- Jan 2, 2008
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This is my take on how headphone sensitivity is properly measured and how headphones benefit from additional amplification rather than just using them out of an ipod.
HEADPHONE SENSITIVITY MEASURMENTS
Just as with speakers headphones, which are mini speakers have a ‘sensitivity’. A low sensitivity headphone will need more power to drive it to a given level than a high sensitivity headphone. But it is not just about volume. A low sensitivity headphone needs an amp to drive it so as to bring out all of its sound qualities (sound stage, clarity, dynamics, detail etc) to their best level. Not amping a low sensitivity headphone is like putting a Mini engine in a Jaguar. It will still drive, but not the way it was intended. Even high sensitivity phones will benefit from being amped for the same reason, but less so.
If you look at the specifications for headphones you do not find a ‘sensitivity rating’. Instead you get a list which includes ohms and SPL (Sound Pressure Level). Ohms dictates the relationship between resistance, current and voltage. The higher the resistance the more current is needed to overcome that resistance. With headphone specifications the higher the number of ohms the more current the amp needs to provide. In effect it measures the ‘load’ presented to the amp.
However, the ‘sensitivity’ of the headphones is not just down to the ohms. SPL measures the amount of power is needed to drive the headphones to a given volume. According to Sennheiser a difference in SPL of 1db is just about perceptible. Doubling the SPL is equivalent to 6 db. A high SPL means that less power is needed to get to a given volume of sound. In effect it shows how much ‘power’ is needed by the headphones. (Some companies measure SPL in db/mW and others in db/v and I accept at the moment it is not clear who does what and the relation between them)
Using the following headphones as examples we can assess how sensitive they are.
Grado SR80 - 32ohms SPL 98
Sennheiser HD201 - 24ohms SPL 108
Sennheiser PX200 - 32ohms SPL 115
Sennheiser mx500 - 32ohms SPL 125
AKG K702 - 62 ohms SPL 105
Goldring NS1000 - NR on - 300ohms SPL 101 (NR is noise reduction)
Goldring NS1000 - NR off - 100ohms SPL 93
The Grado SR80s have 32ohms and an SPL of 98. So whilst they need more power than most of the other headphones here to reach a given volume, they present less of a load to the amp. So that means they are of a medium sensitivity. They show that just because a headphone has lower ohms, it does not necessarily follow that they are sensitive. SPL is important as well.
The Sennheiser HD201 are full sized headphones, the PX200 are smaller portable headphones and the mx500s are buds to put in your ear. The HD201s present an amp with the lowest load of all and have a pretty high SPL. The smaller headphones actually present a slightly higher load at 32ohms, but they need even less power to get a certain volume, particularly the smallest mx500s with an SPL of 125. So they are all sensitive, but it is the mx500s that are the most sensitive because their SPL is so high. The HD201 and PX200s are about the same, even though the HD201s have fewer ohms.
The AKG K702s are often cited as being very insensitive. They are 62ohms, so present more of a load to an amp than Grados at 32ohms, but an SPL of 105 is higher than the Grados, so they need less power. So they are not as insensitive as they are often claimed to be, particularly when you consider the Goldrings.
The Goldring NS1000 have NR (noise reduction) and can be used with NR on or off. Their ratings are different depending on which is used. With NR on they present a high load to the amp at 300ohms, but they actually need less power to drive them with an SPL of 101 than with NR off at SPL 93. Whilst with NR off more power is needed, the headphone present less of a load at 100ohms. Still, they are the least sensitive headphones here.
So ‘sensitivity’ is based on both ohms and SPL.
HEADPHONE SENSITIVITY IN ACTION.
For all we can get out of the specifications, we need real examples of using different headphones with different amplifiers. Sensitivity is important in deciding on the amplification needed to get the best out of a headphone. Take three amps, the ipod Classic (which contains an amp) the FiiO E5 and the X-CANV8P. The ipod’s power output I cannot find, but it is reasonable to say it is low. The FiiO outputs 0.5 watts, the X-CAN 1.3 watts. The ipod is the least powerful, the X-CAN the most.
In listening tests (by me) the X-CAN will drive all of the above headphones’ to volumes way above that which is safe for ears and the headphones themselves. Not only that, the X-CAN will bring out the best in all of the headphones in terms of clarity, soundstage etc. Plugging tiny buds like the Sennheiser mx500s into an X-CAN is total overkill, as they are very sensitive and will run to their best capabilities with less power, such as from the FiiO and the ipod. The difference is more noticeable with the less sensitive headphones.
The FiiO with its 0.5 watts will also drive all of the headphones, including the Goldrings, to too high a volume for the ears. But it cannot match the X-CAN with the less sensitive headphones for overall sound quality. Sound stage in particular is lacking. The FiiO is remarkably good considering its size and cost. It has a bass boost function, which I find is less effective with low sensitivity headphones than higher ones. So it is noticeable with Senn PX200s, but not much with the Goldrings.
The ipod classic needs maximum volume to get a reasonable level of sound out of the higher sensitivity headphones and it cannot cope with the Goldrings. The sound is weak, strangled and terrible when compared to either the FiiO or X-CAN. The Grados are OK and the sensitive Sennheisers are fine. Though bear in mind, when I was sitting on a noisy bus I found that the FiiO was able to give the portable PX200s a volume to overcome the background noise, without becoming excessive. With the ipod alone the volume was not enough, but you can hear them. You can try this yourself at listening posts at the likes of the Apple Store. Check the volume of the various ipod Classics and Nanos the headphones are plugged into. You should find that they are all at maximum volume to get a decent volume out of the headphones. I have been told that the iphone gets a better volume out of headphones. I will try that the next time I have a chance. Without a doubt though, the FiiO improves the overall sound quality. There is greater dynamic, sound stage, clarity etc.
In my experience, for the above reasons, all headphones benefit from being amped. A good rule of thumb is that if headphones come with only a mini jack (3.5mm, 1/8th inch) connection they can work out of an ipod unamped. If they come with a jack (6.35mm, ¼ inch), even if it can be removed to find a min jack inside, it may work without an amp, but it really needs an amp or you are wasting them and you would be better with more sensitive headphones. Would run insensitive £1000 speakers out of a £100, 20 watt stereo amplifier?
HEADPHONE SENSITIVITY MEASURMENTS
Just as with speakers headphones, which are mini speakers have a ‘sensitivity’. A low sensitivity headphone will need more power to drive it to a given level than a high sensitivity headphone. But it is not just about volume. A low sensitivity headphone needs an amp to drive it so as to bring out all of its sound qualities (sound stage, clarity, dynamics, detail etc) to their best level. Not amping a low sensitivity headphone is like putting a Mini engine in a Jaguar. It will still drive, but not the way it was intended. Even high sensitivity phones will benefit from being amped for the same reason, but less so.
If you look at the specifications for headphones you do not find a ‘sensitivity rating’. Instead you get a list which includes ohms and SPL (Sound Pressure Level). Ohms dictates the relationship between resistance, current and voltage. The higher the resistance the more current is needed to overcome that resistance. With headphone specifications the higher the number of ohms the more current the amp needs to provide. In effect it measures the ‘load’ presented to the amp.
However, the ‘sensitivity’ of the headphones is not just down to the ohms. SPL measures the amount of power is needed to drive the headphones to a given volume. According to Sennheiser a difference in SPL of 1db is just about perceptible. Doubling the SPL is equivalent to 6 db. A high SPL means that less power is needed to get to a given volume of sound. In effect it shows how much ‘power’ is needed by the headphones. (Some companies measure SPL in db/mW and others in db/v and I accept at the moment it is not clear who does what and the relation between them)
Using the following headphones as examples we can assess how sensitive they are.
Grado SR80 - 32ohms SPL 98
Sennheiser HD201 - 24ohms SPL 108
Sennheiser PX200 - 32ohms SPL 115
Sennheiser mx500 - 32ohms SPL 125
AKG K702 - 62 ohms SPL 105
Goldring NS1000 - NR on - 300ohms SPL 101 (NR is noise reduction)
Goldring NS1000 - NR off - 100ohms SPL 93
The Grado SR80s have 32ohms and an SPL of 98. So whilst they need more power than most of the other headphones here to reach a given volume, they present less of a load to the amp. So that means they are of a medium sensitivity. They show that just because a headphone has lower ohms, it does not necessarily follow that they are sensitive. SPL is important as well.
The Sennheiser HD201 are full sized headphones, the PX200 are smaller portable headphones and the mx500s are buds to put in your ear. The HD201s present an amp with the lowest load of all and have a pretty high SPL. The smaller headphones actually present a slightly higher load at 32ohms, but they need even less power to get a certain volume, particularly the smallest mx500s with an SPL of 125. So they are all sensitive, but it is the mx500s that are the most sensitive because their SPL is so high. The HD201 and PX200s are about the same, even though the HD201s have fewer ohms.
The AKG K702s are often cited as being very insensitive. They are 62ohms, so present more of a load to an amp than Grados at 32ohms, but an SPL of 105 is higher than the Grados, so they need less power. So they are not as insensitive as they are often claimed to be, particularly when you consider the Goldrings.
The Goldring NS1000 have NR (noise reduction) and can be used with NR on or off. Their ratings are different depending on which is used. With NR on they present a high load to the amp at 300ohms, but they actually need less power to drive them with an SPL of 101 than with NR off at SPL 93. Whilst with NR off more power is needed, the headphone present less of a load at 100ohms. Still, they are the least sensitive headphones here.
So ‘sensitivity’ is based on both ohms and SPL.
HEADPHONE SENSITIVITY IN ACTION.
For all we can get out of the specifications, we need real examples of using different headphones with different amplifiers. Sensitivity is important in deciding on the amplification needed to get the best out of a headphone. Take three amps, the ipod Classic (which contains an amp) the FiiO E5 and the X-CANV8P. The ipod’s power output I cannot find, but it is reasonable to say it is low. The FiiO outputs 0.5 watts, the X-CAN 1.3 watts. The ipod is the least powerful, the X-CAN the most.
In listening tests (by me) the X-CAN will drive all of the above headphones’ to volumes way above that which is safe for ears and the headphones themselves. Not only that, the X-CAN will bring out the best in all of the headphones in terms of clarity, soundstage etc. Plugging tiny buds like the Sennheiser mx500s into an X-CAN is total overkill, as they are very sensitive and will run to their best capabilities with less power, such as from the FiiO and the ipod. The difference is more noticeable with the less sensitive headphones.
The FiiO with its 0.5 watts will also drive all of the headphones, including the Goldrings, to too high a volume for the ears. But it cannot match the X-CAN with the less sensitive headphones for overall sound quality. Sound stage in particular is lacking. The FiiO is remarkably good considering its size and cost. It has a bass boost function, which I find is less effective with low sensitivity headphones than higher ones. So it is noticeable with Senn PX200s, but not much with the Goldrings.
The ipod classic needs maximum volume to get a reasonable level of sound out of the higher sensitivity headphones and it cannot cope with the Goldrings. The sound is weak, strangled and terrible when compared to either the FiiO or X-CAN. The Grados are OK and the sensitive Sennheisers are fine. Though bear in mind, when I was sitting on a noisy bus I found that the FiiO was able to give the portable PX200s a volume to overcome the background noise, without becoming excessive. With the ipod alone the volume was not enough, but you can hear them. You can try this yourself at listening posts at the likes of the Apple Store. Check the volume of the various ipod Classics and Nanos the headphones are plugged into. You should find that they are all at maximum volume to get a decent volume out of the headphones. I have been told that the iphone gets a better volume out of headphones. I will try that the next time I have a chance. Without a doubt though, the FiiO improves the overall sound quality. There is greater dynamic, sound stage, clarity etc.
In my experience, for the above reasons, all headphones benefit from being amped. A good rule of thumb is that if headphones come with only a mini jack (3.5mm, 1/8th inch) connection they can work out of an ipod unamped. If they come with a jack (6.35mm, ¼ inch), even if it can be removed to find a min jack inside, it may work without an amp, but it really needs an amp or you are wasting them and you would be better with more sensitive headphones. Would run insensitive £1000 speakers out of a £100, 20 watt stereo amplifier?
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