Transcription
Listen, I'm not saying like, if we're saying which company has avoided releasing turds, none of them make the list. We have to go to a completely different space. Yeah, like you would have. I don't even. I was thinking about that, what company has never, or has released the fewest awful headphones? And you know what the funny thing is? It's probably Stacks, because Stacks barely ever changes anything. What about Moondrop? IEMs, aren't real.
So, over the past several years, I've become more of an IEM guy. And these days, I tend to use IEMs more often than not. They've been getting better and better, and I guess there's a sense in which we're currently living through a golden era of solid IEM releases across the market. However, there are ways in which IEMs are objectively worse than over-ear headphones. Notice the language here, "objectively worse." And we never seem to talk about this. So, in today's video, that's what we're going to [Music] do.
If you're an IEM lover, I hope you're getting fired up to post, post in the comments about how your experience with this IEM or that IEM is so much better than any over-ear that you ever heard. And in fact, there are ways in which IEMs can be better, which I'll also get into in this video. But there are absolutely things you should know before making any IEM purchase decision, especially if you're the kind of person basing those decisions off of objective information, such as measurements. And this video is going to get very technical, very fast, so I hope you're ready for this. So, let's get going here.
And the first thing to talk about is the fact that IEMs have more variance in terms of how they're received compared to over-ear headphones. That is a fairly uncontroversial take here. And if you consider the outcome of the best currently available preference research from Harman, you'll find that there's a difference in terms of the spread of preferences, particularly when it comes to how much bass people want. So the range for IEMs is different from the range for over-ears. The question is, why? It's sound to the eardrum in both cases, and the use condition for both being worn on the head rather than heard at a distance like speakers is the same.
On the one hand, we could say that people just have stronger and more varied preferences within your headphones. But there needs to be a deeper and more compelling explanation than that. In fact, I'd argue that preferences vary significantly enough that the same product could be received as generally enjoyable by one person and completely intolerable to someone else. In fact, I know that this is the case. And this is part of why I think it makes more sense to talk about targets rather than a singular target, like what you get with Harman IE. But that's a separate point.
Instead, there's a good reason to point to our individual anatomy as being at least partly responsible for this kind of strange result in preference variation. So let's get into the most likely explanation for why this is. And I say "most likely" here because the question of what do people prefer has been a little bit more thoroughly studied than why do people prefer. But here's a start.
When you're wearing IEMs, and when you're measuring them, the PA, this bit here, the outer ear bit, it's being bypassed. Since the IEM sits at the ear canal entrance, uh, so there's none of this getting involved. This means there's literally no interaction between the sound-producing device and the PA the way that there is with over-ear headphones, um, apart from where it sits in the canal entrance. And so the effect of your PA on the incoming sound doesn't occur the way that it does for over-ear headphones and speakers. And the problem here is that the brain expects the effects of the PA on incoming sound. That's just how you hear the world.
Now, to explain what this means, we have to once again go over the importance of the head-related transfer function, or HRTF for short. And of course, we use the diffuse field HRTF because that's the appropriate sound field for headphones. And there's an extremely comprehensive article on this by Listener that I'll leave it, uh, linked in the description. Uh, so definitely check that out if you're new to HRTF or diffuse field and basically what's going on there. But for today, remember that an HRTF is the impact of the head and ears on incoming sound. And every person, every head has its own unique HRTF. And this consists of various features of our anatomy such, such as the name suggests, the head and its various features like the ear along the path to the eardrum. And these effects are different depending on the head and depending on the ear.
And if you weren't already aware, these effects are also what's being simulated by the head and torso simulators we use to measure headphones. In particular, here, the GRAS 43AG with the KB 5000 PA and the B&K 5128, which is the full mannequin head. And each rig has its own unique physical features and corresponding effects. So here you can see the estimated effects of the PA on sound as it goes to the eardrum. And here you can see the effects of Mr. B&K 5128 PA right here, which is currently the most advanced industry standard headphone measurement rig. And here you can see the effect of the GRAS PA right here.
Now, why does this pose a challenge for in-ear headphones? So PA effects shown here are going to be different for every individual, as I mentioned. And those effects are going to be expected at the eardrum because that's how each of us hears the world with the whole auditory system, PA and all. In theory, this means that if an IEM tuning matches the PA effects for one person, it may sound, sound totally normal to them, but meaningfully weird to someone with drastically different PA effects. Because remember, those effects are not being included when the IEM is bypassing those features. So with over-ear headphones, this is less of a worry because each person's PA effects don't need to be assumed, they're actually impacting the sound. But once again, with IEMs, those effects need to be assumed.
Of course, this doesn't account for preference. Who is to say that an overestimation or an underestimation isn't preferred by a given individual? This really is what muddies the water here. But when we consider the ears used on standard measurement equipment like this one here from GRAS, there's actually a good chance that the PA effects for those heads, diffuse field HRTFs, don't match yours.
Now, despite this, we still have to assume some PA contribution is there because, again, the brain expects a PA contribution at the eardrum. So what PA should we choose? We actually don't want to use the diffuse field HRTF of the 5128 with its PA effects baked in because when you compare this to the population average diffuse field from Harman's measurement rig, the 5128 PA effects would be on the brighter end of the spectrum. In other words, for anyone with ears similar to the 5128's here, IEMs that perfectly match its diffuse field HRTF features when measured, uh, you know, things are likely to sound reasonable to that person. But we know that this would be more treble energy compared to the PA effects of a population average.
As it happens, the GRAS PA here also overestimates the relative to population average, just in different ways. So it is an anatomical representation of a human being, but it is not necessarily population average for the ear bit. And again, I want to stress that this doesn't really matter all that much for over-ear headphones since the PA is actually impacting the sound. But in any case, we also wouldn't want to use just the population average diffuse field HRTF on its own because the IEM is still interacting with the canal of the 5128, and we want to include that interaction. This is one of the key benefits of that system.
So this is a problem. All of which is to say that it's much more difficult to predict how an IEM is going to sound to an individual compared to over-ear headphones. But we do have a working solution for this. So to account for both of these variables, the canal effects we do want, and the APIN effects we don't, we can actually use an approximated diffuse field head-related transfer function generated by a community member named Joel. Shout out to Joel. And some within the community already know about this. You may have heard of JM1. That's that's basically what this is.
So the idea here is that it chooses between the 5128 canal effects and the population average PA effects based on how much each factor would contribute to the overall HRTF. So we have 5128 canal with population average PA effects added to it. So for example, at 2 kHz, the canal is the primary contributor to the diffuse field HRTF. So the combined diffuse field HRTF uses more of the 5128 here. But at 5 kHz, the canal basically doesn't contribute at all. So the synthesized version here uses more of the population average data. And this is the best that can currently be predicted for the average expected APIN contributions to an IEM measurement. But even this isn't perfect, and it may change in the future when better data becomes available, specifically the sound transmission function of the 5128 canal itself. And we can actually measure that.
So with the use of population average PA effects, you might think that the problem of predicting IEM goodness has been solved. But not exactly. At best, it's been improved. Even if we can account rather well for the effects of the average human PA and the canal of the measurement rig, you are not the measurement rig. Measurement rigs generally serve as useful simulations of human anatomy, though the 5128 is the first time this has been truly realized all the way down to the eardrum. Whereas the 711 coupler, shorter and overall smaller cylindrical chamber, is very unlike the average ear canal anatomically.
Unfortunately, even if we account for the average expected PA contributions in our process, the outer ear and middle ear still have a large part to play in why our experiences when listening to an IEM may vary widely from the measurements we take on either of these rigs. So if you're still watching at this point, you're probably already deep into the weeds on headphone measurements, especially when it comes to IEMs. And you will likely be familiar with the 8 kHz resonance on typical IEM measurements. But what you might not know is that this resonance peak is the result of a length mode corresponding to a distance roughly 21.4 millimeters between the IEM and the eardrum. This is potentially one of the largest factors when it comes to variance between IEM listeners.
So the length of the occluded air volume, and therefore the location of the resonance peak that you might see on the graph, isn't only affected by the length difference of our actual canals, but also how deeply we insert the IEMs. And unfortunately, how deeply we insert is up to a whole bunch of different factors. And you may have remembered that video I did on the 7Hz Timeless, and I had real trouble actually getting it to stay inserted fully in my ear based on the shape of the shell. This is what I'm talking about. And that's just one of the factors.
So how much the shell ergonomics limit insertion, the circumference of the canal entrance, the profile of the first few millimeters of the ear canal, what type and size ear tips you use, and how the IEM's drivers are internally oriented in the shell, all affect the length of this air volume. And the crazy thing about this is that depending on the ears, some of these factors can even vary between the two ears of the same person. So humans are weird. In any case, because there are so many factors that will determine the length and the air volume when an IEM is inserted in the ear, it's tough to claim that any one measurement of an IEM at a single insertion depth is going to be representative for people, even when you use an exceptionally well-founded anatomical average like the industry standard headphone measurement rigs we use and an idealized diffuse field head-related transfer function like the one mentioned earlier for IEM analysis.
Now, one way to make a dent in this problem, and what I've started doing, is measuring at varying degrees of insertion depth to see how the IEM may respond in varied circumstances. So this is why even when using the PA on the 5128, for example, I will sometimes also use flange tips because that is also going to have an effect. The problem here is that I don't think many listeners are even aware of how big a difference this can make. I certainly wasn't, at least until I tried the Audio Sense DT200, which is one of the best IEMs I've ever measured on the B&K 5128. And I know that this is an IEM that many people love. There's a whole cult following behind this IEM. But I personally found it to be quite grating at around 6 kHz. And the expectation here is that apart from the fact that my outer ear is different, and therefore the HRTF would be different, uh, my ear canal is also longer than that of the B&K 5128's.
Now, there are also other reasons why certain common IEM designs are often worse than over-ear headphones, and it has to do with distortion. This is less of a problem now than I think it may have been in the past, but it is still something worth noting. So as you will probably know, many well-regarded IEMs make use of multiple balanced armature drivers. And while there is a benefit to using these, there's also a downside. They tend to have comparatively elevated third and elevated fifth harmonic distortion, compared to, well, both over-ear headphones typically, but then also IEMs with other, uh, design choices for their drivers. And I will also note that this is normal for these types of configurations, for balanced armature driver configurations to have higher harmonic distortion. It's, it's super common with BA BA-based IEMs.
So what's the downside? On the one hand, there is debate about the audibility of these distortion products, especially with music. But there's also an argument that this could be responsible for the dreaded BA timbre designation that you typically come across in certain audiophile circles. I'm not going to say definitively that this is what it is because I don't know, but it really wouldn't surprise me if that's the case, given that these aren't ultra-low order products, which will be harder to hear. So elevated third and elevated fifth are further away from the fundamental, meaning that they, there's a chance they could be outside the masking window. And this really is more of a nitpick, since most BA-based IEMs already can be tuned with a bass shelf in mind, or maybe you have like a hybrid configuration that has dynamic driver bass, and so that's not really an issue if you're trying to boost the bass or something like that.
So, IEMs can still be better. Why? Okay. So apart from massive form factor benefits to portability and the fact that IEMs are often far more comfortable since you don't have to wear a heavy thing on your head, there are absolutely ways in which IEMs can be better than over-ear headphones. And I say "can" because that doesn't necessarily mean they always are. So number one, IEMs put the sound source closer to the eardrum, and they do a good job of isolating you, given that they also function kind of like an earplug. And if you compare this to most closed backs, you are, you are likely to get a far more palatable sound signature at significantly lower price tags with IEMs than comparable, you know, over-ear closed-back headphones.
And the reason for this is, depending on the IEM design, they are far easier to tune to the intended sound signature the manufacturer is going after than trying to get the acoustics right for over-ear headphones. Or to put it another way, you can be far more specific and deliberate when tuning an IEM than you can be with over-ears. And this is in large part down to the ability to tweak different regions of the frequency response through the use of multiple drivers and other electrical components. This is really where the benefits of using multi-driver configurations comes in. It's not always a requirement, but it does make that easier.
Now, at the same time, that doesn't necessarily mean they always get it right, or even that the more common tunings we see have gotten it right. In fact, they haven't. And the problem here is that the most commonly used couplers to measure IEMs, that being either the official 711 couplers or 711 clones, have less than accurate acoustic competence. So what is acoustic impedance? Acoustic impedance is the relationship between the air pressure, which for our purposes is frequency response, and the actual flow of air. A high acoustic impedance means that for a given amount of air movement, the pressure is higher. And a low acoustic impedance means that for the same amount of air moving, the pressure is lower.
And you might ask, well, why is this? Well, let's think about it like this. Imagine for some reason that you're tasked with pushing an elephant into a shipping container. It's going to be a little bit tight, and you probably are going to need a bit of force, but the elephant will fit. And you pushing it isn't going to put it under massive pressure. Now imagine that you're trying to push that same elephant into a Volkswagen. So number one, the elephant probably isn't going to survive the process. And number two, it's going to be under a lot of pressure because you're trying to fit a big elephant into a much smaller space.
So the question is, how is this related to headphones? Well, the elephant is the air, and the thing pushing it is the driver. When an IEM is sealed against your ear canal, there's a fixed volume of air between the driver's surface and your eardrum. And as the driver moves forward, it forces that air into a smaller space. Since the amount of air can't get smaller if there's a seal, this forces the pressure in your ear canal to rise. But the amount that it rises depends on how much the volume changed. And when acoustic impedance is low, the effective size of the container, that is your ear, is larger, meaning that changing it by a fixed amount raises the pressure by less than it would if it were smaller.
This is where the difference is between the 5128 and the older 711 couplers matters. The newer and more accurate measurement systems are larger at lower frequencies in a way that better matches the average human ears. So what this means is that with these older 711 couplers, results at lower frequencies, in particular with in-ear headphones, are bound to be a bit off. And you can see why this matters when we compare IEMs with dynamic drivers for the bass against IEMs with balanced armature drivers for the bass, across both the GRAS 711 standard coupler here and the B&K 5128 here.
And what this means is that identifying what's good in IEMs is still somewhat of a frontier being figured out in a way that hasn't needed to be done or considered with over-ear headphones. So while yes, you can get better tunings with in-ear headphones, that doesn't necessarily mean that they're aiming for the right thing. In fact, while there are good IEMs on the market, manufacturers regularly don't. And that's because of some of these limitations.
But more importantly, if there's one thing I want you to take away from this video, because I know that this is long and convoluted and complicated, the takeaway that I want you to leave with is that there's no guarantee that what you see on the graph when it comes to IEMs is going to translate to how you hear this product. It's way closer with over-ear headphones than it is with in-ear headphones. And that's what I want to leave you with.
So does that mean that I'm going to stop using IEMs? No. In fact, I'm going to use them even more, and I would encourage other people to use them as well. But you should at the very least be aware of some of these limitations, some of these issues currently in the IEM market. And also recognize that your anatomy is going to have a particularly important influence on how you hear these things. It's worth being equipped with some of this information when you are approaching graphs for IEMs, when you're considering this for a purchase. Because it used to be maybe, oh, graph looks good, you know, some reviewer says, oh, technicalities are good, uh, therefore I'm probably going to like it. But I would really caution you about that.
I think it's worth trying out some of these cursor-based sweeps or learning how, how maybe your anatomy differs from, uh, the anatomy of standard, uh, measurement rigs, but also from maybe other people out there who you might love something. Maybe you'll find, oh, there's a resonance there that you don't like, or maybe you'll find that something out there that somebody doesn't like, you do. And, um, so this is why I think it's worth understanding how your own anatomy, um, relates to what you see there on the graph. It's not easy to do, and I get that this is not everybody's going to do this. But remember, we're only ever listening out of our own two ears. And for that reason, I don't think it's good enough to be able to say, well, this person likes it, it graphs reasonably well, therefore I will like it too. Um, there is a good chance that you're not going to hear it the same way the graph shows, but also not the same way that that other person heard it.
So that's basically what I want to leave you with. Uh, and that's going to do it for this video. Uh, once again, if you're interested in more deep dives on these subjects, there will be links in the description for these articles. We have these deep dive articles up on headphones.com. So if you guys are curious, uh, definitely check that out. You can also chat with me and other like-minded audio folks in Discord. Also link below. And until next time, I'll see you guys later. Bye for now.