[supernaut9]

I've sometimes wondered if the construction of an iem might effect the outcome of EQ. For example, would the treble of an iem with 64s tubeless tia drivers be impacted more greatly due to being directly in the nozzle as opposed to something with tubes and a closed driver? Would this be a negligible impact, or would there be no difference at all?
Maybe this is a dumb question since if that were the case, pregain might affect the overall tuning of an iem, which doesn't seem to be the case. Any thoughts appreciated, even if it's just to call me a dunce.

 

[castleofargh]

There are situations where EQ won't just do what you set it to do. For starters, if the driver is already reaching its limit at a certain frequency and listening level (like maybe showing a massive treble roll off), a boost with EQ is likely to boost distortions more than the amplitude at the requested frequency. That might be related to your question in the way some driver movements might be hindered by some tech causing, say, some airflow restriction or something moving alongside the driver/airflow, causing perhaps some other nonlinear impact.
The other example is when there is cancellation (electrical with some poorly set crossover, or acoustic probably only at high frequency on an IEM as for strong cancellation of bigger wavelengths you need more space than an IEM has in total).

For your specific question, yes the sound is greatly impacted by a decision like using or not using tubes to guide the flow (even with tubes there are still interactions between drivers and issues for the high frequency). But I don't think this has a notable impact on your ability to EQ both. They just would have very different FR at the start and from that would naturally come different issues and limitations, but probably similar to having been acoustically tuned in any other way. Can we really attribute those consequences for using the tubes? It might get more rhetorical than anything.

My experience using REW to test the impact of my EQ and to try and correlate measurements with my personal preferences on a bunch of IEMs over the years, has been that EQ applies quite reliably on IEMs regardless of how many drivers, tubes or no tube, sealed or not we find in the IEM. Again, with the clear caveats I mentioned.


Maybe unrelated to your question, it might be good to keep in mind how the treble graphs shown online are almost never:
1/accurate. Most are smoothed graphs, instead of showing the utter chaos full of local cancellations that the high frequency range usually is.
2/ exactly what you're getting in your own ear canal with your own fit and selected tips.

 

[supernaut9]

There are situations where EQ won't just do what you set it to do. For starters, if the driver is already reaching its limit at a certain frequency and listening level (like maybe showing a massive treble roll off), a boost with EQ is likely to boost distortions more than the amplitude at the requested frequency. That might be related to your question in the way some driver movements might be hindered by some tech causing, say, some airflow restriction or something moving alongside the driver/airflow, causing perhaps some other nonlinear impact.
The other example is when there is cancellation (electrical with some poorly set crossover, or acoustic probably only at high frequency on an IEM as for strong cancellation of bigger wavelengths you need more space than an IEM has in total).

For your specific question, yes the sound is greatly impacted by a decision like using or not using tubes to guide the flow (even with tubes there are still interactions between drivers and issues for the high frequency). But I don't think this has a notable impact on your ability to EQ both. They just would have very different FR at the start and from that would naturally come different issues and limitations, but probably similar to having been acoustically tuned in any other way. Can we really attribute those consequences for using the tubes? It might get more rhetorical than anything.

My experience using REW to test the impact of my EQ and to try and correlate measurements with my personal preferences on a bunch of IEMs over the years, has been that EQ applies quite reliably on IEMs regardless of how many drivers, tubes or no tube, sealed or not we find in the IEM. Again, with the clear caveats I mentioned.


Maybe unrelated to your question, it might be good to keep in mind how the treble graphs shown online are almost never:
1/accurate. Most are smoothed graphs, instead of showing the utter chaos full of local cancellations that the high frequency range usually is.
2/ exactly what you're getting in your own ear canal with your own fit and selected tips.

Thanks for the great reply. It was my suspicion that the impact is mostly negligible since I feel like I'd have heard something about it by now, but I had an inclination towards the other direction so I'm glad my curiosity is satisfied. I guess at the end of the day it's best to rely on your ears, especially concerning treble.

 

[KinGensai]

Necro time.

I actually have a question that arose when reading this. @castleofargh Have you noticed any harmonic or linear distortion notably introduced by EQ applied in the extreme (>+5 dB for instance)?

 

[bigshot]

I've been using equalizers in my system for decades. Back in the 70s and 80s, the pots were noisy with lots of spill and prone to ground loop problems and distortion with high corrections. I finally bit the bullet and got a pro grade Rane equalizer which solved those problems. Since I've been using digital EQ I haven't run into any problems at all. Back when I was transferring 78s, I would do 5dB plus corrections all the time to subtract the RIAA curve and apply the proper EQ for that particular 78. I never had any problems at all with distortion, only clipping, which was easily corrected by lowering the levels across the board.

I think that a lot of the fears of EQ among audiophiles are holdovers from the days of the crummy ten band graphic equalizers in the 70s.

 

[castleofargh]

Necro time.

I actually have a question that arose when reading this. @castleofargh Have you noticed any harmonic or linear distortion notably introduced by EQ applied in the extreme (>+5 dB for instance)?

Yes and no. As I said, what I maybe noticed(it’s so hard to say that something else changed when the massive EQ has so much impact on my perception of sound already), but surely measured, is the impact of the driver being pushed louder(or elsewhere being attenuated).
When you measure THD for example, the output level is important for the result. Asking the driver to make a bigger movement to achieve louder sound, is when it might just mechanically say ”nope, can’t do”. And the opposite, if the boosted area was at 90dB SPL and when applying your +5 somewhere, you also lower the overall gain by 5dB, it is then possible to measure an improvement from the other frequencies being 5dB quieter.
Bigshot makes a good point, I only used digital EQ in the last... I IDK... 2 decades at least, and always made sure not to clip or push my amp beyond its comfort zone when testing stuff.

 

[KinGensai]

Ok, so if I understand correctly, applying EQ to the gain region and compensating by reducing pre-amp gain will generally result in equivalent or possibly better THD readings due to overall reduction in possible overexcursion of the transducers, right? I generally set my volume to around where I hear vocals clearly, so increasing gain in that region isn't a problem.

 

[bigshot]

If you aren't hearing any distortion, it's likely not an issue. The problem areas would be mostly in the bass. If you try to push the bass too much in headphones that aren't good with bass in the first place, it's going to distort.

 

[KinGensai]

Right, generally it's easier to hear distortion in the bass so that part's manageable. That's also somewhat soft limited by needing to manage masking of the lower mids, so I've been able to tune bass pretty easily.

The question arose because I am having a harder time judging if I am hearing distortion in the treble (10k+). I'm not sure how much I can push ESTs before they start audibly distorting.

 

[VNandor]

Ok, so if I understand correctly, applying EQ to the gain region and compensating by reducing pre-amp gain will generally result in equivalent or possibly better THD readings due to overall reduction in possible overexcursion of the transducers, right? I generally set my volume to around where I hear vocals clearly, so increasing gain in that region isn't a problem.

If this is how you use EQ then it is generally correct in your case. However, most people also compensate for the reduction of the pregain by increasing the amp output, so the average level stays around the same but the "boosted" (or technically less reduced) parts of the response will be played at a higher level than before the EQ.

I actually have a question that arose when reading this. @castleofargh Have you noticed any harmonic or linear distortion notably introduced by EQ applied in the extreme (>+5 dB for instance)?

Something to consider is that the point of EQ is to introduce well-controlled linear distortion to the signal. If you don't notice the distortion caused, then the EQ you applied is pointless in practice.

EQ can cause a massive increase of harmonic distortion when used incorrectly. The easiest example of when you should not use EQ is when trying to correct certain parts of the room response (for speakers). Standing waves can cause massive boosts and cuts in the frequency response which is especially noticeable at lower frequencies. The cuts are caused by the destructive interference between the direct and the reflected signal. In theory, you wouldn't hear anyhting aside from a really short impulse if the signal was reflected perfectly and if the direct and reflected sound were completely out of phase (180 degree phase difference). In practice, it's unlikely they are perfectly out of phase and its never reflected perfectly so you end up with something like a -10 or even -20dB cut in the area where this interference occurs. Now think about it, what would happen if you tried to boost this problematic frequency by let's say, 6dB? Ideally, you get a 6dB boost in your direct sound. However, the reflected sound's level increases proportionally with direct sound's level. As the result, the louder direct sound will still be considerably attenuated by the reflection because the reflection also gets louder. So the overall output level stays the same but the speaker gets 2x the voltage, which means 4x power, the cone has to move more (and there you go, larger excursion "always" causes more nonlinear distortion, the speaker will give you the distortion associated with the higher input level), the coil heats up more, it's bad times all around and it's for nothing because the cut in the frequency response remains uncorrected. While room reflections do not affect headphones, reflections still do happen with headphones, especially closed ones.

The question arose because I am having a harder time judging if I am hearing distortion in the treble (10k+). I'm not sure how much I can push ESTs before they start audibly distorting.

Think about how harmonic distortion works. As the name implies, the distortions are harmonically related to the fundamental. At a 10kHz fundamental the second harmonic would be at 20kHz which might be heard when it's at a particularly high level compared to the rest of the music (and your ears are still at a perfect condition). In practice, good luck finding music where it's not completely masked by the rest of it. The level of the third and upward harmonics are basically irrelevant at that frequency. It might indicate the levels of other nonlinear distortions such as IMD as an example but at that point, you should be interested in the level of IMD and not guess IMD based on THD because THD is inaudible around such high frequencies.

 

[bigshot]

Most headphones have plenty of high end ability. It is possible to crank super audible frequencies and make your ears distort. Generally, you just EQ up to 10kHz and leave that last octave be. There isn’t much up there of value in music, and you probably can’t hear up to 20, so it doesn’t matter.

 

[KinGensai]

Thanks. I appreciate the explanation, I'll have to learn more about distortion in depth.

 

[VNandor]

Thanks. I appreciate the explanation, I'll have to learn more about distortion in depth.

I thought you already knew what THD is but got a bit confused about it.

Harmonic distortion is a type of nonlinear distortion. Harmonic distortion means that if you have an input frequency of f, you'll have additional output frequencies at exactly 2*f, exactly 3*f and so on... Harmonic distortion is one of the more "benevolent" type of distortion, it's not easy to notice it compared to other types of distortions, and even if it's noticed, low order even numbered (2nd and maybe 4th) distortion can sound actually pleasing. Higher order distortion sounds bad, it doesn't matter if the harmonic is odd or even. If you ever noticed distortion that you would describe as "buzzing", that's what high order distortion sounds like. When the harmonics are at the integer multiples of the fundamental, there's not much to be worried about when the fundamental is at already 10kHz.

The "Total" part of THD means that all the distortion products are summed together. A high second harmonic combined with a low third harmonic could produce the same THD as a low second harmonic combined with a high third one but they could sound quite different.

Something else to point out is that THD is a ratio. Its value is always given in a unitless number, such as % or dB.
To be more precise, it's the ratio of the RMS value of all harmonics compared to the RMS value of the fundamental.
This has an interesting implication. If the amount of distortion produced by a speaker is perfectly even across all the frequencies but the fundamental is not, the THD will still vary over the frequencies. The THD shoots up at places where the fundamental is relatively weak and goes down at ranges where the fundamental is stronger.

You brought up linear distortion previously. The difference between linear and nonlinear distortion is that nonlinear distortion produces output frequencies that are not present in the input signal. Linear distortion never produces new frequencies, it just changes the existing ones.
The difference between generic nonlinear distortion and harmonic distortion is that harmonic distortion generates harmonics only at the integer multiples of the fundamental specifically but this does not hold true to nonlinear distortion in general.

 

[bigshot]

In the case of bass like I was talking about it is mechanical, not electronic. You can’t boost bass to make a transducer do what it isn’t designed to do. It hits a wall and puts out noise.

 

[KinGensai]

Thanks, that's a lot less complicated than what I was reading on the subject lol. I had a rough idea what distortion is and sounds like, but this is very helpful disambiguation.

Math explodes my bird brain DX

One more thing: If I'm not wrong, reducing the impact of harmonic distortion is the entire point of using multiple drivers in an IEM right? IIRC, BAs exhibit notably high 3rd order harmonics, so the reason why BA arrays are used is to isolate the frequency bands in such a way as to limit the impact of those harmonics, right? Was there another reason this configuration is nearly ubiquitous?