The Talking Machine Forum — For All Antique Phonographs & Recordings

It seems to be an axiom among some who care about such things, that sound isn't amplified while passing from a record through a reproducer and through a horn. Eric Reiss says it very definitely in the "Acoustics" chapter of The Compleat Talking Machine:

It is well to note that these soundwaves are not amplified at any point in acoustic machines. Sounds are merely produced and given a direction, like talking through the garden hose. (Fifth Edition, p. 45)

Okay, I confess -- I can't wrap my head around this. How is sound not amplified, i.e. made bigger, more ample, by passing through a horn? I might just be running up against a particularly dense something in my cranium, but to me, sending sound through a horn and a garden hose are not at all alike. One gets you bigger sound; the other gets you the frustration of wasting time, not being able to hear anything, and also possibly an earful of water.

I've seen a number of statements similar to Mr. Reiss's, both online and in print. I've searched a number of variants of "acoustic amplification of sound" and so on, and much of what I've found seems to suggest that, duh, passing sound through a cone or horn to make it louder is amplification.

So what's the deal here? Is it just some kind of a semantic thingy? I'm hoping somebody will know the science well enough to be able to explain it to me like I'm a five year old, because that seems to be about where I am with this question. I have a feeling that this isn't really all that complicated, but I don't get it.

Humm. Well granted I may be missing something technical here, but it seems to me that without question the purpose of a horn is amplification. Just try removing the horn and listening (or trying to) a record without it!!

Clay

Mr. Reiss, meet Mr. Megaphone!
A megaphone, speaking-trumpet, bullhorn, blowhorn, or loud hailer is a portable, usually hand-held, cone-shaped acoustic horn used to amplify a person’s voice or other sounds and direct it in a given direction. The sound is introduced into the narrow end of the megaphone, by holding it up to the face and speaking into it, and the sound waves radiate out the wide end. The megaphone increases the volume of sound by increasing the acoustic impedance seen by the vocal cords, matching the impedance of the vocal cords to the air, so that more sound power is radiated.

This is from Wikipedia and refers to voice but the principle should be the same no matter what the sound is. How loud would an Edison Home be with a length of garden hose attached? Does a rubber listening tube work in free air or do you need to put the end in an ear to hear anything?

Cody K wrote:So what's the deal here? Is it just some kind of a semantic thingy?

Almost - in a way, it depends on your definition of 'amplify'. But technically the statement is correct.

An electrical amplifier increases the electrical signal from a pickup, i.e. it adds energy. But with a horn, you only have the energy produced by the soundbox/reproducer, and the horn cannot add anything to that (it is a passive component) - otherwise, acoustic gramophones/phonographs would be something along the lines of a perpetual motion machine, breaking the laws of thermodynamics. How entertaining would that be!

A horn is just a 'waveguide', allowing the sound to redevelop some degree of frequency balance, and giving it directivity. Also, the whole speaking length of tonearm and horn offers an impedance (resistance) to the soundbox, optimising its efficiency by giving it the right loading to 'work against'.

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.

Orchorsol! -- I said like I'm a five year old! I know UK kids are smart, but...could you explain what you mean in your last paragraph in a way that an American kid can understand? I think I understand the basic idea of channeling sound waves so that they sort of "snowball" in a way, producing a larger sound. I have no real grasp of the technical aspects of this, though. You seem to know the science -- can you expand on it some more? And something more about the idea of impedance, and how that resistance works? Please and thank you!

A further question: something on the order of the Auxetophone -- would that be properly termed amplification in that it boosts the soundwaves by adding energy in the form of compressed air to the mix (which, of course, most horn systems don't do), and would that be enough to make the difference in terms of whether the sound could properly, officially, be called "amplfied"?

Cody K wrote:Orchorsol! -- I said like I'm a five year old! I know UK kids are smart, but...could you explain what you mean in your last paragraph in a way that an American kid can understand? I think I understand the basic idea of channeling sound waves so that they sort of "snowball" in a way, producing a larger sound. I have no real grasp of the technical aspects of this, though. You seem to know the science -- can you expand on it some more? And something more about the idea of impedance, and how that resistance works? Please and thank you!

Oh dear, what have I started here... The maths gets really complex, way beyond me, and I only have an outline understanding of the science in general. I'm not sure I can explain any of it adequately. You basically got it yourself there with the snowball/larger sound comment. Beyond that it gets really complex - this is a great article (and incidentally, it touches on the Wilson horn designs which EMG and Expert used) http://kolbrek.hoyttalerdesign.no/image ... rticle.pdf

Impedance - the shape of the horn, as well as the small space behind the reproducer diaphragm and the narrow start of the tonearm, all tend to 'constrain' the diaphragm compared to how it would be if it were just held in a ring in the open air. It has to work harder and this also has the effect of making it follow the groove much better (as opposed to flapping about in a more uncontrolled manner). If this complex system is designed with all the elements in really good harmony, and with a horn flare that's sympathetic to sound waves developing purely (as in say Victor/HMV Orthophonics, or EMGs/Experts) we get fantastic sound quality.

I don't necessarily disagree with other posters - in layman's terms, horns do amplify, but in strict scientific terms they don't.

I'll have a go at the layman's explanation... ( for better or for worse )...

While technically, the horn playing small-end toward large-end does not "amplify" the sound per se, it confines and directs it, sort of achieving the same apparent result. It works the same in reverse - the large end will "collect and direct" sound waves, and direct them down the tapering tube to the listening end.

(Recording horns evolved to be relatively long, with a fairly skinny taper, whereas "amplifying" horns tend to flare more quickly, and ended in a larger bell."


Sort of along the lines of "there's no such thing as a "vacuum" " as our chemistry & physics teachers hectored us in school...

But Hoover, Electrolux, Eureka and Kirby have all sold millions of "vacuum-cleaners", a "vacuum leak" in our auto-engines or player-pianos causes poor performance, etc.


Even if that's not "Technically how it works", that's the apparent effect; if you have an cylinder player, play a cylinder with the horn removed... the music is there, but not very loud. You can approximate the same thing with a disc player, just using the bare reproducer, or the reproducer and crook ( and a junk record )...

The superiority of Victor's exponential Orthophonic horn was due to careful matching of the horn's dimensions and proportions to acoustic impedences, as opposed to the 1890's approach of basically just sticking a funnel onto the reproducer.

I believe the Orthophonic horn in a Credenza is over 8ft long, if you straightened it out... the other genius in its design, was "folding" it into a more compact package without compromising its effectiveness.


A funnel is "better than nothing", but only slightly - it favors some frequencies better than other...


The Auxetophone is unique... it employs a special "comb valve" inside the reproducer which basically uses a small amount of acoustical energy from the record and needle-bar to control a larger amount of air / energy provided by the blower. Kind of physical equivalent of the electronic amplifier...

A Phonograph Horn is like a transformer in electronic circuits. It serves to match the input (the diaphragm in the soundbox) to the room air (the output). It allows the sound-box movement of the diaphragm to be efficiently coupled to the room air, thus maximizing the transference of sound waves into the room air. Larger horns do this better than smaller horns. It doesn't increase the vibration of the diaphragm of the soundbox, that stays the same, and is dependent on sound box design and the record being played. It just dramatically increases the efficiency of how the movement of the diaphragm (the air it moves) is coupled to the room air.

This is a most interesting subject- and the posts have been fascinating -albeit somewhat hard to wrap ones head around - but very informative. Regards, Johnyy