How Do Speakers Work?

Speakers are electronic devices that convert power signals into sound. Invented by Chester W. Rice and Edward W. Kellogg in 1925, speakers allow us to hear the different audio files we have, including music, movie dialogues, radio channels, and TV series. Speakers come in various forms. Some are tower speakers, bookshelf speakers, in-wall speakers, ceiling speakers, and car speakers. Your typical pair of headphones or earphones are speakers, as well, although they are tinier versions that allow you to use them directly for your ears. But, how do speakers work? This article aims to discuss speakers’ physics, permitting you a simplified window into the workings of your most essential music accessory.

Despite their vast technological advancements, modern speakers still have the same primary attributes as their first ancestor. A dynamic audio driver’s idea is still the primary basis of all modern speakers’ immediate development and function, as we will see later in this discussion. Hence, that tiny wireless earbud in your hands and the huge booming box in your home studio system have the same main attributes that permit you to enjoy your favorite playlist and movies. They also allow you to hear the other person when you’re chatting over the phone.

What are the Parts of a Speaker?

Before we discuss how these exemplary devices work, let’s start with the parts of your speaker. What goes where, and what are their functions?

How Do Speakers Work?

Now that we know the different parts of this sound device, we need to know the speakers’ specific physics. How do speakers work? How do they produce sounds?

As mentioned, speakers work by their conversion of an electric current into motion or mechanical energy. The mechanical energy produced compresses the air inside the speaker and converts it into sound pressure level (SPL)—or sound, in simple terms.

As electric current passes through a specified coil wire, it encourages the buildup of a magnetic field. Inside a speaker, the electric energy that passes through the provided voice coil allows the said voice coil to produce an electric field that then communicates or interacts with the magnet’s magnetic field incorporated in the device.

In electricity, you need to know that like charges get to repel each other while dissimilar ones attract each other. So, when a sound signal goes through the voice coil, the waveform vibrates or goes up and down, causing the voice coil to be repelled and attracted by the magnet.

Consequently, the cone upon where the voice coil is placed gets to move back and forth. The corresponding back-and-forth movement develops pressure waves which we, then detect as sound waves or sounds.

How Does Sound Work With Speakers?

As we said, the cone’s back-and-forth motion develops pressure waves that we get to recognize as sound waves. Sound travels via pressure waves. When the particles in the air move and vibrate, they also move the particles beside them. This phenomenon allows sound to travel further through its designated medium. So, the faster the air pressure gets to change, the higher the sound frequency as well. The back-and-forth movement of the speaker’s cone pushes the air particles that then alter the air pressure and develops the sound waves we get to discern.

What does Speaker Impedance Mean? (Speaker Ohm Ratings Explained)

When reading about speakers and their specific features and functions, you typically encounter the term impedance. What does it mean, and how does it impact your speaker?

Impedance, which is symbolized as Z, refers to measuring a given circuit’s opposition to an electric current. In short, it refers to how much a circuit gets to fight against the charge flow. Concerning the speakers’ physics, impedance—rated in Ohms—originates from the speaker’s voice coil wire’s resistance and its resulting inductance created by being winded into a coil. The inductance created also contributes to resistance or impedance, which then depends on the level of frequency that travels through the voice coil. In general, speaker impedance is obtained from being a resistor (R) and an inductor (L). In simple terms, speaker impedance is the overall resistance to the electric current that travels through the equipment’s voice coil.

Because the voice coil wire is wound into a tight coil, the resulting structure produces inductance. Inductance refers to the electromotive force caused by the wire circuit generated due to the change in the electric current flow, as in the voice coil wire being wound into a coil. Inductance and resistance are different from each other—the former gets altered parallel to the frequency level and is termed inductive reactance.

This means, then, that the created magnetic fields of the voice coil resist or oppose the flow of the electric current provided.

As we look further into the physics of speakers and the specific workings of inductance, the speaker’s overall resistance or impedance isn’t as simple as the total computation of resistance plus inductive reactance. As it happens, it’s computed as the algebraic sum, square root of the sum of the squares—of each separate value. In the physics of speakers, inductive reactance is typically symbolized as Xl. It is rated in Ohms, as well, which is not unlike standard resistance.

To explain much further, measuring speaker impedance requires you to generate the geometric sum of the resistance produced by the voice coil wire winding and the separate resistance produced due to its inductance at a provided frequency level.

Nevertheless, if all these mathematical formulas and scientific verbose are starting to confuse you, you merely have to remember a few things:

• Your speaker’s impedance is either greater than or equal to its voice coil wire resistance. This phenomenon can be conveniently measured via an Ohm meter.
• While most speakers are provided with an impedance rating written on their packaging, usually included in its blurb, it’s just an intelligent estimate to be used for compatibility purposes. It doesn’t precisely offer your speaker’s exact impedance level.
• Your speaker’s impedance level fluctuates—it can go up or go low a bit, depending on the frequency levels of the audio that gets played. This means that if you’re more into high-frequency audio files, your speaker’s impedance level increases. If you tend to listen to low-frequency sound files, your speaker’s impedance decreases.

Using a test meter would show you that your speaker’s voice coil Ohms is much higher than its provided impedance rating—an 8-Ohm speaker may have an actual rating of 14 Ohms, and 4-Ohm one may have a real-time rating of 7.2 or 7.6 Ohms.

Frequency Response: Why is it Important?

When discussing the physics of speakers, it is also essential to look into the frequency response feature. Why is it so important to know this?

The speaker frequency response refers to measuring a speaker’s performance level concerning a given frequency. This element is measured by Hertz (Hz). Your speaker’s frequency response range refers to the frequency coverage—the levels of frequency that your device gets to detect and reproduce, allowing you to hear such volumes—measured by decibels (dB)— distinctly.

Humans typically get to detect a frequency range of 20 Hertz to 20 kiloHertz (kHz). Subsequently, many speakers tend to have a more comprehensive frequency response range. Some are indicated to have 17 Hz to 35 kHz, while others even have a wider coverage. Most, however, have the same standard frequency response range of 20 Hz to 20 kHz, which is already a superb coverage considering that it sufficiently matches our own. As it happens, most audio files are recorded in this specific frequency range, as well.

It is crucial to know your speaker’s specific frequency response range for the following reasons:

• You get to match various speakers in two- or three-way systems.
• You get to opt for the best speaker based on audio frequency coverage, thereby getting excellent sound quality.
• This measured estimation allows you to design or formulate your speaker system or speaker crossover—an essential skill, especially for audio technicians and hobbyists.
• You get to appropriately correct your system’s audio performance when purchasing the proper digital signal processor (DSP) or equalizer, allowing you to get your needed peaks or dips.

Nevertheless, not all speakers are provided with detailed graphs and explanations of the specific performance levels. You can most often obtain adequate information from reliable retailers who cater to more advanced speaker designers and usually stock naked or bare speakers.

Likewise, many of those off-the-shelf, generic speakers do not provide you with precise frequency response range measurements in their accompanying literature. Most of them merely offer rough estimates. Some high-end alternatives, however, give you correct frequency response coverage numbers. Nevertheless, if you want to get into the physics of speakers, you can also obtain the proper equipment to measure your speaker’s precise frequency response range. You can get a real-time analyzer (RTA) plus a top-quality mic to measure this.

With your speaker’s frequency response range is its sensitivity rating. Sensitivity rate refers to your speaker’s capacity to produce sound at different volume levels. This element is measured in decibels (dB), as already mentioned above. In plain terms, this refers to the loudness that your device is capable of. It is essential to know this specifically when you’re attempting to compare a couple of speakers for their corresponding performance.

Sensitivity rating is different from one speaker to another. Tweeters vary in performance level, as well. They are considered efficient when they are capable of producing more audio at a provided level of power. You also need to know that subwoofers require more power to move a heavier cone to produce adequate sound.

When purchasing speakers, you need to remember that tweeters—treble speakers—get to produce a sensitivity rating of 93 to 102 dB, midrange ones offer 89 dB or more, and subwoofers provide an estimate of 87 dB.

Why are Speakers Mounted in Boxes?

As we further elaborate on the physics of speakers, we also necessitate a brief discussion of why speakers are mounted in boxes. We already know that as soon as your speaker driver’s cone begins moving, it gets to create pressure waves, both at its front side and from its backside. As this pressure wave travels forward, it also pushes the air particles, which produces positive pressure. This particular movement simultaneously creates negative pressure as it pulls the air particles at the back.

Thus, if the entire wavelength corresponding to the echoed signal’s frequency larger than the driver—or its designated size, then the pressure produced at both sides of the driver will negate each other. If this occurs, the bass response—the low frequencies—becomes inaudible. You can effectively check this phenomenon out—remove your driver from its provided encasement, and you’ll notice that the sound produced is noticeably smaller or less in quality as compared to when the driver is encased in its box.

So, to effectively avert the canceling out between the pressure formed at the back of the driver and the one created at its front, you should place the driver inside a large and sturdy enclosure. Hence, closed encasements or boxes are needed to prevent bass cancellations. To be more specific, your speaker’s box must be airtight, as well, to hinder such low-frequency negation.

Conclusion

In reality, it isn’t a downright necessity to go far deep into the physics of speakers. Nevertheless, suppose you want to purchase the best speaker currently available in the market. In that case, it is better to have a bit of knowledge about its different features or parts and their corresponding functions. Knowledge, they say, is power, and understanding your speaker’s intricate workings allows you to decide how to improve its usage or even opt to replace it based on your newfound speaker comprehension.

While a speaker’s primary function is to produce audible sound, it is also far better to obtain a speaker that allows you to listen to various audio files irrespective of their specific frequencies and your preferred loudness. An efficient speaker must reproduce whatever kind of audio performance you want, allowing you vast enjoyment as you sit back and finally rest for the day.

Hence, this physics of speakers’ narrative is merely a guide that solely aims to provide you with added knowledge about the different basic functions of a speaker’s various parts, enabling you to choose what best works for you and your intended speaker usage.

While most manufacturers would tell you that their speakers could provide you with top-quality audio performance, you need to bear in mind that such promises do not necessarily reflect actual aftersales reality. A lot of these speakers found in various audio equipment stores are of the generic, off-the-shelf kind. Many of them merely provide you with rough estimations of their impedance rating, frequency response range, and sensitivity rating. 

By knowing the essential workings of these functions, you get to have an appropriate and educated estimation of each speaker’s actual ratings and performance level. If at all, knowing more about these functions permits you to identify a speaker that’s genuinely worth investing in.