[TheVoxHumanus]

I'd really like to understand what these two specs actually mean, and how they relate to each other.

I guess I'm most concerned about the released specs for the new UE product, it has a pretty high sensitivity (117db/mw) but it has a pretty high impedence (32ohms).

My problem with the higher-end IEMs (Shure) is that I can hear hiss on ALL of my sources. It's very, very frustrating. I certainly hope that despite the high sensitivity, the high impedence will dampen the hiss.

 

[Iron_Dreamer]

Sensativity tells you how much power a headphone needs. The lower the sensativity, the more power hungry they are.

Impedance tells you whether their power demand leans toward more current (low impedance) or voltage (high impedance).

A common misconception is that high impedance cans are more power hungry, because they generally need a higher volume setting than low impedance cans. This is merely because the volume dial controls output voltage, which of course a high impedance headphone needs more of. Sensativity is the true measure of how power hungry a headphone is.

 

[hardstyler]

While we're talking about sensitivity does anyone know why most headphones in this database http://headphones.warzone.org/ especially Sennheiser ones have lower db values than on their official sites?

Is it just different measuring standards? 1V vs. 1mw or something like that?

 

[Carl]

Sensitivity doesn't really matter with headphones (well, generally speaking), as most amps are more than capable of producing enough volume within it's specified impedence range.

The higher the impedence of a headphone, the quieter it'll be and the easier a load it'll pose to the amplifier. As headphones range quite widely in impedence (~16Ω to ~600Ω), impedence will make the most difference in volume terms.

Hiss is independant of both of these. It's caused by source, amp, and any noise that is introduced by cabling.

 

[facelvega]

Not exactly. Let me try to explain to the best of my knowledge how this would work, with examples.

Sensitivity is the volume of sound produced by a headphone per unit of electrical energy, while impedance is the amount of current a device will draw from the amplifier in the first place. This is why higher impedance is easier to drive-- it's taking less energy from the amp.

e.g., running off its 9V battery, a Xenos OHA-REP will deliver 185mW to a 32 ohm headphone, but only 35mW to a 300 ohm one. (according to the Xenos website, I chose the Xenos because they give very full specifications)

So let's figure the maximum sound pressure level (SPL) for three headphones from an OHA-REP, two with an impedance of 32 but different sensitivities, and one with an impedance of 300 but about the same sensitivity as one of the 32's. We'll use j-curve's handy excel sheets.

Grado SR line (32;98db/mW)-- 121dB

Senn HD580/600 (300;97)-- 112dB

AKG K26p (32;110)-- 133dB

now for fun, let's throw in a K701 (120;93). The Xenos does 75mW into 120.-- 112dB

In general terms, 10dB difference equals about ten times the real pressure and twice the perceived volume. Our three different figures here (112, 121, 133) equal a maximum of really rather loud, extremely loud, and unbearably loud. Of course, you'd likely be losing sound quality to play at full volume, so you could say that the Xenos with a decently strong source in (a whole other ball of wax, that, here let's just say something stronger than an iPod) will be just enough for your K701 or HD600, plenty for your Grado, and overkill for your K26p.

Also notice that the K701's lower impedance in relation to the Senn makes up for its lower sesitivity to produce the same maximum SPL. Interesting, no? The high-impedance phones do have some advantages, though: little or no sound floor hiss, and you can plug in more than one in parallel.

 

[lipidicman]

Great post, I am going to study it a little more later

I am interested in this:
Quote:

Originally Posted by facelvega The high-impedance phones do have some advantages, though: little or no sound floor hiss, and you can plug in more than one in parallel.

Do the headphone splitters work in series or parallel? Common sense told me that two high impedance phones would be a bad idea, but I guess this was wrong!

 

[PiccoloNamek]

Quote:

Hiss is independant of both of these. It's caused by source, amp, and any noise that is introduced by cabling.

Are you sure? Because my Shure E4Gs sure to pick up a lot of hiss from my Total Bithead and/or iPod, but my ER4Bs do not pick up any hiss at all from the same setup. Even in high gain mode, my ER4s still pick up less hiss than my E4Gs do in low gain mode.

 

[lipidicman]

My understanding with hiss is that with lower impedance cans you have the volume lower and therefore your signal is smaller compared with the noise floor. Basically, Its a S/N ratio AFAIK.

My CX300 hiss like mad in my XCAN, whilst my HD650 is near silent. I know I have the pot higher with the 650. I know the CX300 is much lower impedance (16ohm) and a lot more sensitive (though I dont have the figure)

I could be wrong however, so don't shoot me

 

[Meyvn]

Quote:

Originally Posted by TheVoxHumanus I'd really like to understand what these two specs actually mean, and how they relate to each other. I guess I'm most concerned about the released specs for the new UE product, it has a pretty high sensitivity (117db/mw) but it has a pretty high impedence (32ohms). My problem with the higher-end IEMs (Shure) is that I can hear hiss on ALL of my sources. It's very, very frustrating. I certainly hope that despite the high sensitivity, the high impedence will dampen the hiss.

Sensitivity is the greater thing that affects loudness; Sennheisers have an impedance of 300Ω, and a fairly normal sensitivity (97 or so), whereas my K1000 has an impedance of 120Ω, and an insanely low sensitivity, 74. The K1000 is MUCH harder to drive. By the way, 32Ω is actually quite a low impedance for headphones. Anything below 60 generally produces a hiss in IEMs. Personally, if you want to fix the hiss, I would try the ER4p to s adapter, which is essentially just a resistor in a cable.

Quote:

now for fun, let's throw in a K701 (120;93). The Xenos does 75mW into 120.-- 112dB

Actually, the K701 has an impedance of 62.

 

[monkeymadness]

There are so many really smart people on head-fi. Yet why can't we have one difinitive clear cut answer to this impedance/sensitivity question? Why are there still so many variances between peoples responses? Is'nt there some simple formula that everyone recognizes to be true in all circumstances?

This makes me wonder...if you guys cant agree, then how can those in the industry agree on a single standard and what it means to sound and how to measure it!

How can we know that the people making the IEM's for example, actually know what they are doing with respect to this question?

 

[PeterR]

Quote:

Originally Posted by TheVoxHumanus I'd really like to understand what these two specs actually mean, and how they relate to each other. I guess I'm most concerned about the released specs for the new UE product, it has a pretty high sensitivity (117db/mw) but it has a pretty high impedence (32ohms). My problem with the higher-end IEMs (Shure) is that I can hear hiss on ALL of my sources. It's very, very frustrating. I certainly hope that despite the high sensitivity, the high impedence will dampen the hiss.

Ok, in simple terms, with headphones there are basically 3 specs to look at:

- efficiency: How loud they go with 1mW input power, measured in dB(SPL)/mW (to confuse people, this is sometimes also refered to as power sensitivity).

- (voltage) sensitivity: How loud they go with 1 V input voltage, measured in dB(SPL)/V.

- impedance: You can think of it as a fancier term for the probably more familiar resistance, used when dealing with AC circuits (with stuff like capacitors and inductors this becomes a complex number that varies over frequency, hence the distinction). It is a measure for how much something opposes the passing of current. The higher the impedance, the more voltage drops for a given current. This is called Ohm's law:
Voltage=Impedance * Current.

Just two more equations: Power = Voltage * Current
And, because Ohm's law tells us that current can be calculated from voltage and impedance:
Power = Voltage^2 / Impedance.
So for a given input voltage (think of it as the position of your volume control), the smaller the impedance, the more power your amplifier has to deliver.

To summarize:
dB/mW: How much power is needed (regardless of impedance), high figure -> "easy to drive"
dB/V: How much you need to turn up the volume

impedance: the ratio of voltage/current. Low impedance -> low voltage, much current - high impedance -> high voltage, low current

Knowing the impedance, you can translate dB/V into dB/mW. Let's say you have 32 Ohm cans for example. 1 V into 32 Ohms is (see formula above) 1 V * 1V / 32 Ohm = 0.03125 W or 31.25 mW. 31.25 mW is 31.25 times more than the reference for the efficiency figure. To express this in dB, you need to calculate 10*log(31.25)=14.9. This is what you need to add to the efficiency figure to get the sensitivity. If you have a 32 Ohm can with i.e. 100 dB/mW efficiency, sensitivity is then 114.9 dB/V.
Same calculation for a 300 Ohm can: 1V^2/300=0.0033 W = 10*log(3.3) dB(mW)=5.2 dB(mW). So a 300 Ohm can that needs the same power will have a sensitivity of only 105.2 dB/V, almost 10 dB less than its 32 Ohm counterpart. This means even though the 300 Ohm can isn't any more power hungry, you need to crank up the volume considerably higher (and if it's a low voltage portable you might hit the end stop while trying) to get the same level. That's why some people perceive high impedance cans as "hard to drive", althought it's technically not the case.

 

[hardstyler]

Quote:

Knowing the impedance, you can translate dB/V into dB/mW. Let's say you have 32 Ohm cans for example. 1 V into 32 Ohms is (see formula above) 1 V * 1V / 32 Ohm = 0.03125 W or 31.25 mW. 31.25 mW is 31.25 times more than the reference for the efficiency figure. To express this in dB, you need to calculate 10*log(31.25)=14.9. This is what you need to add to the efficiency figure to get the sensitivity. If you have a 32 Ohm can with i.e. 100 dB/mW efficiency, sensitivity is then 114.9 dB/V. Same calculation for a 300 Ohm can: 1V^2/300=0.0033 W = 10*log(3.3) dB(mW)=5.2 dB(mW). So a 300 Ohm can that needs the same power will have a sensitivity of only 105.2 dB/V, almost 10 dB less than its 32 Ohm counterpart. This means even though the 300 Ohm can isn't any more power hungry, you need to crank up the volume considerably higher (and if it's a low voltage portable you might hit the end stop while trying) to get the same level. That's why some people perceive high impedance cans as "hard to drive", althought it's technically not the case.

Ok I get it now, thanks for this info.

 

[milkpowder]

Quote:

Originally Posted by PeterR Ok, in simple terms, with headphones there are basically 3 specs to look at: - efficiency: How loud they go with 1mW input power, measured in dB(SPL)/mW (to confuse people, this is sometimes also refered to as power sensitivity). - (voltage) sensitivity: How loud they go with 1 V input voltage, measured in dB(SPL)/V. - impedance: You can think of it as a fancier term for the probably more familiar resistance, used when dealing with AC circuits (with stuff like capacitors and inductors this becomes a complex number that varies over frequency, hence the distinction). It is a measure for how much something opposes the passing of current. The higher the impedance, the more voltage drops for a given current. This is called Ohm's law: Voltage=Impedance * Current. Just two more equations: Power = Voltage * Current And, because Ohm's law tells us that current can be calculated from voltage and impedance: Power = Voltage^2 / Impedance. So for a given input voltage (think of it as the position of your volume control), the smaller the impedance, the more power your amplifier has to deliver. To summarize: dB/mW: How much power is needed (regardless of impedance), high figure -> "easy to drive" dB/V: How much you need to turn up the volume impedance: the ratio of voltage/current. Low impedance -> low voltage, much current - high impedance -> high voltage, low current Knowing the impedance, you can translate dB/V into dB/mW. Let's say you have 32 Ohm cans for example. 1 V into 32 Ohms is (see formula above) 1 V * 1V / 32 Ohm = 0.03125 W or 31.25 mW. 31.25 mW is 31.25 times more than the reference for the efficiency figure. To express this in dB, you need to calculate 10*log(31.25)=14.9. This is what you need to add to the efficiency figure to get the sensitivity. If you have a 32 Ohm can with i.e. 100 dB/mW efficiency, sensitivity is then 114.9 dB/V. Same calculation for a 300 Ohm can: 1V^2/300=0.0033 W = 10*log(3.3) dB(mW)=5.2 dB(mW). So a 300 Ohm can that needs the same power will have a sensitivity of only 105.2 dB/V, almost 10 dB less than its 32 Ohm counterpart. This means even though the 300 Ohm can isn't any more power hungry, you need to crank up the volume considerably higher (and if it's a low voltage portable you might hit the end stop while trying) to get the same level. That's why some people perceive high impedance cans as "hard to drive", althought it's technically not the case.

I think this is the best explanation so far. Thanks a lot.

The bit that I don't understand is why you need to take the natural log of 31.25 and then multiply by 10. Also, please can you explain why you need to add the solution to the efficiency figure to get the sensitivity. Thanks a lot!

 

[pegasus21]

I think what he meant is to convert from dB/mW to dB/V. Look at the link to the other thread earlier.

BTW, if say Alessandro Music Series 1 has a spec that reads 100db/mV, if we want to convert that to dB/V, do we just add 30dB to it? 10*log1000 = 30dB.

http://www.alessandro-products.com/headphones.html

Thanks.

 

[PeterR]

Quote:

Originally Posted by milkpowder The bit that I don't understand is why you need to take the natural log of 31.25 and then multiply by 10. Also, please can you explain why you need to add the solution to the efficiency figure to get the sensitivity. Thanks a lot!

Ok. Sensitivity is output per 1 V. As we know the impedance, we can calculate that 1 V gives us 31.25 mW. Now, if 1 mW gives us 100 dB(SPL), 31.25 mW will give us 31.25 times that amount obviously. Our hearing doesn't work very linear and covers an enormous range, so we use a logarithmic scale to specify levels. One Bel (the "B" in dB) is the base 10 logarithm of the ratio of two figures. If P2 is 10xP1, the difference is 1 B. More commonly used is the "deci"-Bel, which means 1/10 of a Bel. 1 B = 10 dB. The nice thing with a logarithmic scale is that you can multiply by adding. A power ratio of 31.25:1 is log(31.25)=1.5 B = 15 dB.
So 1V into 32 Ohms means 15 dB more power than 1mW. If 1mW gives us 100 dB(SPL), 15 dB more input power gives us also 15 dB more output, so 1V in means 115 dB(SPL) out.

Quote:

I think what he meant is to convert from dB/mW to dB/V

Works in both directions of course.

Quote:

BTW, if say Alessandro Music Series 1 has a spec that reads 100db/mV, if we want to convert that to dB/V, do we just add 30dB to it? 10*log1000 = 30dB.

Yes, I think it's a typo though, 100 dB/mW sounds more reasonable.

Edit: Wasn't paying attention, sorry. The dB figure is a power ratio. 1000 times the voltage means 1,000,000 times the power, so you'd have to add 60 dB.