If you are new to car audio, I’m sure you’ve heard someone talking about voice coils or voice coil configurations. I know, personally, I have received multiple questions from individuals not familiar with car audio about voice coils, what they are, and what they do in terms of function.
In this post, I will try to answer some of the most common questions I have received about voice coils to help those who are still confused in regard to the speaker, or subwoofer, voice coil.
What Is A Voice Coil?
A speaker’s voice coil is a winding of copper, aluminum, or copper-clad aluminum wire that is wrapped (coiled) around a former, sometimes called a bobbin, that is attached to a speaker cone. The voice coil is what gives the speaker cone its movement by reacting to the magnetic field of the motor structure.
By sending current through a speaker or subwoofer voice coil, a magnetic field is created within the gap between the magnet structure and the voice coil. This reaction, as previously stated, causes the cone to move. Adding a waveform, as in music, the cone will react in such a way that it is able to reproduce the music or audio signal.
Because a speaker must move freely, and frequently, the components must be made in such a way that they are light-weight, but also strong enough to handle the abuse of possible distorted audio signals or louder-than-normal volume levels. In their design, voice coils must be constructed to be as light as possible, but there is a trade-off to this as well. Being light-weight, a voice coil is also pretty delicate. Applying too much current, or even a clipped (distorted) audio signal will damage the voice coil over time. It is a pretty thin line to balance when it comes to the construction and durability of a voice coil.
Most people get confused when they hear the term “power handling.” Power handling is not really how much power the speaker or subwoofer can handle, but more the heat resistance of the voice coil and its components such as the wire, wire insulation, adhesive, and former materials. Most subwoofers and speakers are designed with cooling features, such as heatsinks or pole-piece vents, that help to dissipate heat away from the voice coil, thus improving power handling. The way the voice coil sits within the magnetic gap can also help cool the coils as well.
Overhung vs. Underhung Voice Coils
A majority of voice coils today are known as “overhung” voice coils. This means that a portion of the voice coil is protruding from the top of the magnetic gap of the motor structure, while the remainder lives within the gap. This design feature not only allows for greater cone movement (Xmax), it also allows for adding cooling for the voice coil as a portion of it is not concealed within the gap. There is a drawback to overhung voice coils, and that is added mass. The larger coil winding adds mass to the voice coil’s weight making it slightly more difficult to move with the magnetic force. This leads to speakers that have lower sensitivity.
Another way speaker manufacturers construct their speakers is with an “underhung” voice coil. This means that the entire voice coil winding is below the top plate, completely within the gap of the motor structure. The shorter coil winding reduces overall voice coil mass, making the speaker’s sensitivity higher. In an underhung configuration, the voice coil can maintain constant electromagnetic force within the gap, but over a limited range of motion (less Xmax). The reason? The winding of the voice coil is shorter and if it is pushed past its “mechanical limit”, the voice coil can leave the gap causing greater amounts of distortion, and causing overheating of the coil.
Copper or Aluminum Wire?
In most speaker applications, the voice coil is wound with copper wire due to its ability to conduct current, and the ability to withstand higher amounts of heat. Copper is also used because it allows for an easily made, yet dependable, all-purpose voice coil at a fairly affordable manufacturing cost.
If a speaker manufacturer requires its speakers to maintain maximum sensitivity or extended higher frequency response, an all-aluminum wire may be used to lessen the overall moving mass of the voice coil. Aluminum wire has about a third of the mass of comparably sized copper wire but has only about 61% of the conductivity of the copper wire. In order for the Aluminum wire to have similar functionality and power handling to a copper wire voice coil, the cross-section of the aluminum wire coil must be at least 56% larger than that of the copper voice coil.
There are uses for both types of wire, and a speaker or subwoofer should not be judged because of one or the other. It all boils down to the use of the specific speaker and its overall design. There are pros and cons to each that should be considered when deciding which voice coil configuration, or construction, you should use in your car audio system.
Voice Coil Impedance
I’ve made a previous post about impedance and its definition, but in case you haven’t read my previous posts, here is a quick review. Impedance is the resistance of current through the voice coil. The lower the impedance, the more current can flow through the voice coil. For example, a 2-ohm voice coil will have less resistance than a 4-ohm voice coil. This translates into how much power your amplifier can feed into your speaker or subwoofer, but that’s another topic.
Voice Coil Configuration
Subwoofers can come in a multitude of voice coil configurations. This means the resistance of the voice coil (impedance), or number of voice coils, can vary depending on how the subwoofer is configured. For instance, subwoofers of the same manufacturer may come in a single voice configuration with varying impedances, or they may come with dual-voice coil configurations with varying impedances. While single voice coil subwoofers are easier to wire, subwoofers with dual (or multiple) voice coils offer more wiring options, making them a little more versatile when matching the subwoofer to an amplifier and its power handling capabilities.
I hope this article has given you some basic knowledge in regard to voice coils and their form and function within a speaker or subwoofers. For someone new to car audio, having this basic knowledge of a subwoofer, or speaker’s, voice coil should help you to understand exactly how a loudspeaker voice coil functions.
** Please note that this article provides general information on loudspeaker voice coils in a car audio system. Keep in mind that not all vehicles are the same and may require different installation methods and techniques to ensure a safe and effective install. By no means, am I a professional mechanic or car audio installer, and D4S and I, are not liable for any damages caused to your person or vehicle by following these instructions. Please consult a professional if you have any questions or concerns regarding your own vehicle and how to perform modifications such as the one explained in the previous statements.