating combined with impedance).
Headphone amplifiers are voltage sources; therefore the voltage sensitivity is most useful for comparison of speakers. However, if only the power sensitivity is known, a form of Ohm’s Law can be used to convert to voltage sensitivity or by using online calculators. When the voltage sensitivity is known, the maximum volume for a pair of headphones can be calculated if the maximum amplifier output voltage is also known. The appropriate voltage specification is root mean square (RMS) voltage, often denoted VRMS .
Consider the case of an amplifier with an output voltage VRMS = 1.0 volts; connected to headphones with sensitivity of 100 decibels SPL per volt = 100 dB (SPL)/V. The maximum volume that can reach the ears for this case is 100 decibels.
Power consumption of headphones is determined by the applied voltage and the drawn current. Headphone amplifier power is typically specified in milliWatt (mW).
Choosing Headphones
The most important considerations in choosing headphones are tonal balance and overall sound quality. Clearly, the impedance and sensitivity of headphones are important considerations; as well as the specifications of the amplifier intended to drive the headphones. There are other considerations as well such as build quality, comfort, aesthetics, value and affordability. The intended use is of great importance, as closed-back may be better for going to the gym or travelling via public transportation, and open-back may be better to achieve great sound for private uses. A gaming headphone has different user requirements than one intended solely for listening to music on a mobile phone. User preferences such as in-ear, on-ear, or over-ear certainly come into play. The reputation of the manufacturer, serviceability, and the warranty for a given set of headphones are also important considerations.
Transducer Technology
The driver elements within headphones are electroacoustic transducers; that is they convert electrical energy to acoustic energy. Some of the more common transducer technologies in modern headphones include: planar magnetic, balanced armature, dynamic, and electrostatic. Less common driver elements include ceramic, air motion transformer, and ribbons. Excellent designs are possible with any of these technologies, and each has pros and cons in the attempt to reach excellent designs.
Introduction
Headphones are electroacoustic transducers (speakers) that convert electrical energy to acoustic energy; designed for a single person to listen, rather than a group. In the colloquial, headphones are known as cans. Historically, headphones originated from the telephone receiver earpiece, and were the only way to listen to electrical audio signals prior to the advent of amplifiers that could power speakers to produce sound. In 1958, John C. Koss, an audiophile and jazz musician, produced the first stereo headphones. Previously, headphones had monophonic sound directed to both ears, and were used only by the US navy, telephone and radio operators, and those in similar industries.
Mass market headphones are often marketed with features that can include noise-cancelling, built-in FM radios, waterproofing, and smart technology. High end headphones are luxury products often constructed with high quality components, and are designed to show the state of the art of headphone technology. Even with with high end headphones though, there are some misses and not all of them end up sounding good. Many of the higher end headphones are designed to be used with accessories such as external amplifiers called headphone amplifiers and combination headphone amplifier / digital-to-analog converters (DACs). Some high end headphones are designed specifically to be used with mobile phones. Mass market headphones typically work fine with mobile phones or other low powered devices.
Headphones designed to cover the ears are often characterized as either open-back (with an open grill on the back side of the ear cups) or closed-back, with no openings. Traditionally, open-back designs have allowed for easier production of high quality headphones; however many excellent products are of closed-back design.
The open-back / closed-back distinction, though colloquially common, is not ideal for characterizing all modern headphones. There are arguably two principle volumes from the standpoint of a headphone, the space in front of the driver (between the driver and the ear), and the space behind the driver (typically the cup, open air for some designs). Both of these volumes may be sealed or conversely have some degree of leak relative to the outside air. The connection of these two volumes to each other is of great significance with respect to headphone acoustic performance. Some headphones have a closed back to each cup but isolate noise poorly because both the rear volume and the front volume are not isolated from the exterior air. An open back is found on some headphones that have completely sealed ear chambers.
In most cases, with open-back use, sound will emanate into the nearby environment; and in most cases with closed-back use there is not nearly as much leakage. In general, closed-back has the advantage that they can be used when others are around, such as on airplanes. A more limited number of headphones are designed as semi-open, and the back is only partially open.
Some headphones are designed to fit directly into the ear (not cover the ear); and these are called in-ear monitors (IEMs); and they have become increasingly popular. The better IEMs have excellent sound quality, but may not feel as comfortable as over-ear headphones, especially for long listening sessions. IEMs are lighter, smaller and easier to store and transport than over-ear headphones.
Some of the companies that manufacture headphones include: Focal, Audeze, ZMF, HiFiMan, Sennheiser, Stax, Fostex, Grado, DCA, Denon, Final, AKG and Shure.
Earbuds are small ear pieces that unlike IEM's do not go into the ear canal and do not sit on the ear but are tucked into the concha of the ear.
The sound quality is often lacking as it is very difficult to get a good seal. These types of ear phones are often included as freebies with portable gear; and consequently are not recommended for high quality sound. They have the advantages of low cost (or no cost) and portability; as for example the Apple Earpod.
Another type of headphone is called an on-ear headphone, that doesn’t completely go over the ear, nor does it fit directly in the ear. On-ear headphones sit on the pinnae where over-ear sits around the pinnae onto the skull. Depending on the size of one's pinnae and the available room within the pads some over-ear headphones are partially on-ears for certain people. This usually leads to a poor seal and poor performance. On-ear headphones are not as popular as the other types; and not noted for sound quality. They may not feel as comfortable as over-ear; however they can feel less hot (or warm) for extended use and are more suited for on the go use.
The reason for the many different types of headphones is due to historical reasons and advances in technology that have led to better manufacturing techniques, smaller and more efficient transducers, and marketing for specific types of uses; gaming for example. The invention of many things such as mobile phones and laptop computers have influenced the headphone market, and subsequently the technology, considerably.
Impedance
Impedance is a measure of the opposition to current that a circuit exhibits when a voltage is applied to the circuit. Impedance is similar to resistance; however typically includes other aspects that oppose current, beyond just resistance, such as capacitance and inductance. Most headphones have significant inductance and small amounts of capacitance, in addition to resistance. Therefore, when headphones are connected to a power source, there is a reactive load, and impedance is present; and the magnitude of this impedance is a measure of opposition to current that a particular set of headphones exhibit. Headphone impedance is typically measured at frequencies of 500 Hz or 1 KHz and specified in units of Ohms (Ω).
Knowledge a headphone's impedance can help determine how much voltage headphones will need to produce a reasonable listening volume. High impedance headphones require the use of a headphone amplifier to perform properly. High impedance headphones cannot be powered well from the output jack of a smartphone or other low powered device.
Mobile phones and other low powered devices can typically power headphones up to 32 Ohms (32 Ω). When headphone impedance is between 33 Ω and 100 Ω it may (or may not) be possible to generate enough volume from a low powered device; however it is likely that an improved performance will be attained with the use of a headphone amplifier. Many headphones have impedance specifications in the range from 100 Ω to 300 Ω and these will definitely require a headphone amplifier.
In general, high impedance headphones require more voltage. Although high impedance headphones produce less volume for a given amplifier output level they are coveted because of their ability to handle electrical signals quite well; enabling more accurate and vivid sound. Typically high impedance headphones cost more than low impedance headphones. However, there are some excellent designs of headphones with relatively low impedance.
An amplifier used to power headphones, including headphone amplifiers and amplifiers within a low powered device, has an output impedance specification. The amplifier should have an output impedance less than of the impedance rating of the headphones; and the lower the better with respect to amplifier output impedance. An arbitrary statement that appears on many web sites is that an amplifier should have an output impedance less than 1/8th of the impedance rating of the headphones. Some experts believe 1/10th is a more appropriate ratio. Following the 1/10th guideline will help to ensure a flat frequency response when listening to the headphones.
Headphone impedance can vary with the frequency of the incoming signal; thus in these cases, the actual impedance can vary from the specified impedance when the headphones are in use. However, some headphone designs have little to no impedance change over the audible frequency range.
Sensitivity
Sensitivity is a measure of how effectively headphones (or other loudspeakers) convert electrical signals into sound; thus indicating how loud the headphones will be for a given electrical drive level. Sound pressure level (SPL) is typically measured in units of decibels (dB). There are two methods of measuring and specifying sensitivity:
- In decibels (dB) of SPL at one milliwatt = [ dB (SPL) @ 1 mW ]; or
- In decibels of (dB) of SPL at 1 volt = (dB (SPL) @ 1V):
Often voltage sensitivity specs from manufacturers depict only a number and leave out the units of measure (dB/mW or dB/V) for proper interpretation. Some manufacturers show dB/mW whereas others (who like to show high numbers) depict dB/V values. Yet other manufacturers do not even specify voltage sensitivity; rather they post maximum sound pressure levels (SPLs), based on their maximum power rating. All this corresponds to an un-standardized chaotic mess. The end user should be aware that the most convenient efficiency number that can be used to directly compare headphone efficiency numbers is the dB/V number (which if unknown can be calculated from dB/mW rating combined with impedance).
Headphone amplifiers are voltage sources; therefore the voltage sensitivity is most useful for comparison of speakers. However, if only the power sensitivity is known, a form of Ohm’s Law can be used to convert to voltage sensitivity or by using online calculators. When the voltage sensitivity is known, the maximum volume for a pair of headphones can be calculated if the maximum amplifier output voltage is also known. The appropriate voltage specification is root mean square (RMS) voltage, often denoted VRMS .
Consider the case of an amplifier with an output voltage VRMS = 1.0 volts; connected to headphones with sensitivity of 100 decibels SPL per volt = 100 dB (SPL)/V. The maximum volume that can reach the ears for this case is 100 decibels.
Power consumption of headphones is determined by the applied voltage and the drawn current. Headphone amplifier power is typically specified in milliWatt (mW).
Choosing Headphones
The most important considerations in choosing headphones are tonal balance and overall sound quality. Clearly, the impedance and sensitivity of headphones are important considerations; as well as the specifications of the amplifier intended to drive the headphones. There are other considerations as well such as build quality, comfort, aesthetics, value and affordability. The intended use is of great importance, as closed-back may be better for going to the gym or travelling via public transportation, and open-back may be better to achieve great sound for private uses. A gaming headphone has different user requirements than one intended solely for listening to music on a mobile phone. User preferences such as in-ear, on-ear, or over-ear certainly come into play. The reputation of the manufacturer, serviceability, and the warranty for a given set of headphones are also important considerations.
Transducer Technology
The driver elements within headphones are electroacoustic transducers; that is they convert electrical energy to acoustic energy. Some of the more common transducer technologies in modern headphones include: planar magnetic, balanced armature, dynamic, and electrostatic. Less common driver elements include ceramic, air motion transformer, and ribbons. Excellent designs are possible with any of these technologies, and each has pros and cons in the attempt to reach excellent designs.
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