Microphone Mystique

Microphones…the Acoustic Era

Posted on Updated on

Three cheers for Gorilla Inventors!

Emile Berliner - MicrophoneMicrophone of Caveat April 11, 1877 with mouthpiece added

Berliner blasts the Bell patent pork in 1876:

1. Who was Emile Berliner?  2. What did he do that pissed off Thomas Edison?  3. Who takes credit for the first carbon microphone patent in 1877?

The unveiling of Alexander Graham Bell’s telephone in 1876 inspired Emile Berliner, a young man with rudimentary knowledge of electricity & physics to improve on the telephone’s transmitter.  He invented a “loose contact” metal-to-metal transmitter (type of microphone) to function as a telephone speech transmitter, then wrote and filed the patent himself, causing a stir among the titans of technology.  Thomas Edison followed his lead and filed patent applications for the carbon microphone in June 1877.  After a long legal battle, Edison emerged the victor, and the Berliner patent was ruled invalid by both American and British courts.

Berliner was quickly picked up by Thomas Watson of the American Bell Telephone Company and employed as a researcher until 1884 when he set out with new wife, Cora & his recently acquired American Citizenship to pioneer in Washington DC as an independent Researcher & Inventor.  In 1886, he began working on his greatest contribution to the world: the gramophone…making possible the recording and reproduction of sound using disc records

Ok let’s take a closer look at the “micro” drama:

4. What is a liquid transmitter?  Describe how it works…  5.  Who invented it and when?

In 1876 a liquid transmitter (variable -resistance device) was developed by Elisha Gray & Alexander Graham Bell (simultaneously):

the user talked into a black funnel-shaped mouthpiece at the base of which is a stretched membrane diaphragm.  A metal pin through the centre of the diaphragm extends down into a metal cup containing dilute acid.  An ohmmeter between the cup and the pin will show fixed resistance.  Movement of the diaphragm causes the pin to move up and down in the liquid, varying resistance accordingly. Connecting wires from the pin and cup, in series with a battery & telephone receiver would produce articulate speech in the receiver when speaking into the mouthpiece
6. Why did box telephones fail?  7.  What invention improved on the magneto transmitter? 8.  Who introduced a chemical reaction to transmitter design?

Bell’s box telephones (magneto transmitters) worked well as receivers but as transmitters, their signal output was too weak to carry any great distance.  User had to shout into the mouthpiece only to be barely heard on the other end three miles of wire away.  Transmitter design would have to be improved…enter competition from Western Union…Thomas Edison’s lampblock carbon unit, “the Blake” (variable-resistance transmitter) with improvements in sensitivity & reliability courtesy of our favourite rogue, Berlinger, outperformed Bell’s Magneto type until Henry Hunnings came on the scene in 1879 with a new transmitter design using granules of coke between the diaphragm and a metal backplate.  In 1886, Edison improved on Hunnings design by designing a small button-type container and using processed anthracite granules.  In 1892, A.C. White pushed the button  by using a polished carbon block as a rear plate and a similar block in front against a mica disc, with the carbon granules in between.  The mica disc worked like a piston.  Known as the Whit “solid-back” type, it was the industry’s first reliable transmitter and was used from 1892 until about 1925

9. Who invented wireless telegraphy?  10. How did that spark interest in improving microphone technology?  11. How did Goldschmidt get around the low current capacity of the telephone transmitter?

The telephone transmitter as the only available microphone in 1900, was finding other applications thanks to the invention of wireless telegraphy by Nikola Tesla in 1895.  Gorilla inventors were trying to modulate wireless radio waves so that speech could be sent on them.  As there were no amplifying currents in those days, the microphone was connected into the antenna and had to carry the circuit’s full current.  Only very low-power radio transmitters could accommodate the use of the telephone transmitter whose maximum current capacity was about one-half ampere, leading to the use of multiple microphones with a common mouthpiece.  Rudolph Goldschmidt (a fan of Jersey Shores) introduced a patented circuit for working microphones in parallel to address the problem of failure of the group due to the short circuit of one transmitter.

12. What is a flame microphone? 13.  What is a liquid microphone?  14. When was the magnetic modulator invented?  By who? And for what market?

The hunt for high-power microphones revived earlier patents for condenser transmitters (Edison in 1879 & Dolbear in 1881) and sparked a culture of electronics experimentation & inquiry between 1900 & 1915.  Berliner made a high-current carbon microphone that was air cooled by a fan mounted under the microphone…noisy! Blondell & Chambers developed flame microphones based on spark rods in an oscillating circuit adjusted just short of sparking, using speech vibration to alter the gas supply pressure and vary a flame’s resistance in the gap which would cause sparking to occur.  Liquid or “hydraulic” microphones came upon the scene at this time using the flow of a fine stream of conducting liquid from a reservoir traveling about five feet until the stream would break into droplets.  Sound variations on an elastic diaphragm were driven by a metal diaphragm behind the mouthpiece to carry the pressure of the stream, producing  a variable resistance in proportion to the sound on the diaphragm.  Using 65 volts at 12 amps (780 watts) a one-horsepower microphone was possible (until someone opened a door or sneezed).  The development of heavy-current microphone relays by Fessenden & Dubilier as well as advancement in circuit design by C. Egner & J.G. Holmstrom furthered the cause of high-current microphone technology.  In 1911 the “magnetic modulator” was invented by Alexanderson, a transformer that could handle up to 75 kilowatts for use with an RF alternator.  General Electric picked up on this technology, producing smaller transformers for the 5 to 100 watt transmitters used in Amateur Radio.

15. What was the necessity that lead to improved communications such as noise cancelling technology in microphones?  16. Who were the major players?  17. What device was used to broadcast Woodrow Wilson’s speech in 1919?

World War I created an immediate demand for improved communications and Western Electric, General Electric & The Magnavox Company with the help of vacuum tube technology put the microphone back into a simple circuit leading to the development of  “noise-cancelling” hand held microphones for the military.  These companies introduced various styles of “loudspeakers”  and amplifiers for public address systems including Western Electric’s “Chauphone”  and Magnavox’s “Telemegaphone” which was used to broadcast President Woodrow Wilson’s speech to 50,000 Americans gathered in the San Diego Stadium in 1919.

18. When did Amateur Radio go Pro?  19. What was the transmitter of choice in 1920 for commercial broadcasting?  20. What is a tomato can?  21. What manufacturers were still in the game in 1931?  22.  Who introduced the first bi-directional microphone?

Radio amateurs found themselves sought after as entertainers thanks to the  “candlestick telephone” (Western Electric transmitter No 323) and in 1920, commercial broadcasting was born. Westinghouse launched several radio stations in 1920 & 1921, picking up the microphone slack with the development of the “dishpan” microphone which permitted mellowing out of the squeaky high-pitched sound of the telephone transmitters with bass and midrange.  Improvements on this design with a condenser element was known as a “tomato can” popularized by General Electric who made most of the microphones sold by RCA between 1919 & 1927 including the “bullet” in 1926.  By 1931, Western Electric (a subsidiary of the American Telephone & Telegraph Company) however, emerged as the leader in microphone engineering waxing Westinghouse & General Electric and despite the explosion of small microphone manufacturers such as Electro-Voice, only RCA survived as a major contender with the introduction of the 44A ribbon velocity bidirectional microphone.






Most microphones today use electromagnetic induction (dynamic microphone), capacitance change (condenser microphone), piezoelectric generation, or light modulation to produce an electrical voltage signal from mechanical vibration. – See more at: http://www.historyofrecording.com/Microphones.html#sthash.3ozDmoqB.dpuf

compare with modern microphone technologies:

electromagnetic induction (dynamic mic);  condenser capacitor change (condenser mic); light modulation (mechanical vibration produces a voltage signal)

Twenty Questions about using Microphones

Posted on Updated on

Q#1 – Where should you place a microphone (ideally) to record vocals?

Firstly, if you clap your hands and get an echo effect, you should consider deadening the room using carpet, blankets, drapes, or other sound absorbing materials. Move your mic setup toward the room’s center to avoid reflective surfaces (walls/glass/etc).   Vocalist should be roughly 6 – 8 inches away from the microphone. Getting too close to the microphone tends to increase bass response and can create problems with plosive sounds – those popping Ps, Bs, Ds, and Ts.   Too much further increases the risk of picking up room ambiance and the effect of the vocalist “being in a bowl”.  A constant distance from the microphone will provide the greatest tonal balance

Q#2 – What’s a simple way to prevent unwanted noise?

Use a pop shield between the mic and the vocalist to prevent “bumping” sounds on “B” and “P” sounds.  A nylon stocking stretched over a wire (or wooden) hoop works.  Place the shield midway between the mouth and the microphone

Q#3 – Is there a way to test microphone placement?

To find the best location, wear fully enclosed headphones to monitor the microphone output while you move the mic around the performer.  As he/she through the material, you can choose the best microphone position by ear

Q#4 – What is “close miking”?

When miking at a distance of 1 inch to about 1 foot from the sound source. This technique generally provides a tight, present sound quality and does an effective job of isolating the signal and excluding other sounds in the acoustic environment

Q#5 – What is “distance miking”?

Distant miking refers to the placement of microphones at a distance of 3 feet or more from the sound source. This technique allows the full range and balance of the instrument to develop and it captures the room sound. This tends to add a live, open feeling to the recorded sound, but careful consideration needs to be given to the acoustic environment

Q#6 – What is “ambiant miking”?

Placing the microphones at such a distance that the room sound is more prominent than the direct signal. This technique is used to capture audience sound or the natural reverberation of a room or concert hall

Q#7 – How do you reduce the risk of phase anomaly when “stereo miking”?

This risk of phase anomaly can be reduced by using the X/Y method, where the two microphones are placed with the grills as close together as possible without touching. There should be an angle of 90 to 135 degrees between the mics. This technique uses only amplitude, not time, to create the image, so the chance of phase discrepancies is unlikely

Spaced Pair X/Y Method

Q#8- How can you use microphone placement to reflect different sound character ?

When you are getting a microphone placement for your singer, make sure to move the mic around sideways and up & down to see if you can get a better sound. Get closer and farther away. Change the angle and experiment with different polar patterns (pickup patterns).  When you do that, you’ll notice the sound changing character. A breathy sound close, more natural farther away. There are a lot of different subtle voice character changes in relation to position to the voice.   Keep in mind the style and spirit of the song. Some songs need a different character of voice (i.e. bright and bold vs. soft and dreamy). The singer can also change positions and vocal techniques during the song to change the character.   This is the real art in mic placement and technique. There is no shortcut to this other than experience

Q#9 – What is “bleeding” and how do you avoid it?

Bleeding occurs when the signal is not properly isolated and the microphone picks up another nearby instrument. This can make the mixdown process difficult if there are multiple voices on one track. Use the following methods to prevent leakage:
Place the microphones closer to the instruments
Move the instruments farther apart
Put some sort of acoustic barrier between the instruments
Use directional microphones

Q#10- Do foam wind shields prevent popping?

Some microphones come with foam wind shields that fit over the microphone grille, but in practice they tend to be ineffective against anything more than a gentle breeze, and they are no match for a full-on plosive. Furthermore, the thickness of foam invariably absorbs some high frequencies, causing the sound to become noticeably duller than it should be. Wind shields can be handy in live performance to stop the mic filling with drool, but they have a very limited effect on popping

Q#11 – How do you mike an acoustic guitar?

There are two optimum points for microphone positioning – either near the bridge or by the twelfth fret.  Placing the microphone in front of the instrument’s sound hole,  usually increases low frequency response to the point of making the instrument sound “boomy.”
Twelfth Fret Placement: Placing the microphone roughly 2 – 4 inches from the twelfth fret and aimed directly at the strings will generally produce a warm, full bodied sound with good tonal balance. Using this technique, the sound hole’s contribution will be moderated since the microphone is not pointed directly at it.
Bridge Placement: Similarly, you can position the microphone so it is 3 – 6 inches from the guitar’s bridge. This will generally produce a somewhat brighter tonal quality. You should also be prepared to experiment positioning the microphone slightly off-axis should you find yourself capturing too much low frequency response from the guitar’s sound hole

Q#12 – How do you mike a piano?

Ideally, you’ll want a minimum of two microphones. Usually, the microphone capturing the higher strings is assigned to the left channel and the microphone capturing the lower strings is assigned to the right channel in the final stereo mix, though the stereo spread generally is not hard left and right. While a single microphone can be used, the lower and upper extremities of the instrument will likely be compromisedIf you are using a single microphone to record a grand piano, position the microphone approximately 8 inches from the piano hammers (to reduce mechanical noise) and 8 – 11 inches above the strings – centered over the piano’s mid point. Pan position should be centered and the piano’s lid should be at full stick

recording piano positioning

Using a single microphone for an upright piano, it is generally recommended that you record from above, as placement of the microphone in the lower center may interfere with the performer’s ability to access the pedals and the microphone will likely pick up excessive pedal and other mechanical noise. Position the microphone just over the open top, centered over the instrument:

Piano diagram

Q#13- How do you mike a drum kit?

Stereo Overhead Pair: Position the two microphones approximately 16 – 20 inches above the performer’s head – separated laterally by roughly 2 – 3 feet and placed 5 – 6 feet out in front of the drum kit. Adjust the two microphone’s Pan position so that you achieve a good stereo spread, though generally not hard left and right
Single Overhead Microphone: Position the microphone approximately 16 – 20 inches above the performer’s head – centered in front of the drum set, and placed 5 – 6 feet out in front. The microphone’s Pan position should be centered for mono drums

Recording Drums

Q#14 – How do you mike an amplified speaker?

The mic should be placed 2 to 12 inches from the speaker. Exact placement becomes more critical at a distance of less than 4 inches. A brighter sound is achieved when the mic faces directly into the center of the speaker cone and a more mellow sound is produced when placed slightly off-center. Placing off-center also reduces amplifier noise.  A bigger sound can often be achieved by using two mics. The first mic should be a dynamic mic, placed as described in the previous paragraph. Add to this a condenser mic placed at least 3 times further back (remember the 3:1 rule), which will pickup the blended sound of all speakers, as well as some room ambience. Run the mics into separate channels and combine them to your taste

Q#15 – How does a Dynamic microphone work?

A microphone is a transducer, a device that changes information from one form to another. Sound information exists as patterns of air pressure; the microphone changes this information into patterns of electric current. In the magneto-dynamic, commonly called dynamic, microphone, sound waves cause movement of a thin metallic diaphragm and an attached coil of wire. A magnet produces a magnetic field which surrounds the coil, and motion of the coil within this field causes current to flow. The principles are the same as those that produce electricity at the utility company, realized in a pocket-sized scale. It is important to remember that current is produced by the motion of the diaphragm, and that the amount of current is determined by the speed of that motion. This kind of microphone is known as velocity sensitive

Q#16 – How does a Condensor microphone work?

In a condenser microphone, the diaphragm is mounted close to, but not touching, a rigid backplate. (The plate may or may not have holes in it.) A battery is connected to both pieces of metal, which produces an electrical potential, or charge, between them. The amount of charge is determined by the voltage of the battery, the area of the diaphragm and backplate, and the distance between the two. This distance changes as the diaphragm moves in response to sound. When the distance changes, current flows in the wire as the battery maintains the correct charge. The amount of current is essentially proportional to the displacement of the diaphragm, and is so small that it must be electrically amplified before it leaves the microphone

Q#17 – What are the various microphone pick-up patterns?

Q#18 – What is a “ribbon” microphone?

also known as a ribbon velocity microphone, a ribbon microphone uses a thin, electrically conductive ribbon placed between the poles of a magnet to generate voltages by electromagnetic induction.  Ribbon microphones are typically bidirectional, meaning they pick up sounds equally well from either side of the microphone

Q#19 – What is “reflection” & “absorption” of sound waves referring to?

Sound waves are reflected by surfaces if the object is as large as the wavelength of the sound. It is the cause of echo (simple delay), reverberation (many reflections cause the sound to continue after the source has stopped), and standing waves (the distance between two parallel walls is such that the original and reflected waves in phase reinforce one another).  Sound waves are absorbed by materials rather than reflected. This can have both positive and negative effects depending on whether you desire to reduce reverberation or retain a live sound

Q#20 – What is “diffraction” & “refraction” of sound waves referring to?

Objects that may be between sound sources and microphones must be considered due to diffraction. Sound will be stopped by obstacles that are larger than its wavelength. Therefore, higher frequencies will be blocked more easily than lower frequencies.  Sound waves bend (refraction) as they pass through mediums with varying density. Wind or temperature changes can cause sound to seem like it is literally moving in a different direction than expected