This is how I make a seal cut at the nose on my kid's Zimi mask so that it fits better around her nose bridge, thus eliminating gaps around each side of her nose. The fit factor went way up on fit testing with this hack!

Finally, here is the omnimask with the speech diaphragm, and a mic for amplification. It sounds really good, and lip reading and smiles are all available!

Here is the omnimask *without* the speech diaphragm, shown with the original exhalation filter on the chin. Very muffled, even with the personal amplifier I am wearing.

Finally, let's do a sound comparison test for teaching! Here is a clip in a 3M Aura. Good sound quality, but no facial expressions or smiles or lip reading accessibility.

How can I still breathe with the exhalation valve taken out? Easy, remove the little silicone valve piece from one of the inhale valves. This will only work with the pancake filter adapters, not the original Omnimask filters.

Here is a video showing how the speech diaphragm is attached. It's taken out of a different respirator, the Honeywell North RU8500 Half Mask.

Here's how things look and sound in the mask, which I modified to put a black circular speech diaphragm from another respirator in where there is usually a filtered, muffled sounding exhalation valve at the chin. It fits perfectly: