Cone breakup is a phenomenon that all speaker designers must work with. I have spent many hours trying to “shift” cone breakup out of the speaker listening range or trying dozens of engineering ideas to either dampen cone breakup or control it.
Cone breakup happens when the movement of the cone changes from pistonic motion (which is uniform up and down motion), to erratic motion, with different parts of the cone face moving independently.
In a perfect world, the ideal motion of a speaker cone would be pistonic. In other words, the cone component of the speaker would be uniform and would move as one body.
In the real world, as we move through the frequency range from low to high frequencies, we will reach a specific resonant frequency point when the behaviour of the cone will no longer be pistonic. At this point, we see cone breakup.
In this article I will cover cone breakup in greater detail, sharing what I have learned from my experience of designing speakers.
I will cover:
- What does the cone do in a speaker?
- What does a pistonic cone mean?
- What is speaker cone breakup?
- How do you measure speaker cone breakup?
- Is cone breakup good or bad?
- Does speaker cone breakup affect sound?
What Does The Cone Do In A Speaker?
Before jumping into exactly what cone breakup is and what it looks like, let’s refresh on what the cone in a speaker does.
The cone in a speaker oscillates at the frequency of the input signal. The air molecules that are in contact with the speaker cone face are excited by the cone movement. In return, this causes sound waves which reach our ears as sounds that we hear.
It can help to visualise this before discussing cone breakup because the way the cone moves affects the sound we hear.
If the face of the cone is moving as a uniform body, with pistonic up and down motion, it will move the air coherently and sound waves will move beautifully through the air and we will hear “good” sound.
If the face of the cone is moving erratically, then the air will be excited erratically. This will create sound waves that are out of phase and cancel each other. This will not sound so good.
What Does A Pistonic Cone Mean?
Before fully getting under the hood of cone breakup, it is important to know what “pistonic” means in terms of speakers.
When we say that a speaker cone is pistonic, we are referring to the coherent up and downward motion of the speaker cone; just like the movement of a piston.
Pistonic motion is good. In a perfect world, a cone would have pistonic motion across the entire frequency range; however, this is not the case.
At lower frequencies, speaker pistonic motion is very easy to achieve. However, as we move into the mid-band and higher frequency range, the shorter wavelength of the higher frequencies can cause problems. At a certain point, which depends on factors such as cone design and cone material, the cone motion will no longer be pistonic.
What Is Speaker Cone Breakup?
Speaker cone breakup happens at a certain frequency, at which point the cone resonates erratically. Instead of pistonic motion, the cone face will move out of phase with other parts of the cone face.
Although it is not always possible to physically see cone breakup because of the high speed of the speaker cone, if you find a woofer cone where you can see cone breakup, you notice that, at a certain frequency, you may see the cone distort.
This might manifest by one local area of the cone moving out of sync with the rest of the cone creating a localised “bump” on the cone.
This can be very rare to spot, as most speaker designers will ensure that cone breakup will happen outside of the specified frequency range of the speaker.
The following image shows cone breakup. This is a cross-section view of a speaker cone.
The image below shows cone breakup and how different parts of the cone face are moving out of phase.
How Do You Measure Speaker Cone Breakup?
Professional speaker designers will measure cone breakup using laser scanning equipment, for example using the Klippel Scanning Vibrometer (SCN).
Highly precise and accurate, the Scanning Vibrometer (SCN) is a non-contact measurement device that can accurately capture mechanical vibrations and geometry data from different objects, such as cones, diaphragms, panels and enclosures.
With its three actuators,—one rotational and two linear—this device employs a laser displacement sensor to delicately move over an area determined by you.
At each measurement point, a stimulus that attains adequate spectral resolution activates the transducer.
The following image shows the type of data this machine can generate. In the following example, we can see a cross-section of a measured cone, including a 3D-generated image of the laser-scanned face of the cone. This example is showing vibration at 3046Hz.
You can see how powerful the Klippel system is at debugging and visually inspecting speaker cone behaviour. To learn more about Klippel and its other speaker diagnostic systems, visit the website here.
Is Cone Breakup Good Or Bad?
Not all cone breakup is bad. It is possible to factor cone breakup into your speaker design in order to give a boost at a certain frequency.
At the end of the day, the cone is just responding to a resonant frequency. A resonant frequency is a specific frequency at which the cone will vibrate at a greater rate.
The frequency at which the cone will resonate will depend on the mass of the cone and the physical design of the cone i.e. the size and shape.
Every physical object has a resonant frequency. Since the cone will vibrate at a greater rate at the resonant frequency, it will give a loudness boost at the point.
Speaker designers can harness this boost and ensure that:
- It is outside the listening range of the speaker
- It is at the crossover point of the speaker.
Having a boost in speaker output at the crossover frequency can keep the speaker SPL (output) loud, allowing for a smoother transition at the crossover.
This, of course, takes skill and a great understanding of the design on the behalf of speaker designers.
Does Speaker Cone Breakup Affect Sound?
Speaker cone breakup affects the sound. Since the speaker cone face moves erratically, it will move the surrounding air erratically, producing poor-quality sound.
If we do not factor speaker cone breakup into the design and place it at or above the crossover frequency where it is outside of the recommended range of the speaker, the listener will hear it.
Final Thoughts
Speaker cone breakup is a phenomenon that can be used to our advantage when designed correctly, but it is best that we keep cone breakup outside of the recommended frequency range of the speaker.
With careful consideration and attention to detail from experienced speaker designers, it is possible for speaker cones to remain pistonic throughout their entire recommended operating range.
By understanding how this affects sound quality, we are well-equipped consumers with knowledge of what makes a good speaker sound great in terms of performance and longevity.
