[breez]

Quote:

Originally Posted by AudioRookie I am uncertain of what the 'nominal impedance' affects within the headphones (clarity, distortion, volume, etc)

Clarity, distortion; no correlation at all. Volume; assuming same efficiency, the higher impedance model wants more voltage and thus the volume knob needs to be turned higher (it basically controls the output voltage of the device) for same volume.

 

[pbalcer]

Quote:

Originally Posted by AudioRookie Hello again, Does this mean that it is going to be harder to achieve the same volumes on the Sennheiser HD6XX that I am currently achieving on the Sennheiser HD515? If this is the case, why is the higher level of 'nominal impedance' used in the more expensive range of headphones?

Hi,

I think I migh add my $0.02 regarding the subject of impedance vs. volume.

Impedance does affect the volume but not exactly in the way one might think.
The volume (or loudeness) of a headphone is defined by the sound pressure. Look for the "SPL" (Sound Pressure Level) figure to find out how sensitive the headphones are. Usualy the SPL is defined for 1 mW of driving power - in such case it is expressed in [dBm]. But some manufacturers define SPL for 1V driving signal (which on the nominal impedance gives power P = U^2 / (2*R); for R=300 ohm it would be 1.67mW) - the SPL is expressd in [dB].

When you want to compare how loud the headphones are you will have to find their SPLs for the common denominator (usualy 1mW) - if the SPL is given for something different than 1mW, you will have to recalculate it. Let's say we have SPL = 102 dB / 1V for 300 ohm headphones- which means SPL = 102 dB/1.67mW. We need the SPL for 1mW, which is 1/1.67 (or 0.6) smaller power. Power ratio results in 10*log(0.6) = -2.22 dB weaker sound pressure. Therefore our SPL is (102 - 2.22) dB / mW which means SPL = 99.8 dBm.

Once you have the SPLs you can tell which headphone is louder. But there is one more thing you have to take under consideration as well: the ability of the source to drive the cans with the appropriate power. For example most portable things have the output power specifed for 30 ohms load (cans).

If the manual says 10 mW/30 ohm power it means that it can drive only 30 ohms cans with 10 mW. Power P = (U*I)/2 (U and I in this equation are amplitudes!); the P = 10 mW/30 ohm means that the maximum amplitude is U = 0.77V (according to the equation U = SQR(P * 2R)). This voltage can drive 300 ohm cans with power P = 1 mW roughly (accroding to the equation: P = U^2 / 2R).

Now imagine we have two cans: 30 ohm, SPL = 96 dBm and 300 ohm, SPL = 100 dBm. If you drive them both from the same portable walkman that can output 10 mW/ 30 ohm, the 30ohm headphones will be louder beacuse the walkman will drive it with 10 mW while the 300 ohm cans will be driven with only 1 mW. This will result in the pressure levels of 106 dB for 30 ohm headphones (10 mW is 10 times higher than 1 mW which means +10dB) vs only 100 dB for 300 ohm headphones.

Conclusion: impedance is not enough to compare the loudness. SPL must be used for this purpose. The impedance is used only to assess the driving capability of the source.

Sory for the long post.
Hope this helps.
Piotr

 

[Born2bwire]

Quote:

Originally Posted by Manveer http://www.answers.com/topic/nominal-impedance http://www.google.com/search?q=%22no...en-USfficial In electrical engineering or audio, the nominal impedance of an input or output is the equivalent impedance of all of the output or input circuitry of a device lumped into one (imaginary) component. An impedance is a combination of resistance, capacitance, and inductance. It can be thought of as a resistor that changes values at different (sine wave) frequencies.

I don't think you could say it any better than that. Personally, I hate it when people say impedence is resistance because there is a subtle difference which the quoted definition hits right on the head. Impedence takes into account resistance, capacitance, and inductance. The result of which is that the resistance (the real part of impedence, the complex part is the conductance/inductance) will vary according to the applied frequency.

This means that depending on the frequency of the signal, the properties of the circuit change. A system that has an impedence with a large capacitance or inductance will vary greatly over the frequency range of sound. The end result being that a 80 Hz bass hit may see a higher resistance than a 15 Khz sound, causing the bass to be repressed. In terms of strict volume, you generally just want to pay attention to the sensitivity of the headphones. Cans of the same impedence will have different degrees of drivability (if I may use such a term) that is best expressed by the sensitivity of the cans. For example, the K1000's are notoriously hard to drive but they actually have a low-medium impedence.

 

[cyan]

The replies are just very helpful for me to get a clearer picture of the scenerio.
However this is really an interesting question that remains unanswered.

"why is the higher level of 'nominal impedance' used in the more expensive range of headphones?"

I really wanna know why the higher-class headphones usually comes with higher norminal impediance? Are there more rounds of coil on their driver?

 

[Born2bwire]

Quote:

Originally Posted by cyan The replies are just very helpful for me to get a clearer picture of the scenerio. However this is really an interesting question that remains unanswered. "why is the higher level of 'nominal impedance' used in the more expensive range of headphones?" I really wanna know why the higher-class headphones usually comes with higher norminal impediance? Are there more rounds of coil on their driver?

I'm not sure what they mean when they report the impedence of headphones. Technically speaking, impedence is a complex number: Z = R + j*X, where j is the square root of (-1). The real part, R, is the resistance and the imaginary part, X, is the reactance. If X is positive, the impedence is inductive. If X is negative, the impedence is capacitive. Both R and X will change with frequency. At low frequencies, capacitance dominates while at high frequencies inductance dominates. Now I have not found out what is specifically being reported by companies when they give the impedence of their headphones. Are they reporting the real part of the impedence or the magnitude of the impedence (I assume though that they are taking the impedence at 1Khz)? For the most part I believe that it is the resistance of the headphones for the reason stated below. So I usually treat impedence as more or less a guideline as to how the headphones act as a load. Low impedence cans will usually pull more current out of your amp for the same amount of power in comparison to high impedence cans. So when people say that an amp performs better with Senn HD580's than Grado's, I keep that in mind if I'm thinking about using other low impedence cans with that amp.

More turns in the voice coil would increase inductance and thus increase the positive reactance, but ideally you would want to design a purely resistive load. That is, we do not want the lump circuit to be capacitive or inductive because then it's behavior as a load will vary with frequency, arising in variations in the frequency response of the headphones. So when designing headphones, I'm sure that the designers would in the end add a capacitive or inductive element to tweak the impedence so that it is only resistive. For this reason I lean toward the belief that you can take the impedence rating of a can pretty much as the resistance.

 

[Manveer]

Quote:

Originally Posted by AudioRookie Well if you haven't figured out by my forum name, I have no idea about the technical jargon in relation to audio devices. Whilst I'm sure his intentions may have been good, I am slightly insulted that he has implied that I have not bothered to search this out. I have searched this out, but have not found a resource that was able to explain it in generalised terms for people (such as myself) with limited knowledge on the topic. I am uncertain of what the 'nominal impedance' affects within the headphones (clarity, distortion, volume, etc), and why the more expensive range of headphones have a higher 'nominal impedance'. I don't know how or why headphones work the way they do, but what I do know is that a good set of headphones can really enhance the audio experience. If the above mentioned definition of 'nominal impedance' is as simplified as it gets, then I guess I am plain out of luck. Thanks.

You are asking two questions:
-What is impedance?
-How does this change the sound of headphones?

I don't know enough to give you the technical details of how impedance affects the sound (other than what I've already read in this thread). I can generalize and use somewhat ambiguous terms like "adds warmth," but I don't think that's really accurate.

I do know what impedance is, so I found a credible source with an eloquent explanation for you. I assumed that everyone learned about resistance in high school physics, and impedance is just a more generalized form of resistance (as Born2bwire explained) which takes into account inductance and capacitance as well as resistance.

All this "technical jargon" isn't that complicated if you just take some time to learn basic circuit analysis. Once you understand that, you can understand the technical explanations that have already been provided. It's not that simple to explain the effect of impedance on the sound of headphones accurately without overgeneralizing.

 

[Born2bwire]

Quote:

Originally Posted by Born2bwire More turns in the voice coil would increase inductance and thus increase the positive reactance, but ideally you would want to design a purely resistive load. That is, we do not want the lump circuit to be capacitive or inductive because then it's behavior as a load will vary with frequency, arising in variations in the frequency response of the headphones. So when designing headphones, I'm sure that the designers would in the end add a capacitive or inductive element to tweak the impedence so that it is only resistive. For this reason I lean toward the belief that you can take the impedance rating of a can pretty much as the resistance.

I probably should make a correction to this. If we look at the impedance and frequency graphs of the HD650, courtesy of Headroom, we see that the synergy of the system is more complex then I originally stated.

We can see that the impedance has a resonance at around 60 Hz. If the frequency response of the drivers were strictly proportional to impedence (i.e: power output of the drivers is proportional to the electrical power sent to the voice coil which is proportional to the resistance of the load) then we would expect a sharp drop in the frequency response of the cans. But viewing the frequency responce, the cans are fairly linear. The increase from 300 to around 500 Ohms correlates to a change of a little less than 3 dB (3 db would be 300 to 600 or halving the power) but a quick glance at the frequency response graph quickly shows that this does not occur physically. I think the other consideration would be the mutual inductuctance between the voice coil and the magnet on the driver and also the physical characteristics of the driver itself. The effects of the inductance between the voice coil and the magnet (the inductance of the coil alone is due to the self inductance of the coil but by placing the magnet in there you now have another system of inductance) probably would be measured by the impedance of the cans itself. But the driver itself (the membrane, magnet, etc.) is a damped oscillator and thus has it's own mechanical resonance. So the driver probably has a single resonance slightly around 60Hz to make up for the loss of power from the increased impedance. This makes sense because we see that in the higher frequencies, the inductance of the headphones is now taking hold and causing an increase in the impedence. But the frequency response does show a decreasing trend in the higher frequencies. So the driver may only have a single resonant point and so the decreased power at the higher frequencies correlates in a decreased response.

This is all purely conjecture on my part and I'm assuming a rather simple harmonic oscillator as the model for the driver. In the end the only absolute lesson to walk away is that no single characteristic of the headphones will define it's performance. It's an amalgomation of physical and electrical systems over a range of frequencies. The end result is that you have to take into account the combined behavior of the physical and electrical properties and thus looking at only one side of the problem does not give the full picture.

 

[Jigglybootch]

Quote:

Originally Posted by Born2bwire More turns in the voice coil would increase inductance and thus increase the positive reactance, but ideally you would want to design a purely resistive load. That is, we do not want the lump circuit to be capacitive or inductive because then it's behavior as a load will vary with frequency, arising in variations in the frequency response of the headphones.

Actually, a resistor will vary with frequency as well. One has to take into account the inductance and capacitance of the leads, as well as leakage capacitance (though this is typically ignored). So in actuality, up until a certain frequency, a resistor will have perfectly linear impedance, but once it reaches a certain frequency, the resistor will act as a capacitor. Once it reaches an even higher frequency, the resistor will act as an inductor.

For the frequencies we're dealing with, you don't really need to worry about that though.

 

[RascaLdodo]

i have 2 buy a headphone for my express music cellphone....but lil bit m confused b/w the impedance which is given in tech specs. 
I please to listen music moreover a bass lover too...is this impendance affects bass of the sound?? plz help me, what shud i do either buy a 16 ohm or 32 ohm impedance of headphone
 
thnkz!!

 

[RascaLdodo]

i have 2 buy a headphone for my express music cellphone....but lil bit m confused b/w the impedance which is given in tech specs. I please to listen music moreover a bass lover too...is this impendance affects bass of the sound?? plz help me, what shud i do either buy a 16 ohm or 32 ohm impedance of headphone thnkz!!

 

[Anewills]

I never took physics in highschool or college (so far), so a lot of the more technical descriptions are just words to me and I have no idea of the meanings.  From what I've been told, you should pick a headphone with an impedance level that matches your source?  I have an iphone as my main source with an impedance of 32 ohm, so does a 32 ohm impedance headphone work best for it?

 

[duncan1]

In a loudspeaker system say with a loudspeaker of 8 OHMS impedance a output transformer is most efficient with an output impedance of 8 OHMS -that's VERY simply put.
           Nominal impedance is a value of X at a set frequency./frequencies/ test 8 OHMS at DC.
            This is putting  it very simply.!
                  There are a LOT of algebraic maths to this.