Do horns amplify sound?

[Henry]

So remember, once you wind your machine up, no additional power is being supplied. The horn merely dissipates the bulk of that power by directing a compression wave in a single direction. If you want to call that amplification, that's fine with me, but technically it's not.

If the amplitude of the sound wave(s) coming out is greater than their amplitude at the source, then the sound has been amplified. See my description of the mouthpiece/trombone relationship.

[Marco Gilardetti]

Henry, it is only your assumption that wave amplitude is wider at a gramophone's mouth than at its throat. Actually, the acoustic pressure in a horn is greater at the throat and decreases at the mouth.

As already written, a horn is not an amplifier. It is an acoustical impedance adapter. It does not amplify anything but only helps in using better a given amount of energy, so that it can give an effect rather than be elastically dispersed.

I understand that common sense would tell that something is "amplified", but physics don't work on common sense. The fact that the amplification effect is only apparent is reported and underlined on the very early pages of all books on horn loading theory (page 9 on Dinsdale, page 9 (again!) on Viappiani, and so on...).

Your trombone example is completely off, I'm afraid, because in a gramophone horn you don't want to put in resonating vibration the air column of the duct, actually you want to avoid it at all costs. Once again, a gramophone horn is not a resonator, it is an impedance adapter.

[startgroove]

There is a related discussion on this topic here: http://forum.talkingmachine.info/viewto ... 51&start=0

[Henry]

Henry, it is only your assumption that wave amplitude is wider at a gramophone's mouth than at its throat.

Marco, I said "IF the amplitude...," not IS. I intentionally worded the statement that way, as a hypothetical, not a given.

[Marco Gilardetti]

OK! Then please reword my sentence as "Should you really think that it is so, then you would implicitly assume that..."