Is there any theoretical reason why open-back over-ear headphones should be able to outperform IEMs after EQ'ing?

[pwjazz]

Sorry but I disagree here.

Once a passive crossover filter has introduced group delay, it will necessarily be present in the acoustical output.

That’s absolutely not to say it will be audible, of course.

FWIW, here are measurements of my QT2 and HD58X taken on a MiniDSP E.A.R.S. Unfortunately the HD58X measurements were taken at a lower SPL than the QT2, but I don't know that this would affect phase response.

Salient points:

• These show both the group delay as well as the excess group delay. Excess group delay is defined as the group delay beyond what one would see in a minimum phase system with the same frequency response.
• Until we get into the high treble, the QT2 seems to have a much smoother phase response than the HD58X. I don't know what this means in terms of audibility, but perhaps it's caused by the HD58X interacting with the MiniDSP's artificial ear?
• In the high treble though, the QT2's phase response doesn't look so hot. Again, not sure how audible it is, and for better or for worse I'm functionally deaf above 14 KHz anyway, but still it looks nasty. Also, the E.A.R.S. is not particularly precise at higher frequencies, so I'd take this with a grain of salt. Still, I assume this is the single wide-band BA driver running into its limits. This sort of thing might explain why some IEMs use multiple BA drivers that are tuned for different frequency ranges - yes the crossover might introduce some unwanted frequency response and phase response, but it's probably minor compared to this mess.
• We see an interesting feature on the QT2 at around 920 Hz, where we also see an interesting kink in the frequency response (not shown) and a bump in distortion (also not shown). I suspect that this is the crossover point between the dynamic driver that handles the bass/low mids and the BA driver that handles the higher frequencies.
• At the kink, we do in fact see slightly increased group delay, but it's on a similar order of magnitude as the general group delay on the HD58X. Also, the excess group delay is practically 0 because it follows the kink in the frequency response.

So, long story short, yes the crossover introduces some unwanted features, but in this particular case it does not seem to introduce excess group delay.

 

[pwjazz]

here are measurements of my QT2 and HD58X

For completeness, here is my LCD2C, the most expensive of the bunch.

Again, I don't know about the audibility of such things, but the group delay looks like a slightly worse version of the HD58X. I think the fact that the LCD2C's group delay diverges the most from its excess group delay implies that it has the most uneven frequency response of the bunch.

 

[pwjazz]

Since I'm having so much fun with it, here are the KZ ZST, Etymotic HF5 and Beyerdynamic DT 1990 Pro.

• Both of the IEMs demonstrate an unattractive phase response in the treble. The ZST is a 2 driver hybrid like the QT2 while the HF5 is a single BA driver. It looks like the 2 driver hybrids like the ZST and QT2 manage to push the unattractive phase response higher into the frequency range, so perhaps they are in fact using differently tuned BA drivers for the high range than the one in the HF5 that has to cover the full frequency spectrum. Again though, take my treble measurements with a grain of salt.
• Phase response on the DT 1990 looks really nice compared to the other over ears I showed. Distortion (not shown) is also spectacularly low. Maybe I shouldn't have sold it

 

[andreasmaaan]

Nothing.

But when combined with the comb filtering that does happen in the ear, which varies by person, the whole goal of trying to create a time aligned, phase coherent set of drivers at millimetric distances is just a hot mess of 'why bother'.

I agree

EDIT: on second thoughts, although I stand by my post with regard to high frequencies, I think I'd want to avoid too much group delay in the midrange and low treble in an IEM. I can reliably discern LR4 group delay in the 1-3KHz range using headphones with music (haven't tried other frequencies or filters). That means it's at least audible, and therefore something to try to avoid probably (although possibly a lesser evil in many cases).

 

[andreasmaaan]

@pwjazz how are you calculating the excess group delay in these measurements?

 

[pwjazz]

@pwjazz how are you calculating the excess group delay in these measurements?

I'm letting Room EQ Wizard do it More precisely, I ran a sine sweep from 20 Hz to 20 KHz, typically from my LG V20, sometimes with an amp like a Topping NX4 in the path. I then have REW estimate the impulse response delay and calculate the minimum phase response based on the frequency response. The excess group delay falls out of that.

 

[RayDunzl]

Until we get into the high treble, the QT2 seems to have a much smoother phase response than the HD58X. I don't know what this means in terms of audibility, but perhaps it's caused by the HD58X interacting with the MiniDSP's artificial ear?

Here are my MartinLogan electrotatic dipoles (orange, foreground) vs JBL 305p (blue), unsmoothed.

The ML have much less room interaction.

A nearfield measurement of the JBL would result in a much smoother display.

Here is a JBL LSR 308 measured from about a meter, unsmoothed, same scale:

So, do you have interaction with the ear appliance? Don't know.

 

[Blujackaal]

If your using DSP/binaural on a IEM, I don't much reason why a open back would outperform. The ER4SR out perfoms dynamic's on ADSR/transient and has much better bass THD than the HD6xx/58X, like 0.6% for the SR vs over 2% on the 6XX at 100db.

Then there's open back IEM's like the E5000, EX1000 and few more that give a soundstage boost without DSP/binaural.

 

[Deleted member 16543]

One reason is the backwave absorption. With closed IEM the backwave creates a lot of pressure (higher than the one it creates in the canal), that needs to be absorbed somehow, or it keeps ringing in the enclosure until it dies down. This can sound muddy, in comparison to open back headphones, which simply let the backwave escape out of the enclosure.
Another reason is the acoustical impedance seen by the eardrums in comparison to a normal type of listening situation. The air load effect changes going from nothing on the head to over ear headphones to in ear ones.
Yet another reason is the somewhat unnatural stretching of the ear canal when inserting in ear headphones.
The bass build up that relies on the resonance effect of the volume size and shape between driver and eardrum could possibly be taken care of with simple EQ, but it's another reason for a difference between the two, although this time not necessarily in favor of over ear headphones.