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Technical Specification Terms

Most headphone packages will list the "specifications," which attempt to describe in technical terms how a pair of headphones will sound. Equipment specifications are sometimes overstated, but in the case of headphones, they may be entirely misleading. It bears repeating that because headphones operate so close to the ears, the sound of a pair of headphones can depend on the shape of the listener\'s head and ears. Headphones with "good" specs may not sound good, and those with "bad" specs may not sound bad.

Click on the terms to read about it:

Bass Port: If a driver is placed in a sealed enclosure, it will have an inherent tendency to move back to its original position after it has moved to equalise the air pressure inside the enclosure. While this can be favourable for producing sounds more accurately and reducing unnecessary resonances (thus avoiding colouring the sound), it increases the power required to move the driver (and to overcome the difference in air pressure) and limits the drivers bass response.

One way for manufacturers to overcome this problem is to put “bass ports” onto the enclosure. Bass ports essentially allow the equalisation of air inside and outside the enclosure and allowing the driver to be more “floppy”. This increases bass response and also lowers the power needed for the driver to produce sound. Adding vents onto the enclosure design however reduces the accuracy of the driver as it is now more “floppy”, although this problem can be overcome by “tuning” the bass ports.

Tuning a bass port essentially means placing the vent in a strategic position on the enclosure to ensure that air is only equalised when it should be (i.e. When the driver is reproducing low frequencies) and to behave like a sealed enclosure when the driver is reproducing higher frequencies. In effect, tuning the bass port allows the driver and enclosure to get the best of both worlds.

 

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Diffuse Field Equalization: There are two types of built-in headphone equalization that attempt to "flatten" the perceived frequency response: free-field and diffuse-field. Free-field EQ assumes that the listener is in front of a sound source in a listening environment without echos, such as the wide outdoors. Diffuse-field EQ substitutes a room with reflecting walls and can be more natural sounding than free-field EQ. The method for measuring DF flatness is defined under the IEC 60268-7:1996 standard. Because diffuse-field EQ is based on an "average" head/ear shape and room model, it may not appeal to all listeners or sound natural with all recordings. A binaural recording may or may not benefit from diffuse-field EQ, depending on how the recording was made (e.g., whether the microphone was inside the dummy ear), so be sure compare models with and without DF EQ. Headphone manufacturers are increasingly standardizing on DF equalization

 

↑ back to top

Distortion: How accurately the headphones reproduce sounds and given in a percentage of signal distorted. Lower is better - 1% distortion or less (at maximum power). Tests have shown that 1% distortion is at the threshold of audibility. Headphones have less distortion at loud levels than speakers.

 

↑ back to top

Frequency Response: The range of frequencies that the headphones can reproduce effectively. The audible bandwidth is 20 Hz - 20,000 Hz (or 20kHz). Outside that range, sounds are not audible to most human ears (except the occasional sound professional and of course, "golden ear" audiophiles - who can often hear into the Megahertz range). Ultra-low frequencies (less than 20Hz) are more felt than heard. Beware claims of a measured "flat" frequency response (sometimes listed as 20Hz to 20kHz +/- 3dB). A headphone with a true flat response will sound terrible, because what the ears perceive as a "flat" response actually has many peaks and valleys due to interaction of the sound with the listener\'s head before it reaches the ears. Instead, headphones are often equalized to sound flat. See diffuse-field equalization below.

 

↑ back to top

Impedance: A measure of headphone load on an amplifier and stated in ohms. This factor is less important with solid state amplifiers, which can drive most headphone impedances, but can be significant with tube amplifiers, which are more sensitive to load impedances. Both consumer and professional headphones generally have impedances of less than 100 ohms. There are professional models rated at 200 ohms or more to minimize loading effects on distribution amplifiers which are often drive a whole bank of headphones at one time. Be aware that very high impedance phones may require more power - on the order of Watts instead of milliWatts.

 

↑ back to top

Microphonics: The tendency for a component to induce audible noise into the amplifier circuit when mechanically disturbed.  Tubes are the most common microphonic component, and they will usually make an audible "thump" or "ring" when tapped.  Occasionally, the problem is severe enough in combo amplifiers to cause uncontrollable  from the speaker to the tube, resulting in a "squealing" or "howling" noise when the volume is turned up loud.  Although it is not commonly known, capacitors can also be quite microphonic.  Different types have different levels of microphony, with ceramic types usually being the worst.

This definition has led to microphonics been commonly used to describe "The "thump" usally heard when wearing an isolating earphone and moving (walking, running, etc) is caused by bone conduction.  It happens all the time, but the noise around you covers it up.  There is also a "scratching" (could not think of a better word) noise that you sometimes hear as the cable moves across your body, or inside your jacket. This is also a vibration like in the bone conduction.  Wearing the cable up and over your ears almost always gets rid of this as the soft tissue around your ear acts as a dampner.

 

↑ back to top

Soundstage: It refers to the 3D space the IEM creates. Generally, the further away the speakers from the ears, the larger the soundstage is going to be. IEM’s all have an inherent problem of being very close to the ear drum. This means that the sound produced by the driver is not “shaped” by the ear and ear canal before it hits the eardrum as we are used to, which can cause the sound to appear as if it was coming from the centre of the head.

Manufacturers have counteracted this problem by modifying the response of the IEM’s and various software enhancements can also create the illusion of a larger soundstage by leaking the left and right channels into each other or amplifying differences in stereo sounds.

 

↑ back to top

Transducers (a.k.a. Drivers): There are two major types of transducer being used on IEM: Dynamic and Balanced Armature (BA) transducers.

Dynamic (moving coil) transducer is often found on low to entry class IEM due to their easy availability and lower cost (relative to BA transducer). They commonly range from 8mm to 16mm in diameter. Dynamic transducer is known for their ability to create a more powerful bass response since relatively more air is moved during sound reproduction. More air movement means stronger bass sensation as we tend to ‘feel’ more about low end bass than actually hearing it. The downside of using dynamic transducer on IEM is its larger side. Also worth noting, many big brand name manufacturers use dynamic transducer of relatively low sound quality in their IEM, therefore you should avoid most of them as much as possible if sound quality is your priority. Of course, there are also IEM manufacturers specialize in producing high end dynamic transducer IEM, most noticeably Future Sonics, one of the very first IEM manufacturers.

BA transducer has the benefit of being really small, therefore you can easily find many IEM maker using 2 or 3 BA transducers in each side of their ‘phone. By dedicating at least one of the BA transducer as a woofer, multi-ways IEM tend to perform better on bass than most single-way BA transducer IEM (but not always). The use of multiple BA transducers partially solves the bass problem as BA transducer moves a lot less air than dynamic transducer (and noticeably less low end bass). The downside of BA transducer is its higher price tag.

There are also hybrid IEMs (e.g. Ultimate Ears Super.fi 5 EB) that utilize both dynamic and BA transducer together in order to have the best of both worlds. However, review of such type of IEM often contains mixed opinion.

Most headphone packages will list the "specifications," which attempt to describe in technical terms how a pair of headphones will sound. Equipment specifications are sometimes overstated, but in the case of headphones, they may be entirely misleading. It bears repeating that because headphones operate so close to the ears, the sound of a pair of headphones can depend on the shape of the listener\'s head and ears. Headphones with "good" specs may not sound good, and those with "bad" specs may not sound bad.

Click on the terms to read about it:

Bass Port: If a driver is placed in a sealed enclosure, it will have an inherent tendency to move back to its original position after it has moved to equalise the air pressure inside the enclosure. While this can be favourable for producing sounds more accurately and reducing unnecessary resonances (thus avoiding colouring the sound), it increases the power required to move the driver (and to overcome the difference in air pressure) and limits the drivers bass response.

One way for manufacturers to overcome this problem is to put “bass ports” onto the enclosure. Bass ports essentially allow the equalisation of air inside and outside the enclosure and allowing the driver to be more “floppy”. This increases bass response and also lowers the power needed for the driver to produce sound. Adding vents onto the enclosure design however reduces the accuracy of the driver as it is now more “floppy”, although this problem can be overcome by “tuning” the bass ports.

Tuning a bass port essentially means placing the vent in a strategic position on the enclosure to ensure that air is only equalised when it should be (i.e. When the driver is reproducing low frequencies) and to behave like a sealed enclosure when the driver is reproducing higher frequencies. In effect, tuning the bass port allows the driver and enclosure to get the best of both worlds.

 

↑ back to top

Diffuse Field Equalization: There are two types of built-in headphone equalization that attempt to "flatten" the perceived frequency response: free-field and diffuse-field. Free-field EQ assumes that the listener is in front of a sound source in a listening environment without echos, such as the wide outdoors. Diffuse-field EQ substitutes a room with reflecting walls and can be more natural sounding than free-field EQ. The method for measuring DF flatness is defined under the IEC 60268-7:1996 standard. Because diffuse-field EQ is based on an "average" head/ear shape and room model, it may not appeal to all listeners or sound natural with all recordings. A binaural recording may or may not benefit from diffuse-field EQ, depending on how the recording was made (e.g., whether the microphone was inside the dummy ear), so be sure compare models with and without DF EQ. Headphone manufacturers are increasingly standardizing on DF equalization

 

↑ back to top

Distortion: How accurately the headphones reproduce sounds and given in a percentage of signal distorted. Lower is better - 1% distortion or less (at maximum power). Tests have shown that 1% distortion is at the threshold of audibility. Headphones have less distortion at loud levels than speakers.

 

↑ back to top

Frequency Response: The range of frequencies that the headphones can reproduce effectively. The audible bandwidth is 20 Hz - 20,000 Hz (or 20kHz). Outside that range, sounds are not audible to most human ears (except the occasional sound professional and of course, "golden ear" audiophiles - who can often hear into the Megahertz range). Ultra-low frequencies (less than 20Hz) are more felt than heard. Beware claims of a measured "flat" frequency response (sometimes listed as 20Hz to 20kHz +/- 3dB). A headphone with a true flat response will sound terrible, because what the ears perceive as a "flat" response actually has many peaks and valleys due to interaction of the sound with the listener\'s head before it reaches the ears. Instead, headphones are often equalized to sound flat. See diffuse-field equalization below.

Impedance: A measure of headphone load on an amplifier and stated in ohms. This factor is less important with solid state amplifiers, which can drive most headphone impedances, but can be significant with tube amplifiers, which are more sensitive to load impedances. Both consumer and professional headphones generally have impedances of less than 100 ohms. There are professional models rated at 200 ohms or more to minimize loading effects on distribution amplifiers which are often drive a whole bank of headphones at one time. Be aware that very high impedance phones may require more power - on the order of Watts instead of milliWatts.

 

↑ back to top

Microphonics: The tendency for a component to induce audible noise into the amplifier circuit when mechanically disturbed.  Tubes are the most common microphonic component, and they will usually make an audible "thump" or "ring" when tapped.  Occasionally, the problem is severe enough in combo amplifiers to cause uncontrollable  from the speaker to the tube, resulting in a "squealing" or "howling" noise when the volume is turned up loud.  Although it is not commonly known, capacitors can also be quite microphonic.  Different types have different levels of microphony, with ceramic types usually being the worst.

This definition has led to microphonics been commonly used to describe "The "thump" usally heard when wearing an isolating earphone and moving (walking, running, etc) is caused by bone conduction.  It happens all the time, but the noise around you covers it up.  There is also a "scratching" (could not think of a better word) noise that you sometimes hear as the cable moves across your body, or inside your jacket. This is also a vibration like in the bone conduction.  Wearing the cable up and over your ears almost always gets rid of this as the soft tissue around your ear acts as a dampner.

 

↑ back to top

Soundstage: It refers to the 3D space the IEM creates. Generally, the further away the speakers from the ears, the larger the soundstage is going to be. IEM’s all have an inherent problem of being very close to the ear drum. This means that the sound produced by the driver is not “shaped” by the ear and ear canal before it hits the eardrum as we are used to, which can cause the sound to appear as if it was coming from the centre of the head.

Manufacturers have counteracted this problem by modifying the response of the IEM’s and various software enhancements can also create the illusion of a larger soundstage by leaking the left and right channels into each other or amplifying differences in stereo sounds.

 

↑ back to top

Transducers (a.k.a. Drivers): There are two major types of transducer being used on IEM: Dynamic and Balanced Armature (BA) transducers.

Dynamic (moving coil) transducer is often found on low to entry class IEM due to their easy availability and lower cost (relative to BA transducer). They commonly range from 8mm to 16mm in diameter. Dynamic transducer is known for their ability to create a more powerful bass response since relatively more air is moved during sound reproduction. More air movement means stronger bass sensation as we tend to ‘feel’ more about low end bass than actually hearing it. The downside of using dynamic transducer on IEM is its larger side. Also worth noting, many big brand name manufacturers use dynamic transducer of relatively low sound quality in their IEM, therefore you should avoid most of them as much as possible if sound quality is your priority. Of course, there are also IEM manufacturers specialize in producing high end dynamic transducer IEM, most noticeably Future Sonics, one of the very first IEM manufacturers.

BA transducer has the benefit of being really small, therefore you can easily find many IEM maker using 2 or 3 BA transducers in each side of their ‘phone. By dedicating at least one of the BA transducer as a woofer, multi-ways IEM tend to perform better on bass than most single-way BA transducer IEM (but not always). The use of multiple BA transducers partially solves the bass problem as BA transducer moves a lot less air than dynamic transducer (and noticeably less low end bass). The downside of BA transducer is its higher price tag.

There are also hybrid IEMs (e.g. Ultimate Ears Super.fi 5 EB) that utilize both dynamic and BA transducer together in order to have the best of both worlds. However, review of such type of IEM often contains mixed opinion.

Sensitivity (loudness): A measure of headphone efficiency in dBs SPL per milliwatt of input. A low number means that the headphones need more power to sound as loud as those which have a higher sensitivity. Headphones for portables need to be fairly sensitive because of the lower power output of portable stereos. Modern dynamic headphones have sensitivity ratings of 90 dB or more. When shopping for portable headphones, look for a sensitivity rating of 100 dB or greater.

Sensitivity (loudness): A measure of headphone efficiency in dBs SPL per milliwatt of input. A low number means that the headphones need more power to sound as loud as those which have a higher sensitivity. Headphones for portables need to be fairly sensitive because of the lower power output of portable stereos. Modern dynamic headphones have sensitivity ratings of 90 dB or more. When shopping for portable headphones, look for a sensitivity rating of 100 dB or greater.