The reason I stated that I don't have any scientific evidence is basically that I couldn't find a large measured difference in any measurement on our AP system. When I'm designing a headphone I go by half millimeter increments (both in driver distance from the ear and baffle thickness) to see the results both in measurement and subjective impressions. This was one of those things that you can hear but the measurements don't really change much. This differs with every driver and every design as well, which is why it's hard to settle on "one" design working for every headphone and driver. It's all subjective what is "best" in the end anyways right!? The distortion and CSDs change much more based on airflow, cup design and driver design than anything else. There's also a good possibility that this thinning of the baffle around the driver causes a cumulative effect that is minor in all the measurements but can be detected in subjective listening easier. Here's the THD of the v closed VS the v open. The open actually has the thinner baffle around the driver - although the THD is slightly lower in the bass (dotted), it's the closed design that raises the distortion slightly in the low bass. This is measured at 94 dB. EDIT: It's worth mentioning, that although the distortion in the low bass measures a touch higher on the V Closed, I don't hear a distinguishable difference in listening between open and closed.