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Term 2 Theory Prep > Loudspeakers > Flashcards

Loudspeakers Flashcards

1
Q

DEF: transducer

A

a device which converts one form of energy into another

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2
Q

Who and when - patent for first moving coil transducer?

A

Ernst Seimans 1874

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3
Q

name 4 types of transducer

A

moving coil, ribbon, electrostatic, piezoelectric

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4
Q

What is the mechanism in a moving coil loudspeaker?

A

moving coil and permanent magnet

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5
Q

what family of transducers do dome tweeters belong to?

A

moving coil family

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6
Q

common application for ribbon transducers

A

tweeters, high frequency applications

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7
Q

how does an electrostatic transducer work?

A

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

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8
Q

DEF:

bimorphs

A

piezoelectric elements used for audio transducers that are made up of 2 benders (two layers of piezoelctric material)

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9
Q

waht are benders used for?

A

piezoelectric and used for high frequency drivers only b/c they have very limited excursion (change of shape)

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10
Q

what is it used for:

phrasing plug/acoustical transformer

A

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

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11
Q

DEF:

baffle

A

the front face of the speaker which serves as mounting surface for the speaker driver units

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12
Q

DEF:

loading

A

how the enclosure or coupled equpment causes the speaker to physically react

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13
Q

purpose of the baffle

A

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

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14
Q

DEF:

dipole

A

enclosre - speaker mounted on a flat panel

polar pattern - equal radiation in two directions (forward and backward)

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15
Q

folded baffle vs. unfolded baffle

A

size difference but both have the same loading characteristics (provided they have similar surface area)

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16
Q

DEF:

sealed enclosures

A

essentially a closed box, with better low end response than a flat baffle

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17
Q

DEF:

acoustic suspension

A

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.

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18
Q

DEF:

wadding

A

padding used to line the enclosure of a loudspeaker that reflects HF from the back of the driver

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19
Q

sealed enclosures - resonant frequency

A

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

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20
Q

what is a bass reflect (vented) enclosure?

A

enclosure with a port to allow low frequency resonance to escape. Allows smaller speakers to produce lower frequencies than sealed enclosures.

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21
Q

impedance response of typical bass reflex speaker

A

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

22
Q

auxilary bass radiators

A

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

23
Q

horn loaded enclosures

A

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

24
Q

folded horns

A

(think megaphones)

horn mouth should be at least 1/4 of wavelength of their cutoff frequency

folded to reduce bulk

25
Q

high freq horns

A

usually driven using compression drivers (much like reversed dome tweeter)

specifically designed to drive high impedance at the horn throat

26
Q

DEF:

crossovers

A

splits audio signal into two or more bands to deliver it to the appropriate driver

27
Q

types of crossovers

A

high level passive

low level active

28
Q

function of high level passive crossover

A

take high level signal directly from power amp and split it between drivers using capacitors for high end and inductors for the low end

29
Q

function of low level active crossover

A

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

30
Q

DEF:

bi-amping

A

using multiple amplifiers for a single speaker (ie. one for driver one for tweeter)

31
Q

high level passive vs. low level active

A

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

32
Q

Loudspeaker sensitivity

A

measured in dBs

sensitivity = speaker’s loudness

a mic is placed 1m away, 1w of power applied to speaker, higher dB reading = better sensitivity

33
Q

loudspeaker impedance

A

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

34
Q

Def:

loudspeaker frequency resonse

A

comparison of the spearkers on axis power output vs. frequency output

35
Q

typical full range speaker response

A

~ 30 Hz to 1kHz +/- 3 dB

meaning all frequencies within that range are reproduced w/in 6 dB range

36
Q

DEF

loudspeaker efficiency

A

percentage of acoustic power output radiated in all directions

ie. if two speaker have same sensitivity, one with widest dispersion is more efficient

37
Q

DEF:

power handling

A

indicates the amount of pwer the speaker can take from amp without damage

38
Q

how is power handling specified?

A

continuous power ( aka. rms power)

continuous program

peak power

EIA (electronic industries association)

39
Q

how is continuous power (rms power) tested

A

using sine wave, resulting in maximum heating of voice coil

40
Q

how is continuous program tested

A

using complex waveform, resulting in max. heating of the voice coil

41
Q

how is peak power tested

A

using puls or short signal, resulting in max. excursions of voice coil

42
Q

how is EIA tested

A

using clipped shared noise, resulting in thermal capacity and max excursion of the speaker

43
Q

DEF:

compliance

A

force exerted by the suspension of a speaker (i.e. measure of stiffness)

44
Q

DEF:

damping

A

relationship between the speaker and the amp

higher damping factor = amp has great control of speaker movement

45
Q

DEF:

Directional characteristics

A

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

46
Q

effect of placing boundary behind speaker

A

causes radiated sound to be reflected and increases spl but as much as 3dB

47
Q

DEF:

half space loading

A

when the sound is radiating into half as much space, increasing the SPL up to 3dB

48
Q

DEF:

quarter space loading

A

speaker is placed between two boundaries, sound radiating into quarter the space increases SPL up to 6dB

49
Q

DEF:

eighth space loading

A

speaker placed between 3 boundaries, increasing SPL up to 9dB, sound radiating into 1/8th of the space

50
Q
A

Term 2 Theory Prep (11 decks)

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