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Use an L-pad (attenuator) with ultra low impedance IEM's?

solderdude

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When the impedance is constant I would not bother at all.
When the headphones in question all play very loud at low volume settings I would add a passive attenuator.

What headphone amp (or specs) are we talking about ?
Looks like something with a TPA6120A output stage.
 

ab1985

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When the impedance is constant I would not bother at all.
When the headphones in question all play very loud at low volume settings I would add a passive attenuator.

What headphone amp (or specs) are we talking about ?
Looks like something with a TPA6120A output stage.
The headphone is the AKG Y40.
The amp is Topping DX3pro.
An example of passive attenuator?
 

solderdude

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Acc. to Amir the output R of the DX3Pro = 1 Ohm (so in reality probably closer to 0.2 Ohm ?)

index.php


I would just use it normally unless you hear background noise.
Even when the output R would be 10 Ohm it is perfectly O.K. to use the Y40 on a 10 Ohm output.

the ifi is a passive attenuator for instance.
 

solderdude

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LOL... then you should have mentioned it was the ldac version.

In your case it doesn't matter. You can safely use the Y40 on a 10 Ohm output. There is no change in tonal balance and the difference in damping current is negligible nor does the driver seem to depend on electrical damping given the almost flat impedance.
Nothing to worry about.

I would just use it normally unless you hear background noise.
 

ab1985

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LOL... then you should have mentioned it was the ldac version.

In your case it doesn't matter. You can safely use the Y40 on a 10 Ohm output. There is no change in tonal balance and the difference in damping current is negligible nor does the driver seem to depend on electrical damping given the almost flat impedance.
Nothing to worry about.

I would just use it normally unless you hear background noise.
ok ... so the rule of thumb that one impedance must be 1/8 of the other? when should it be applied and when not?
 

solderdude

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Only when the impedance varies wildly (MA IEM) or substantially (say... HD599) or the driver in question relies on electrical damping (such as speakers).
Neither is the case here (with the Y40)

For that reason it is a 'rule of thumb' , something to be 'on the safe side just in case' and not a hard requirement / law.
 

ab1985

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Only when the impedance varies wildly (MA IEM) or substantially (say... HD599) or the driver in question relies on electrical damping (such as speakers).
Neither is the case here (with the Y40)

For that reason it is a 'rule of thumb' , something to be 'on the safe side just in case' and not a hard requirement / law.
ok ... very clear. which between the "dependence of the impedance on the frequency" and the "sensitivity" is more influential to understand whether or not to use an attenuator? with planar magnetic, for example (like hifiman he4xx)?
 

solderdude

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When sensitivity is high (audible noise when the volume is turned down) this is THE reason to use an attenuator.
Impedance variance in low impedance headphones is better resolved by using a low output R headphone out but when this isn't possible and there is more than enough output power avaiabl then a passive attenuator may be a good idea.

For planars attenuators are not needed because the impedance is flat and usually they aren't really that sensitive.
 
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xthechar

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HI @solderdude (or anyone else who knows), I have a Mackie 802vlz4 mixer with a 60 ohm headphone output impedance (https://mackie.com/sites/default/files/PRODUCT RESOURCES/MANUALS/Owners_Manuals/802VLZ4_OM.pdf). I really like the mixer! I didn't realize the impedance was so high when I bought it. I use it for casual listening because it's hooked up to a bunch of different sources I listen to audio from and it's not convenient to headphone output all over the place.

I normally use the Philips Fidelio L2, whose output impedance ranges from 18 to 22 ohms (https://www.innerfidelity.com/images/PhilipsL2.pdf). I'm not really sure if this is a large variation -- I guess not? Either way, I am using a very small range of the volume pot, and that's already with a lowered volume on my DAC (controlled via my computer, from 40/100 to 70/100 depending on the source). I think the iEMatch would be a good candidate for this setup, to both dramatically improve impedance matching and to give me some more room on the headphone volume pot on my mixer.

What do you think?

Separately, I have a question about the logic of using one of these voltage division attenuators to perform impedance matching. My understanding is that the amp (i.e. the headphone output jack) will "see" the output impedance of the sum of the two resistors, or at least 17 ohms for the iEMatch on the ultra setting. Doesn't this still produce an impedance mismatch with the headphone out jack, since the headphone out jack is still 60 ohms and the iEMatch which is standing in for a pair of headphones will be at 17 ohms, or just about the same as my headphones anyway? My guess is that this is true, but doesn't matter because the iEMatch's impedance doesn't vary with frequency. Is that correct? If not, how does this actually produce output impedance matching? Where is my gap in understanding?

Thanks for your help in advance.
 

solderdude

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HI @solderdude (or anyone else who knows), I have a Mackie 802vlz4 mixer with a 60 ohm headphone output impedance (https://mackie.com/sites/default/files/PRODUCT RESOURCES/MANUALS/Owners_Manuals/802VLZ4_OM.pdf). I really like the mixer! I didn't realize the impedance was so high when I bought it. I use it for casual listening because it's hooked up to a bunch of different sources I listen to audio from and it's not convenient to headphone output all over the place.

I normally use the Philips Fidelio L2, whose output impedance ranges from 18 to 22 ohms (https://www.innerfidelity.com/images/PhilipsL2.pdf). I'm not really sure if this is a large variation -- I guess not? Either way, I am using a very small range of the volume pot, and that's already with a lowered volume on my DAC (controlled via my computer, from 40/100 to 70/100 depending on the source). I think the iEMatch would be a good candidate for this setup, to both dramatically improve impedance matching and to give me some more room on the headphone volume pot on my mixer.

What do you think?

Without the voltage divider you would get about + 0.6dB more bass so that's not very much.
You can use something like the ifi match and get more travel on the volume control and remove the 0.6dB boost.

Separately, I have a question about the logic of using one of these voltage division attenuators to perform impedance matching.
My understanding is that the amp (i.e. the headphone output jack) will "see" the output impedance of the sum of the two resistors, or at least 17 ohms for the iEMatch on the ultra setting. Doesn't this still produce an impedance mismatch with the headphone out jack, since the headphone out jack is still 60 ohms and the iEMatch which is standing in for a pair of headphones will be at 17 ohms, or just about the same as my headphones anyway?

There is no such thing as impedance matching in the sense of impedance matching in HF and cables.
Amplifiers can be suited to drive low impedance headphones, high impedance headphones and some are intended to drive anything from low to high impedances.
In that sense one could say using an amplifier intended for low impedance headphones is not a good match nor vice versa.
This however is not the technical meaning of the words 'impedance matching'


My guess is that this is true, but doesn't matter because the iEMatch's impedance doesn't vary with frequency. Is that correct?

The load to the amp will be constant, well actually it varies so little it is of no practical consequence but the ifi version is a fairly low impedance load. As it is intended for IEM's these usually load the amp about similarly.
The G1217 version has a friendlier load of 33 Ohm.
 

xthechar

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Thanks for the help. Pardon my misuse of the term "impedance matching."

I guess the question I still feel I don't know the answer to is whether or not the load the amp sees operates in the same way for the attenuator as it does for the headphones themselves. Does it matter what load the amp sees in the case that the attenuator is plugged in, in the exact same way that it matters if headphones are plugged in? Or does the attenuator work in a different way which does not require a high (~ *8 as the "rule of thumb") impedance relative to that of the amp?

I hope my question is clear.
 

xthechar

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A follow-up question would be as follows. For the G1217, the voltage ratio between ~96 (load amp sees) and ~60 (amp) is about 1.6, but the ratio between ~16 (headphones) and ~3.2 (output impedance headphones see) is about 5.

For the ifi iEMatch on ultra, the ratios would be 77/60 = 1.28 and 16/1 = 16.

The answer to my above question might help determine which device would perform better given the amp and headphones I have. Naively, one might just look at the ratio between the headphones and the impedance they see (16 vs 5), and conclude the ifi does better. But I assume that the ratio between the amp and the load the amp sees matters too.
 

Bob-23

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Hobbyists know how to deal with it practically and mathematically, how to reduce output voltage resp. output impedance. The divider circuit not only divides output voltage but also works as an impedance changer. But the understanding might be a bit tricky and somehow counterintuitive.

This video by Curtis Meyer may deepen your understanding::
 

solderdude

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Thanks for the help. Pardon my misuse of the term "impedance matching."

I guess the question I still feel I don't know the answer to is whether or not the load the amp sees operates in the same way for the attenuator as it does for the headphones themselves. Does it matter what load the amp sees in the case that the attenuator is plugged in, in the exact same way that it matters if headphones are plugged in? Or does the attenuator work in a different way which does not require a high (~ *8 as the "rule of thumb") impedance relative to that of the amp?

I hope my question is clear.

The headphones are not purely resistive. When loading the amp directly it 'sees' a not purely resistive load. Because of voltage division the frequency response is (slightly) altered.
The attenuator is purely resistive. The amplifier thus 'sees' a resistive load. The load is linear and the frequency response won't be changed.

When you connect the a headphone to the adapter the load the amplifier 'sees' is not varying between 18 and 22 Ohm (20% variance) anymore but (in case of the G1217 adapter) but between 35.79 and 35.87 Ohm (0.2% variance).

From the headphones viewpoint without adapter it is driven from a 60 Ohm source. With the adapter it will be driven from 3.2 Ohm. This is a factor 20 lower.

The 'price' one pays is the headphone signal is attenuated. Here comes the tricky part (and the reason why I suggested the G1217 adapter (which one can build themselves as well) is that the load the amplifier sees is 'better' for the amplifier and the attenuation of the filter is less than when the ifi were used because of the 60 Ohm output resistance.
 

Bob-23

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A follow-up question would be as follows. For the G1217, the voltage ratio between ~96 (load amp sees) and ~60 (amp) is about 1.6, but the ratio between ~16 (headphones) and ~3.2 (output impedance headphones see) is about 5.
We are here only interested in the latter ratio: from the headphones' perspective we look back (hopefully not in anger).
 

solderdude

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A follow-up question would be as follows. For the G1217, the voltage ratio between ~96 (load amp sees) and ~60 (amp) is about 1.6, but the ratio between ~16 (headphones) and ~3.2 (output impedance headphones see) is about 5.

For the ifi iEMatch on ultra, the ratios would be 77/60 = 1.28 and 16/1 = 16.

The answer to my above question might help determine which device would perform better given the amp and headphones I have. Naively, one might just look at the ratio between the headphones and the impedance they see (16 vs 5), and conclude the ifi does better. But I assume that the ratio between the amp and the load the amp sees matters too.

One would have to look at the attenuation one would get when loading the amp directly, with the ifi and with the G1217.

without adapter the attenuation = -12.7dB
with IE-match in high attenuation = -37.5 dB (so 24.8 dB lower in level compared to direct)
with IE-match in low attenuation = -25.5dB (so 12.8 dB lower in level compared to direct)
With the ifi ear-buddy = -29dB (so 16.3 dB lower in level compared to direct)
with G1217 = -30.8dB (so 18 dB lower in level compared to direct)


Without adapter the load = 18 Ohm (also the ear-buddy is 18 Ohm but resistive), with the ifi it is even lower (16 Ohm) with the G1217 it is 35 Ohm
 
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xthechar

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By the way I ended up building my own attenuator cable (came to about $12 in parts from Aliexpress). My first guess of the best resistors was to use 33ohm on the amp side and 2.2 ohm on the headphone side. It worked great, I now have my headphone volume at unity gain on my mixer (as opposed to about 8 o'clock) and still have plenty of headroom on my volume control (going up to about 80/100 instead of 60/100 or so before). Whether I can hear an audible difference? Haven't ABXed it yet but I doubt it. Sometimes I feel like the mix sounds a bit more balanced on some tracks but it could very well be placebo. It was a fun little project and it's nice to have a bit more usable range on my mixer's volume knob, and it's nice to know that I don't have to worry about what headphones I plug into it. I'm also a bit less scared of accidentally blowing my ears out if the volume control gets accidentally turned up.
 
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