[GlassGC]

When I do the arm’s length test, I can hear the xs better and clearer than the hd600, which I can barely hear at all, even though subjectively wearing them they are the same loudness. This is also supported by the Qudelix 5k dB calculation. However, because they’re more v-shaped, I don’t need to feel the xs as loud as the hd600 on my ear. How can this be? Is it distance from the ear? Supposed planar vs dynamic sound/impact? Something about the cup design or earpads?

 

[VNandor]

While I don't understand what you are trying to say and ask exactly, this happens most likely due to a combination of the qudelix not reporting the sound pressure levels as accurately as you are presuming it (which is guaranteed to happen for a variety of reasons) and the sound pressure level not being only parameter that affects the perception of loudness.

The qudelix works out the sound pressure level by taking the headphone's measured sensitivity/efficiency reported by the manufacturers (or maybe even third party sites) alongside with some other data. The sensitivity for the headphone is by far the most unreliable data that the qudelix uses for the calculation. It's based on a single frequency using dummy heads. Different manufacturers might use different standards for measuring it. The headphone could be far less or far more sensitive when its placed on your head. Music also uses a range of frequencies so the single frequency sensitivity measurement is not going to be perfectly applicable to the real-world listening scenario as well.

Aside from that, if you somehow acquired the sound pressure level at your eardrum with a reasonable accuracy and matched that during listening that still wouldn't guarantee a match in the perceived loudness. The loudness is not something that can be directly measured as it is a subjective descriptor of sound. Of course, there are some models that try to quantify loudness and how to measure it. Sound pressure levels are measured in pascals and it's often expressed as decibel ratios while loudness can be measured in phons, or in something literally called "loudness units".

You could start off reading how the qudelix works here and about equal loudness contours and phons here, and about loudness units here.

 

[GlassGC]

Thank you very much! I’m definitely new to all this and still learning the vocabulary to articulate everything, so I appreciate all the information! I will definitely check out those links, especially the one about the idea of loudness units.

 

[VNandor]

Thank you very much! I’m definitely new to all this and still learning the vocabulary to articulate everything, so I appreciate all the information! I will definitely check out those links, especially the one about the idea of loudness units.

The wiki itself does not give much info on it but it links to some pdfs that describe some standardized ways to measure loudness. I think this link is the most technical and hard to understand from the bunch. The equal loudness contours and phons revolve around the same idea but it's just more simple and easier to understand because it's not as all encompassing as the much more modern loudness standards.

 

[castleofargh]

When I do the arm’s length test, I can hear the xs better and clearer than the hd600, which I can barely hear at all, even though subjectively wearing them they are the same loudness. This is also supported by the Qudelix 5k dB calculation. However, because they’re more v-shaped, I don’t need to feel the xs as loud as the hd600 on my ear. How can this be? Is it distance from the ear? Supposed planar vs dynamic sound/impact? Something about the cup design or earpads?

Before anything else, I need to ask. What is the point of listening to a headphone at arm length? ^_^

About a likely answer, it could be a mix of variables like suggested above, but I personally would bet on a simple big driver VS small driver. It's similar logic to how loud an IEM would sound at arm's length when it sounds as loud while in the ear.
At the very least, without getting into other slightly complicated considerations, the low-lowmid frequency range will get much quieter on the 600 the instant the seal is lost. Extra distance is the cherry on the cake, but a lot has already been lost because the seal and defined internal volume was integral to the acoustic design.

 

[VNandor]

Before anything else, I need to ask. What is the point of listening to a headphone at arm length? ^_^

Okay, that actually clears up what he means... I didn't even consider that he means this in the literal sense. My first reply is kind of misleading if that is what he meant.

In that case, I think the most likely answer is a combination in the difference of how much these headphones rely on proper seal and how close the driver membranes are supposed to be to the ear. When listening to headphones from an arms length and one of them is supposed to be very close to your ear, that's going to drop in volume way more than a headphone that's meant to be somewhat farther from your ears.

Just think about it, in a free-field case, the pressure halves for every doubling of the distance. If you start level matching a headphone while they are on your head, maybe one of the headphone's membrane is about 4cm from your ear while the other one is only about 2cm. If you then listen to these headphones from an arm's length, let's say 64cm, then in the first case you increased the distance by 16 times, while in the second case, you increased the distance by 32 times. This surely would play a huge part in it. This is related to driver size in a way (the closer the drivers the smaller they can be) but I think this is the actual underlying explanation aside from the sealing issue. Essentially, it's very unlikely that two headphones would drop the caused pressure levels at your ears by the same amount if you removed them from your head and placed them far away from your ears so of course their perceived volume is also going to be different.

I know this case certainly should not be considered free field but I don't know the attenuation from the top of my head for other (idealistic) cases.

 

[GlassGC]

Before anything else, I need to ask. What is the point of listening to a headphone at arm length? ^_^

As I get into audio I’m paranoid about listening too loudly, and I read that a rough test was holding them at arm’s length, and if you hear the music clearly it’s too loud. Everything y’all have said makes it apparent that this is very very very rough, and things are much more complicated! Thank you for the discussion.

Just think about it, in a free-field case, the pressure halves for every doubling of the distance.

This all makes sense! I imagine there’s more to it as you said, but it kind of confirms my suspicion that all these factors might be influencing how the distance might change the loudness differently for each one, and it’s not necessarily that they actually are that different when wearing them.

 

[castleofargh]

Okay, that actually clears up what he means... I didn't even consider that he means this in the literal sense. My first reply is kind of misleading if that is what he meant.

In that case, I think the most likely answer is a combination in the difference of how much these headphones rely on proper seal and how close the driver membranes are supposed to be to the ear. When listening to headphones from an arms length and one of them is supposed to be very close to your ear, that's going to drop in volume way more than a headphone that's meant to be somewhat farther from your ears.

Just think about it, in a free-field case, the pressure halves for every doubling of the distance. If you start level matching a headphone while they are on your head, maybe one of the headphone's membrane is about 4cm from your ear while the other one is only about 2cm. If you then listen to these headphones from an arm's length, let's say 64cm, then in the first case you increased the distance by 16 times, while in the second case, you increased the distance by 32 times. This surely would play a huge part in it. This is related to driver size in a way (the closer the drivers the smaller they can be) but I think this is the actual underlying explanation aside from the sealing issue. Essentially, it's very unlikely that two headphones would drop the caused pressure levels at your ears by the same amount if you removed them from your head and placed them far away from your ears so of course their perceived volume is also going to be different.

I know this case certainly should not be considered free field but I don't know the attenuation from the top of my head for other (idealistic) cases.

I get the logic, not the arm length thing because honestly just holding the headphone a little differently would easily create bigger changes in distance. There is also the directivity of the sound to account for.
TBH when I started thinking about this, I went real far and lost myself in potential but complex interactions that I have no clue how to properly predict. Plus in my life I only ever did math about waves treating the source as a point and that clearly isn't going to cut it for that situation. My very first and obvious idea was driver size(wider wavefront meaning way more energy while the local air pressure can be the same as when facing the small driver), second was frequency response difference making the sealed tuning feel as loud while the "free air" tuning having some significant differences, could end up having similar overall energy but different loudness perception(plus some thought about change in sensitivity from the eardrum when listening to very quiet sound from a distance as opposed to on ear and probably more than 60-70dB SPL). Third was that the left and right driver would cancel out a lot of energy from facing each other just right, but I let you imagine the brain hurt while trying to consider various scenarios, distances, frequencies and wondering how different the wavefront was on planar... arrrrggggghhhhh. I kept on pilling up the possibilities for a while, then I gave up, like I always do when I know my efforts aren't going to achieve anything. I'll never get a proper answer for all those hypotheses, so why bother(good old, "can you do anything about? If not, let it go").

I'd still vote me and driver size as main cause for perceived loudness difference at a distance, no matter deeper reason why. And as I cannot prove anything, I'll use the best arguments when not proving anything: agree to disagree, it's subjective, just listen!


@GlassGC , I would indeed guess that the arm length thing is not very reliable for an estimate of safe listening. Usually, I'd go with "if it feels loud, it's too loud". Of course, that must be done while in a quiet room for reference, not while on the street next to passing cars. Consider some reasonable limits and keep track of how much louder(and just as important, how long) you go under noisier circumstances. It's like music in a car, how often do you come back to your car in the morning to find that the radio is really loud? It certainly didn't feel that loud after driving for an hour with a window open(or with a very noisy engine on the highway). It is good to set a mental limit(volume number, knob position) while it's quiet, and if the ambient noise or your love for the track pushes you over, at the very least, only do it for a short duration. Ideally, don't do it at all, but then again, we're only humans.

 

[gregorio]

As I get into audio I’m paranoid about listening too loudly, and I read that a rough test was holding them at arm’s length, and if you hear the music clearly it’s too loud.

I’m not sure where that comes from. Although there is a slightly similar practice often taught to student music/sound engineers: The HPs are worn around the neck when first plugging-in and pressing play. This is because professional studio equipment (particularly mixing desks) have a lot of different signal paths, connections, routing options and signal levels and it can be easy to plug your HPs into the wrong one (or the right one but at the wrong level) and cause hearing damage. In fact, I personally used to know someone who had plugged their HPs into the wrong output connector on a desk, it blew their HPs and after about 2 weeks in a coma, he woke-up with permanent and pretty much total hearing loss!

After hearing his story, I was always adamant that my students got into the habit of putting their HPs around their neck to start with. This technique doesn’t give you any real idea of level, beyond just identifying really extreme levels.

G