Loudspeaker Materials 101: The Cone [VIDEO]

If the heart of a loudspeaker is the voice coil, then the cone is the mouth.

In a loudspeaker, the voice coil is an electromagnet that, when electrified, interacts with the permanent magnet by alternating its polarities. That interaction causes the voice coil to move in a piston-like motion. The cone is coupled to the voice coil, so when the voice coil moves, the cone moves, and sound is produced.

One of the most critical components in a loudspeaker is the cone, also called the diaphragm. While all parts of the loudspeaker play an essential role in faithfully reproducing sound, the cone is the element that is directly responsible for producing what we hear.

In a loudspeaker, the cone is a thin, semi-rigid membrane that vibrates to produce sound. Its purpose is to reproduce the voice coil signal waveform accurately. A poor reproduction means acoustic distortion of the intended sound.

What Does a Cone in a Loudspeaker Do?

A loudspeaker is an electromechanical device that converts electrical signals into sound by using the interaction between a voice coil and a permanent magnet. Typically, an electromechanical motor converts electrical energy into mechanical energy by generating rotational motion through electromagnetic forces. However, in a loudspeaker, the magnetic interaction causes the voice coil to move in a reciprocating motion rapidly.

Since the cone is attached to the voice coil, when the voice coil moves, so does the cone. As the cone moves back and forth, it compresses and rarefies the air around it, generating sound pressure waves. The sound pressure waves constitute acoustic energy. When combined with another loudspeaker, phenomena like interference and phase alignment occur. These interactions can enhance or detract from certain frequencies, changing the soundstage and overall listening experience.

Direction Matters

In a loudspeaker, the voice coil and cone are suspended so they can move freely when electricity is applied. This movement is essential for converting electrical signals into sound. However, this freedom also means there's a risk of the cone and voice coil becoming misaligned, which can lead to distortion or even damage to the loudspeaker. That's where the spider and surround come into play.

The surround is a flexible ring that connects the outer edge of the cone to the basket (also known as the frame) of the loudspeaker. Surrounds prevent the cone from tilting or wobbling, ensuring it can smoothly move in and out. Unwanted vibrations and resonances can occur during the regular operation of the loudspeaker, potentially coloring the sound or causing distortions. The surround acts as a dampener to prevent this from happening.

Deeper within the loudspeaker is the spider (also called the damper). The spider is a corrugated, flexible disc that connects the basket to the voice coil and the inner portion of the cone. It helps keep the voice coil aligned correctly in the magnetic gap and allows the voice coil and cone to move smoothly in a piston-like fashion.

Together, the spider and surround maintain the precise alignment and controlled movement necessary for accurate sound reproduction, preventing distortion and ensuring the longevity of the loudspeaker.

Attributes of Loudspeaker Cones

Early attempts at loudspeakers utilized flat diaphragms. Flat diaphragms can be seen in modern loudspeakers and work well for what they are designed for, but early flat diaphragms tended to flex and bend when driven by the voice coil, leading to non-uniformed movement. That flexing would lead to parts of the diaphragm to move out of phase with other parts, resulting in distortion and a loss of fidelity.

Because of the shortcomings of a flat diaphragm, a cone-shaped diaphragm became the standard for loudspeakers. The three-dimensional structure of the cone is more resistant to bending and flexing, causing the diaphragm to be more rigid. This rigidity ensures that the diaphragm moves as a single unit, pushing air efficiently to produce sound waves without distortion. Additionally, cone shapes influence the directionality of sound. The angled surfaces of the cone help project sound waves forward, creating a more focused and directional sound field. This focus means that sound energy is concentrated where needed most, improving clarity and reducing unwanted reflections and echoes. Cone shapes also allow for more surface area, enhancing sound propagation.

In addition to rigidity, a cone must also possess a low mass. Rigidity and low mass are essential combinations that allow the cone to respond quickly to movements from the voice coil without deforming. This requirement leads to another challenge, which is what material a cone is made of because both qualities can sometimes seem contradictory; lightweight materials may lack stiffness, and rigid materials can be heavy.

Materials Used for Loudspeaker Cones

At first glance, all loudspeakers may appear similar, and understandably, the average person might think they're universally interchangeable. However, loudspeakers are carefully designed for specific applications and purposes, utilizing particular materials to meet those needs. The material chosen for the cone is selected based on the intended use of the loudspeaker. For instance, a water-resistant material will likely be used if a loudspeaker is used in outdoor applications. A material with aesthetic appeal might be preferred if it's intended for a bookshelf loudspeaker.

Common Cone Materials:

Paper Cones

Paper is the most commonly used material for loudspeaker cones due to its excellent balance of lightness, rigidity, and internal damping. This combination allows for accurate sound reproduction with minimal distortion. Paper cones are made from a blend of wood and cotton (rag) fibers, bonded together with strengthening agents.

The fiber blend can be adjusted to fine-tune the mechanical properties of the cone. Longer fibers offer increased strength and flexibility, making them ideal for cones that handle a wide range of frequencies and larger movements, such as those in woofers. In contrast, shorter fibers create a stiffer cone, which can help reduce distortion in specific frequency ranges.

Polypropylene Cones

Polypropylene is a thermoplastic polymer widely used due to its versatility and durability. Polypropylene cones are particularly common in loudspeakers, especially in outdoor and car audio systems. This material is lightweight, moisture-resistant, and has excellent internal damping properties. While it may not be as rigid as some alternatives, polypropylene strikes a good balance for many applications. Its durability against humidity and temperature fluctuations makes it suitable for environments where loudspeakers might be exposed to the elements.

Metal Cones

Metal cones, made from materials like aluminum or titanium, are commonly used in high-performance loudspeakers, particularly for midrange and high-frequency drivers. Their high stiffness and low weight enable precise movement and accurate sound reproduction. However, metal cones can be susceptible to resonances, which manufacturers address through various design improvements. These cones are especially suitable for applications where rigidity is essential and flexing must be minimized.

Carbon Fiber and Kevlar Cones

Carbon fiber and Kevlar cones provide excellent stiffness-to-weight ratios and durability, making them ideal for high-end loudspeakers where performance is paramount. These materials enable precise sound reproduction with minimal distortion. However, their higher cost restricts their use to premium products. They are commonly found in select car and home audio systems that emphasize superior performance.

Acrylic-Treated Cloth and Synthetic Fabrics

Acrylic-treated cloth and synthetic fabrics are used in specialized applications requiring resistance to environmental factors. These materials are treated to withstand moisture, heat, and UV exposure, providing flexibility and durability. They are common in kiosk and drive-thru loudspeakers and some professional audio equipment where environmental resilience is necessary.

Material Selection Based on Application

The choice of cone material is crucial in loudspeaker design, as it significantly affects performance, durability, and suitability for various environments. Materials such as polypropylene or treated fabrics are preferred for outdoor loudspeakers because of their resistance to moisture and UV light. These materials help the loudspeakers endure environmental factors without sacrificing their performance.

High-frequency drivers, known as tweeters, require lightweight and highly rigid materials, such as metal alloys or specialized fabrics. This combination allows them to reproduce high frequencies accurately without distortion, as they can respond quickly to rapid changes in the audio signal.

Conversely, low-frequency drivers, or woofers, benefit from materials that can accommodate larger movements and provide effective damping. Materials like paper with longer fibers or composite materials are ideal, as they can displace more air to produce deep bass sounds while minimizing unwanted resonances.

The Right Cone for the Job

Knowing which cone is best for the application of a loudspeaker requires expertise and experience. Partnering with a loudspeaker manufacturer with a deep understanding of what cone and other components are needed for a reliable loudspeaker in your unique application will make your product stand out.

MISCO offers comprehensive engineering services and can conduct extensive testing on every design and manufacture of loudspeakers here in the United States. MISCO is also able to promise the delivery of reliable loudspeakers thanks to our superior design and stringent end-of-line testing. Additionally, MISCO has a complete catalog of off-the-shelf solutions to help our customers save time and money on their projects.

If you are looking for a new partner for high-quality, reliable loudspeakers, contact MISCO today. A member of our team can help find the right solution to meet the specific needs of your project.