Engineers Garage

  • Electronic Projects & Tutorials
    • Electronic Projects
      • Arduino Projects
      • AVR
      • Raspberry pi
      • ESP8266
      • BeagleBone
      • 8051 Microcontroller
      • ARM
      • PIC Microcontroller
      • STM32
    • Tutorials
      • Audio Electronics
      • Battery Management
      • Brainwave
      • Electric Vehicles
      • EMI/EMC/RFI
      • Hardware Filters
      • IoT tutorials
      • Power Tutorials
      • Python
      • Sensors
      • USB
      • VHDL
    • Circuit Design
    • Project Videos
    • Components
  • Articles
    • Tech Articles
    • Insight
    • Invention Stories
    • How to
    • What Is
  • News
    • Electronic Product News
    • Business News
    • Company/Start-up News
    • DIY Reviews
    • Guest Post
  • Forums
    • EDABoard.com
    • Electro-Tech-Online
    • EG Forum Archive
  • DigiKey Store
    • Cables, Wires
    • Connectors, Interconnect
    • Discrete
    • Electromechanical
    • Embedded Computers
    • Enclosures, Hardware, Office
    • Integrated Circuits (ICs)
    • Isolators
    • LED/Optoelectronics
    • Passive
    • Power, Circuit Protection
    • Programmers
    • RF, Wireless
    • Semiconductors
    • Sensors, Transducers
    • Test Products
    • Tools
  • Learn
    • eBooks/Tech Tips
    • Design Guides
    • Learning Center
    • Tech Toolboxes
    • Webinars & Digital Events
  • Resources
    • Digital Issues
    • EE Training Days
    • LEAP Awards
    • Podcasts
    • Webinars / Digital Events
    • White Papers
    • Engineering Diversity & Inclusion
    • DesignFast
  • Guest Post Guidelines
  • Advertise
  • Subscribe

Audio Filters: The working and classification of speakers – Part 4

By Diksha October 14, 2024

In the previous tutorial, we discussed the classification and working principle of microphones. We learned that the microphone is an input transducer that converts sound waves into electrical signals. These audio signals are then amplified by a preamplifier and transferred to a main audio unit.

The unit might include an amplifier and/or filter circuit, or have circuitry that connects with a computer to save and store the audio. Audio that’s amplified or stored is reproduced using another type of transducer — a speaker. 

Typical Image of Speaker

A speaker

A speaker is a type of output transducer that converts an electrical signal into an audio signal. Speakers are typically enclosed in a rectangular or square-shaped cabinet or casing, although there are many types of casings.

The enclosure and the loudspeaker
You might question the need for a cabinet or casing that holds a speaker but it’s an important element of this type of transducer. 

Speakers produce sound via a diaphragm, a thin, paper-like membrane that moves back and forth in the presence of a sound wave (you’ll recall the diaphragm from the tutorial on microphones). Now, the front surface of a speaker, which is typically in the shape of a cone, will produce a sound wave of high air pressure. However, the back surface of this cone lowers the air pressure.

The sound generated from the front and back speaker is the same only their phase differs — the lower frequency sound (from the back) produces a larger wavelength than the high-frequency sound (from the front). The lower frequency sound wave will diffract more, essentially canceling out the front and back waves, which silences the bass frequency.

So, this is why there’s always a need to properly enclose the speakers. But the shape of this casing affects the quality of the sound (discussed below).

There are also different types of speakers/transducers, which produce different types of audio frequencies. Each transducer is called a driver, and the cabinet is known as a loudspeaker.

As a single speaker is incapable of providing a full range of audio frequencies, a loudspeaker offers driver units to support the frequencies. Essentially, a speaker driver is an electroacoustic component that makes a loudspeaker work.

The three different driver units include:

1. Tweeter –  for high-frequency ranges
2. Mid-range driver  –  for middle-frequency ranges
3. Woofers  – for low-frequency ranges

Types of speakers
Speakers can be classified in several different ways, including on the basis of amplification, construction, and casing.

Amplification
In terms of amplification, there are passive and active speakers.

  • Passive speakers – has no built-in power amplifiers and, therefore, must connect to an external power amplifier to achieve high-power output. Most commercially available speakers are passive, which allows for their small size.
  • Active speakers – include an inbuilt power amplifier for high and low-frequency sounds. Often referred to as powered speakers, these active ones live up to their name and are typically heavy and bulky. As a result, they’re used less commonly than passive speakers. 
Image showing Construction and Working of Conventional Speakers

The construction of conventional speakers.

Construction
The classification of speakers based on their construction includes conventional, electrostatic, and ribbon speakers. 

Conventional speakers – the most common type of speaker. It consists of a voice coil that’s attached to a diaphragm and a permanent magnet. When an oscillatory electric current is passed through the coil, it creates a magnetic force, thanks to the permanent magnet. This generates a mechanical motion in the diaphragm, which produces sound waves.

Electrostatic speaker –  designed with its diaphragm between.two rigid and perforated metal plates. The diaphragm, which is a thin metal sheet, has the opposite charge of the perforated metal plates. As a result, each plate attracts the diaphragm with an equal and opposing force compared to the total force on the diaphragm, which is zero.

Image showing Construction and Working of Electrostatic Speakers

The construction of electrostatic speakers.

However, this force changes when an audio signal is applied to the metal plates. So, when plate ‘A’ is more positive than plate ‘B,’ the diaphragm moves toward plate ‘A,’ and vice versa. Each time an audio signal changes its signal, it causes a push-pull movement between the diaphragm and the plates. This “flexing” produces sound.

These kinds of speakers are less responsive to low-frequency signals and tend to be heavy and costly. Not surprisingly, they’re used less commonly than conventional speakers.

Ribbon speakers – comprised of a tall, thin metal ribbon (typically aluminum), which is suspended between two magnetic plates. When an audio signal is applied to the ribbon, it’s repelled and attracted to the magnetic plates (similar to how the electrostatic speaker’s plates react with its diaphragm).

This generates a vibration that produces sound. These types of speakers are also less responsive to low-frequency signals but, since the ribbon is so lightweight, it responds quickly to any signal changes. 

Image showing Construction and Working of Ribbon Speakers

The construction of ribbon speakers.

Image of Closed or Sealed (Acoustic Suspension) Enclosure for Speakers

Closed casing

Casing
Speakers can also be classified based on the type of casing or enclosure that they have and there are five common types: closed/sealed, ported, free air, band pass, and transmission line casings.

Closed or sealed (acoustic suspension) – an airtight enclosure, so when the driver moves back and forth, it will continually change the air pressure. This increases the pressure on the diaphragm, causing it to move back and forth quite quickly — producing crisp and accurate audio. 

Image of Ported or Bass Reflex Enclosure for Speakers

Ported casing

Ported (bass reflex) – this type of enclosure has is a hole in front of it, which equalizes the pressure inside and outside of the driver. Although it does not require any extra power to operate, it typically results in a less clean or clear audio output. But this type of casing has less distortion compared to the other enclosures.

Free-air (infinite baffle) – the woofer is mounted on a baffle, which isolates the front from the back wave. The baffle or the board extends so much that even the longest wave can never reach the front wave. As this system cannot practically be implemented, the free-air casing is typically a large, sealed box that requires low power and has little distortion. 

Image of Infinite Baffle or Free Air Enclosure for Speakers

Free-air casing

Band pass  – the speaker is placed in an enclosure and the sound emanates from built-in ports. There are different types of band-pass enclosures, depending on the order (such as the 4th, 6th and, so on).

In a 4th-order band pass, for example, one side of the speaker is placed in a closed enclosure while the other side is in a ported enclosure. In this case, the woofer sounds louder than the bass reflex but has a narrower frequency response.

Image of Band Pass Enclosure for Speakers

Band-pass

Transmission line (acoustic labyrinth) –the back wave of this speaker passes through a complex labyrinth (an irregular network path), which is of a fixed length and dampens the sound. This allows greater control and use of the speaker energy, providing a strong, low-frequency response that can reach the subsonic range (>45Hz).

Horn – this enclosure entails a horn-shaped casing that extends from a narrow to a broad diameter, making it easier for the sound waves to transit through the speakers. Ideally, the size of the horn in this enclosure must suit to the frequency range of the audio output. For example, a greater frequency should use a larger horn.

Image of Transmission Line Enclosure for Speakers

Transmission-line casing

The horn casing is best suited for tweeter and mid-range drivers. For woofer drivers, folded-horn enclosures can be used and take up less space.

These are the most common type of casings used for speakers, however there are several other options available. Examples include dipole, wall, push-pull, quarter and tapered-wave enclosures and others.

Image of Straight and Folded Horn Enclosure for Speakers

Straight and folded-horn casings.

In the next tutorial, we’ll learn about the basics of audio filters. 

You may also like:


  • What are the top development boards for AI and ML?

  • What are top applications of CAN protocol?

  • What are the two types of hardware filters?

  • What are hardware filters and their types?

  • What are the different types of integrated circuits?

  • What are the top programming languages for machine learning?

Filed Under: Audio Electronics, Tutorials

 

Next Article

← Previous Article
Next Article →

Questions related to this article?
👉Ask and discuss on Electro-Tech-Online.com and EDAboard.com forums.



Tell Us What You Think!! Cancel reply

You must be logged in to post a comment.

EE TECH TOOLBOX

“ee
Tech Toolbox: 5G Technology
This Tech Toolbox covers the basics of 5G technology plus a story about how engineers designed and built a prototype DSL router mostly from old cellphone parts. Download this first 5G/wired/wireless communications Tech Toolbox to learn more!

EE Learning Center

EE Learning Center
“engineers
EXPAND YOUR KNOWLEDGE AND STAY CONNECTED
Get the latest info on technologies, tools and strategies for EE professionals.

HAVE A QUESTION?

Have a technical question about an article or other engineering questions? Check out our engineering forums EDABoard.com and Electro-Tech-Online.com where you can get those questions asked and answered by your peers!


RSS EDABOARD.com Discussions

  • Exporting sensor readings as data...
  • Inconsistent Charge Termination Voltage with battery charger
  • 21V keeps getting shorted to my UART line.
  • Voltage mode pushpull is a nonsense SMPS?
  • Voltage mode push pull with extra DC blocking capacitor

RSS Electro-Tech-Online.com Discussions

  • Is AI making embedded software developers more productive?
  • Why can't I breadboard this oscillator?
  • using a RTC in SF basic
  • Parts required for a personal project
  • Cataract Lens Options?

Featured – RPi Python Programming (27 Part)

  • RPi Python Programming 21: The SIM900A AT commands
  • RPi Python Programming 22: Calls & SMS using a SIM900A GSM-GPRS modem
  • RPi Python Programming 23: Interfacing a NEO-6MV2 GPS module with Raspberry Pi
  • RPi Python Programming 24: I2C explained
  • RPi Python Programming 25 – Synchronous serial communication in Raspberry Pi using I2C protocol
  • RPi Python Programming 26 – Interfacing ADXL345 accelerometer sensor with Raspberry Pi

Recent Articles

  • GigaDevice launches GD32C231 MCU series with 48MHz Cortex-M23 core and 64KB Flash
  • Advanced Energy releases 425 W CF-rated medical power supply in 3.5 x 6 x 1.5-inch format”
  • LEM combines shunt and Hall effect sensing in 2000 A current measurement unit
  • What is AWS IoT Core and when should you use it?
  • AC-DC power supply extends voltage range to 800 V DC

EE ENGINEERING TRAINING DAYS

engineering

Submit a Guest Post

submit a guest post
Engineers Garage
  • Analog IC TIps
  • Connector Tips
  • Battery Power Tips
  • DesignFast
  • EDABoard Forums
  • EE World Online
  • Electro-Tech-Online Forums
  • EV Engineering
  • Microcontroller Tips
  • Power Electronic Tips
  • Sensor Tips
  • Test and Measurement Tips
  • 5G Technology World
  • Subscribe to our newsletter
  • About Us
  • Contact Us
  • Advertise

Copyright © 2025 WTWH Media LLC. All Rights Reserved. The material on this site may not be reproduced, distributed, transmitted, cached or otherwise used, except with the prior written permission of WTWH Media
Privacy Policy

Search Engineers Garage

  • Electronic Projects & Tutorials
    • Electronic Projects
      • Arduino Projects
      • AVR
      • Raspberry pi
      • ESP8266
      • BeagleBone
      • 8051 Microcontroller
      • ARM
      • PIC Microcontroller
      • STM32
    • Tutorials
      • Audio Electronics
      • Battery Management
      • Brainwave
      • Electric Vehicles
      • EMI/EMC/RFI
      • Hardware Filters
      • IoT tutorials
      • Power Tutorials
      • Python
      • Sensors
      • USB
      • VHDL
    • Circuit Design
    • Project Videos
    • Components
  • Articles
    • Tech Articles
    • Insight
    • Invention Stories
    • How to
    • What Is
  • News
    • Electronic Product News
    • Business News
    • Company/Start-up News
    • DIY Reviews
    • Guest Post
  • Forums
    • EDABoard.com
    • Electro-Tech-Online
    • EG Forum Archive
  • DigiKey Store
    • Cables, Wires
    • Connectors, Interconnect
    • Discrete
    • Electromechanical
    • Embedded Computers
    • Enclosures, Hardware, Office
    • Integrated Circuits (ICs)
    • Isolators
    • LED/Optoelectronics
    • Passive
    • Power, Circuit Protection
    • Programmers
    • RF, Wireless
    • Semiconductors
    • Sensors, Transducers
    • Test Products
    • Tools
  • Learn
    • eBooks/Tech Tips
    • Design Guides
    • Learning Center
    • Tech Toolboxes
    • Webinars & Digital Events
  • Resources
    • Digital Issues
    • EE Training Days
    • LEAP Awards
    • Podcasts
    • Webinars / Digital Events
    • White Papers
    • Engineering Diversity & Inclusion
    • DesignFast
  • Guest Post Guidelines
  • Advertise
  • Subscribe