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Author Topic: Mechanical amplification?  (Read 5019 times)

Jonathan Johnson

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Mechanical amplification?
« on: December 07, 2014, 01:51:09 am »

Last night I got to wondering, is there any way to amplify live audio without using electricity?

I don't mean to focus acoustic energy such as you might with a conical horn, or use a resonant chamber to tune energy to a single frequency (as in a wind instrument), but to take a variable audio signal, and with the addition of energy from another source, produce an output signal identical to the input but with a larger amplitude -- with no perceptible latency?

I have no practical reason for asking, it was just something that popped into my head so I figured I'd throw it out here for your bemusal.
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Steve M Smith

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Re: Mechanical amplification?
« Reply #1 on: December 07, 2014, 03:27:00 am »

Yes.  There used to be pneumatic amplification using compressed air.  It used to be used for music at ice rinks and other public events.

http://en.wikipedia.org/wiki/Compressed_air_gramophone

Speech amplification was also possible.

http://www.vias.org/crowhurstba/crowhurst_basic_audio_vol1_028.html

I suspect the speech/music was accompanied by a fairly loud hissing sound.


Steve.
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John Roberts {JR}

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Re: Mechanical amplification?
« Reply #2 on: December 07, 2014, 11:04:30 am »

Last night I got to wondering, is there any way to amplify live audio without using electricity?

I don't mean to focus acoustic energy such as you might with a conical horn, or use a resonant chamber to tune energy to a single frequency (as in a wind instrument), but to take a variable audio signal, and with the addition of energy from another source, produce an output signal identical to the input but with a larger amplitude -- with no perceptible latency?

I have no practical reason for asking, it was just something that popped into my head so I figured I'd throw it out here for your bemusal.
To look at this properly in the classic electrical amplifier the audio has been converted to electricity before and used to modulate an electrical power source, then that electrical output is converted back to sound.

Sound energy could be used to modulate air flow, or water flow, or even flame (?), but I am not aware of any practical direct conversion of this modulated (DC) flow, into linear AC sound. I guess a mechanical modulated air pressure amplifier could make a class B version combining pressure and suction, giving new meaning to a push-pull amp. I suspect some variants use some form of distortion of generate an AC audio term  from a modulated DC stream.

Electricity is useful stuff, and sound reproduction using it is pretty well developed. I guess in the hot summer time a modulated water pressure amp could be cool(ing).

JR

[edit] a modulated steam whistle could warm the audience in winter....[/edit]
« Last Edit: December 07, 2014, 11:24:38 am by John Roberts {JR} »
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Steve M Smith

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Re: Mechanical amplification?
« Reply #3 on: December 07, 2014, 02:54:56 pm »

Sound energy could be used to modulate air flow, or water flow, or even flame (?)

Flame?...  Oh yes!!




Steve.
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Jonathan Johnson

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Re: Mechanical amplification?
« Reply #4 on: December 07, 2014, 09:12:57 pm »

Cool stuff! It's fascinating to discover different ways of doing things, especially without the benefit of something (electricity) you would consider essential to the process (audio amplification).

I was imagining something like power steering.
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Tim McCulloch

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Re: Mechanical amplification?
« Reply #5 on: December 07, 2014, 09:56:23 pm »

Flame?...  Oh yes!!




Steve.

And you can warm your hands in front of it. :)
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Steve M Smith

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Re: Mechanical amplification?
« Reply #6 on: December 08, 2014, 01:32:04 am »

And you can warm your hands in front of it.

Or make toast!


Steve.
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Mike Sokol

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Re: Mechanical amplification?
« Reply #7 on: December 08, 2014, 03:07:52 pm »

Or make toast!

I remember reading about a phonograph amplifier that used steam or compressed air for power. Similar principal with the needle directly moving a valve that released more or less steam/air. Soggy toast though, so I like the flame version better. I see that you plumbed the Flame-Phone into your existing house's natural gas line. Woo-Hoo!!!  ;D
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Steve M Smith

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Re: Mechanical amplification?
« Reply #8 on: December 08, 2014, 04:44:15 pm »

I see that you plumbed the Flame-Phone into your existing house's natural gas line.

This predates natural gas in the UK.  We used to have what was known as 'town gas' which was the gas released when coal was heated.

It was stored in huge pressurised containers called 'gasometers.


Steve.
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Mike Sokol

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Re: Mechanical amplification?
« Reply #9 on: December 08, 2014, 04:58:22 pm »

Found the air powered speaker I was talking about. The Auxetophone was built 20 years before tube amplification and it's LOUD and surprisingly good sounding. Just for our UK friends, note the aluminium "misspelling on the patent.  ;D

And here's a youtube of it working with all the mechanics: https://www.youtube.com/watch?v=J7SV65DFNy8


So now we have spec air compressors for our gigs in addition to generators?  :o

=======================================

 I have found a brief reference that says: "1898: The compressed air Auxetophone is first used to broadcast records of operatic arias from the tops of the Blackpool Tower in England and the Eiffel Tower in France." This was one Short's first prototypes; it gives you an idea of just how loud this thing could be.
      
Below: One of Short's patents, this one dated 1901.

This version of the air valve appears to have a grid-type valve y hinged at the bottom that approaches and recedes from a series of slots to control the air supply, which enters at a'.

Fig 1 shows a voice-amplification system, with a microphone-type diaphragm at the right, which moves the valve via rod v.

Fig 6 appears to show a cylinder-phonograph version, with stylus m contacting the cylinder.

CHARLES PARSONS.
In 1903 Short sold the patent rights to Parsons, and that year another British patent (No 10468) was granted, following Sir Charles' improvements to the air valve, the critical part of the system. In a letter written in 1921 to Sir Ambrose Fleming (The inventor of the thermionic diode valve) Parsons says:

"I worked at this subject as a hobby in my workshop at home and tried many types of valve- double-beat, slide-valves with multiple openings, then a form of valve made of sheet metal on edge like a fireworks cracker, and lastly the "comb-valve"- much the best because it delivered a flat-faced sound wave into the trumpet and it is not liable to be impeded or struck by small particles of dirt. It is similar to Short's. I made valves of comb pitches from 1/50 of an inch for reproducing from faint phonograph records, up to some of 1/4 inch pitch for attachment to double-bass stringed instruments. The very fine ones were made of hard gold, the rest of magnalium.* The air-valve reproducer was shown at the Royal Society about 1904, on a gramophone. Professor Johnston Stoney, FRS, was much interested, suggested the name "Auxetophone", and treated the matter mathematically.

If the motion of the valve is expressed in a series of sine terms (Fourier) the the sound wave produced is the first differential, and consequently the harmonics are much increased in amplitude above the fundamental, and the tone much increased in richness. This was found to be the case when used on the gramophone or when actuated from the bridge of a stringed instrument.

It was shown soon afterwards in the Library of the Royal Institution and notices appeared in the papers, and then Short's letter reached me. Previously I had not made any patent search and was not aware of his patent. Edison's had either been cited by the Patent Office or Marks and Clerk had known of it.

It appeared that Short had played an instrument on the top of the Eiffel Tower some years before. He (Short) was at that time connected with Colonel Gouroagh of the Edison Company, but when I met him he had very little money and readily assented to sell his patent to me for �700 down, and an agreement for four years at �400 per annum. Soon afterwards, the Gramophone Company of 21 City Road bought mine and Short's rights for gramophones and phonographs for all countries for �5000. I retained the rights for musical instruments.
The valve you have (taken to pieces) was made by Short in our Shops (at Heaton) and was played on a double-bass at the Promenade Concerts at Queen's Hall all one winter about 1906.

We spent much time and money in endeavours to introduce it on violins, 'cellos, and double-bass instruments, but were virtually blocked or boycotted by the Musical Fraternity, because they found it would reduce the number of executants from one-fifth to one-tenth for the same volume of sound. I dropped the whole matter, and Short was employed on other work including experimental attempts to make diamonds. He left our service about 1914 to join his brothers making sea-planes, and he died in about 1917, leaving �70,000, having made large profits from the Short Folding Wing Sea Plane.

The limiting factor to greater magnification of sound by means of an air-valve seemed to be viscous resistance in passing through minute apertures. Experiments showed that this was very marked below 1/1000 inch aperture. Hence there results a limit to the fineness of the comb. I was never able to obtain an actual magnification of the voice by means of an air-valve, Your (Fleming's) ionic valve has solved this problem."

* An alloy of aluminium and magnesium.

This letter appears to indicate that Parsons was interested in compressed-air amplification and developed the comb-valve before he bought Short's patent, which shows a different kind of valve. Perhaps it was the patent on the general principle, rather than the details of the valve technology, which Parsons wished to acquire.

It also raises the question of whether Short's voice-amplifier actually worked; Parsons says he could not make one that worked. Note also that Parsons does not seem to appreciate that one amplified double-bass is not remotely the same thing as five basses playing in chorus. And one can hardly blame musicians for being unenthusiastic about an invention intended to put most of them out of work.

How exactly did the air-control valve work? Since sound consists of positive and negative pressure changes, you might imagine that while the machine was "quiescent" there was a steady flow of air which was increased for positive excursions and decreased for negative ones. If this was not the case- and this point currently remains obscure- then the sound waveform would have been half-wave rectified, which would explain the poor sound quality. The supply of air to both sides of the tonebox may be related to this, or it may be to do with balancing the valve to reduce the frictional forces on it.

Later versions of the air-valve introduced partial balancing so that the relatively small needle forces could better control the pressurised air. A spring-loaded piston powered by the air supply acted on a wire-spring lever attached to the valve cover.
Parsons' first experimental air-valves had combs made of boxwood, the slits being cut with a jeweller's saw. The air pressure used in early tests was 2 to 3 psi.

Despite Parsons' and Short's efforts, the subjective results were apparently still somewhat short of perfection. One reaction from an Edinburgh journal was:
"Have you heard the auxetophone? It is to be hoped not. All Mr. Parsons' turbines will be wanted to take long-suffering humanity out of earshot of his diabolical invention".

The following letter was sent on 18th May 1909 by Sir Henry Wood, who co-founded the Promenade concerts in 1895:

"Dear Mr Parsons,
I am making a new orchestral arrangement for next season's Promenade Concerts at Queen's Hall of Wagner's "Siegfried" and I particularly want to do the scene with the Dragon's voice.

On the stage, this is always sung into a very large megaphone, but in my arrangement I want to do it on a very big bass tuba. do you think it would be possible for me to utilise your auxetophone? Of course I have never heard a tuba reinforced by your splendid invention, but perhaps during June, when I shall be fairly free, you could arrange for me to bring my player down."

Unfortunately nothing came of this innovative proposal, for Sir Henry wrote in the following June:

"Very many thanks for your kind letter. I had hoped to be able to the Royal College on the day you suggested, but was prevented. I now find that a bass tuba played into an ordinary very large megaphone (which I am having made by Hawkes*) gives the desired effect. With kind regards and many thanks..."

* Who went on to become part of the famous musical company Boosey & Hawkes.

A Victor auxetophone-gramophone was demonstrated to the public in November 1906 at a Trade Exhibition at Earl's Court. Mr S H Sheard recalled that the correct operating pressure had not yet been determined:

"We used about six or seven pounds to the square inch, with the rather amusing result that those of the audience who took the front rows of chairs very quickly clapped their hands to their ears and made their way to the back of the building. It was subsequently found that a pressure of not more than two-and-a-half pounds to the square inch was adequate." Which if nothing else proves that varying the operating pressure was a viable way of altering the volume.

In 1922-23, when wireless broadcasting had become established, the long-neglected auxetophones were resurrected at Parsons' Heaton works by Mr A Q Carnegie, one of Parsons' colleagues. A gramophone-type valve was driven by a magnetic motor, producing a high-volume output at a time when the capabilities of electronic valve amplifiers were very limited. The idea was not however pursued, one reason being that the patents had expired and this would limit the profitability of future business. The loudspeaker was still in use at the Heaton works in 1933.

Parsons took out three patents in all:

No. 10,468 (1903) Improvements in Sound Reproducers or Intensifiers applicable to Phonographs, Gramophones, Telephones and the like.

No. 10,469 (1903) Improvements in and relating to musical instruments.

No. 10,892 (1904) Improvements in and relating to Reproducers or Resonators for Gramophones, Phonographs and the like.
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