How Do Small Speakers Produce Bass Frequencies?


Large subwoofers can really make us feel the bass frequencies of music and sound but smaller speakers may surprise us with the amount of perceived bass they are capable of producing.

How do small speakers produce bass frequencies? Small speakers are generally less capable of producing bass frequencies than larger speakers, though several techniques allow small speakers to produce notable bass. Enclosure design, speaker throw, passive radiators and digital-signal processing may improve bass response in small speaker designs.

In this article, we’ll go through the various techniques that speaker manufacturers use that allow their smaller speakers to produce remarkable bass frequencies.

Related article: Do Headphones Have Subwoofers & How Do HPs Produce Bass?


What Are Bass Frequencies?

Before we get started, let’s define bass frequencies.

Bass frequencies are at the lower end of the audible range of human hearing (20 Hz – 20,000 Hz).

Though there is no set standard for the frequency bands of sound and audio, the bass ranges can be loosely described by the sub-bass and bass ranges below:

  • The sub-bass frequency range is often defined as 20 Hz – 60 Hz
  • The bass frequency range is often defined as 60 Hz – 250 Hz

Bass frequencies are perceived, in musical terms, as having lower pitch.

They also have longer wavelengths than mid-range and high-end frequencies. The lower the frequency, the longer that wavelength.

The relationship between sound frequency and wavelength is defined as:

f = v / λ

Where:
f is the frequency of the sound wave
v is the velocity of sound within the medium (typically air for human hearing)
λ is the wavelength of the sound wave

More information can be found on the frequency-wavelength relationship in the graphs and writing of my article The Fundamental Frequencies Of Musical Notes In A=432 & A=440 Hz.

Before we begin our discussion of small speakers and bass response, it’s also critical to understand that humans do not hear all frequencies equally.

In fact, we have a rather coloured hearing response that is most sensitive between about 500 Hz and 6 kHz. Though we are capable of hearing low-end bass frequencies, we have a much harder time hearing them than the mid-range frequencies. We actually feel low-end frequencies more than we hear them.

Our frequency-specific hearing is described in the Fletcher-Munson curves, pictured below:

Fletcher-Munson Curves

Without getting too far into the study of acoustics and psychoacoustics, let’s recap what we now know about bass frequencies:

  • Bass frequencies are perceived as having a lower pitch.
  • Bass frequencies have long wavelengths.
  • We do not hear bass frequencies as well as we hear mid-range frequencies.
  • We tend to feel bass frequencies more than we hear them.

With these facts about bass sound frequencies fresh in our minds, we have a great framework to begin our discussion on small speakers and their bass responses.


Size Matters… Usually

Generally speaking, and all else being equal, larger speakers are more capable of producing bass frequencies than smaller speakers.

This is why subwoofers (designed to produce low-end frequencies) are notably larger than tweeters (designed to produce high-end frequencies).

But why is this the case?

Let’s take a 40 Hz bass frequency as an example. We could send this 40 Hz sine wave audio frequency to a tweeter and a subwoofer. The tweeter and the subwoofer would, in theory, vibrate back and forth 40 times per second and produce the bass frequency.

So far so good.

However, just because two speakers are both capable of vibrating at a relatively low frequency, doesn’t mean we’ll hear the low frequency as having the same amplitude.

The perceive level of the bass has to do with the amount of air the speaker is capable of moving. More air movement means the sound waves will have higher sound pressure levels and will be perceived as being louder.

We must consider the area of the speaker diaphragm and the excursion of the diaphragm when calculating the amount of air and, therefore, the loudness of the sound waves a speaker is capable of producing.

With all damping and inefficiencies aside, larger speakers will require less excursion (vibrational movement) to produce the same volume of sound because their areas will push more air. Smaller speakers require more excursion (vibrational movement) to produce the same volume of sound.

But why does this apply to bass frequencies, in particular?

Well, as we’ve mentioned in the previous section What Are Bass Frequencies? human hearing is not very sensitive to bass frequencies. In order to effectively hear bass frequencies, the amplitudes of the low frequencies must be relatively high (compared to the mid-range range frequencies our ears are “tuned” to hear with greater clarity).

When it comes to pushing a lot of air at low frequencies, large speakers are preferred.

Large speakers are typically designed to have longer throws (the maximum amount of possible excursion). Larger excursions are practical in the design since the diaphragms are larger. In other words, a large speaker can move to-and-fro more than a smaller speaker while simultaneously oscillate through a shorter distance relative to its diaphragm diameter.

So larger speakers, generally speaking, have the capacity to push more air than smaller speakers due to their increased area and their greater excursion limits.

Subwoofers, which are designed to produce bass frequencies, have larger surface areas and longer throws then mid-range woofers and tweeters. The increased sound pressure level is required to produce perceived bass.

So larger speakers more equipped to handle bass frequencies though it does not necessarily mean that a larger speaker will produce more bass than a smaller speaker.

All this is to say that small speakers can produce bass frequencies but large speakers are preferred.

Small speakers, conversely, are preferred when producing high frequencies. This is because it is easier to vibrate them very quickly (remember the upper end of human hearing is 20,000 Hz) with a more accuracy and less power.

With that in mind, let’s have a look at the ways in which small speakers can produce impressive amounts of bass.


Speaker Excursion

Speaker excursion refers to the displacement of the speaker’s diaphragm or the amplitude of the speaker’s movement.

As discussed, speaker excursion is one factor when it comes to the speaker diaphragm pushing air. All else being equal, a greater excursion means the speaker will push and pull more air and produce louder sound waves.

Small speakers have a relatively large area and, therefore, rely on excursion to produce “loud” sounds.

So by improving the excursion in the design of a small speaker, the small speaker may be able to produce bass frequencies we are capable of hearing. It should do so without the distortion that would come as a result of a design with a poorer excursion.


Passive Radiators

A passive radiator is a non-conductive speaker-like device that can be included in an enclosure with an actual speaker.

The passive radiator or “drone cone” is designed with similar construction as the regular speaker, only without a voice coil and magnet assembly.

The passive radiator system takes the sound that would otherwise be trapped in the speaker enclosure and uses it to excite a carefully tuned resonance. This tuning allows the entire speaker unit (even of a “small speaker”) to more easily produce its lowest frequencies at audible amplitudes.


Waves Audio MaxxBass

Another method to improve the bass response of a small speaker (or any speaker, for that matter) is with digital-signal processing.

Of course, EQs could be used to boost the relative amplitude of the bass frequencies in the audio signal that drivers the speaker. However, if the small speaker is not designed to handle the increase in amplitude, this bass boost could result in distortion and a poor listening experience.

Waves Audio has developed an interesting DSP called MaxxBass that produces perceived bass.

It does so by adding harmonics to the signal that trick our brains into hearing lower fundamental frequencies that are related to the added harmonics but are not actually added to the audio signal or produced by the speaker.

So with MaxxBass, a smaller speaker can effectively produce the added upper harmonics that will cause us to hear more bass without actually producing more bass frequencies.

This strategy works well for small speakers with limited low-end frequency response.

As an aside, I first learned about the psychoacoustic phenomenon of the “missing fundamental” in Daniel J. Levitin’s fascinating book This Is Your Brain On Music (link to check the price on Amazon).


Related Questions

What are the different types of speakers? There are plenty of different types of speakers and even a variety of ways to differentiate and define “type”. The three main ways to distinguish speakers are by their size and role in a system; their form factor or application, and by the type of driver/transducer they use to convert audio into sound.

Speaker driver size/types:

  • Subwoofer
  • Woofer
  • Squawker (mid-range woofer)
  • Tweeter
  • Full-range

Speaker form factor/application:

  • Subwoofer
  • Wall/ceiling speaker
  • Computer/phone speaker
  • Studio monitor
  • Soundbar
  • Outdoor speaker
  • Car speakers
  • Bluetooth speakers

Speaker driver transducer types:

  • Moving-coil dynamic (electrodynamic)
  • Magnetostatic/planar magnetic
  • Ribbon
  • Electrostatic
  • Moving-iron
  • Piezoelectric
  • Magnetostrictive

To learn more about the various speaker transducer types listed above, check out my article How Do Speakers & Headphones Work As Transducers?

What are the top 10 loudspeaker brands? There are plenty of awesome consumer; professional; studio; live sound, and hi-fi speaker brands on the market. Though certain brands perform best in different regards, 10 of the best speaker brands are:

  1. Klipsch
  2. KEF
  3. Bose
  4. Harman Kardon
  5. Bowers & Wilkins
  6. Sennheiser
  7. Definitive Technology
  8. Sony
  9. MartinLogan
  10. Magnepan

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