Lesson 2 Paging Systems: Constant Voltage and Self Amplified Systems

Question 1

Purpose of a Paging System:

Answer 1

• Delivers important audio announcements
• It’s at the proper level with clarity
• Easily understood

Question 2

Two Ways to Accomplish Paging (Voltage):

Answer 2

1. 25V or 70V centralized amplifiers with passive speaker

2. 24V power supply self-amplified speakers

Question 3

Self-Amplified Systems:

1. Each speaker has a small ___.
2. ___ wires - ___ for audio, ___ for 24V DC power.
3. Power supplies located in various areas and require (may) multiple ___ ___.

Answer 3

1. amplifier.
2. Four / two / two
3. power supplies

Question 4

Why Use a Self-amplified System?
1. Low signal levels prevent ___.
a Not wise to run 70V systems in same cable with __ .
b Similar signals on 24V systems prevent ___.
c Must use care concerning cable ___ (voltage drop)

2. Convenient ___ Expansion
   a Easy to connect extra ___ ___,
   b Self-amplified speakers can be used to expand ___ systems.
3. Cost effective for ___ ___.
   a Designed with much smaller ___ levels
   b Lower cost of ___ (amplifiers)

Answer 4

1. crosstalk
   a analog phone lines
   b crosstalk
   c length
2. System
   a power supplies
   b 70V
3. small installations
   a output
   b equipment

Question 5

Loop Start Interface/Power Supply:

1. __V talk battery supply for loop start ports
2. Buffered audio output for up to ___ self-amp speakers
3. 450 mA, 24V DC power supply for ___ equipment
4. Integral flanges and rubber feet for ___ or ___ mounting
5. ___ terminal barrier strip

Answer 5

1. 24
2. 25
3. external
4. wall or shelf
5. 6

Question 6

Level Controls (Buffer/Expander/Volume Control):

To address the needs of emergency announcements, the ___ has a bypass feature that allows emergency announcements to be heard at high levels regardless of the volume setting. The ___ contains a bypass trim feature that allows some adjustment to the bypass level.

Local volume controls allow people working in an area to control the level of ___ and ___ for their needs.

Answer 6

BUFEX

BUFEX

paging and background music

Question 7

Name some benefits of BUFEX:

Answer 7

• Local volume control for a group of speakers.
• Provides buffering for up to 150 self-amplified speakers.
• Allows self-amplified speakers to work with 100/70/25V systems, expanding existing systems.
• Continuously variable attenuator.
• Rugged and attractive stainless steel wall plate with engraved lettering.

Question 8

Signal Level Control:
The SLC provides a simple and cost effective way to remotely control the ___ of a network of up to 150 speakers. Simply wire in series with the ___ ___ to the desired group of amplified speakers.

Answer 8

volume level

audio feed

Question 9

Some benefits of SLC:

Answer 9

• Volume control for network of up to 150 speakers.
• Easy install, wire with audio feed to speakers.
• 10 position settings plus off
• Secure terminal strip connections.

Question 10

Why use 70V Ouputs?

Answer 10

Low currents allow long runs.
- 70V systems can handle extremely long lengths of wire to connect the speakers to the amplifier, and they can power a large number of speakers in each system.

• When sending power signals over long distances, it is important to minimize the amount of current flowing in the wire. High currents allow too much power or electrical energy to be wasted in wires in the form of heat.

Question 11

Power and Ohms Law:

1. To lower the amount of ____ ____ (Watts)
   a Voltage is ___
   b Current is ___
   c Power supplied at the ___ is the same (70w)

2.  To ensure compatibility of voltage changes
     a A step down \_\_\_ \_\_\_ is used
     b Located on the \_\_\_
     c \_\_\_ at various levels
     d Typical is \_\_ Ohm speaker

Answer 11

1. POWER LOSS
   a increased
   b reduced
   c amp

2.  
     a audio transformer
     b speaker
     c Tapped 
     d 8

Question 12

Controlling Speaker Power Draw and the Benefits:

1. Output of central amp is designed to limit ___ ___ ___ supplied to speakers.
2. Maximum power output remains the same regardless of the amp’s ___ ___.
3. Manufacturers can design speakers that consume a specific amount of power from the ___.

Answer 12

1. maximum output voltage
2. power capability.
3. amp.

Benefits:

• Speakers will not consumer more power than they are designed for.
• They will not blow-out from using an amp that’s too powerful.
• Each speaker’s power consumption is known - the correct power is the total power drawn by all speakers.

Question 13

What two things make a 70V speaker and definition:

Answer 13

Step Down Transformer: Used to convert the high voltage/low current amp signal to the low voltage/high current signal that the speakers use.

Taps: Primary side of the step-down transformer (side that connects to the amp) has a number of connections (called taps or power taps) that can be used to select the peak power the speaker will consume from the amp.

Question 14

Why use taps?

Answer 14

• The more power the speaker consumes, the louder the sound from the speaker.
• By tapping speakers for lower power in quiet areas and for higher power in noisier areas, the sound level of the paging system can be controlled and balanced.
• Sound level of system can be balanced
  
  • important that tapping is done properly
  • need to measure ambient noise in areas to determine proper taps
• Some systems have a test tone to be used for this.

Question 15

Amplifier Output Types

Answer 15

70V Output - primary for paging systems
Direct Output - used with low impedance speakers
- Has low frequency response (bass) and low impedance speakers (4 Ohm)
25V, 16 and 8 Ohm - used for stricter building code requirements.

Question 16

Amplifier Input Types

Answer 16

Auxiliary input (AUX)

• Most common input used in paging
• Connects music sources
• Usually an RCA Jack
• Referred to as “High-Z” (high impedance)
• “Unbalanced input”
• Must use shielded cable to avoid induced noise
• Limit input cables to 6’.
• Longer cable = more noise.

Question 17

Telephone Input (TEL):

Answer 17

Designed to be used with page port options with telephone systems.

TEL input is a 600 Ohm transformer coupled input

• matches the impedance of the telephone port
• electrically isolates amp from PBX or EKS
• provides a balanced input with noise immunity

Question 18

Microphone Input (MIC)

The traditional paging amplifier input is the ___ input.

MIC inputs were the primary announcement source until connection to the ___ ___ became possible.

MIC inputs are still used in ___ ___ applications today.

Answer 18

microphone .

telephone system

public address

Question 19

Microphone Input (MIC):

1. When connected properly, a microphone can be hundreds of feet away from the ___ and still provide clear, quiet audio.
2. MIC inputs are the most ___ of all amplifier inputs and tend to pick up ___ in an area.
3. To combat the noise pickup problem, MIC inputs are ___. Just like TEL inputs, the ____ of the input provides a high level of noise immunity.
4. MIC inputs are made to have a fairly ___ input impedance, which makes it difficult for electrical noise to get induced. The ___ impedance effectively keeps down noise, which makes its signal level ___.

Answer 19

1. amplifier
2. sensitive / stray electrical noise
3. balanced / balancing
4. low / low / smaller

Question 20

Microphone Input (MIC):

1 Microphone cable is always shielded / unshielded.

2. The input requires ___ connections; ___ for the balanced signal and ___ for the shield ground.
3. You can reverse the balanced signal leads and the system will still work properly. However, is you mis-wire the ___ ___, the amp can be unstable and start to oscillate. When this occurs, the amp may heat up enough to cause it ___ ___ to shut it down or it may produce very distorted sound.

Answer 20

1. shielded
2. three / two / one
3. ground connections / protection circuits