[BK783]

As I'm always wearing glasses, I especially pay attention to the part in reviews where they test if seal of the pads makes a difference in sound quality. Some headphones require perfect seal or sound suffers, usually bass disappearing. Others seem to be mostly immune to this effect.

To make it a bit easier to find suitable headphones, can anyone explain why this is?

What causes some headphones to massively suffer if there's the slightest breach in seal, and others don't seem to mind? Is it the pads (material, size, depth?) or the cup design? The driver? The basic sound tuning?

 

[mammal]

Seal means that there is resistance (your face/ear), rather than air escaping through the cracks, aka free floating. Some headphones are voiced/made for non-seal, they tend to be less efficient and require much more power to move the air and produce low frequencies. That's also why often than not IEMs are so much more sensitive, they require much less drive to move the air, since the membrane is so much smaller and your ear produces a seal. Not scientific explanation at all, but that's the way I understood it from various videos on Youtube. I hope someone get to correct me or expand on my answers.

 

[BK783]

So if I understand you correctly, low sensitivity headphones, the ones that require an amp, are the ones that are most likely to suffer from loss of seal?

 

[mammal]

Think of it the other way around, headphones that do not require seal, they require a lot of power, as they are pushing a lot of air, they tend to have low sensitivity. I am not sure if it also works the other way around.

 

[BK783]

Interesting. Had not thought of it in this way. I'll have to check with various headphone reviews and see if this could be a good clue to how headphones will respond to seal breach. Thanks!

 

[MayaTlab]

Perhaps these couple of posts could help :
https://www.reddit.com/r/headphones/comments/7t2wdw/how_much_do_semiopenback_headphones_leak_in_and/
https://www.reddit.com/r/headphones/comments/a1w0fh/how_does_the_t2_vent_mod_work/eawziv0/

 

[ADUHF]

Mammal makes an interesting point re the sensitivity. That's not somethin I'd really considered before.

Generally speaking though, I think closed headphones will be more sensitive to seal-related issues than open headphones. That's the way I've always sort of looked at it anyway. The seal could effect the sound on some open headphones as well though.

 

[BK783]

Thanks MayaTlab and ADUHF for your contribution!

I agree that seal is more important for closed backs. But there are closed backs that seem to care little about seal too. Perhaps there's enough 'holes in the seal' any way you wear them and adding more openings through glasses doesn't matter anymore?

Edit: the Oratory1990 explanations MayaTlab links to are very enlightening! Thanks again!

 

[mammal]

I agree that seal is more important for closed backs. But there are closed backs that seem to care little about seal too. Perhaps there's enough 'holes in the seal' any way you wear them and adding more openings through glasses doesn't matter anymore?

Not all open back are fully open (construction barriers, magnets in the way), and not all closed back are fully closed (pads breathe and leak). I have also seen CIEM/IEMs that have a vent on purpose.

 

[MayaTlab]

But there are closed backs that seem to care little about seal too.

Well, the better ones in that regard by a mile are ANC headphones that can use their inward facing mics to adjust bass output in real time, in general below 1khz or so, to compensate for breach of seal. Headphones like the XM3/4, Bose QC35(II) or 700, the AirPods Max, can do it.
Solderdude at DIYaudio measures how these headphones behave when seal is breached, for example the XM3 and QC35 :
https://diyaudioheaven.wordpress.com/headphones/measurements/brands-st-x/wh-1000x-m3/
https://diyaudioheaven.wordpress.com/headphones/measurements/bose/qc35-ii/
You can see how constant their bass response is in active mode even when seal is breached. Heck you can even see how they can use the feedback mic to reduce THD .
A very useful site for this problem is Rtings, because they actually measure headphones' bass response (below a few hundred hz) on five real humans and merge their results with their dummy head measurements above that (methodology : https://www.rtings.com/headphones/tests/sound-quality/frequency-response-consistency).
A typical dynamic closed back variance because of anatomical / seal variations :
https://www.rtings.com/headphones/1-4/graph#1671/4007
A really poorly conceived closed back in regards to susceptibility to breach of seal :
https://www.rtings.com/headphones/1-4/graph#669/4007
A typical "semi open" planar, ie with a closed front volume :
https://www.rtings.com/headphones/1-4/graph#670/4008
A typical fully open :
https://www.rtings.com/headphones/1-4/graph#18987/4008
And the closed back ANCs, nearly as good as the fully open :
https://www.rtings.com/headphones/1-4/graph#16490/4008
https://www.rtings.com/headphones/1-4/graph#565/4008
https://www.rtings.com/headphones/1-4/graph#896/4008
https://www.rtings.com/headphones/1-4/graph#16092/4008