Speakers have become commonplace in our day-to-day lives. Wherever there is electricity and electrical power, speakers can function (and often do).
Why do loudspeakers need power, and how are they powered? Loudspeakers require power if they have built-in amplifiers, active transducer elements, and/or built-in wireless receivers. Speakers and monitors requiring power typically get it from wall sockets (power mains), but some get power from batteries or specialized amplifiers.
In this article, we’ll discuss each of the reasons a speaker may require power, along with the powering methods necessary for getting these speakers their power. We’ll also describe the inherently passive nature of the speaker design and why speakers may not require power.
Related My New Microphone articles:
• The Ultimate Loudspeaker Buyer’s Guide
• Top 10 Best Loudspeaker Brands (Overall) On The Market Today
• How Do Headphones Get Power & Why Do They Need Power?
The Passive Loudspeaker
Yes, I know it's odd to start an article titled “Why Do Loudspeakers Need Power & How Are They Powered?” by stating that many loudspeakers do not even require power.
If we think about a speaker in its most basic form, we have a transducer that converts audio signals (electrical energy) into sound waves (mechanical wave energy).
The vast majority of loudspeakers use an electrodynamic type driver to convert audio into sound. This type of driver works on electromagnetic principles and is passive in design. It does not require power to function!
Let's have a look at an oversimplified cross-sectional diagram of an electrodynamic speaker driver:
In this speaker driver design, the audio signal (AC voltage) is applied across the voice coil, which produces a varying magnetic field in and around the coil.
The voice coil is attached to the speaker cone and is suspended in a cutaway in the magnetic structure. The spider suspension keeps the voice coil from moving in the X and Y axes.
This varying magnetic field causes the coil to oscillate back and forth about the Z-axis. The cone moves along with the coil and produces sound waves that effectively mimic the waveform of the applied audio signal.
All this happens without any power being applied to the system. Of course, the analog audio signal required to drive the speaker transducer is electrical by nature, but it is not truly considered as powering the speaker.
For more info on analog signals and speaker transducers, check out my article Are Loudspeakers & Monitors Analog Or Digital Audio Devices?
All that being said, only a portion of electrodynamic drivers are used in completely passive speaker constructions. There are plenty of speakers with electrodynamic elements that require power to function. Any electrodynamic speaker with a built-in amp or wireless receiver will need electrical power to produce sound.
The Active Components Of Speakers
We've already briefly mentioned the active components of speakers that require power to work.
Let's now list them out and discuss each individually in greater detail:
Built-In Speaker Amplifiers
The most common reason why a speaker requires power is that it has a built-in amplifier.
Amplifiers apply gain to the audio signal. This electrical gain comes from the source that powers the amp.
Note that all speakers require amplifiers to bring the line level signals of an audio playback system up to speaker level. It is the speaker level signals that can effectively drive the speaker transducers/drivers.
All amplifiers require power to function. So then, speakers with built-in amps require power to function properly.
Fully passive speakers will rely on an external amplifier to boost the audio signal level. This speaker level signal is then fed through the speaker's passive crossover network before driving the drivers.
Active speakers, on the other hand, generally have amplifiers built into their design.
This often includes the preamplifier, which feeds a line level signal into an active crossover network. Each of the active crossover network's frequency band-specific outputs is then boosted by its own dedicated power amps before driving its dedicated driver.
This process requires power (for the preamp and power amplifiers).
It's important to note that, although these active components are often designed into the speaker itself, they do not necessarily need to be. Active speakers, therefore, find themselves in a bit of a grey area when it comes to requiring power or not.
Then there are powered speakers, which are slightly different from active speakers.
Note that all active speakers are considered powered though not all powered speakers are active.
The powered speaker has the same signal path and gain stages as the aforementioned passive speaker. However, the preamp and power amp are positioned inside of the speaker. Therefore, all powered speakers require power to function properly.
Wireless Signal Receiver
If a speaker is inherently wireless, it requires power. This is because its built-in wireless receiver unit requires power. With the rise in the popularity of Bluetooth, wireless speakers have become very common.
The wireless receiver is designed to receive the wireless carrier signal (often in the radio frequency spectrum) and decode the audio (modulation signal) from it.
This requires power.
In addition to decoding the intended audio signal from the wireless device, the wireless speaker must also amplify the audio signal and sometimes separate the frequency bands via a crossover.
This, too, requires power.
Active Driver Type
Electrostatic loudspeakers often require power to charge up their transducer element.
Unlike the passive electrodynamic driver previously mentioned, the electrostatic driver works on electrostatic principles (hence the name) and requires a fixed charge on its diaphragm.
Electret material is often used in electrostatic headphones and condenser microphones.
To learn more about electrostatic headphones and condenser microphones. check out my articles The Complete Guide To Electrostatic Headphones (With Examples), What Is A Condenser Microphone? (Detailed Answer + Examples) and The Complete Guide To Electret Condenser Microphones.
However, the larger electrostatic speakers often opt for a separate DC-biasing power source to produce the fixed positive charge on their diaphragms.
To quickly go over how electrostatic loudspeakers work, the positively charged diaphragm is sandwiched closely between two perforated conductive metal stator plates that act as a sort of parallel-plate capacitor.
The diaphragm and stator plates are insulated from one another, and the driver is designed so that the diaphragm will not touch the stator plates.
A special amplifier boosts the audio signal well above the voltage necessary to drive a typical loudspeaker while dropping the electrical current way down.
This amplified signal is then applied across the stator plates.
At any given point, the stators will have equal but opposite electrical charges. Therefore, the positively charged diaphragm will be pulled toward one plate and pushed by the other at any given point.
This causes the diaphragm to move and produce sound. Since the stator plates are perforated, the sound can escape the driver and be heard by the listener.
Here is a simplified cross-sectional diagram of an electrostatic driver:
Loudspeaker Powering Methods
Loudspeakers can be powered via a power cable connected to the power mains, by batteries (internal or replaceable), or they may draw power via their connection to a digital device (i.e., computer speakers are often powered through the USB connection).
Powering Speakers Via Power Mains
Most stationary active and powered speakers will be powered via the power mains of your house, venue, etc.
These speakers include the surround sound system in home theatres and living rooms, studio monitors in studios, live sound speaker stacks in live venues, and etcetera.
When possible, it's often beneficial to connect these speakers to the same wall plug (either directly or via a power bar/conditioner) along with all the other audio equipment in the system. Doing so will connect all the audio equipment to a common ground and help tremendously to reduce the dreaded 50/60 Hz ground loop hum.
The Mackie MR824 is an 8-inch studio monitor that is powered via the power mains.
The Electro-Voice ELX200 is a 10″ powered loudspeaker. It, too, gets its power from the power mains.
Powering Speakers Via Internal Batteries
Modern wireless speakers will typically be powered via internal rechargeable batteries.
The JBL Charge 4 is a Bluetooth speaker with an internal rechargeable battery.
Powering Speakers Via Replaceable Batteries
Some portable speakers can be powered via replaceable batteries.
The Philips SBA1710 is an example of a portable speaker powered via replaceable batteries (2x AA).
Powering Speakers Via Digital Cable
Some computer speakers will have their internal amps powered via the digital connection they make with the computer.
With USB, for example, +5 VDC is carried on pin 1 and can be used to power the connected speakers.
The Creative Labs Pebble USB are computer speakers that get their power via USB. They receive power from the same USB cable that sends the digital audio from the computer to the speakers.
Note that they also have a 3.5 mm stereo plug for audio, but this connection will not supply power.
How do wireless Bluetooth speakers work? Bluetooth speakers receive their intended digital audio signals via the Bluetooth protocol (pulse-shift keying modulation on RF carrier waves between 2.400 to 2.485 GHz). The speaker's built-in components then convert the digital audio to an analog signal; crossover the signals if necessary; amplify the signal(s) and send them to the drivers to produce sound.
Which is better, 4-ohm or 8-ohm speakers? All else being equal, speakers with lower impedance will require more power to produce the same sound pressure level and are usually reserved for high-power or hi-fi amplifiers. However, there are many other specifications and subjective listening that determine the quality of a speaker. Therefore, it is false to state that all 4-ohm speakers are better than their 8-ohm counterparts.
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