Microphones Flashcards
how does a dynamic mic work
works via electromagnetic induction. A cone is attached to a coil of wire which moves in the field of a magnet. When the diaphragm vibrates, the coil moves in the magnetic field, producing changes in current that directly relate to the changes in air pressure.
how does a ribbon mic work
works via electromagnetic induction. When the long thin strip of conductive foil moves within the magnetic field it generates a voltage that directly relates to the changes in air pressure
how does a condenser mic work
diaphragm acts as one plate of a capacitor, and the vibrations produce changes in the distance between the plates and therefore a change in electrical energy
what are the two types of condenser mics
true condensers and electrets
what’s the difference between a true condenser and an electret
true condenser needs power to charge the back-plate of the diaphragm. electret has an already-charged back-plate that remains charged for the life of the mic however, both still need voltage to run
what are the three main types of transducers
1) electro-dynamic / dynamic (moving coil, ribbon and printed ribbon) 2) condenser (incl. electret, PZM/boundary) 3) piezo or crystal-based
dynamic moving coil mics - transient response & sensitivity
slower transient response and lower sensitivity to small pressure variations because of relatively heavy moving parts
dynamic ribbon mics - transient response & sensitivity
sensitive to small variations in pressure due to light moving parts, give more accurate transient response than moving coil mics
dynamic moving coil - transparency
genrally add colour in the high mids (5-10kHz)
dynamic moving coil - durability
generally very durable, can handle high SPL
dynamic ribbon - transparency
generally add colour, high frequency roll-off, proximity effect
DEF: proximity effect
a directional mic’s increase in bass response as the sound source approaches the diaphragm
dynamic ribbon - durability
fragile
PZM (boundary) mics - transparency & amp sensitivity
do not have off-axis colouration, present even frequency response and high sensitivity, you also get less of the room tone
printed ribbon mics - durability
more durable than traditional ribbon mics
printed ribbon mics - transient response
good transient response due to light moving parts
DEF: comb-filtering
comb-filtering creates peaks and troughs in frequency response, and is caused when signals that are identical but have phase differences
identify this polar pattern
omnidirectional
identify this polar pattern
subcardioid
identify this polar pattern
cardioid
identify this polar pattern
supercardioid
identify this polar pattern
hypercardioid
identify this polar pattern
figure-of-eight (bidirectinal)
cardioid - sensitivity
approx 6 dB less sensitive to from sides
approx 15-25 dB less sensitive from rear
hypercardioid - sensitivity
approx 12 dB less sensitive from sides
two null points at +/- 110 degress off-axis
supercardioid - sensitivity
approx 9 dB less sensitive from sides
two null points (least pickup) at +/- 125 degress off axis
bidirectional/fig-8 - sensitivity
most sensitive from front and back
rejects sound at sides
condenser mics - sound and application
high-fidenilty, detailed sound with lots of clean high frequencies.
very sensitive due to thin diaphragm
good for high top end content, acoustic guitars and voices
Require phantom power
what microphones generally have a proximity effect?
microphones with directional polar patters
dynamic mics - sound and application
edgy high frequencies
presence peak 2-5 kHz
lack of air in top end
slower response
good for close mic’d sources, percussive sounds, heavy bass/midrange content and live vocals
do not need phantom power
ribbon mic - sound and application
warm, smooth sound quality.
top end roll off at ~10 kHz
sounds darker
fragile
popular for horns and guitar amps.
does not require phantom power
tube/valve mic - sound and application
warm coloured, lots of even harmonics
fragile
usually have their own power supply and thus do not need phantom
good for vocals
DEF:
frequency response
the lowest and highest frequencies that the mic can pick up well
cardioid - pickup pattern
picks up best in front of the mic
partly rejects sounds approaching sides or rear of mic
rejects sound best toward the rear
supercardioid - pickup pattern
picks up best in front of the mic
partly rejects sound approaching the sides or the rear
‘tighter’ or more narrow pickup than cardoid
has small pickup area in the rear of mic
hypercardioid - pickup pattern
picks up best in front
partly rejects sounds approaching sides and rear
‘tighter’ more narrow pickup than supercardoid
omni - pickup pattern
picks up equally wel in all directions
has no proximity effect
figure-of-eight - pickup pattern
picks up best in front and behind the mic
rejects sounds to the sides
DEF:
impedance
the mics effective output resistance at 1kHz
what is considered low, medium and high impedance for microphones?
low: 150-600 ohms
med: 1000 - 4000 ohms
high: above 25 kilohms
do you want the impedance of a mic to be low, medium, or high?
why?
low impedance
the higher the impedance of a mic the more likely you are to pick up hum or lose high frequencies when the signal runs through cables
DEF:
self-noise
a measure of how noisy a mic is
what is considered a good, very good, or great self-noise spec for a mic?
good: 25 dBA
very good: 20 dBA
excellent: 15 dBA
What is considered a very good self-noise spec for a mic mounted directly on an instrument?
30 dBA
how much power is supplied by phantom power?
12-48 volts DC
DEF:
side-address
the mic picks up best from it’s side
you aim the side of the mic at the sound source
what is considered a good, very good, or excellent signal to noise ratio in a mic?
good: 69 dB
very good: 74 dB
excellent: 79 dB or higher
what is considered a very good signal to noise ratio if the mic is mounted on the instrument?
why?
64 dB
b/c the instrument’s signal is so much louder than the mic’s noise
DEF:
end-address
the mic picks up best from it’s end
you aim the end of the mic at the sound source
what does a mic’s sensitivity spec tell you?
how much output voltage a mic produces when driven by a certain SPL
high sensitivity mic vs. low sensitivity mic
which puts out a stronger signal when both are exposed to equally loud sound?
high sensitivity mic puts out a stronger signal than a low sensitivity mic
low sensitivity mic will need more gain from mixer which usually results in more noise
What is a typical sensitivity spec for a condenser mic?
5.6mV/Pa (high sensitivity)
typical sensitivity spec for a dynamic mic?
1.8 mV/PA (medium sensitivity)
typical sensitivity spec for a ribbon or small dynamic mic?
1.1 mV/Pa (low sensitivity)
proper wiring to make sure mic cables do not reverse polarity
pin 1 shield, pin 2 white, pin 3 black
or
pin 1 shield, pin 2 red, pin 3 white or black
two types of mic preams
tube
solid state
advantages of tube preamps
adds warmth and fullness
distorts more musically – produces even-order harmonics
when driven adds a natural sounding, musical compression
advantages of solid-state preamps
less distortion until they reach clipping point – great for adding clear gain
quicker transient response and retain more high frequency information (great for transient instruments)
generally more efficient, produce less heat and require less maintenance than tubes
why use a preamp with a transformer
more true-to-life
less noisy and produces less hum when connected to other gear compared to transformerless designs
impedance optimal ratios
mic : pre
5 : 1
10 : 1 - ideal
increasing impedance from low to high (if impedance is variable) gives what results?
increase in volume as you get higher
less dark and mid-heavy tone, more airy high frequency content
potentially more room tone
appears to flatten out mic’s frequency response
benefits of large diaphragm mics
captures more acoustic energy and generates a higher signal voltage
meaning
larger diaphragm mics generally have lower self-noise than small diaphragm
benefits of small diaphragm condensers
great transient response - small diaphragm can follow sound waves more accurately
extended high frequency response
very consistent pickup pattern
large diaphram - applications
vocals and spoken word
solo instruments you want to appear rich and vibrant
small diaphragm - applications
piano, acoustic guitar, other stringed instruments
drums (OH, snare, hh, cymbals) and perc
how does a pzm/boundary mic work
condenser mic mounted facing a metal plate
works by using the phenomenon that occurs near a reflection point, the sound signal and reflection combine to create comb filtering, which creates peaks and valleys in the frequency response
should you filter mics before or after EQ
before
without eq how can you change the tone of a mic
position it off axis
