Two old PA systems were very popular

PUBLIC ADDRESS SYSTEM

A Public Address System (PA System) is an electronic sound amplification and distribution system used to make announcements or play audio to a large group of people in public, private, or institutional spaces.

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🔧 Basic Components of a PA System:

1. Microphone 🎤

   • Captures the speaker’s voice.

2. Mixer 🎚️

   • Combines audio from multiple sources and controls volume and tone.

3. Amplifier 🔊

   • Increases the sound signal strength so it can drive loudspeakers.

4. Loudspeakers 📢

   • Convert amplified electrical signals into sound that can be heard by an audience.

5. Wiring & Power Supply ⚡

   • Connects and powers the components.

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📍 Where PA Systems Are Used:

• Schools – For morning announcements, bells, or emergency instructions.
• Railway Stations / Airports – To inform passengers.
• Public Events – Rallies, concerts, religious gatherings, etc.
• Factories & Offices – For communication and safety alerts.
• Shopping Malls – For music or emergency messages.

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🛠️ Types of PA Systems:

1. Simple PA System

   • One mic + one speaker, used in small gatherings or classrooms.

2. Large PA Systems

   • Multiple mics, speakers, and amplifiers with zoning capabilities (different volumes in different areas).

3. Wireless PA System

   • Uses radio or Wi-Fi signals instead of cables.

4. IP-based PA System

   • Connected over computer networks; used in smart buildings and campuses.

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⚠️ Important Features:

• Volume control
• Emergency alert capability
• Feedback suppression
• Battery backup (for emergencies)

Two PA systems were very popular in beginning of first decade of 2000 was called horn loudspeakers or public address (PA) horns. These are typically used for announcements in large open areas such as schools, railway stations, and public events because they can project sound over long distances.

• The top drawing labeled "Horn" is a basic horn speaker.
• The bottom one labeled "loudspeaker" is also a horn-type PA speaker, often seen mounted on poles or walls.

Both are efficient at focusing sound in one direction and amplifying voice or alarm signals.

Here's what these two types are commonly called:

1. First Image (Short, Wide Horn):
   This is a Reflex Horn Speaker or PA Horn Speaker. It’s used widely for indoor and outdoor announcements, especially in schools, temples, mosques, railway stations, etc. It has a wider mouth, providing better sound dispersion in a broader area.

2. Second Image (Long, Narrow Horn):
   This is a Long-Range Horn Speaker, often referred to as a Megaphone-style Horn or Tannoy Horn (Tannoy is a popular brand, but the term is colloquially used for these). It's designed for directional long-distance sound projection, commonly used in large grounds, rallies, or processions.

Both are part of the Public Address (PA) System family and work with amplifiers to deliver loud, clear audio over distances.

What is it's structure and working principle

Great question! Let’s break down the structure and working principle of a horn loudspeaker, like the ones you've shown:

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1. Structure of Horn Loudspeakers:

A horn loudspeaker has the following key parts:

a. Driver (or Compression Driver):

• This is the actual electromechanical transducer.
• It converts electrical audio signals into mechanical sound vibrations.
• Placed at the narrow end (throat) of the horn.

b. Horn (Flared Tube):

• The flared section (like a funnel) that amplifies sound.
• Starts narrow at the throat (driver end) and widens toward the mouth.
• Shapes can vary (conical, exponential, etc.) depending on the design.

c. Diaphragm and Coil (Inside the Driver):

• The diaphragm vibrates due to the current flowing through the voice coil in a magnetic field.
• These vibrations generate sound waves.

d. Mounting Bracket:

• Used to fix the speaker in the desired direction or location (wall, pole, etc.).

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2. Working Principle:

Step-by-Step Process:

1. Electric Signal Input:

   • Audio signals (from a mic or amplifier) are fed into the driver.

2. Electromagnetic Vibration:

   • The voice coil inside the driver reacts to the electric signal by moving back and forth in a magnetic field.
   • This causes the diaphragm to vibrate and produce sound waves.

3. Sound Transmission into Horn:

   • These vibrations enter the throat of the horn, where the cross-section is small.

4. Horn Amplification:

   • As sound waves travel through the horn, the widening shape helps match the acoustic impedance between the driver and the air.
   • This results in amplification of the sound, without needing more power.

5. Efficient Sound Propagation:

   • The horn’s shape projects the sound waves in a specific direction, making the sound louder and able to travel longer distances.

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Advantages:

• High efficiency (loud sound from less power)
• Directional projection
• Durable and good for outdoor/public use

Disadvantages:

• Lower audio quality (not suitable for music)
• Bulky in size

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What is the role of long Rod in middle, in first pucture

The long rod in the middle of the first loudspeaker image (compression driver type horn speaker) is called a phase plug or center rod (sometimes part of the driver’s throat assembly). Here’s what it does:

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Role of the Long Rod (Phase Plug):

1. Directs Sound Waves:

   • It helps guide the high-frequency sound waves from the diaphragm toward the horn’s throat and out into the horn efficiently.

2. Reduces Interference:

   • It prevents phase cancellations by ensuring sound from different parts of the diaphragm reaches the horn in phase.

3. Improves Clarity and Efficiency:

   • Especially important for speech intelligibility and clarity in public address systems.

4. Maintains Uniform Sound Spread:

   • It helps distribute sound more evenly across the mouth of the horn.

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So, that central rod is a critical part of the acoustic engineering to ensure the sound remains loud, clear, and well-directed. 

What are the types of these loudspeaker, that we say in physics

In physics (or acoustics), loudspeakers like the horn-type you showed are classified based on how they generate and project sound. Here are the main types of loudspeakers as understood in physics or engineering terms, especially focusing on PA horn speakers:

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1. Based on Sound Generation Mechanism:

a. Electrodynamic (Moving Coil) Loudspeaker:

• Most common type (used in horn speakers too).
• Uses a diaphragm attached to a voice coil placed in a magnetic field.
• When current flows, the coil vibrates, moving the diaphragm and generating sound.

b. Piezoelectric Loudspeaker:

• Uses piezoelectric crystals that vibrate when voltage is applied.
• Often used in compact or high-frequency horns (like buzzers or tweeters).

c. Electrostatic Loudspeaker:

• Uses a thin charged diaphragm between two conductive plates.
• Not used in PA horns — more common in high-end audio systems.

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2. Based on Sound Propagation & Construction:

a. Direct Radiating Loudspeakers:

• Sound is emitted directly from the diaphragm into the air.
• Common in regular speaker boxes (not horn types).

b. Horn Loudspeakers:

• Use a horn to amplify and project sound.
• The ones in your images fall into this category.
• More efficient and directional than direct radiators.

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3. Based on Horn Shape (Specific to Horn Speakers):

a. Conical Horn:

• Simplest shape (cone-like flare).
• Used where wide dispersion is needed.

b. Exponential Horn:

• Expands exponentially from throat to mouth.
• Provides better impedance matching and frequency response.

c. Hyperbolic Horn:

• Special flare to optimize both low and high frequencies.

d. Tractrix Horn:

• Smooth curvature to reduce distortion and reflection.

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4. Based on Frequency Range:

a. Tweeter Horns:

• Designed for high frequencies (above 2 kHz).
• Smaller and sharper throat and flare.

b. Midrange Horns:

• For human voice frequency range (~300 Hz to 2 kHz).
• Used in public address systems.

c. Bass Horns:

• Rare in PA systems due to size.
• Designed for low frequencies (20 Hz to 300 Hz).

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If you're referring to textbook physics, then moving coil loudspeaker with horn attachment is what you'd usually find under sound chapter discussions. 

Which type of loudspeaker are in the image?

The loudspeakers shown in your images are:

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Horn Loudspeakers with Electrodynamic (Moving Coil) Drivers

This combines two classifications:

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1. Type by Mechanism:

• Electrodynamic Loudspeakers
  • These use a voice coil and diaphragm inside a magnetic field.
  • It's the most common mechanism used in PA systems.
  • Current flows through the coil → vibration of diaphragm → sound waves.

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2. Type by Sound Projection:

• Horn Loudspeakers
  • These use a flared horn to amplify and direct sound efficiently.
  • The horn acts as an acoustic transformer matching the impedance between the diaphragm and the air.
  • These are highly efficient and designed for long-range, directional public announcements.

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So, to summarize:

• The speakers in your images are Electrodynamic Horn Loudspeakers.
• Specifically, they are used in Public Address (PA) Systems for voice projection over large areas.