How do speakers work
The principles of speaker driver technology haven’t changed in close to a century despite substantial breakthroughs in speaker design and manufacturing.
Almost every loudspeaker on the market today, from your phone to your home theater system, uses Edward Kellogg and Chester Rice’s 1925 dynamic driver.
However, how do speakers actually operate?
Let us begin with the fundamentals.
How speakers work: the basics
A loudspeaker’s driver is the basic electroacoustic component that enables it to perform its function.
When used as a transducer, its job is to convert one kind of energy into another.
To put it another way, this transducer converts the amplified electrical waves from your playback device, be it your phone or the cartridge of your turntable, into sound pressure waves in the air for your ears to hear.
The speaker’s driver is an electromagnetic motor, which is both simple and effective.
The rear of a speaker has two terminals where an amplifier sends a signal.
They connect to a cylindrical coil of wire suspended in the space between two permanent magnet polarities, where the current flows.
Faraday’s law dictates that this coil swings back and forth within the magnetic field as the current going through it alternates in direction with the signal provided.
One end of the speaker cone is connected to the moving coil, which moves the cone back and forth.
An airtight surround or suspension holds this cone in place around its perimeter.
When the cone moves, it exerts pressure on the air around it, causing sound waves to be generated.
It’s a fact that the speaker driver is positioned in a box, but why?
What’s the point of having a box if the driver can produce sound on its own?
What about the little details like portholes and the like?
Why are speakers mounted in boxes?
When the cone of a speaker driver moves, a pressure wave is generated from the front and the back.
There is a positive and negative pressure created by it as it travels towards you while pulling back the air.
Pressure generated by the driver’s two sides will effectively cancel each other out when the wavelength of the replicated signal is large compared to the driver’s size.
As a result, low frequencies (bass) are rendered inaudible at any practical distance.
Remove a driver from its enclosure if you wish to give this a go at home.
After the speaker is disassembled, you’ll hear a “tinny” sound.
Keeping the pressure wave from the back of a speaker cone from cancelling out the wave from the front is critical to ensuring that the speaker works at all frequencies
Because of this, you can create the similar effect by mounting the driver in an extremely big and hard sheet of material (a baffle).
Because a wide baffle is required to prevent low-frequency cancellation, this isn’t an option in the majority of cases.
Closed boxes make it easier to accomplish this.
Mechanical features of the driver and box size combine to determine a closed-box loudspeaker system’s low-frequency response.
The air in the box acts like a spring against which the cone pushes and pulls, and that system has a resonance frequency below which its output diminishes significantly..
Loudspeakers must be airtight to prevent cancellation, which can occur if there are any leaks in the box.
Why do some speakers have holes in them?
In the front or rear of many speaker boxes, you may observe circular apertures or slots.
What you’re looking at is a bass reflex enclosure, which has ports or vents.
When you blow air over an open beer bottle and a note is heard, a bass reflex enclosure operates in the same way.
Because the volume of air inside the bottle fluctuates with the amount of liquid in the bottle, the note changes.
The scent would be altered even further if the bottle’s glass neck could be stretched
If you want to fine-tune the sound of your bottle, you can change its port dimensions (the bottle’s neck) or its enclosure volume.
For systems that are properly tuned, this results in an additional boost in low-frequency performance immediately below the loudspeaker response rolloff point.
As previously said, this requires custom port tuning for every single driver and enclosure combination.
Even if the cone diameter of the new driver is the same as the old one, the box and port tuning will no longer be acceptable and the sound will be distorted.
Same idea, but with a mass-loaded, unpowered speaker cone providing bass resonance with enclosed air volume in passive radiator loudspeakers.
Tweeters and woofers
Now, you may have observed that most loudspeakers include more than one speaker driver—usually a smaller diameter one on top of a larger one—especially when they go larger than small portable boom boxes.
Multiple drivers of various sizes are used in speakers for a variety of reasons.
One driver may be capable of covering practically all the audible frequencies, but it has a number of drawbacks.
The bass will be difficult to hear if the driver is too small because it won’t be able to move enough air to do so.
Larger drivers can move more air, but as the frequencies they reproduce rise, speakers become more directional.
Beaming is a term for this.
Frequency and wavelength are directly proportional to each other, and speaker drivers typically begin beaming at a frequency equal to their cone’s diameter.
As a result, the higher frequencies can only be heard if you’re directly in line with the speaker.
It’s not a nice speaker or a balanced sound.
There is a simple solution to this problem: a variety of drivers in varying sizes, each tuned to a specific frequency range (bass and treble, or bass, middle, treble).
A crossover is a frequency splitting network in the speaker box that works in conjunction with this notion
High-frequency drivers are assigned to tweeters and low-frequency drivers to the crossover.
Why it’s worth knowing how speakers work
There is no need to know how speakers work to appreciate their music.
It’s usually a good idea to learn about audio equipment before you invest a lot of money on it.
It’s easier to spot charlatans when you have a firm grasp of the fundamentals on which to build your understanding.
Additionally, understanding how speakers function might aid in the diagnosis of issues.
Also, if this article has piqued your interest, there are numerous web places where you may discover how to make your own using widely available components.