Loudspeakers Flashcards
DEF: transducer
a device which converts one form of energy into another
Who and when - patent for first moving coil transducer?
Ernst Seimans 1874
name 4 types of transducer
moving coil, ribbon, electrostatic, piezoelectric
What is the mechanism in a moving coil loudspeaker?
moving coil and permanent magnet
what family of transducers do dome tweeters belong to?
moving coil family
common application for ribbon transducers
tweeters, high frequency applications
how does an electrostatic transducer work?
made up of 2 perforated rigid plates with a large flat, extremely light weight diaphragm between them. perforations allow sound to pass through. high DC polarising voltage is applied to a diaphragm which turns the system into a capacitor. Audio signal is applied to rigid outer plates, modulating the outer plates and the diaphragm moves freely within the constraints according to the input sound signal
DEF:
bimorphs
piezoelectric elements used for audio transducers that are made up of 2 benders (two layers of piezoelctric material)
waht are benders used for?
piezoelectric and used for high frequency drivers only b/c they have very limited excursion (change of shape)
what is it used for:
phrasing plug/acoustical transformer
used to disperse high frequency content away from the driver in a piezoelectric speaker to stop the HF content from interacting near teh driver and causing cancellations
DEF:
baffle
the front face of the speaker which serves as mounting surface for the speaker driver units
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loading
how the enclosure or coupled equpment causes the speaker to physically react
purpose of the baffle
Baffle increases the distance between the two sides of the speaker preventing cancellation. The larger the baffle, the less likely you are to have phase cancellation, but they have little effect on high frequencies, which don’t have the same cancellation problem because they move faster
DEF:
dipole
enclosre - speaker mounted on a flat panel
polar pattern - equal radiation in two directions (forward and backward)
folded baffle vs. unfolded baffle
size difference but both have the same loading characteristics (provided they have similar surface area)
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sealed enclosures
essentially a closed box, with better low end response than a flat baffle
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acoustic suspension
Acoustic suspension (air suspension or sealed box) is a type of loudspeaker speaker enclosure design which uses one or more loudspeaker drivers mounted in a sealed box or cabinet. Reduces bass distortion that can be caused by stiff motor suspensions in conventional loudspeakers.
DEF:
wadding
padding used to line the enclosure of a loudspeaker that reflects HF from the back of the driver
sealed enclosures - resonant frequency
have a large low end bump
cone size and volume of air box affects resonant frequency
larger cabiness have lower resonant freq than smaller ones
all factors must be taken into account in the design
what is a bass reflect (vented) enclosure?
enclosure with a port to allow low frequency resonance to escape. Allows smaller speakers to produce lower frequencies than sealed enclosures.
impedance response of typical bass reflex speaker
Driver’s free air resonant frequency (not loaded by cabinet) peak ~25 Hz
dip for duct’s resonant frequency ~40 Hz
peak around 70 Hz
double hump characteristic of bass reflex system
auxilary bass radiators
enclosure with main functioning drive and a passive radiator/drone cone (no voice coil or magnet) that increases bass response
used if a port would be too long for the enclosure
horn loaded enclosures
used for situation where you need to throw the sound far
better directivity
high impedance at the throat, low impedance at the mouth
flare rate and length determines cutoff frequency where the horn stops being able to control the diaphragm
important not to give horns frequencies below their cutoff–will cause diaphragm to flap and distort causing damage to equipment
folded horns
(think megaphones)
horn mouth should be at least 1/4 of wavelength of their cutoff frequency
folded to reduce bulk
high freq horns
usually driven using compression drivers (much like reversed dome tweeter)
specifically designed to drive high impedance at the horn throat
DEF:
crossovers
splits audio signal into two or more bands to deliver it to the appropriate driver
types of crossovers
high level passive
low level active
function of high level passive crossover
take high level signal directly from power amp and split it between drivers using capacitors for high end and inductors for the low end
function of low level active crossover
splits line level audio before the signal goes into the power amplifier
each driver will have their own amplifier
more efficient with high level pressure but lose dBs through capacitance/inductive crossover
DEF:
bi-amping
using multiple amplifiers for a single speaker (ie. one for driver one for tweeter)
high level passive vs. low level active
high level passive requires more powerful amp as low frequencies eat up a ton of power and can cause severe clipping of HF material if amp isn’t powerful enough
low level active crossovers increases headroom as each frequency band has it’s own amp so less powerful amps can be used
Loudspeaker sensitivity
measured in dBs
sensitivity = speaker’s loudness
a mic is placed 1m away, 1w of power applied to speaker, higher dB reading = better sensitivity
loudspeaker impedance
for speakers use the term “nominal impedance” meaning it’s impedance varies with frequency
related to power it can extract from amp – high impedance load draws less current, low impedance load draws more current from amp
Def:
loudspeaker frequency resonse
comparison of the spearkers on axis power output vs. frequency output
typical full range speaker response
~ 30 Hz to 1kHz +/- 3 dB
meaning all frequencies within that range are reproduced w/in 6 dB range
DEF
loudspeaker efficiency
percentage of acoustic power output radiated in all directions
ie. if two speaker have same sensitivity, one with widest dispersion is more efficient
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power handling
indicates the amount of pwer the speaker can take from amp without damage
how is power handling specified?
continuous power ( aka. rms power)
continuous program
peak power
EIA (electronic industries association)
how is continuous power (rms power) tested
using sine wave, resulting in maximum heating of voice coil
how is continuous program tested
using complex waveform, resulting in max. heating of the voice coil
how is peak power tested
using puls or short signal, resulting in max. excursions of voice coil
how is EIA tested
using clipped shared noise, resulting in thermal capacity and max excursion of the speaker
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compliance
force exerted by the suspension of a speaker (i.e. measure of stiffness)
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damping
relationship between the speaker and the amp
higher damping factor = amp has great control of speaker movement
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Directional characteristics
most common mode of spec horizontal and vertical dispersion given separately as degrees
boundaries of angle usually taken where sound drops by 6 dB on either side
angle give as a +/- value
only refers to mids and highs, lows are taken to be omi
effect of placing boundary behind speaker
causes radiated sound to be reflected and increases spl but as much as 3dB
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half space loading
when the sound is radiating into half as much space, increasing the SPL up to 3dB
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quarter space loading
speaker is placed between two boundaries, sound radiating into quarter the space increases SPL up to 6dB
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eighth space loading
speaker placed between 3 boundaries, increasing SPL up to 9dB, sound radiating into 1/8th of the space
