Without drivers, speakers would be incapable of producing sound. These transducers effectively convert audio signals to sound waves, allowing us to hear a sonic representation of audio.
The size of each driver is a determining factor as to how well the speaker will perform.
What is a good driver size for a loudspeaker? The proper size of a loudspeaker driver is determined by its role in the speaker system. A subwoofer should be relatively large (typically 8″ or more), while a tweeter should be relatively small (typically 1″ or less). Mid-range woofer driver sizes are usually over 2″ and are design-dependent.
So there's no one-size-fits-all answer. In this article, we'll discuss how different speaker driver sizes are preferred for different tasks within a speaker system in an attempt to answer, “What is a good driver size for a loudspeaker?”
What Are Loudspeaker Drivers & How Do They Work?
Loudspeaker drivers work as transducers, converting electric energy (audio signals) to mechanical wave energy (sound waves).
As a side note, speaker drivers are notoriously inefficient and lose a lot of energy as heat.
To learn more about speaker efficiency, check out my Full Guide To Loudspeaker Sensitivity & Efficiency Ratings.
Though there are other types of speaker drivers (electrostatic, magnetostatic, ribbon, etc.), the majority of speaker drivers are “dynamic”. They are built with a voice coil suspended in a magnetic structure and work on the principle of electromagnetic induction.
Here is a simplified cross-sectional illustration of such a speaker driver:
So, the speaker driver is this entire device. As we'll get to momentarily, an individual loudspeaker can have multiple drivers (and many do). First, though, let's discuss how a dynamic speaker driver works.
The process “begins” with an amplified audio signal travelling through electrical lead wires to the voice coil in the speaker.
The AC audio signal passing through the voice coil creates an alternating magnetic field due to electromagnetic induction.
A magnetic field is created when there is an electrical current passing through a conductor. Since the signal current is alternating, the magnetic field experienced by the coil is also alternating.
The voice coil is attached to the speaker cone and is suspended within a magnetic structure. As the coil experiences an alternative magnetic field, it will oscillate within the permanent magnetic structure, thereby mimicking the shape of the audio signal.
The diaphragm/cone will move with the voice coil. The movement of the diaphragm creates air pressure changes through the pull and push motions. Changes in air pressure at the speakers propagate sound waves through the medium that interact with the environment and eventually reach our ears.
The diaphragm size and the size of the driver play a role in determining the optimal frequency response and maximum sound intensity level the driver will produce.
To learn more about speaker drivers, including the alternative types, check out my article What Are Speaker Drivers? (How All Driver Types Work).
General Speaker Design
There are plenty of speaker designs on the market. Some use a single driver (many subwoofers, for example), while others use a variety of different-sized drivers (floor-standing hi-fi speakers, for instance).
When it comes to the most general speaker designs, drivers are often described by the frequency bands they produce. As was discussed previously, driver size is a factor in frequency response.
Let's consider 5 speaker driver types:
- Subwoofer: largest—for very low frequencies
- Woofer: large—for low frequencies
- Mid-range: mid-sized—for mid-range frequencies
- Tweeter: small—for high frequencies
- Super-tweeter: smallest—for very high frequencies
Subwoofer drivers tend to require larger enclosures to produce the lowest frequencies and are, therefore, most commonly found as separate units.
The KS118 is a direct-radiating 18-inch subwoofer that has a 3600-watt Class D amplifier module.
Its frequency response (to -10 dB) is from 35 Hz to 111 Hz, with an adjustable crossover that allows the user to define the high-end roll-off. It's capable of producing a whopping 136 dB @ 1 m (peak) maximum sound pressure level.
Other speakers will often have some combination of the remaining 4 driver sizes/types.
2-way speakers typically have a woofer and tweeter; 3-way speakers typically add a mid-range driver to the design; 4-way speakers will often include a super-tweeter.
Note that some drivers may be doubled-up, tripled-up (or more) in a given loudspeaker design.
Let's consider examples of 2-way, 3-way and 4-way speakers.
The NTi A3 is a popular bookshelf speaker from Polk Audio. This 2-way speaker has a 1″ dome tweeter and a 6.5″ woofer.
The Dynaudio Evoke 50 is a popular 3-way Hi-Fi floor-standing speaker from Dynaudio. It has 4 drivers:
- 1-1/8″ Cerotar coated silk soft-dome tweeter
- 5-1/2″ Esotec+ MSP (Magnesium Silicate Polymer) cone midrange
- dual 7″ Esotec+ MSP (Magnesium Silicate Polymer) cone woofers
The Quested HM415 is a high-end, high-price, large-format 4-way monitoring system with a built-in amp and crossover. It features 7 drivers:
- 4 x 15″ bass woofer
- 1 x 8″ low-mid woofer
- 1 x 3″ high-mid tweeter
- 1 x 1.5″ high tweeter
Coaxial speakers will have 2 or more drivers designed on a single axis, while standard/component speakers will have their drivers separated.
The JBL GTO629 is an example of a 2-way coaxial speaker with a 6.5″ woofer and 1.5″ tweeter. It offers a frequency response of 53Hz-21kHz and a power rating of 180 watts of peak power (5W-125W RMS).
Speaker crossovers effectively split incoming audio signals into separate frequency bands and assign the bands to their proper drivers.
Note, too, that an amplifier is needed to amplify the audio signals to speaker level in order to drive the speaker drivers properly. The amp can be designed within the speaker itself (active/powered speakers) or as its own separate unit (to drive passive speakers).
This is a basic but adequate discussion on loudspeaker design for this article.
For more information on the topics I touched on in this section, check out the following My New Microphone articles:
• Differences Between Mid-Range Speakers, Tweeters & Woofers
• Why Do Loudspeakers Need Enclosures?
• Complete Guide To Speaker Power Handling & Wattage Ratings
• What Is A Speaker Crossover Network? (Active & Passive)
• What Are The Differences Between Passive & Active Speakers?
• Why Do Speakers Need Amplifiers? (And How To Match Them)
The Best Driver Sizes For Loudspeakers
Drivers are essential components of loudspeakers, allowing for the conversion of audio to sound. As a rule of thumb, loudspeakers should be equipped with two or three drivers to convert the broadest range of frequencies possible.
Since no known driver can optimally reproduce frequencies across the entire human hearing range, it's common to find three drivers in a single loudspeaker.
Once again, a crossover is used to split these signals between the three drivers without causing any delay in the transmission.
What Are The Frequency Ranges Of Each Driver Size?
Individual loudspeaker drivers are designed to handle different frequencies. For better sound transmission, there should be a balance between high, medium, and low frequencies.
To understand how they all work, it's best to look at the frequency each driver can handle without exerting too much pressure on the speaker. Of course, these “types” of drivers do not all share the exact specifications.
The exact size and performance of the driver are dependent on more than just its size. That being said, the following generalities hold true in most situations. Mind the overlap as the speaker-specific specifications vary greatly:
- ≥ 8″ diameter
- ≤ 100 Hz
- 5″ – 12″ diameter
- 20 Hz – 2 kHz
- 2″ – 8″ diameter
- 150 Hz – 5 kHz
- ≈ 1″ diameter
- ≥ 2 kHz
- ≤ 1″ radius
- ≥ 10 kHz
An adequate loudspeaker should have at least two drivers installed, i.e., the tweeter and the midrange or woofer driver. In most cases, loudspeakers come equipped with all three.
Subwoofers are made especially for low-frequency reproduction and often only have large subwoofer drivers.
Do Bigger Magnets Mean Better Speakers?
As a whole, magnets are crucial to how sound waves are produced through [dynamic/moving-coil] speakers. As a result, bigger and/or stronger magnets help to create louder sounds.
The electric current that travels to the voice coil charges the entire area, which creates an electromagnetic field. An opposing magnetic field is required to help move the speaker's cone, which is achieved by a magnetic structure. When the two magnetic fields oppose and attract, they create vibrations and, ultimately, sound.
A larger magnet creates a more opposing magnetic field, which will generate greater excursion of the speaker diaphragm/cone and more sound.
Of course, the size and strength of the magnet should be appropriate for the driver's size. Tweeter drivers have smaller magnets compared to bass or mid-bass drivers since they're more delicate by design and are only meant to produce high-end frequencies.
So the answer to “Do bigger magnets mean better speakers” is “not necessarily”.
The size of the magnet is less important than its magnetic strength, and the magnet's strength must be appropriate to the driver's purpose in the speaker/sound system.
For more information on magnets and loudspeakers, check out my article Why And How Do Speakers Use Magnets & Electromagnetism?
What Is A Good Driver Size For Headphones? The best driver size depends on the design of the particular headphones. Earphone drivers are usually 8mm – 15mm in diameter, while headphone drivers are typically 20mm – 50mm. A larger driver produces stronger sound waves (particularly in the bass/sub-bass), but this doesn’t mean they sound better.
Related article: What Is A Good Driver Size For Headphones?
What are the differences between large-diaphragm condensers (LDCs) and small-diaphragm condensers (SDCs)? LDCs generally have a diaphragm diameter greater than 1″ while SDC diaphragm diameters are typically less than 1/2″ (this means there’s a grey area in between). LDCs are often quieter and have more character, while SDCs benefit from more accurate/consistent frequency, transient, and polar responses.
Related article: Large-Diaphragm Vs. Small-Diaphragm Condenser Microphones
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