As I've tried to explain that (certainly not in the way that I believe) brass instrument lips don't hit against each other in the vibrating portion (at least not when actually playing an instrument and doing so properly) but vibrate independently in unison - as with a bassoon or oboe double reed. There are people subscribed here and across the world who believe otherwise. I'm not responsible for what other people believe, but can only be responsible for my own beliefs.
I've pointed out that - when playing in the LOW range - it is much easier (when there is a way to make a video of it from inside a mouthpiece) to see that the lips don't hit - as the teeth are so far apart and a typical player's embouchure pivot is more vertical, as compared to in the high range - certainly when using these camera mouthpieces (whereby the cameras themselves are incapable of repositioning - as the lips reposition during typical playing in different ranges - as well as being possibly not being completely capable of instantly re-focusing as an embouchure pivot changes) the arch-shaped opening becomes very tiny and hard to discern (as well as the upper lip overlapping the bottom lip, which hides the tiny opening from the view of the stationary camera).
I finally saw a demo with one of these specific cameras in use whereby a trombonist (rather than producing a single frequency) started in the very low range, went way up into the high range, and then went all the way back down.
In the lower range, it was quite easy to tell that the lips were arched - as a bassoon reed - and vibrating independently, but (just as described above) as the player's lips pivoted (following the movement of the teeth) and the opening became tiny for the very high range, all the camera could see was the two lips overlapped for the pivot (hiding the opening), whereby it appeared that the lips were closed but - keeping track of the parts of the lips from the early part of the video (when the low range was being produced), it then became apparent that (with apologies for redundancy) a natural embouchure pivot was occurring and the tiny tiny opening (high range) was being hidden from the camera.
Anyway "The Science" (not really that, but just simple logic) hints that - if a tone is produced in one manner when low frequencies are being produced - it's extremely unlikely that there is going to be some totally different way that a tone is produced as the frequency increases - whereby frequencies are NOT going to be produced in a totally DIFFERENT manner in the high range. Again, it's just that - with the top lip coming down over the bottom lip for a typical brass player's pivot, and the tiny little arched opening creating the highest frequencies (at that point) being hidden from the view of the stationary camera (even were it that the tiny high range opening was able to be properly photographed by the camera) the two dimensional stationary camera video can misguide a viewer into believing that the lips are totally closed at that point.
Believe it, don't believe it, or post another meme with a really inappropriate insult (which struck me as being sort of offensive and misogynistic).
I saved the two links that I found by emailing them to myself. The videos that I encountered were posted on social media, and it didn't surprise me to see what I saw in the videos, as I was already confident that I understood what's happening with vibrating lips when playing a brass instrument. (I'm willing to link them here...)
I also have a theory (notice the word "theory" - something which later might possibly be applied to the scientific method but - until such happens - it's nothing to do with science) about "double buzzing". I believe that it's caused from practicing or playing for so very long (for so very long for so many continuous days) that one of the two lips (it always seems to me that my bottom lip works harder than my top lip - so I'm suspecting the bottom lip) is simply so tired that (particularly on some somehow-triggering frequency due to a particular instrument/mouthpiece combination ??) one lip simply can't sustain enough tension (with enough arched opening of the two lips) to vibrate in unison with the other and physics/acoustics dictate that the tired lip is going to drop to the next lower related frequency. (It might even be that -:with the arched opening closing too much due to tiredness - the two lips are actually just barely touching, and causing one of them to vibrate half as fast as the other.???) I don't have any devices, nor strict application of the scientific method (whereby the scientific method is the only way where there is any real scientific investigation) to back this up, but I tend to believe this is what is happening. My theory is why I believe that the only way to properly rid oneself of a double buzz issue is to back away from playing for a while, rather than employing some additional playing (via some exercise - and even more playing - which someone recommending such yet additional playing might claim will "cure" it)...in other words, backing off of playing until the overtaxed muscles on the one lip are allowed to recover and heal.
I'd glad to share the links to the two social media hosted videos.
Of course, there's nothing to stop someone from seeing what is there to be seen, and claim do not see it.
me:
Being that I have nerves in my skin and muscles and can feel things, when I'm playing very low frequencies in the range around three ledger lines low G and lower - and I can feel that my centers of my lips are at least a quarter of an inch apart - with it being very difficult for me to imagine that there's any way possible that my lips could be touching when producing those very low and very loud frequencies. To restate in a different way, not only do I not feel them touching each other at all, but I could not possibly imagine them being able to touch each other that far apart from each other. Finally, neither "consensus" (an opinion-related word, and not a science related word) nor "name dropping" (not part of the scientific method) are going to cause me to believe differently about this. Again, I'm not responsible for what others believe, whether there's some 11-year-old student or a 55-year-old brass playing celebrity.
finally:
I've had two or three younger players send me notes over the course of this long debate to thank me for expressing my beliefs in regards to this. It's not that their lips - when playing - were ever hitting against each other in the middle when they were playing, but it seems as though - when they quit believing that was occurring - their sound (according to them) actually began improving, and - for that - I received private notes of thanks.
Playing a musical instrument is an extremely complicated thing. Sometimes we want to completely know and understand what's going on - regarding physiology, and - sometimes - thinking too much about the physiology of playing can lead to hang ups.

