Gilmore Audio planars revealed

But you do agree that the membrane can be lighter than the total mass of the air it moves.

A confusing statement. In a longitudinal wave (such as a sound wave), molecules of "air" are displaced from a median position by varying amounts producing regions of compression (as the membrane moves forward) and rarefaction (as the membrane moves backwards) along the axis of propagation. The molecules end up where they started once the wave has passed. The wave moves - the air does not.

The very basis of a wave is the transmission of energy without the transport of matter.

I agree that it is desirable to have a membrane with as low a mass as possible without sacrificing stiffness. The thickness achieved in the design you are referring to is amazing.

Regards,

Dear Sellerwithintegrity,

Sound involves the actual movement of air molecules.

The air molecules only vibrate. Each individual particle of the medium (air) is temporarily displaced and then returns to its original equilibrium position.

Waves can be divided into two categories: mechanical and electromagnetic. The very nature of this classification is that electromagnetic waves can propagate in a vacuum. You are correct that sound waves are not like light waves, although we lost the "ether" some time back ;-), but they are waves, and share some fundamental characteristics.

Another categorization of waves is into longitudinal waves (such as sound waves), transverse waves (where the disturbed particles vibrate perpendicular to the direction in which the waves move), and surface waves (where the particles undergo circular motion).

Let me give you another example of a wave to demonstrate that the individual particles don't in fact move. You are at a big football game, and the "wave" is started by the boisterous beer drinkers in section B. They jump up, hands in the air, and sit down. Observed by their neighbours, who at the right moment jump up ... and so it goes. Watching from the Goodyear blimp, we observe the wave travel around the stadium a few times until it dies out through boredom. But the lads in section B are still there. They didn't run around the stadium with their hands in the air, did they? No, they have to stay in the cheap seats.

Regards,

Dear Sellerwithintegrity,

Could you PLEASE refer to the poster you are replying to?

You just made 6 posts and I'm having trouble connecting the dots. On a previous occasion in this thread, you made 5 posts in a row, and one of them was a reply to me - so I had a vested interest in working out which was which.

Regards,

Duke,

The example given above of the "wave" in the football stadium is actually a transverse (or shear) wave, with particle motion perpendicular to the direction of wave propagation.

Of course it is. I noted that waves could be classified into three types. My point was to indicate that the particles do not move from their equilibrium position, but vibrate about it.

Sound waves are pressure waves, and most importantly are set in motion by physical displacement of the air particles.

That's close enough.

The mass of the air displaced by the diaphragm movement can be calculated and compared to the mass of the diaphragm itself.

On the face of it, this seems like a reasonable statement, but please describe how we should do this.

We surely count all the molecules of air in contact with the diaphragm, since they are certainly disturbed. They in turn disturb their neighbours - do we count those? They have neighbours too. Where do we stop?

If we only count the molecules in contact with the diaphragm, is that the mass we seek? It surely would be lighter than the membrane.

Do we reason like this - we consider the maximum excursion of the diaphragm (this would be for the loudest possible volume at the lowest frequency the membrane can produce) and multiply this by the area of the membrane and come up with a volume. Now we consider the density of the air (depends on temperature and humidity) and thus we have a mass. Is this it?

But the speaker hardly ever plays at this volume or at that low frequency, so does the statement "the mass of the membrane is lighter than the air it moves" have to be qualified with volume and frequency specifications? This was not done.

The problem I see is that the phrase is colourful and exotic, but not reasonable. It's a turn of phrase, an advertising slogan. That I don't mind, as the world of hifi is filled with such slogans. But it's not truth.

Regards,