[Prog Rock Man]

Rather than hijack another thread I though I would start a new one. Here is the exchange in the other thread...

Quote:

Originally Posted by Menisk /img/forum/go_quote.gif Um.. No. The impedance just tells you if it's going to need more current or voltage. The sensitivity tells you how easy it is to drive. Pretty sure my 300ohm Sennheisers are going to be easier to drive than a pair of 120ohm K1000s.

I was going by specifications of headphones, which I have not seen listing 'Sensitivity' and taking it that since impedence is the opposition faced by a circuit and is measured in ohms, that that indicated how hard a headphone is to drive.

I feel a new post coming on rather than hijacking this one......

So, what measurement is used to determine how easy or hard a headphone is to drive?

 

[MrGreen]

Efficiency (in the most literal sense: Electrical Energy -> Acoustic Energy).
This is influenced by various factors such as the voice coil, components used (metals etc), mass of the driver, size of the driver, strength of the magnet and how well the driver responds to positive and negative charge. If you want something more in depth you'll have to seek out someone with more expertise.


For the reccord, the sensitivity doesn't tell you how easy something is to drive; it tells you how easy it is to make go loud (notable since it is usually given /mW). As an example, the DT880 are fairly difficult to drive well (otherwise it is slow, has ungodly highs and is anemic in the bass), although very easy to make loud at 96 or 98 dB (cant remember which) per 1mW, whilst the MS1 is 100dB which is a fairly small difference.

If you want to tell how easy it is to "make sound good"; the easiest way is your own ears. Headphones, inspite of their rather simple design are complex acoustic constructions consisting of housing, drivers, magnets etc. Determining how well a transducer will move/sound [as opposed to how much it will move] to my knowledge is quite difficult to do in that it is a combination of many factors including slew rate, voltage swing and current provided by the amplifier as well as those inside the headphone itself.

 

[Uncle Erik]

Yes, efficiency is measured in Decibels (dB).

When you think about efficiency, it helps to think about what is happening in a physical sense. You have a magnet and a voice coil. Running electricity through the voice coil makes it move back and forth with respect to the magnet. How strong or weak the magnet is effects how much power has to go through the coil to make it move. Next, the properties of the coil itself (inductance, resistance, etc.) tell you how well the coil handles electricity put into it. Some coild are better at handling small
amounts.

Next, you have to look at the cone of the driver that the coil is attached to. Is the cone heavy? That saps efficiency. If the cone is especially stiff or hard to move (aside from mass) that can hurt efficiency.

Also, whether a headphone is open or closed probably has something to do with this, too. If a driver is closed, you can use the enclosure itself to generate a little more pressure, which could increase efficiency.

 

[Bilavideo]

Sensitivity is just the headphone version of SPL. How loud will these mothers go? Impedence measures resistance. The greater the impedence the more current you'll need to drive your cans. A 32 ohm Grado is easy enough to drive that you don't need an amp. A 600 or 700 ohm headphone will need an amp.

 

[iancraig10]

Uncle Erik. Your replies are SO informative. I really understood that and I didn't feel like I'm an idiot for being told!!!

You really have the knack. I've read a few of your posts when these technical things appear and they're a really good read when you reply.

Many thanks

Ian

 

[Wmcmanus]

Whether it cries when you tell it that is looks fat.

 

[MrGreen]

Quote:

Originally Posted by iancraig10 /img/forum/go_quote.gif Uncle Erik. Your replies are SO informative.

hmph.

Quote:

Originally Posted by Uncle Erik /img/forum/go_quote.gif Yes, efficiency is measured in Decibels (dB).

For the record, efficiency is measured in percentiles and is reflected in sensitivity, which is measured in dB.

 

[the search never ends]

Quote:

Originally Posted by MrGreen /img/forum/go_quote.gif hmph. For the record, efficiency is measured in percentiles and is reflected in sensitivity, which is measured in dB.

I love Uncle Erik, but. you are correct.

 

[the search never ends]

Quote:

Originally Posted by Wmcmanus /img/forum/go_quote.gif Whether it cries when you tell it that is looks fat.

LMAO. you described sensitivity, not efficiency.....your subtle correction?
Or always the wise guy? Edit: Both (as always my opinion is subjective)

 

[Duggeh]

Quote:

Originally Posted by Bilavideo /img/forum/go_quote.gif Sensitivity is just the headphone version of SPL. How loud will these mothers go? Impedence measures resistance. The greater the impedence the more current you'll need to drive your cans. A 32 ohm Grado is easy enough to drive that you don't need an amp. A 600 or 700 ohm headphone will need an amp.

Incorrect.


SPL is the headphone version of SPL. And Sensitivity is the headphone version of sensitivity. Sensitivity has nothing to do with how loud a headphone will go. That is a factor of its power handling.

Additionally, the greater the impedance, the more voltage swing you need per level of current. The lower the impedance, the greater the level of current for the voltage swing. 4-ohm speaker drivers require double the current throughput of 8-ohm speakers for example. Not the other way around.

There are 2000ohm headphones which sound rather pleasing right out of an ipod. And 4-ohm headphones which barely make a noise from the same ipod. Similarly, there are 32-ohm headphones which sound good out of that ipod and 600-ohm headphones which sound like ass.

The proliferate misconception on this website is that more ohms means needs more power means need a bigger amp means Grados are 32 ohms so sound fine without an amp and Sennheisers are 300 ohms so they need an amp.

Really, both benefit greatly from amplification but different amps perform differently into the different loads that the headphones have and an amp which is particularly good for Grados, may not shine so well with a Sennheiser (although that is in itself another iffy generalisation).


As for what physical design aspects determine how sensitive or efficient a headphone is. I can honestly say I've no idea. Factors will include the magnet, the coil and the diaphragm, but what particular changes in the construction of each will do I couldn't tell you with any confidance.

 

[Prog Rock Man]

Using my own cans as an example

Grado SR80 32ohms SPL 98
Senn PX200 32ohms SPL 115
Senn mx500 32ohms SPL 125
AKG K702 62ohms SPL 105
Goldring NS1000 100ohms SPL 93 (with NR off)
300ohms SPL 101 (with NR on)

Each of them out of an ipod without any amplification

Grado SR80 low volume and sound weak
Senn PX200 absolutely fine
Senn mx500 absolutely fine
AKG K702 low volume sound weak
Goldring NS1000 hardly any volume and sound terrible with NR on or off.

So there is just as much of a correlation between ohms to whether the ipod can successfully drive a headphone as SPL. But neither is a complete indication of how well an ipod works unamped.

So Iam lead to conclude that both ohms and SPL are an indication of how sensitive headphones are, but as has been said, neither are definitive,

When I say successfully drive the headphone I mean can the ipod produce enough volume that you not need to maximise it and how big a drop in sound quality is there from how the headphone performs amped with my X-CAN.

 

[iancraig10]

Uncle Erik. Your replies are SO informative.

Quote:

Originally Posted by MrGreen /img/forum/go_quote.gif hmph. For the record, efficiency is measured in percentiles and is reflected in sensitivity, which is measured in dB.

Now don't go all humpy on me. Say what the problem is.

Now ask yourself, did I mean it or not?

(A nicked quote from Dirty Harry except it was to do with luck)

Ian

 

[plonter]

Quote:

Originally Posted by Bilavideo /img/forum/go_quote.gif Impedence measures resistance. The greater the impedence the more current you'll need to drive your cans. A 32 ohm Grado is easy enough to drive that you don't need an amp. A 600 or 700 ohm headphone will need an amp.

that's what I though in the beginning,but it turns out that this is not so simple.
for all of you experts here... I understood a long time ago that this "rule" mentioned in the quoted post above is not intirely correct and that the sensitivty (or SPL...) also plays an imprortant role in determine if a headphone will be hard or easy to drive.

so..impedance is not the only factor that determines the headphone ability to be driven without an amp, but in the case of the GRADO 32ohm and sennheiser 300ohm IT IS THE IMPEDANCE that's calling the shot!

just tell me if i am correct in the next assumption:
given two headphones with the same SPL level, the more the impedance, the harder it will be to drive?

 

[MrGreen]

Quote:

Originally Posted by plonter /img/forum/go_quote.gif just tell me if i am correct in the next assumption: given two headphones with the same SPL level, the more the impedance, the harder it will be to drive?

I suggest you read up on ohms law (probably other laws relating to voltage wouldnt hurt either).

Let's say we have two headphones with sensitivity of 100dB/W (this is way too low, 100dB/mW is more accurate but this is for the sake of easy calculation so its straight forwad) and one with 35 ohms and the other with 350 ohms.

V=IR and P=IV
(V = volts, I = Current, R = Resistance, P = Power).

P=I(IR)=I^2R

Let's say we want to drive each headphone to 100dB. We need to supply it with 1W (ass it is 100db/W).

For 35 ohms:
I = (1/35)^1/2 = 0.169(blahblahblah) amps
For 350 ohms:
I = (1/350)^1/2 = 0.053(blahblahblah) amps


Here you can see that the higher the resistance (ohms), the less current required to achieve particular power. Which makes it look that higher ohms = easier to drive, which isnt necessarily true.


If we substitute these values then into the other equation; V=IR we see...
35 ohms:
V = 0.169x35 = 5.916 V
350 ohms:
V = 0.053x350 = 18.708 V

Here we note that higher ohmage results in the need for higher voltage to achieve the required power.

tl;dr: Higher ohms = less current, more voltage
Lower ohms = more current, less voltage
Whichever is easier to drive depends on your amp (eg a cheap tube amp will supply high voltage and low current power and suit higher ohm cans, but do quite poorly on low ohm cans, particularly if it is OTL).


Please note that this is a better indication of how loud the headphone will be driven by an amp rather than how nice it will sound (which to be honest I cannot calculate).

 

[plonter]

thank you for the detailed explenation. I did saw that formula before regarding the same issue but I probably got a head time to understand it fully because I don't exactly know what all the terms mean. so can you please explain to me the terms: voltage and current? what are they and what is the difference?