Lesson 5: Speakers, Horns and Installation Techniques Flashcards
Ceiling Speaker Assemblies
Requires a stretcher when placed in a drop ceiling, typical to place an enclosure on the back but not required by the code.
Drop-in Ceiling Speaker
Replaces the ceiling tile, no tile cutting required if tiles are 2x2.
Metal Box Speakers
Used when speaker cannot be recessed or speaker is likely to be subject to physical damage.
Wall Baffle Speakers
Used when speaker cannot be recessed, not used very often, as changes in wood preference changes often.
Horn Speakers
Highly directional, typically most rugged of all speaker types, usually much higher power levels then other speaker types.
High Fidelity Ceiling Speakers
Very good quality sound, used where music will be played relatively loud, quite heavy and usually requires a support wire.
Flush Surface Mount Ceiling Speakers
Used when speaker cannot be recessed, looks similar to the recessed speaker type and not very good quality.
Pendant Speakers:
Hung from the deck by a support cable, allows the speaker to be hung closer to the listener.
Attenuators
Allows for volume control on constant voltage speakers, these should almost never be used.
Speaker Problems:
out of phase
transformer loss
impedance matching
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.
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.
16
Parallel
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.
Hum, noise or cross talk
cannot
Speaker lines can be balanced/unbalanced/both.
Care should be taken to as much separation as possible between ___ and ____ lines.
Both
speaker and input
Impedence matching in series / parallel.
series ZT = Z1 + Z2 + ... + ZN
parallel ZT = 1
\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_
1 /Z1+1/Z2+.....1/ZT
Look at 16-25 `Other considerations for speakers without transformers
- Power distribution
- Loud speaker/amplifier mismatching
- Line / power losses in direct connected systems.
Power distribution in series / parallel.
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.
Loudspeaker / amplifier mismatching
Upward / downward
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 .
Line / power losses in direct connected systems.
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.
In direct connected systems, what gauge of wire should be used in runs of 50-100” and runs greater than 100’.
18 AWG is 50-100’
16 AWG or larger runs greater than 100”.
Impedance matching with transformers (loudspeaker matching transformers) 70V and 25V
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.
What are two “musts” with impedance matching with transformers?
The appropriate power matching transformer must be used.
Ensure the amp isn’t overloaded.
25V and 70V constant voltage distribution systems
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)
Line matching transformers
Are connect in parallel across the amp’s output, different wire taps can be used on same cable. See PG 35
When different taps are used on the same line, what should you do?
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.
