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InfoComm CTS > CTS Loudspeakers > Flashcards

CTS Loudspeakers Flashcards

1
Q

Point source speaker system:

A

Point source works better with a high ceiling so you can get even coverage. Works well for concert or keynote.

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2
Q

Distributed system:

A

Evenly spaced speakers, usually in the ceiling. When it’s important for coverage to be very even.

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3
Q

Ceiling distributed system coverage is measured at what Hz?

A

2,000 Hz

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4
Q

Center to center coverage or 50% overlap positives:

A

Very even coverage at most frequencies

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5
Q

Center to center coverage or 50% overlap negatives:

A

Requires lots of speakers, overlap can cause frequency cancellation which negatively affects the sound quality, can add too much acoustic energy to the space.

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6
Q

Center to center has how much dB of variation?

A

1.2 dB. Very little!

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7
Q

When coverage is measured at 2,000 Hz what will the lower and higher frequencies be like?

A

Lower will have wider coverage, higher will have a more narrow coverage.

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8
Q

Edge to edge coverage positives:

A

Acceptable coverage at speech frequencies, inexpensive, very little speaker interaction.

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9
Q

Edge to edge coverage negatives:

A

The most uneven coverage, may have dead spots in the corners.

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10
Q

Partial overlap positives:

A

Good compromise. Most often used. Acceptable 2.6 dB variation.

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11
Q

Partial overlap negatives:

A

It’s a compromise:
May not be as even in frequency response
Some negative interaction from nearby loudspeakers
Adds some acoustical energy to space

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12
Q

Point to point systems are measured where?

A

At ear level (seated is 4 ft or 1.2 meters)

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13
Q

For loudspeakers what does Q represent?

A

Loudspeaker directivity, or coverage pattern.

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14
Q

Each ring in a loudspeaker polar plot is a change of how many dB?

A

6 dB

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15
Q

Loudspeaker coverage angle is measured at what point?

A

The -6dB or “6 dB down point”

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16
Q

Loudspeaker polar plot shows…

A

Coverage angle (sometimes at different frequencies)

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17
Q

What does Ohm’s law define?

A

The relationship between current, voltage, and resistance in an electrical circuit as proportional to applied voltage and inversely proportional to resistance.

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18
Q

What’s the difference in how Ohm’s law relates to AC and DC?

A

Ohm’s Law defines the electrical relationships in direct current (DC) circuits. It will also, however, help approximate for alternating current (AC) circuits. AC circuit calculations are frequency dependant, and Ohm’s Law does not account for the influence of frequency in a circuit.

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19
Q

What is current?

A

The rate of electrons flowing through a circuit per second.

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20
Q

What is current measured in?

A

Amperes. In math it’s represented by I for “intensity” or A for “amperes”.

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21
Q

What is voltage?

A

The electrical potential to create current flow in a circuit.

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22
Q

How is voltage symbolised?

A

V for “volts” or E for “electromotive force”

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23
Q

What is resistance?

A

The property opposition of the flow of electrical current.

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24
Q

What is resistance measured in and represented by?

A

Measured in ohms, represented by R for “resistance”.

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25
Q

What are the 4 variables used in calculations about circuits?

A

I (amperes, or current), V (voltage), R (resistance), P (power)

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26
Q

Define an electrical circuit.

A

A closed loop path that goes from a power source, through a load, and back to the power source.

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27
Q

What three things does every circuit have to have?

A
  1. Conductive material (wires)
  2. Voltage source (battery)
  3. Load (light source)
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28
Q

State Ohm’s Law, finding for current

A

I = V / R ( Current = Voltage / Resistance)

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29
Q

Current in a circuit is proportional to what?

A

Current is proportional to applied voltage. When voltage increases, current will also increase if the resistance stays the same.

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30
Q

As impedance increases and current remains constant, voltage does what?

A

Increases.

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31
Q

If voltage stays constant, an increase in resistance will cause a ________ in current?

A

Decrease

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32
Q

How are current and resistance related?

A

Current and resistance are inversely proportional.

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33
Q

If a circuit is like water in pipes, what would the Voltage, Current, and Resistance be?

A

Voltage is a basin full of water (potential), Current is the water flowing through the pipe, Resistance is the size of the pipe.

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34
Q

What’s the difference between resistance and impedance?

A

“Resistance” is used with DC circuits (batteries). “Impedance” is used with AC circuits (loudspeakers.)

35
Q

Ohms law, finding for Resistance:

A

R = V / I

36
Q

Ohms law, finding for Voltage

A

V = I * R

37
Q

Draw the Ohm’s Law Formula wheel

A

V on the top, I bottom left, R bottom right. divide separates top and bottom, Multiply separates the two bottoms sections.

38
Q

What’s the formula to calculate power?

A

P = I * V

39
Q

How are current and power different?

A

Power is consumed as it travels along the circuit and never makes it back to the source. Usually lost as heat. Current does make it back to the source.

40
Q

What’s the relationship between power and current or voltage?

A

They are proportional. If current increases, so does power. If voltage increases, so does power.

41
Q

Draw the Power Formula Wheel

A

Power at the top, Current (amps) on the bottom left, Voltage bottom right.

42
Q

What’s the core formula for power?

A

P = I * V

43
Q

What’s the core formula for Ohm’s Law (or Current Formula)?

A

V = I * R

44
Q

Define impedance

A

Total opposition to current flow in an AC circuit. It’s resistance AND forces that oppose changes in current (inductive reactance) and voltage (capacitive reactance). Impedance is frequency dependent.

45
Q

Impedance is dependent on what?

A

Frequency.

46
Q

Impedance takes into account what three things?

A

Resistance, inductive reactance, capacitive reactance.

47
Q

What is inductive reactance?

A

Opposition to changes in current

48
Q

What is capacitive reactance?

A

Opposition to changes in voltage.

49
Q

What does it mean to wire speakers in a series?

A

Each is connected to the next. Positive from power amp connects to positive of 1st speaker. Negative of 1st speaker connects to positive of 2nd. Negative of 2nd connects to positive of 3rd, etc. Last amp completes the circuit by connective to the amp’s negative terminal.

50
Q

What’s the formula for the Circuit Impedance of speakers wired in Series?

A

Zt = Z1 + Z2 + Z3… Zn —- where Zt = total impedance of the loudspeaker circuit and ZN = the impedance of each speaker.

51
Q

What does it mean to wire speakers in parallel?

A

The positive of every speaker is attached to the positive of the amp, and the negative of every speaker is connected to the amp’s negative terminal.

52
Q

What’s the formula for the circuit impedance of speakers wired in Parallel with all the same impedance?

A

Zt = Z1/ N (if they all have the same impedance). Where Zt = total impedance of the system, Z1 = impedance of each loudspeaker, N = quantity of loudspeakers in the circuit.

53
Q

What’s the formula for the circuit impedance of speakers wired in Parallel with differing impedances?

A

Zt = 1/ ( (1/Z1) + (1/Z2) + (1/Z3)… (1/Zn) )

54
Q

Which are easier to install and troubleshoot – series or parallel?

A

Parallel loudspeaker circuits!

55
Q

How do you wire loudspeakers in both series and parallel? (A series/parallel circuit)

A

“Branches” are wired in series (usually all speakers in a branch have the same impedance). Each branch is connected to the positive and negative lines of the amp (Parallel).

56
Q

What formula would you use to calculate total impedance of a series/parallel circuit?

A

Calculate each branch according to it’s own formula, then use the parallel formula for the rest.

57
Q

What’s a transformer?

A

Passive electromagnetic device. At least 2 coils of wire (inductors) with no electrical connection between them, usually sharing an iron based core. This common core concentrates the magnetic lines of force created by the current flow in the primary coil, which induces a voltage in the secondary coil.

58
Q

What is flux?

A

Magnetic lines of force.

59
Q

What are magnetic lines of force called?

A

Flux

60
Q

What’s a 1:1 transformer?

A

Has equal number of primary windings as secondary windings.

61
Q

What’s a 1:1 transformer used for?

A

To isolate one circuit from another. (An isolation transformer).

62
Q

What’s a 1:2 transformer?

A

Has twice as many windings on the secondary side as on the primary.

63
Q

What’s a 1:2 transformer used for?

A

Twice as much voltage is induced on the secondary side. Called a step-up transformer.

64
Q

Why does a step-up transformer work?

A

The flux from the conductors on the primary side cut across twice as many conductors on the secondary side, which induces voltage across twice as many conductors.

65
Q

What’s a 2:1 transformer?

A

A step-down transformer. Half as many windings on the secondary side.

66
Q

In a constant voltage system, what would you use a step up transformer for?

A

Used at the power amp to increase the voltage and impedance and decrease the current.

67
Q

25V, 70V, and 100V systems are examples of what?

A

Constant Voltage systems.

68
Q

What’s another name for a constant voltage system?

A

A high-impedance system.

69
Q

What are the advantages of a high-impedance system?

A

Can distribute over a large area with less loss.

70
Q

Where would you commonly find a 25V system in the US?

A

In schools

71
Q

What constant voltage system is typically used outside of North America?

A

100 V

72
Q

What’s the most common constant voltage system in the US?

A

70 V

73
Q

Why are constant voltage systems called that?

A

Because the amplifier voltage is “constant” across all the loudspeakers, up to the point of the amplifier’s power capacity.

74
Q

high-impedance systems work how?

A

Speakers are wired in parallel, but each speaker has a transformer that steps the signal level down to a usable level.

75
Q

Advantages of a high-impedance system?

A
  1. ) Greatly reduced current, which means reduction in wire gauge.
  2. ) Can distribute over long distances without losing signal strength.
76
Q

What’s the disadvantages of a high-impedance system?

A

May suffer from reduced frequency response and some signal reduction (transformer insertion loss) if lesser quality transformers are used.

77
Q

What’s a Direct Couple system?

A

Where the amp is connected directly to the voice coil wires of the loudspeaker. If there are several speakers they can be wired in series, parallel, or series/parallel.

78
Q

What’s another name for direct couple speaker systems?

A

Low impedance

79
Q

Low impedance systems are designed for low impedance loudspeakers. What impedances are included?

A

16 ohms, 8 ohms, or 4 ohms

80
Q

What are the advantages of a direct couple system?

A

Good low frequency response, better quality, and more power than constant voltage systems.

(This is because the transformers in a constant voltage system absorb energy.)

81
Q

What are the disadvantages/challenges of a direct couple system?

A
  1. Power losses due to resistance in the wiring because of the low impedance.
  2. This means greater wire gauge.
  3. When you work with lots of loudspeakers on one channel the wiring can get confusing if you use series/parallel
  4. It becomes important to make sure the impedance of the loudspeaker matches the amp output.
82
Q

Speakers wired in series are…

A

always direct coupled. They can’t use constant voltage.

83
Q

Speakers wired in parallel are…

A

either direct coupled or constant voltage.

84
Q

Speakers wired in series/parallel are…

A

always direct coupled. They can’t use constant voltage.

InfoComm CTS (8 decks)

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