If you are starting out your career in speaker design, or are an audio enthusiast, you will have heard the term “speaker Q” thrown around.
But what does speaker Q mean, and what does it tell us about a speaker’s performance?
Q stands for “quality factor” in a speaker. It is a term used by speaker designers to define how well damped a speaker is, however, it is not an actual measure of damping. Q is the inverse of the damping ratio.
In very simple terms, a low Q means more damping, which results in greater performance control.
In the world of speaker design and speaker impedance curves, Total Q or Qts describes the sharpness of the speaker’s resonance.
I will dive deeper into this very important speaker parameter to understand why speaker Q is important, covering the following:
- Speaker Q explained
- What does Qes & Qms mean?
- How do you calculate Qts?
- What does speaker Q tell us?
- What is a good speaker Q factor?
- How do you measure speaker Q?
Speaker Q Explained
Speakers vibrate to make sound. With these large vibrations comes resonance.
All vibrating objects, including speakers, have a resonant frequency. This is the frequency at which the speaker will vibrate at a higher amplitude.
It is really important to know and understand the resonant frequency of a speaker, as it will impact how the speaker driver responds to the environment it is put in. For example, knowing the speaker’s resonant frequency in advance will allow you to prevent a cabinet from ringing.
But what has speaker resonant frequency got to do with speaker Q?
In order to control a speaker’s resonant frequency, we have to control damping. In the world of speaker design, designers use speaker Q, (also known as Qts or Total Q) to define how well damped a speaker is.
After a speaker is designed, it is measured. Typically, it is placed into an anechoic chamber, with a microphone placed 1m away.
A frequency sweep from 20Hz to 20kHz is played through the speaker and measured.
Using measurement software, an impedance curve is produced below, which shows us the resonant frequency of the speaker. Here is what a typical impedance curve looks like from a measured speaker.
In the context of speaker impedance curves, the Total Q, (Qts) is a measure of the sharpness of the driver’s resonance peak. Total Q (Qts) depends on both the mechanical and electrical characteristics of the speaker.
Total Q (Qts) is calculated from the electrical Q (Qes) and the mechanical Q (Qms).
What Does Qes & Qms Mean?
Qts (or Total Q) is calculated from Qes & Qms.
Qes and Qms are two quantities that quantify the suspension control of a transducer when it reaches the resonant frequency (Fs).
As the voice coil of the speaker moves up and down in the magnetic gap of a speaker, a suspension design allows this movement but also controls this movement so the voice coil and diaphragm assembly do not bounce all over the place, become unstable and break.
The Electrical Q – Qes
The electrical Q of a speaker, known as Qes, is the amount of control coming from the electrical components of a speaker (the voice coil and magnet) which contribute to the suspension system.
The Mechanical Q – Qms
The mechanical Q of a speaker, known as Qms, is the amount of control coming from the mechanical components of a speaker (surround and suspension/spider) which contribute to the suspension system.
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How Do You Calculate Qts?
Qts, ‘Total Q’, is calculated from the electrical and mechanical characteristics of a speaker, Qes & Qms.
Qts is calculated by multiplying Qes by Qms, then dividing that results by the sum of the same. [source]
Qts = Qms × Qes / (Qms + Qes)What Does Speaker Q Tell Us?
Speaker Q tells us how well a speaker is damped.
A high Q value will tell us that there is low system damping.
Damping is the dissipation of energy in a system over time.
In the context of speakers, it is the control of the resonance frequency of the speaker.
A high Q factor means that there is a lot of resonance (the speaker is not well damped or has low system damping) and a low Q factor means that there is little resonance (the speaker is well damped).
If the Q of a speaker system is too high, then the sound will be harsh and fatiguing. If the Q of a speaker system is too low, then the sound will be muddy and lack detail.
What Is A Good Speaker Q Factor?
The best Qts (Total Q) factor depends on the application.
Below is a table which shows some typical Qts values and their suitability. These values are given as a general guide only as there are always exceptions to the rule.Qts (Total Q) Value Comments Less than 0.4 A speaker driver that is well suited to a ported/vented enclosure 0.4 – 0.7 A speaker driver that is well suited to a sealed enclosure. Above 0.7 A speaker driver that is well suited to free-air or infinite baffle application.
According to some experts, a Qts (Total Q) of 0.7 is considered ideal as it balances a smooth lower frequency response with good driver damping, with a very good transient response. [source]
Again, it depends on your application.
The term “infinite baffle” may be confusing if you are new to the world of speaker design. It can be taken literally to mean a speaker mounted on an infinitely large baffle or enclosure.
In the real world, this is not practical, but in practice, the term “infinite baffle” typically implies a closed box which is large enough that it is not an air suspension system. [source]
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How Do You Measure Speaker Q?
In the professional audio industry, Speaker Q is measured using measurement systems such as:
Such systems are used by professional speaker manufacturers and R&D speaker designers, therefore are costly.
If you are looking for a DIY solution or a more affordable solution to measure Speaker Q (including all the Thiele/Small parameters), then I recommend this video which shows how you can do this.
This is great if you are on a budget.
A PC and sound card, including some additional resistors, are needed in addition to your speaker.
To understand the maths and the concepts behind measuring speaker Q in much greater detail, this is a great site that covers the basics.
Final Thoughts
Speaker Total Q can be a confusing term to understand, especially if you are new to the industry.
Personally, I like to view Q in simple terms as the inverse of the damping ratio… low Q means high damping and vice versa.
To measure Speaker Q, you can use a Klippel Analyzer or Audiomatica Clio (both professional measurement systems), or a DIY solution.
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