Do horns amplify sound?

[gregbogantz]

Yes, the issue here is somewhat one of semantics. To a lay person, if something sounds louder with a device than without it, that person is inclined to view the device as an amplifier. And early advertising blurbs for acoustic phonographs typically misused the word in this way. But, technically, that is a misunderstanding of the term. To an engineer or physicist, the term "amplify" specifically means that energy is ADDED to the signal, thus making the output signal larger and containing more power than was present in the input signal. That's the technical definition of an amplifier. A horn used in a sound reproduction (or recording) device does not add power - it is completely passive, not active. As has been mentioned here already, a horn is more properly understood as a transformer of acoustical impedances. Much like an electrical transformer which is also not an amplifier as it is completely passive.

A horn can more easily be understood as a sound concentrating device. As used with a phono reproducer, it takes the sound which would ordinarily just be sprayed in a 360 degree spherical wave at the output of the small reproducer throat and concentrates that acoustic power into a narrow beam that is aimed at the listener. The sound at the listener seems louder than without the horn because much more of the original energy is redirected at the listener instead of "leaking" out of the reproducer nozzle in all directions. This is a crude description of what is happening, but it should be understandable. That said, the transmission efficiency at different audio frequencies of a horn depends on its shape and taper. This has to do with the dynamics and the shape of the audio wavefront as it traverses the length of the horn. Horns with exponential taper are more uniformly efficient over a wider span of the audio spectrum (have a flatter frequency response) than are other simpler shapes of horns such as the conical. That's why differently shaped horns sound different. And the length and size of the horn contributes to its ability to concentrate and direct the longer wavelengths (bass frequencies) toward the listener. That's why a bigger, longer, and properly shaped horn can deliver better bass than can a small, poorly shaped horn.

[estott]

It concentrates the sound and increases the pressure. I'll use the analogy of water, though it isn't exact. Think of a garden hose without a nozzle- the stream is weak. If you put a narrow nozzle on the hose the water stream is cohesive and will project farther. The analogy can't go further because sound waves expand and travel in the air, and water doesn't.

[Cody K]

By Jove, I think I've...well, no, I don't "got" it yet, but thanks to you all I'm a heck of a lot closer than I was when I woke up this morning!

So: Since the output from the reproducer isn't really enhanced in any way by means of energy added to the output, it isn't technically amplified, though the effect is the same or at least very similar. I think that's where the confusion comes in regarding terminology.

Phototone, thanks for presenting it as a kind of an interface between the air around the diaphragm and the air in the room. The horn, then, can be thought of as sort of a go-between connecting the two by confining and directing the sound as Frank notes, and concentrating it as Greg says? Visualizing it that way helps a lot.

I've been listening to these machines since I was prepubescent, around the time of the Punic Wars, but until I read Mr. Reiss's assertion -- just sort of dropped into that paragraph as though it were common knowledge -- it never occurred to me that what I was hearing was anything other than amplification. I had to read that sentence a few times to be sure I was reading it correctly. Then, seeing similar assertions elsewhere in my reading, I was at a loss. Thank you all for your very helpful explanations.

Now I'll be somewhat ready if I have to explain it to a five year old. Lord knows it would be embarrassing to have him or her whip out their smart phone and three minutes later tell me I was full of baloney...

[Cody K]

Estott, you note that by concentrating the sound the horn increases pressure. This brings up something I've always been curious about with regard to the need for airtight soundboxes and, particularly in the case of something like an Orthophonic system, horns. Is it correct to think that the inability of sound to escape via air leaks forces the soundwaves to concentrate more efficiently? Is this "concentration" a matter of air particles confined along the route of the tone arm/horn being made to vibrate sympathetically, creating a "snowball" effect, and the perception of "more" sound through the increase of air pressure? (Am I warm?)

Thank you all for your patience if these questions are really elementary stuff. [/high school dropout/lifelong learner]

[estott]

Estott, you note that by concentrating the sound the horn increases pressure. This brings up something I've always been curious about with regard to the need for airtight soundboxes and, particularly in the case of something like an Orthophonic system, horns. Is it correct to think that the inability of sound to escape via air leaks forces the soundwaves to concentrate more efficiently? Is this "concentration" a matter of air particles confined along the route of the tone arm/horn being made to vibrate sympathetically, creating a "snowball" effect, and the perception of "more" sound through the increase of air pressure? (Am I warm?)

Thank you all for your patience if these questions are really elementary stuff. [/high school dropout/lifelong learner]

I think it's along those lines (not a tech expert here) sealing leaks along the sound path is important, particularly in the arm.

[Jerry B.]

Would it be accurate to compare it with the workings of a shotgun? With a short barrel, the shot is scattered almost immediately. With a longer barrel, the shot is more focused and concentrated in a smaller area. The barrel of the gun does not increase the power of the discharge but it does focus more of the energy to a specific area. Just a thought... Jerry Blais

[estott]

Would it be accurate to compare it with the workings of a shotgun? With a short barrel, the shot is scattered almost immediately. With a longer barrel, the shot is more focused and concentrated in a smaller area. The barrel of the gun does not increase the power of the discharge but it does focus more of the energy to a specific area. Just a thought... Jerry Blais

I think there's something to that, but like the hose analogy it only goes so far

[fran604g]

It concentrates the sound and increases the pressure. I'll use the analogy of water, though it isn't exact. Think of a garden hose without a nozzle- the stream is weak. If you put a narrow nozzle on the hose the water stream is cohesive and will project farther. The analogy can't go further because sound waves expand and travel in the air, and water doesn't.

^This is exactly the analogy I would use. Concentration is not the same as amplification. I guess the same can't be said for mechanical "enhancement", like a water wheel increasing the power of water via a crank shaft?

[FloridaClay]

There is, I think, a distinction to be made with respect to what is being amplified and that is perhaps the generator of the confusion. A basic dictionary definition of amplify is to make larger, greater, or stronger. I can accept, I think, Reiss' notion that sound waves are not being amplified and that having a horn does not increase the sound waves per se. But that is not what most people are talking about when they think of a horn amplifying. They are talking about loudness and there is absolutely no question that that is made greater (amplified) due to all the forces acting on the sound waves that are at work as described in this thread.

Clay

[fran604g]

There is, I think, a distinction to be made with respect to what is being amplified and that is perhaps the generator of the confusion. A basic dictionary definition of amplify is to make larger, greater, or stronger. I can accept, I think, Reiss' notion that sound waves are not being amplified and that having a horn does not increase the sound waves per se. But that is not what most people are talking about when they think of a horn amplifying. They are talking about loudness and there is absolutely no question that that is made greater (amplified) due to all the forces acting on the sound waves that are at work as described in this thread.

Clay

Good point, Clay. I look at it from the point that the sound waves are actually altered when amplified. If you electrically amplify a signal, it becomes different because some frequencies are rolled off, but the perceived loudness is increased across a finite spectrum. Does the amplitude of the sound waves being "pushed" through a horn remain unchanged? Maybe this is a way to answer the ever ongoing question?

Fran