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
DEF:
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)
DEF:
sealed enclosures
essentially a closed box, with better low end response than a flat baffle
DEF:
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
