Just posting a few additional measurements here:
On-head bass response (measured with in-ear mics)
What’s cool about this is that it essentially matches the on-rig results. So the fit is good and I didn’t personally have any issues with the seal.
…however, should you for some reason break the seal, here’s what’s likely to happen:
Green = small leak, Orange = large leak
So you can see the resonance frequency is around 300hz.
But as I said I didn’t have any issues with getting bass extension, just that if someone reports a lack of bass with these, it’s likely due to seal issues.