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Speakers play a vital role in our auditory experiences by transforming electrical signals into the dynamic sounds we hear. Understanding how speakers function and contribute to sound production requires exploring their core mechanisms and essential components. In this blog, we'll highlight what you need to know about using speakers in audio design, including their basic functionality, important specifications, design factors, and types of cones and magnets.

Speaker Basics

Within a speaker, the voice coil and permanent magnet are at the heart of the mechanism. The voice coil, made of wire, is attached to a flexible cone or diaphragm and surrounds the permanent magnet. When the electrical signal flows through the coil, it generates a magnetic field, creating a dynamic interaction between the coil’s magnetism and the permanent magnet (Figure 1).

This interaction causes the coil and its connected cone to oscillate rapidly. These movements push and pull air molecules, creating pressure waves that travel through the air. These waves eventually reach our ears, where our brains interpret them as sound.

Figure 1: An illustration of the basic working principle of a speaker, in which the rapid oscillations of the coil and its connected cone create pressure waves that travel through the air. (Source: Same Sky, formerly CUI Devices)

Going further into the anatomy of a speaker unveils the key components that collaborate to deliver sound: the cone, voice coil, plate, magnet, frame and yoke, and printed circuit board (PCB). The detailed illustration in Figure 2 displays the structure of a typical speaker, separating the components essential to sound production.

Figure 2: A disassembled representation of the typical speaker components. (Source: Same Sky)

Key Speaker Specifications

Beyond understanding speaker anatomy and basic functions, it’s important to consider key specifications and performance criteria when selecting the right speaker for your design.

• Sound Pressure Level (dB): Measures the intensity of sound waves, or how loud a sound is. Factors like distance and environmental conditions affect sound pressure level (SPL), which is measured in decibels (dB).
• Max Input (W): Indicates the maximum power a speaker can handle briefly without sustaining permanent damage.
• Nominal Input (W): Refers to the power a speaker can safely handle during continuous, long-term use.
• Impedance (Ohm): Represents the resistance to current flow from an amplifier. Lower impedance draws more power, making it crucial to match speaker impedance with the amplifier for optimal performance and to prevent equipment damage. Proper impedance matching ensures efficient power transfer and maintains sound fidelity.
• Resonant Frequency (Hz): The frequency at which a speaker vibrates most efficiently, offering a comparison of low-frequency response among different speakers.
• Size (mm): Determines the speaker’s frequency range. Smaller speakers excel at higher frequencies, while larger ones are optimized for lower frequency ranges, such as deep bass sounds. Mid-range frequencies are ideal for reproducing voices.
• Total Q: A Thiele-Small parameter that guides enclosure selection.* A total Q of:
  • 0.4 or lower: Best for vented enclosures;
  • 0.4 to 0.7: Suitable for sealed enclosures;
  • 0.7 or higher: Ideal for free-air, semi-open back, or infinite baffle setups.
    * While these are general guidelines, always evaluate all relevant parameters for the best results.
• Mounting Styles: These include wire leads, through-hole connections, solder pads, and more, providing flexibility for diverse audio system designs.

Key Speaker Measurements & Tests

After selecting a speaker based on the key specifications outlined above, additional measurements and tests are essential to ensure proper integration and optimal performance within your design.

• Frequency Response: In the context of speakers, “response” refers to the speaker’s ability to accurately reproduce input frequencies. When plotted, this data forms a frequency response graph, which visually represents how the speaker responds across a range of input frequencies (Figure 3).
• Stepped Frequency Sweep: Similar to a frequency response test, but focuses on identifying alias frequencies for a more detailed analysis of sound reproduction.
• Level & Gain: Level measures the energy output of a device, while gain represents the ratio of the output level to the input level, helping evaluate performance efficiency.
• Total Harmonic Distortion plus Noise (THD+N): Evaluates harmonic distortion, which introduces unwanted tones to the audio signal. THD+N provides a concise and widely recognized indicator of overall audio quality.
• Phase: Measures time offsets in a periodic waveform relative to a reference waveform. Common tests include input/output phase and interchannel phase for systems with multiple speakers.
• Rub & Buzz: Detects high-frequency harmonic distortions caused by low-frequency inputs, identifying mechanical defects or alignment issues in speakers.
• Thiele-Small Parameters: A detailed set of electromechanical values defining the low-frequency performance of speaker drivers. These parameters, such as total Q, are essential for matching speakers to enclosures and ensuring optimal system design and testing.
• Impedance: Indicates the speaker’s resistance to an alternating current (AC) signal, such as audio from an amplifier. Measured in ohms, impedance ensures compatibility between the speaker and audio system for efficient performance.

Figure 3: Example of a frequency response chart showing how a speaker responds across the sound pressure level (dB) and resonant frequency (Hz). (Source: Same Sky)

Speaker Cones & Magnets

The material used for the speaker cone plays a significant role in sound quality, alongside other factors. Here are the most common speaker cone materials.

• Plastic: Durable, moisture-resistant, and easy to manufacture. Plastic cones offer good damping properties, reducing distortion. Made from composites, costs vary based on thickness, pressing techniques, and size.
• Paper & Cloth: Known for excellent sound quality and self-damping. These cones are made from wood fibers blended with additives like cotton or wool for improved characteristics. They are commonly used in larger speakers due to their lightweight nature.
• Foam: Typically used as part of composites with materials like metal, plastic, or paper to enhance internal loss, minimizing material sound coloration.

The type of magnet used in a speaker also plays a crucial role in its overall construction and performance, with each type presenting different benefits and tradeoffs.

• Ferrite: Affordable, corrosion-resistant, and reliable under high capacity, though heavy and less suitable for portable speakers.
• AlNiCo: Deliver smooth, classic tones and are durable but more expensive. Preferred for high-end applications requiring precise sound tuning.
• Neodymium: Lightweight, compact, and powerful, making them ideal for small, high-SPL speakers, although they are susceptible to shattering.
• Samarium Cobalt: Costly but corrosion-resistant and temperature-stable, offering suitability for harsh environments despite lower strength and shatter risk.

Conclusion

A solid understanding of speaker mechanics enables engineers to create immersive auditory experiences. As we've highlighted throughout this blog, selecting the right speaker involves considering various components and specifications. However, even with a comprehensive understanding of key speaker parameters, proper testing and measurement within your final design are essential for optimal performance. Fortunately, Same Sky (formerly CUI Devices) offers an extensive range of speaker solutions that includes the CMS series, CDS series, and more, providing a solution to achieve the best results for virtually any design.

Nick Grillone wrote the “ All You Need to Know About Speakers in Audio Design” blog, which is updated and republished here with permission.

Author

Nick Grillone
Applications Engineer, Same Sky
Nick Grillone brings over 10 years of customer support experience to the Same Sky Applications Engineering team. His technical and application expertise is particularly focused on Same Sky’s diverse range of audio components, such as microphones and speakers, as well as their sensor technology offering. In his spare time, Nick enjoys all things outdoors with his partner and his dog, including backpacking, camping, cycling, and paddleboarding.