Impedence question - IEMs

[GAD]

I searched, and I read, but I don't get this.

I have ER4Ps. I just got the p->s cable to try it out.

How can increasing the impedance of the path be a good thing? I can see if the natural impedance of the drivers were higher, but to me it seems counter-intuitive that making the impedance higher in the cable makes the drivers behave better. I would think lower impedance would be better.

Obviously I'm not an EE, but I am a ham and can grasp electrical concepts - I just don't have a lot of experience with audio electronics theory - I don't get this one.

Thanks,

GAD

 

[nightfire]

Quote:

Originally Posted by GAD /img/forum/go_quote.gif I searched, and I read, but I don't get this. I have ER4Ps. I just got the p->s cable to try it out. How can increasing the impedance of the path be a good thing? I can see if the natural impedance of the drivers were higher, but to me it seems counter-intuitive that making the impedance higher in the cable makes the drivers behave better. I would think lower impedance would be better. Obviously I'm not an EE, but I am a ham and can grasp electrical concepts - I just don't have a lot of experience with audio electronics theory - I don't get this one. Thanks, GAD

There's two different things at play here. Wires, coils, etc., have both resistance and impedance. Resistance is the measure of difficulty DC current will have passing through the conductor, and impedance is a measure of the difficulty AC current will have passing through the conductor.

The impedance of a motor's coil (speaker/IEM driver) changes with regards to the frequency (for AC signals). Generally the impedance rises with the frequency. A resistor, however, doesn't change (for AC or DC). So what happens is you're raising the overall resistance of the circuit with the resistor, such that a higher voltage will be required for a given current flow, across the frequency spectrum. The ratio of the current flow (between low freq. and high freq.) changes accordingly.

For example (numbers pulled from my ass):

No P->S adapter: 20hz -> 40ohms / 1khz -> 60ohms / 20khz -> 120ohms
With P->S adapter: 20hz -> 115ohms / 1khz -> 135ohms / 20khz -> 195ohms

(You just add the nominal impedance at whatever frequency you're measuring to the resistance of the resistor (75ohms)).

So you can see in this example, without the P->S adapter, the phones have 50% more impedance at 1khz than they do at 20hz (60ohms:40ohms), but with the adapter, they have less than 20% more (135ohms:115ohms).

Less impedance/resistance means more current flow, and more current flow means more volume. Hence, using P->S adapter should make less bass than without (in this example).

This example is exaggerated but I'm pretty sure that's what's happening. The adapter flattens out the frequency curve because the impedance change of the headphones (over the FR spectrum) is a less significant portion of the overall resistance.

Does this make any sense? I'm also not an EE.. so my understanding probably isn't perfect; any corrections welcome.

 

[EsJee]

i read all that.... but just like a college engineering textbook... i think i'm gonna have to read that 5 more times.

 

[GAD]

Interesting if true - I hadn't thought about the AC vs. DC aspect - that makes some sense. All my theory is DC based. Is this confirmed?

GAD

 

[AzN1337c0d3r]

Quote:

Originally Posted by EsJee /img/forum/go_quote.gif i read all that.... but just like a college engineering textbook... i think i'm gonna have to read that 5 more times.

Yup definitely sounds like something from my EE textbooks. I'll lay it out in (hopefully) easier terms for you to understand.

Normally, without impedance adapter, a headphone may measure (note that these numbers are pulled straight out of thin air, they do not reflect real life measurements):

32 Ohms @ 1 KHz
64 Ohms @ 2 KHz

Now, if you add a 100 Ohm adapter, then the same phones measure
132 Ohms @ 1 KHz
164 Ohms @ 2 KHz.

In the case without the resistor, we have a 100% increase in impedance going from 1 KHz and 2 KHz.
(64 - 32)/32 * 100 = 100

In the case with the resistor, we have only a ~24% increase in impedance.
(164 - 132)/132 * 100 = 24.2424

Less % change in impedance leads to a flatter frequency response graph.

However, dynamic headphones are by definition, complex loads with inductance and capacitance. This leads to current-voltage phase differences that can't be fixed with a simple resistor and it would be mighty helpful if headphones manufacturers provide a capacitance/inductance value and or power factor/angle in their specifications.

 

[GAD]

That makes some sense - awesome explanation - thanks!

GAD

 

[Champ04]

Ok, so I have a "is more always better" question.
If adding 75ohms flattens out the frequency.
Assuming an amp could handle the increase, would adding (for example) 750ohms be better yet??

 

[Spyro]

What about the effect of the harmonized decombopulator flux capristor?
(Too much mumbo jumbo to me)

But my understanding in the case of a higher impedance IEM (like ER-4P versus ER-4S) was that a higher impedance enables the IEM to produce a cleaner and more extended frequency? That the "bassier" ER-4P isn't really a deeper bass but lower mids hitting harder and that also the highs can sound siblant/splashy because they can't extend as cleanly. Is this true?

 

[Champ04]

Quote:

Originally Posted by Spyro /img/forum/go_quote.gif That the "bassier" ER-4P isn't really a deeper bass but lower mids hitting harder and that also the highs can sound siblant/splashy because they can't extend as cleanly. Is this true?

I think that is probably quite accurate.

 

[slwiser]

If you go to my gallery I have a series of images from a Japanese web site for many different headphones and I have done this type of equalization for several of the more popular headphones and the ETys. To me this makes complete sense that a flat impedance curve will flatten out the frequency curve. To me it should also make the amp less of an issue since it would be pushing a more stable load if the headphone had a flatter impedance curve. With heavy changes across the frequency curve one would seem to need an amp that would have more current capacity to handle the more difficult load during music transitions. The ER-4P and ER-4S are shown in the table as examples. Most modern amps should have current capacity adequate for a stable load but the issue is how do they respond to dynamic impedance changes with large swings across the frequency range? I hope you don't think this to be thread high-jacking since what I did applies to regular headphones more than the IEMs. But the concept is the same. Note the two that have the largest swings also seem to have a reputation for heavy mid-bass.

 

[Champ04]

That's awesome slwiser!
Thanks!!

 

[Champ04]

Bump.
Any engineers have an answer for #7?

 

[Trager]

Quote:

Originally Posted by Champ04 /img/forum/go_quote.gif Ok, so I have a "is more always better" question. If adding 75ohms flattens out the frequency. Assuming an amp could handle the increase, would adding (for example) 750ohms be better yet??

The answer is probably no. I've often heard it said that you don't actually WANT a perfectly flat frequency response. In addition, audio drivers are reactive elements - that means that their impedance curves are a function of the capacitance (helps to deliver high energy transients, like sudden bass hits or high volume changes), resistance (not dynamically variable), and inductance (which speeds response time). If the resistance is very very high compared to the C/I components, I would guess that you'd have a phone with a very flat frequency response but lousy transients and a rather odd tonal response (my gut feeling tells me that high frequency sounds wouldn't sound that good because the driver would be slow to respond to changes in hf, but I could be very wrong about that).

 

[slwiser]

Quote:

Originally Posted by Trager /img/forum/go_quote.gif The answer is probably no. I've often heard it said that you don't actually WANT a perfectly flat frequency response. In addition, audio drivers are reactive elements - that means that their impedance curves are a function of the capacitance (helps to deliver high energy transients, like sudden bass hits or high volume changes), resistance (not dynamically variable), and inductance (which speeds response time). If the resistance is very very high compared to the C/I components, I would guess that you'd have a phone with a very flat frequency response but lousy transients and a rather odd tonal response (my gut feeling tells me that high frequency sounds wouldn't sound that good because the driver would be slow to respond to changes in hf, but I could be very wrong about that).

It is interesting that the highest rated phones in stock condition have the most flat impedance curves as shown in the table above. Anything less than 20% would probably not be noticeable. The UE9 in normal frequency ranges, L3000 and Qualia are all within that profile. With the ER-4S being right in there as very flat and when driven with a good amp can sound as good as anything. The problem with the ER-4S is that most people want to push them with only their portable units without an adequate amp. I don't believe any of these particular headphones have issues with tonal response or transients. Those that are way out of this range are known to have some odd tonal qualities such as the HD650 (corrected with balance configuration) and the GS-1000 (also much improve when balanced) in the upper mid bass regions for both.

I am attempting to keep the documented impressions across Head-Fi consistent with the measured impedance normalizations above. Your considerations really don't match very well.

You said also: "The answer is probably no. I've often heard it said that you don't actually WANT a perfectly flat frequency response. " Edit: I do not disagree with this. This is very true with headphones. Their frequency curves need to adjusted for the Head Transfer Function.

Another interesting thing is that impedance does not necessarily imply a flat frequency curve if the driver is properly designed for the head transfer function. The impedance curve is more a function of how the amplifier would interact with the driver to support whatever transients are called for. Again if the amp has very deep current capacity for handling difficult loads such as very high end amps then this is not as much of a problem.

 

[HiFlight]

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You said also: "The answer is probably no. I've often heard it said that you don't actually WANT a perfectly flat frequency response. "
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That is very true! On a number of occasions, I have test calibrated my system using an audio sweep generator and a decibel meter. When calibrated for a constant decibel level across the frequency spectrum, the resultant sound is very harsh with overly bright highs, and weak bass.

As the ear does not perceive sound in a linear fashion, a "flat" frequency response sounds very sterile. (A common comment regarding the Ety 4S)