Have you ever been listening to music and wondered how a loudspeaker can create sound? In this detailed article, using clear explanations and diagrams, I’ll explain how they work.
You’ll also learn:
- The parts inside a speaker
- Single cone vs coaxial speakers
- 2 way and 3-way speakers explained
- Speaker crossovers
- What speaker impedance, sensitivity, and frequency response mean
- First things first: What is inside a speaker?
- How do speakers work? Step by step explanation + animated diagram
- What does speaker impedance mean? (Speaker Ohm ratings explained)
- Why is a speaker enclosure needed?
- What is speaker frequency response and speaker sensitivity?
- What are coaxial speakers?
- What is a 2 way speaker? What is a 3 way speaker?
- What is a Bluetooth speaker?
First things first: What is inside a speaker?
A loudspeaker is sometimes called an electrodynamic loudspeaker because it changes electricity into motion via magnetic fields created from the musical electrical signal. A speaker driver is a single speaker assembly used to put together a speaker system.
What is inside a speaker?
Most speakers are made of the following parts that work together to create sound:
- Permanent magnet: A magnet is used to provide a fixed magnetic field surrounding the voice coil to make movement possible.
- Voice coil and bobbin: The bobbin is a round tube attached to the bottom of the cone. A very long and tightly wound wire coil, called the voice coil, creates a magnetic field as electricity flows through it from the musical signal from an amplifier.
- Spider or suspension: the spider is a wavy-shaped thin woven material that supports the voice coil bobbin assembly and helps push the cone back in place as it moves.
- Cone (diaphragm) & dust cap: this a cone-shaped stiff material that’s moved by the magnet & voice coil together to move air & create sound. The dust cap is a thin material (like a “cap”) that covers the opening in the center to keep out dust & dirt.
- Speaker basket: the basket is a cast metal or stamped metal frame that the speaker parts attach to an keeps everything aligned. It also provides a way to mount the speaker assembly to a box.
- Speaker terminals & braided wire: speaker terminals are metal tabs or connectors that connect speaker wire to the speaker. These connect to the voice coil using a flexible braided wire that moves with the cone.
- Surround: this is a flexible and durable circular material (usually rubber or some type of foam) that attaches the top edge of the cone to the basket.
What does a speaker cone do?
A speaker cone (also called a diaphragm) is the main speaker component responsible for creating a sound wave each time it moves air back and forth rapidly. These are typically made of lightweight but stiff materials like pressed paper, plastics, carbon fiber, or even thin metal.
The speaker “cone” name refers to its shape: an inverted cone shape with a central opening where the bobbin & voice coil assembly is attached. A dust cap is attached to the cone over this opening at the bottom to prevent contaminants from getting inside. These are both supported at the bottom by a stiff but flexible material sometimes called the “spider”.
The type and design depends on the speaker. For example, subwoofers produce very large bass sound waves and substantial air movement and need a thicker, more rigid design.
By contrast, tweeters use a very small, dome-shaped, and lightweight design for higher-frequency performance because this sound range uses smaller sound waves.
What does a speaker magnet do?
Loudspeaker magnets are usually a permanent magnet (usually a ceramic or neodymium type magnetic material) with a thin circular gap in which the voice coil is suspended. The magnet provides a stable magnetic field area that attracts or repels the voice coil.
Because the coil develops a magnetic field it’s a bit like an electromagnet in a way. Neodymium magnets are stronger for their size (denser magnetic fields) but ceramic magnets, while larger, are more cost-effective. That’s one reason why ceramic magnets are more popular for speaker use.
Some, but not all, speaker magnets have a hole in the center to help ventilate the voice coil and keep it cool.
What is a dual voice coil speaker?
Dual voice coil speakers offer a second voice coil winding in the same speaker and on the same voice coil bobbin assembly. These types of speakers allow some additional options that single coil speakers do not:
- Flexibility in how they’re wired (2 ohms, 4 ohms, 8 ohms, etc) for better compatibility with amplifiers and stereo receivers.
- For subwoofers or other larger speakers, you can power them with more wiring configurations or even 2 amplifiers each which you can’t do with single voice coil models.
- These can be driven with 2 channels from amplifiers that can’t be bridged for more power.
You’ll most often find subwoofers that are available in a dual voice coil version for a little bit more money.
While they offer more wiring configuration options, dual voice coil (DVC) speakers don’t offer better performance than their single voice coil (SVC) counterparts.
Additionally, speakers like tweeters for treble sound and midrange speakers for instruments & vocals aren’t normally made in a dual voice coil version.
Examples of two speaker bobbins with dual voice coils. Left: the two coils are not together while (right) on this example they’re layered one on top of the other.
How do speakers work? Step by step explanation + animated diagram
In this animated diagram, you can see how a loudspeaker works. A stereo or amplifier drives the speaker with an electrical signal that alternates from positive to negative in the shape of the musical signal.
As it does so, electric current flows through the speaker’s voice coil, creating a magnetic field that causes it to move toward or away from the magnet as it changes from positive to negative. This moves cone assembly that creates sound waves as the air moves rapidly. Speakers use alternating current (AC) that changes direction (polarity) just like sound waves in real life.
How do speakers work full diagram
A speaker (also referred to as a loudspeaker, a name from back in the day) uses an alternating current (AC) electrical power signal and are driven by a stereo or amplifier.
The electrical signal to the speaker is an amplified voltage that’s a duplicate of the original musical signal from an audio source but with enough power to drive the speakers with good volume.
Here’s a step-by-step detail of how speakers work:
- (Starting from the zero output point) An output voltage representing the musical waveform starts and begins to rise. The electrical current starts flowing through the speaker’s voice coil from the positive side to the negative side.
- A magnetic field is created around the voice coil and is the same polarity as the permanent magnet attached to the speaker basket (frame). (Remember that identical magnetic fields repel and opposites attract)
- The cone/diaphragm begins moving forward and creates air pressure, creating sound.
- As the electrical signal voltage rises towards the top of the sine wave in the musical signal, the current increases, and the voice coil increases its magnetic field strength.
- This pushes the cone out even further.
- The signal passes the highest output point and begins to fall. The current starts to fall also and the cone will begin to return closer to its off (zero voltage) position.
- The signal reaches zero (also called the “zero voltage crossover threshold”) and the cone is back where it started.
- The electrical signal begins to reverse as it changes to a negative voltage. When this happens, current flows from the negative voice coil side to the positive, creating a reversed polarity magnetic field.
- The voice coil magnetic field is now the opposite of the permanent magnet that attracts it and the cone begins to move from front to rear (instead of the original rear to front).
- As the signal continues the cone moves in reverse, creating the other half of the sound waves created by the movement of air.
- The amp or stereo output returns to zero and the next audio signal begins as the new signal output voltage starts to rise, with the cycle starting over again.
In a matter of speaking, speakers are just an electric motor of sorts: they are powered by an electrical signal and change it into a mechanical output: moving air to create musical sounds.
Occasionally speakers are referred to as transducers.
What does speaker impedance mean? (Speaker Ohm ratings explained)
Speaker impedance, measured in Ohms, is the total resistance to the flow of electric current through a speaker voice coil.
Unlike standard conductors, as the voice coil is tightly wound in a coil the makes this complicates things because it adds inductance. Inductance is different from resistance as it changes as the frequency changes and this is called inductive reactance.
In other words, when the magnetic fields of the voice coil are created they oppose the flow of electrical current a bit.
Because of the property of physics and how inductance works, the speaker “impedance” (total resistance) isn’t the sum of the resistance and the inductive reactance – it’s a bit more complicated than that.
Instead, it’s the algebraic sum (the square root of the sum of the squares) of each. Inductive reactance is commonly written as “Xl” and is measured in Ohms just like standard resistance.
Speaker impedance formula
If you like fancy math, you can see here how speaker impedance is calculated. It is the geometric sum of the resistance in the voice copper wire winding and the resistance caused by its inductance at a given frequency.
The most important thing to understand about speaker impedance is:
- The speaker impedance is always equal to or greater than the voice coil wire resistance. You can measure this with an Ohm meter.
- The impedance number on a speaker is a general guideline for compatibility, not exactly what the speaker measures.
- The impedance changes slightly (goes up) as the frequency being played increases.
In fact, if you were to use a test meter to measure the Ohms (impedance) of the voice coil on a speaker, you’d find a reading of about 3.2-3.6 ohms or so for a 4 ohm speaker and 6 ohms or higher for an 8 ohm speaker.
Image showing how to measure speaker impedance with an Ohm meter. This measures only the direct current (DC) resistance of the wire in the voice coil, not the total impedance of it with music playing due to inductance. however, it will be very close in most cases and you can tell the standard speaker Ohm rating (4 ohms, 8 ohms, etc).
Where did 4 ohm and 8 ohm speakers come from?
4 ohm speakers (and sometimes 2 ohm) are most commonly used for car stereo systems. The practice began long ago when radios and speakers were first installed from the factory when cars were built.
Because only a lower voltage (12V) is available to power them in cars, it’s more difficult to produce power for the speaker than it is for home stereos where plenty of voltage is available.
8 ohms is most commonly used for home stereo system speakers. Home stereos are powered by a higher voltage source (110V like in the USA) so they’re easier to design and can power higher impedance (8 ohm) speakers easily. In both cases these Ohm ratings became common for home and car speakers.
Why is a speaker enclosure needed?
A loudspeaker enclosure (“box”) is very important for several reasons:
- Keeping forward sound waves from interfering with and canceling the rear ones.
- Allowing low frequency bass sound to be produced properly, tuned, or enhanced.
- Dampening vibration from the speakers as they work.
- Directing how the sound is dispersed.
A speaker box (or “speaker cabinet”) is usually made from a thick material like wood or medium-density fiberboard (MDF) as they’re strong and don’t flex a lot. While a subwoofer or mid range speaker needs to be used in a sealed structure tweeters do not.
That’s because tweeters direct sound only towards the front and don’t produce sound waves towards the rear. In some cases (like for surround speakers) they may be smaller than the front (main) speaker cabinet pair.
What is speaker frequency response and speaker sensitivity?
What is speaker frequency response?
An example of a typical speaker frequency response graph is shown here. Speakers aren’t perfect and don’t produce a perfectly even volume over the range of sound we can hear. Because of that, it’s helpful to know the frequency range they perform well at.
Speaker frequency response is the measured performance of a speaker, in decibels (dB) of volume, over a range of sound frequencies. This is usually the 20 Hertz (Hz) to 20 kiloHertz (KHz) range used as the standard for audio speakers.
The 20-20kHz range is used because it’s the range of sound a human with good hearing can perceive and music is often recorded within.
Speaker frequency response is important for several reasons:
- Matching speakers together for 2 or 3-way systems
- Choosing the best performing speakers for an audio design
- Designing speaker systems and speaker crossovers
- Using audio equipment such as an equalizer or digital signal processor (DSP) to correct areas where the speaker produces too much (a peak) or not enough (a dip)
While some speakers include a graph or other specifications to help you understand how they perform, not all do. It’s something you’ll usually find from retailers who stock bare speakers for more advanced speaker design.
Most off-the-shelf car or home speakers don’t include the actual response graph but instead an approximate range instead. More expensive speakers may do so, however.
If you have the right equipment you can also measure it yourself at home using a real-time analyzer (RTA) program and a high-quality microphone for this purpose.
What is speaker sensitivity?
A speaker’s sensitivity is a measurement made by the manufacturer. It’s a measurement of the volume produced at a fixed sound frequency and (usually) with 1 watt of power is delivered to the speaker at 1 meter (3.28 feet) from the test microphone.
Speaker sensitivity is a manufacturer-provided specification useful for comparing or matching speakers. It’s a measurement of the volume produced, in decibels (dB), from a speaker at 1 meter (3.28 feet) from a test microphone for a single frequency.
The sensitivity parameter is usually expressed as “89dB @ 1W/1M” for example.
In most cases, the standard measurement is the dB volume at one watt of power at 1 meter distance and often a sound frequency like 1KHz (depending on the type of speaker) may be used.
Subwoofers tend to have a sensitivity around 87dB, midrange speakers around 89dB or so, and tweeters as high at 93-102dB depending on the type.
Sensitivity measurement differences
Sensitivity is sometimes measured slightly differently. That’s because a different voltage is needed for 4 ohm vs 8 ohm speakers to produce the same amount of power as the resistance in Ohms (speaker impedance) is different.
Therefore less current flows through an 8 ohm speaker, causing it to receive less power for the same voltage as a 4 ohm speaker.
In that case, a sensitivity of dB at 2.83V/1M may be used for 8 ohm speakers. At 2.83V an 8 ohm speaker develops 1 watt of power. Similarly, for 4 ohm speakers, a dB of 2V/1M may be used.
These measurements aren’t really standardized in the speaker industry, so the measurements provided by a manufacturer may be “1W/M” or “xV/M”, depending on what they happen to provide. When using this measurement to compare or match speakers it’s important to pay attention to this.
What are coaxial speakers?
Coaxial speakers are type of 2-way speaker designed to take up less space and to replace single-cone speakers. They usually include a separate tweeter and one or more crossovers built-in. Coaxial speakers provide improved sound over a single cone speaker and allow more pricing choices and installation options.
Coaxial speakers are 2-way speakers mounted on the same “axis” or in the same speaker assembly. Most coaxial speakers provide a full range cone and add a separate tweeter with crossover for improved sound fidelity & frequency response versus a standard single cone speaker.
Think of coaxial speakers as a middle point between single cone speakers (the most basic speakers, with mediocre or poor performance) and component speakers (separate speakers with an external speaker crossover). They offer good fidelity at an affordable price in most cases.
Coaxial speakers offer several advantages:
- Easy sound upgrade: they’re a drop-in replacement for existing poor-sounding single cone speakers.
- More speaker manufacturing options and price ranges for buyers (different levels of tweeter quality, crossover design, cone materials, etc).
- Somewhat similar performance to separate 2-way component speakers without the need for a bulky separate crossover box.
- They’re very common – in fact, they’re the most popular car speaker upgrade and they’re easy to find when shopping.
- Very affordable: good coaxial speakers can be found for around $25 and up per pair depending on the size & quality.
- Coaxial speakers can fix the poor frequency response (missing sound frequencies) you find with single-cone speakers.
Coaxial vs standard/single cone speakers
Coaxial speakers offer better sound performance than standard single-cone speakers, even those with a “whizzer” cone added to improve the treble sound. They provide a better frequency response because they add one or more cones (usually a tweeter) to produce the upper range of sound (treble, or “highs”) that a single cone usually can’t.
Coaxial speakers sound better
While some cheaper standard speakers may have a “whizzer” cone added, which is a small 2nd cone attached to the larger cone for improved treble, they’re still disappointing. I’ve yet to hear one that sounded very good.
Coaxial speakers, on the other hand, use at least one additional speaker (usually a tweeter) to make up the difference and produce crisper & better-sounding higher frequencies.
In fact, in all my years of car speaker installation work I can’t recall a single standard speaker that wasn’t good enough to keep vs replacing it with a coaxial model.
While factory-installed speakers are often very low cost, coaxial speakers – even for a nice sounding pair – aren’t expensive. You can get a great-sounding pair for $25-$30 or more these days and around $20 if you’re on an extreme budget.
What is a 2 way speaker? What is a 3 way speaker?
What is a 2 way speaker?
2 way speakers use a tweeter and separate woofer, working together, to create the full range of music reproduction. In this type of speaker system, tweeters are supplied only a high frequency sound from a high-pass crossover while the main driver is fed midrange and bass from the low-pass crossover. The result is a very clear & enjoyable sound.
2-way speakers are the most common low-cost speaker design in use today both for home and car stereos. They use a tweeter, receiving only higher frequencies from a high-pass crossover, and a woofer, receiving only bass & midrange sounds from a low-pass crossover, to produce a full range of sound.
In other words, they separate the sound you hear between two speakers for better results than a single speaker alone. This is done because woofers can’t produce higher frequency sounds well and should be prevented from producing treble frequencies.
Similarly, tweeters become distorted when attempting to produce bass or lower-frequency sounds. The use of a 2-way speaker crossover system limits the range of sound each receives, allowing for lower distortion and better sound quality at higher volumes, too.
How does a 2 way speaker crossover work?
2-way crossovers use electrical components to filter and split the electrical music signal from an amplifier or stereo and divide it between the tweeter and woofer, resulting in better sound.
The high-pass crossover blocks distortion-causing bass & midrange the tweeter can’t handle. Likewise, s low-pass filter blocks higher frequencies that a bass speaker cannot reproduce well and that would cause poor performance if used.
As the speakers play, the divided crossover output results in a complete full-range audio output that’s much better than what a single speaker could produce.
What is a 3-way speaker?
3-way speakers are an extension of 2-way speakers with the addition of a 3rd speaker using a bandpass crossover. The 3rd speaker allows improved midrange and even better sound production, lowered distortion, and clarity by offloading midrange sound to a dedicated midrange speaker.
However, the crossover design (depending on the crossover order, or the steepness of the cutoff) is more complicated for those with a sharper cutoff to block unwanted frequencies.
3-way speakers are less common due to the added cost & complexity but are a good choice for speaker builders and audiophiles who want more advanced performance. They also offer the option to get improved sound by using high-performance midrange speakers that are better suited to it than midbass models.
What is a Bluetooth speaker?
Diagram showing how a Bluetooth speaker works. Wireless speakers like this receive the audio signal in a digital format, convert it back to analog, and amplify then drive the loudspeaker inside.
Bluetooth speakers are essentially a portable sound system made up of a battery, an integrated wireless receiver and amplifier, and speakers. They connect to the BT wireless protocol to smartphones, TVs, and more. Music is streamed in a digital format to the receiver then converted back to the original signal before being amplified to power the speaker driver or drivers inside.
Because a battery is used to power them, they’re highly portable and are great when you don’t need a big stereo receiver or amplifier.