Three centimetres

Every argument about voice hardware ends up at the same unglamorous number: how far the microphone is from your mouth.

Sound pressure falls off with distance. Halve the distance and the pressure arriving at the microphone doubles — about 6 dB. Background noise does not get quieter because you moved the microphone closer; it is spread evenly through the room. So every halving of the distance does not raise the signal a little, it lifts the whole signal-to-noise ratio by 6 dB.

Fifteen centimetres and five

The microphone on an ordinary pair of earbuds sits about ten to fifteen centimetres from your mouth. In a quiet room that is fine. Outdoors, one gust of wind or one passing car and the model is handed a signal with a poor ratio, so all it can do is guess. What comes back from a guess always reads slightly wrong, and that slight wrongness is what you spend every day fixing.

We moved the main microphone to the bottom centre of the left rim, port facing down at your mouth. The distance becomes 4 to 7 centimetres — a range, because faces are different sizes. This is not a few percent of improvement. It lifts the entire curve, and it does it without any algorithm involved.

That position has a price

Putting a microphone in the front frame means the wire has to run through a channel moulded into the nose bridge instead of sitting comfortably inside a temple. It means the port faces straight into the wind — so it needs a metal mesh, acoustic foam, and wind suppression in firmware. It means sweat runs off your forehead and lands directly on it — so the port geometry and the internal drainage path exist for its sake.

All of that is downstream of three centimetres. We took the harder front frame, because the other option was a transcript that is always slightly wrong.

Then you can take them off

The geometry has one last move in it. Worn, the main mic is 4 to 7 centimetres away; take the glasses off and hold them to your mouth and the same microphone arrives at 2 to 3 centimetres.

No mode switch, no button, no setting. You have simply shortened the distance with your hand — which is what people already do with a phone, except that this time the microphone was designed for the distance you moved it to. At 2 to 3 centimetres a whisper arrives loud enough and clean enough. That is the whole of what we mean by a quiet-voice engine.

Designing for a gesture where the user takes the product off in order to use it better is unusual. But it is honest about what is happening: the distance is the feature. Anything that shortens it is an upgrade.