Lesson 5: Speakers, Horns and Installation Techniques

Question 1

Ceiling Speaker Assemblies

Answer 1

Requires a stretcher when placed in a drop ceiling, typical to place an enclosure on the back but not required by the code.

Question 2

Drop-in Ceiling Speaker

Answer 2

Replaces the ceiling tile, no tile cutting required if tiles are 2x2.

Question 3

Metal Box Speakers

Answer 3

Used when speaker cannot be recessed or speaker is likely to be subject to physical damage.

Question 4

Wall Baffle Speakers

Answer 4

Used when speaker cannot be recessed, not used very often, as changes in wood preference changes often.

Question 5

Horn Speakers

Answer 5

Highly directional, typically most rugged of all speaker types, usually much higher power levels then other speaker types.

Question 6

High Fidelity Ceiling Speakers

Answer 6

Very good quality sound, used where music will be played relatively loud, quite heavy and usually requires a support wire.

Question 7

Flush Surface Mount Ceiling Speakers

Answer 7

Used when speaker cannot be recessed, looks similar to the recessed speaker type and not very good quality.

Question 8

Pendant Speakers:

Answer 8

Hung from the deck by a support cable, allows the speaker to be hung closer to the listener.

Question 9

Attenuators

Answer 9

Allows for volume control on constant voltage speakers, these should almost never be used.

Question 10

Speaker Problems:
out of phase
transformer loss
impedance matching

Answer 10

Out of phase - speakers may lose up to half of their powers.

Transformer loss = insertion loss. Measured in dB.

Impedence matching - any time 2 or more speakers are connected to a direct connection output.

Question 11

In runs of 100 feet or more, ___ AWG or larger should be used for speaker wiring.
Line matching transformers and speakers are wired in ___ across the amp output.

Answer 11

16

Parallel

Question 12

Running speaker lines in close proximity to other lines such as telephones and RF Cable for considerable distances can induce ___ into the system.

Code requires that all audio signal cables can/cannot be in the same conduit cable or wire way with anything else.

Answer 12

Hum, noise or cross talk

cannot

Question 13

Speaker lines can be balanced/unbalanced/both.

Care should be taken to as much separation as possible between ___ and ____ lines.

Answer 13

Both

speaker and input

Question 14

Impedence matching in series / parallel.

Answer 14

series ZT = Z1 + Z2 + ... + ZN
parallel ZT =      1       
             \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_
      1 /Z1+1/Z2+.....1/ZT
Look at 16-25           `

Question 15

Other considerations for speakers without transformers

Answer 15

• Power distribution
• Loud speaker/amplifier mismatching
• Line / power losses in direct connected systems.

Question 16

Power distribution in series / parallel.

Answer 16

series - like impedance = power distribution;
However, if one loud speaker has 4 ohm impedance and another 8 ohm, the power consumed by the 8 ohm will be twice that of the 4 ohm.
Parallel - like impedance = equal power consumption.
When speakers of different impedances are connected in parallel, the smaller impedance speaker will receive the greater power. ex: 8 ohm and 16 ohm are connected in parallel, the 8 ohm will consume twice the power.

Question 17

Loudspeaker / amplifier mismatching

Upward / downward

Answer 17

Upward - effects power to speaker ex: connecting 8 ohm speaker to 4 ohm amp output. Mismatching cannot ordinarily damage a well designed quality amp.
Downward - should be avoided ex: connecting 4 ohm speaker to 8 ohm amp output overloads the amp and seriously affects both performance and life expectancy and will overload the speaker .

Question 18

Line / power losses in direct connected systems.

Answer 18

Size and length is major consideration, resistance adds to loudspeaker impedance, changes total connected impedance. ex: 8 ohm system with 2 ohm of line resistance (20% line loss) = 10 ohm actual impedance at the amplifier.

Question 19

In direct connected systems, what gauge of wire should be used in runs of 50-100” and runs greater than 100’.

Answer 19

18 AWG is 50-100’

16 AWG or larger runs greater than 100”.

Question 20

Impedance matching with transformers (loudspeaker matching transformers) 70V and 25V

Answer 20

Permits signal to be transmitted at high voltages then stepped down at the speaker. Permits addition of speakers without significant changes necessary to amplifier.

70V systems will transmits 5w 5000’ in #20 AWG with a 10% power loss.

25V systems will transmit 5w 600’ in #20 AWG with a 10% power loss.

Question 21

What are two “musts” with impedance matching with transformers?

Answer 21

The appropriate power matching transformer must be used.

Ensure the amp isn’t overloaded.

Question 22

25V and 70V constant voltage distribution systems

Answer 22

for large multi-speaker installations, doesn’t mean that amp delivers constant voltage of 25V or 70V to the cable. (only when being driven to full rated power)

70V = NEC requirement for Class 2 or 3 wiring. (Some AHJ’s require conduit installation)

Question 23

Line matching transformers

Answer 23

Are connect in parallel across the amp’s output, different wire taps can be used on same cable. See PG 35

Question 24

When different taps are used on the same line, what should you do?

Answer 24

Observe proper phasing
Accidently connecting 25V line transformers to a 70V line will overload the amp quickly. 70V transformers to 25V line will result in inadequate power = reduced sound levels.
Ensure the total wattage taps used does not exceed output rating of amp (this would overload amp, degrade sound quality, and shorten life of amp.

Question 25

Balanced and unbalance line operations

Answer 25

Balanced - neither side is connected to a ground, both sides “float” at the same potential above “ground”. Used to reduce hum, noise, crosstalk, inlines in proximity to: telephone lines, RF Cable, or A/C power lines.

Unbalanced - one side is connected to a ground.

Some amps allow for both balanced and unbalanced 25V and 70V outputs. SEE PG 38 and 39.

Question 26

Used to reduce hum, noise, crosstalk, inlines in proximity to: telephone lines, RF Cable, or A/C power lines. (balanced or unbalanced)

Answer 26

balanced

Question 27

Speaker lines balanced to ground

Answer 27

When lines run in close proximity to input lines or system equipment.

• jumper 25VCT to ground
• lines should be shielded
• shields connected to ground

Question 28

Phasing of loudspeakers

Answer 28

More than two loudspeakers installed, must be phased

• out of phase will lose half their normal volume and will not sound good.
• polarity must be the same in respect to signal flow = phased

Question 29

1. Connect one lead of speaker to a 1.5V dry cell.
2. Briefly touch the other lad to the other speaker terminal.
3. Observe cone diaphragm movement (in or out)
4. Record results on paper.
5. Mark terminal connected to positive pole of dry cell.
   
   • (+) if movement is ____
   • (-) if movement is ____
6. Repeat steps 1-5 on remaining speakers.
7. Connect the appropriate speakers to ensure polarity.

Answer 29

Phasing of loudspeakers

outward
inward