Transducers in Audio ● Transducer: Any mechanism that transforms one form of energy into another form of energy. ○ Physical energy into mechanical energy ○ Physical energy into electrical energy ○ Mechanical energy into electrical energy ○ Vice versa Audio is primarily concerned with turning physical acoustic energy into electrical energy and back again. What are our two most basic audio transducers? scienceaid.net https://socratic.org/questions/what-part-of-the-ear-contains-the-sensory-receptors-for-hearing
From Acoustic to Electric Energy First...a short trip into basic electrical theory...
Michael Faraday
http://www.rigb.org/our-history/michael-faraday Electro-magnetism
Faraday’s Law of Induction: Basically, any change in the magnetic field of a coil of wire will cause a voltage to be induced in a wire. Conversely, any change in the voltage on a coil of wire will cause the magnetic field to change.
This is called electromagnetism, and the field created is called an electro-magnetic field. Capacitance
When two conductors are given an opposite charge, an electric or more specifically a capacitive field is generated around them. When the relationship between the two conductors (for example the distance between them) changes it causes measurable effects on the charges.
http://hyperphysics.phy-astr.gsu.edu/hbase/electric/imgele/cap.png Capacitance
When two conductors are given an opposite charge, a electric or more specifically a capacitive field is generated around them. When the relationship between the two conductors, for example the distance between them, changes is causes measurable effects on the charges.
http://hyperphysics.phy-astr.gsu.edu/hbase/electric/imgele/cap.png ● Alternating Current (AC) vs Direct Current (DC) ○ AC charge changes from positive to negative across the zero axis. ○ DC charge changes from a baseline, usually zero, to some charge.
https://en.wikipedia.org/wiki/File:Types_of_current_by_Zureks.svg Microphones
http://www.shure.com/americas/products/microphones/sm/sm57-instrument-microphone Microphone classifications: Transducer
● Microphones are classified in two different ways; Types of Transducer and Polar Pattern. We have two main types of transducer: ○ Dynamic Microphones are based on a electromagnetic transducer (a coil). ○ Condenser Microphones are based on a capacitive field. Dynamic Microphone
http://artsites.ucsc.edu/EMS/Music/tech_background/TE-20/teces_201.GIF Dynamic Microphones: ● Electromagnetic Coil ● Highly Durable ● Wide range of applications both live and in studio
http://www.shure.com/americas/products/microphones/sm/sm57-instrument-microphone Condenser Microphone
http://artsites.ucsc.edu/EMS/Music/tech_background/TE-20/teces_201.GIF Notice the addition of the Condenser Microphone battery. In order to create the capacitive field, we need a charge. In audio we call this Phantom Power, and it is usually 48 volts.
http://artsites.ucsc.edu/EMS/Music/tech_background/TE-20/teces_201.GIF Condenser Microphone ● Uses capacitive sensing, requires Phantom Power (48v) ● Gold plated mylar over a ceramic plate. ○ Not carrying the weight of the coil, so better transient response. ○ Much more delicate, rarely suitable for live unless specified by the musician. Other types of microphone transducers:
● Ribbon: ○ Electromagnetic, piece of foil is the diaphragm, suspended between two magnets. ○ Very delicate ○ PHANTOM POWER WILL DESTROY A RIBBON ○ Excellent transient response, low noise floor and natural high rolloff make this ideal for delicate sounds: Acoustic guitar, harp, cello, double bass. Other types of microphone transducers:
● Electret ○ Uses capacitive sensing. The ‘plates’ are permanently charged eliminating the need for Phantom Power. Still needs power for a preamplifier. ○ Can be made very small, often used on headset mics, instrument mics, etc. Frequency Response or Curve
● Frequency Response refers to any particular microphones tendency to enhance or attenuate certain frequencies across the spectrum. ● The Frequency Response Curve is always included in the packaging of a quality microphone. ● Microphones with relatively little variation across the spectrum are called ‘flat’ and those with a lot of variation are ‘colored’ or have ‘coloration’. Which you choose is a matter of preference. Frequency Response or Curve
Sure.com https://www.themusickitchen.com/wp-content/uploads/2016/10/AKG-C414.png
Sure sm57 AKG c414 Microphone Classifications: Polar Patterns ● The Polar Pattern is the second part of a microphone classification. ● The Polar Pattern is a description of a particular microphones direction of sensitivity. ● You will often find the Polar Pattern inscribed right on the microphone. You will always find it on the box. Some microphones have multiple polar patterns you can select from.
https://en.wikipedia.org/wiki/Microphone#Polar_patterns
Proximity Effect
A characteristic of cardiod microphones. The proximity effect is the microphone’s tendency to increase the bass response the closer the microphone is to the sound source. From electric to acoustic energy “Speakers”
● The word speaker covers a lot of different kinds of sound making devices. ● Essentially an inversion of the relationship between acoustic and electric energy in a microphone, or the second part of Faraday’s law. ● Some main classification of speakers: ○ Passive vs Active: Means of amplification; Active speakers have an onboard amplifier and are more expensive, passive have an external amplifier and are less expensive. ○ Frequency range they address: Sub-woofers are optimized for bass frequencies (up to around 200hz), Mids (Midrange, range varies, up to 4000-5000hz) and tweeters (2-20+khz) ○ Electromagnetic vs Piezo….. Electromagnetic Driver
https://en.wikibooks.org/wiki/Engineering_Acoustics/Transducers_-_Loudspeaker Piezoelectric Driver ● Certain materials have a relationship between mechanical stress and electric current. ● The effect works both ways: When pressure is applied to the material it creates a voltage and when voltage is applied to the material it distorts. ● Limited to tweeters because of their very short extrusion.
https://upload.wikimedia.org/wikipedia/commons/thumb/6/6e/Piezo_bending_principle.jpg/1280px-Piezo_bending_principle.jpg Separating Frequencies: The Crossover Network
● Speakers that are designed for a specific frequency range necessitate a means of dividing the full frequency range. ● The separation usually occurs as the last step before the amplifiers. The divided signal is then sent to amplifiers that are best suited for the load of their speakers. ● Crossovers are minimum 2 way (lows, highs), usually 3 way (low,mid,high) and sometimes 4+ way. ● Speakers with multiple drivers often have a passive crossover built in. Separating Frequencies: The Crossover Network
https://www.astralsound.com/crossover-slopes.png Separating Frequencies: The Crossover Network
Notice the attenuation around the crossover frequency. This is to prevent the summation of the signals exceeding the actual level. The sharpness of the attenuation is called the slope.
https://www.astralsound.com/crossover-slopes.png Study Notes
● Definition of Transducer. ● Faraday’s Law and electromagnetism. ● Capacitance. ● Microphone classification ○ Types of transducer, advantages and disadvantages ○ Polar Patterns, applications and patterns of rejection ○ Phantom Power ○ Frequency Response ● Proximity effect ● Speaker Classification ○ Passive or Active ○ Driver Type, which driver is suitable for which application ● Crossover Networks ○ Crossover Frequency ○ Slope