Do horns amplify sound?

[edisonphonoworks]

Horns do not amplify sound but match its impedance,and direct it. The longer the horn though the more low frequency response, the shorter, the low frequency waves do not have space to form enough pressure to be heard, on the other hand high frequency energy can be lost or canceled by the long horn. This can be easy to see when you say into a recording horn of different sizes Sister Susie Sewing Shirts for Soldiers, if you say it in a short, horn the S's and Ts will record beautifully as well as the other articulations, however if you use a 5' horn there is more tone and body, but the clarity is lost. An interesting experiment is to record on a cylinder with no horn, with your mouth on the tube that goes into it, and speak, for this purpose you will get a very clear, natual voice recording, even though it is not as loud as with a horn. Reproducers on the other hand can do some amplification with the use of levers, you know how you can lift more weight with a longer handle, this can be done with reproducers, by changing it it will make the end to the diaphragm have more excursion and make things louder.

[Uncle Vanya]

From Wikipedia...
"A horn is a tapered sound guide designed to provide an acoustic impedance match between a sound source and free air. This has the effect of maximizing the efficiency with which sound waves from the particular source are transferred to the air. Conversely, a horn can be used at the receiving end to optimize the transfer of sound from the air to a receiver."

Sounds like an amplifier to me.

If you are serious that would be like saying that a transformer "sounds like a transistor to me". If not, you made a clever jape indeed!

An amplifier increases the power of a signal. The horn of a talking machine or electrical reproducer does not increase the level of sound energy available, it merely takes what energy is available and more efficiently couples it to the room air.

[Chuck]

I agree with most everything said here so far.

Just to add my twist to it:

True amplification of any signal implies that
some outside source of energy is used, and
this external energy is modulated by the weak
input signal.

It is much like using a small force to turn a
valve handle on a fire hydrant, which controls
a very large and forceful stream of water.
The British term for a vacuum tube is a "valve"
and it's a very fitting and descriptive term
because it really is, indeed, an electrical
valve.

For an example of true acoustic amplification,
look no further than the type of reproducers
which have a turning amber wheel that runs
from the machine, and this wheel has a cord
wrapped around it, which is coupled to the
diaphragm and the stylus bar.

The vibrations of the stylus bar alternately
tighten and loosen this cord in such a way
that some of the energy from the rotating amber
wheel gets transfered to the diaphragm. When
these reproducers are working right, they indeed are very very loud! I saw a youtube
video of a Columbia machine that has this setup. This mechanical amplifier even has
background hiss which is reminiscent of the
background noise made by both tube type and
transistor amplifiers.

All of that being said, the horn originally
discussed is a purely "passive" component.
There is no external energy fed in.

It really is an impedance-matching device
very similar to a transformer.

Ever take the speaker leads coming from
an electronic amplifier and try to use them
to listen with a telephone receiver? You can
hear the sound, but it's very faint and distant. Put in an 8 ohm to 1000 ohm impedance matching audio transformer, and then
you can hear nice and loud in the telephone
receiver. Ever try to hook a speaker up
to a headphone jack? That will do about the
same thing, you can hear a signal, but it will
be very weak. In that case, the same transformer can be used, and the 1000 ohm winding will hook to the headphone jack, and the 8 ohm winding hooks to the speaker.

Ever play an Edison Gold Moulded 2 minute
record listening with just the C reproducer
with no horn, no hearing tubes? You can hear
the record, but it sounds weak, tinny and
distant. Put the 10-panel morning glory
horn on there and suddenly the sound fills the
room! Just like the transformer does for
the electrical circuit.

One way to understand what it's doing is to
look at the shape. It starts out at the same
diameter as the reproducer's tube. Gradually
it gets to a larger diameter. The pressure
waves are pushing and pulling the air inside
the horn. Think about what is happening at
each little cross-sectional diameter all along
the way inside the horn. Everywhere along the length of the horn, the air is being pushed and pulled by the air directly behind it, with none of it able to get away.

Out at the extreme large end of the horn, that
air then gets to push and pull on the room's air. It's big enough out there at the large
end of the horn to actually be able to do some
good. Where as the bare reproducer tube is
so tiny that it can't push and pull much
area.

Put your ear right up to it though
and be careful, because then it's really, really loud! (The inside of your ear canal
is not too far different in diameter than the
reproducer's tube is)... but to couple them
closely you've got to get right down there
with it. Or, stand back and hook up your
big horn.

Chuck

[Cody K]

Thank you all for your contributions to this discussion -- I think I've got it now! (Although I've gotta say, edisonphonoworks, once I looked at your diagram, I think I was more confused than ever for a few moments. Math has never been one of my strong points. But that's why you get to make records and I'm a dedicated member of the audience.)

[clevelander]

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[estott]

Dear friends! Thanks a lot for providing me with such essential answers. Just improve your grammar - follow http://royalediting.com/usage-tips-of-passive-voice. Creating a short piece of writing may be as easy as counting to three!

I SUSPECT A VIRUS IN THE LINK

[ChuckA]

If you want to read all the up to date technical details of horns and how they work in 1929, read chapter 5 (page 90) of "Modern Gramophones and Electrical Reproducers". Not an easy book to find, but of course the internet comes through:

https://archive.org/details/ModernGramophones1929


Chuck

[Expert]

The simplest way to describe how a horn of a gramophone works is to concentrate on the air molecules. It is these that are excited and subsequently enlarged. They flow through in the same manner that electricity travels along a cable: not at a constant rate but ebbing and flowing. Because the diameter of the cable remains the same throughout its length the current arrives at the far end in exactly the same state it was at the beginning.

In a gramophone system the increasing diameter of the tone-arm and horn creates energy. As the air molecules are excited by the vibrations from the needle in the record groove, they initially move forward, then backwards -- hitting the previously forward-moving molecules -- thus creating more energy as they again move forward, with a greater space to do so and add more moving molecules as the sound conduit enlarges. Thus the energy increases and the vibrations become louder.

The energy is created at the outset by the movement of the soundbox diaphragm and the space inside the soundbox at the back where it is attached to the tone-arm. It was once thought (and experimented with) that the ideal situation would be to have the tone-arm the same diameter as the soundbox diaphragm; but, as you may now realise, there would be very little energy created to move and expand the air molecules and the resulting sound output would be very weak if not non-existent. It was also discovered that the basis of a good bass response as well as optimum air-molecule energising originated if the tone-arm could be kept narrow for as long as possible. The culmination of scientific thinking and mathematical calculation in respect of gramophone horns dictates a precise rate of expansion relative to length, with as few bends as possible and with the final critical feature being the flare at its mouth — which must be designed to continue the expansion of air in relation to the molecules of air in the room. If the transition from horn to room is too abrupt and there is too much energy created at this point, the result is that a large part of the vibrational energy of the soundwave is reflected back into the tone-arm, and not into the room. When this happens it tends to cancel out and distort the forward moving wave that is attempting to move up the tube and out into the room. In the room there would be a greatly decreased volume and poor fidelity.

[Henry]

Expert has it spot on. Consider a brass musical instrument; I'll use the trombone, since it was my instrument and it also exemplifies the simplest form of acoustic amplifier: a cylindrical tube having a conical taper culminating in a flare at the bell end. If I put my lips to the mouthpiece, detached from the horn, form an embouchure, and blow air into the mouthpiece, you will hear---nothing, except perhaps the faint rush of air passing through the Venturi (narrowing of the mouthpiece throat). But that air (those air molecules) is (are) vibrating at a certain rate or frequency (cycles per second, Herz [Hz]). If I then, while continuing to blow thusly into the mouthpiece, insert said mouthpiece into the receiver of the tube, you will hear, as if by magic, a musical pitch emerge at the bell end. If I vary the breath pressure and the muscular configuration of the embouchure, I can cause other pitches to sound, which will be in the harmonic series of pitches produced by a tube of that length, which for the Bb trombone is about nine feet in the first (closed) position. By extending the slide to any of six other positions, I can produce pitches in the harmonic series with respect to the varying length of the tube, and thus cover the entire range of pitches needed to play music.

By analogy to the phonograph, think of the needle, needle bar, and diaphragm as the lips and mouthpiece, and the fluctuations and variations in the record surface as the breath. If you could detach the sound box from the taper tube, you might hear a very faint version of the recorded sounds. Place that sound box on the tube, and you will, of course, hear those sounds much louder through the tube and horn of the phonograph. As in the trombone, the tube and horn function as acoustic amplifiers in a manner described above in Expert's post.

(By the way, what is commonly referred to as "buzzing the mouthpiece" has little relation to what a brass player actually does when playing. If you insert the mouthpiece into the horn while "buzzing" it, you would produce a most wretched sound. If you are familiar with the Spike Jones recording of "Der Führer's Face," the trombone there is producing that sound!)

[Curt A]

OMG... this is WAY more information than anyone needs to understand...

Boiled down to simplicity:
A phonograph with a needle playing a record with no reproducer or horn = terrible listening experience - there are sound waves, but close to zero discernible sound.
A phonograph with a reproducer and diaphragm playing through a horn = concentrated sound loud enough to listen to... concentrated sound = amplification to my ears...