What is Subwoofer Q? (Qts, Qes, Qms Explained)

Norvan Martin
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When selecting a subwoofer, there are a variety of specifications to take into account.  The three small parameters that primarily determine the frequency response of a subwoofer are compliance or Vas, free-air resonance or Fs, and response time or Qts. 

The Q factor specification can have a dramatic effect on the performance of a sub and is typically expressed through three values called “Qts, Qes, and Qms”. We will take a deeper dive into each value’s meaning as they relate to subwoofer performance in this article.

Q factor Comparison

ParameterDescriptionImpact on Speaker Performance
Qts (Total Quality Factor)Overall quality factor of the speaker, combining both electrical and mechanical properties.Indicates the damping of the speaker. A lower Qts value means tighter control of the speaker cone, often resulting in more accurate bass. Used to determine suitable enclosure type.
Qes (Electrical Quality Factor)Quality factor considering only the electrical aspects of the speaker.Reflects how well the speaker's electrical system converts electrical energy into motion. Lower Qes indicates better control over the motion of the speaker cone by the electrical system.
Qms (Mechanical Quality Factor)Quality factor considering only the mechanical aspects of the speaker.Measures the damping of the speaker's mechanical system. A higher Qms means less mechanical control, which can lead to more resonant and potentially less accurate bass.

What is the Q factor?

Q factor measures how efficiently subwoofers dissipate energy. It plays an essential part in shaping sound quality; so make sure this specification is carefully considered.

The Q factor of a subwoofer measures how its frequency response shifts when signal levels change, with three specific values used for subwoofer description: Qts, Qes and Qms.

Qts – Total Q factor

Qts value measures the total Q factor of a subwoofer by dividing the electrical Q factor (Qes) by the mechanical Q factor (Qms). Qts act as an indication of how subwoofer suspension and voice coil are working together.

Subwoofers with higher Qts values feature smoother frequency response and greater efficiency at low frequencies; conversely, those with lower values may require additional power to produce equal volume output as those with a higher value Qts value.

Qes – Electrical Q factor

Qes is an electrical resistance value used in measuring voice coil resistance on subwoofers. To calculate it, divide the inductive reactance of the voice coil by the resistance of the voice coil and multiply this value by 100% to get the Qes value of the subwoofer voice coil resistance.

Qes values measure how electrical components of a subwoofer interact. A high Qes value will make higher frequencies more effective while potentially less so at lower frequencies.

Subwoofers with low Qes values tend to be less efficient at higher frequencies but may prove more efficient at lower ones.

Qms – Mechanical Q factor

Qms values provide an indicator of the mechanical resistance of subwoofer suspension systems and are calculated by dividing their mechanical resistance by the mass of their moving parts.

Qms value measures how well the mechanical components of the subwoofer interact. A subwoofer with an increased Qms value will likely perform more efficiently at low frequencies but could become less so at higher ones.

Subwoofers with low Qms values tend to be less efficient at lower frequencies while more so at higher ones.

The significance of the Q factor in subwoofers

The Q factor is an important specification to consider when selecting a subwoofer because it can greatly affect the sound quality and efficiency of the subwoofer. Here are some of the ways that the Q factor affects subwoofer performance:

Frequency Response

The Q factor can have an enormous effect on subwoofer frequency response. A subwoofer with a higher Qts value typically offers smoother frequency responses at lower frequencies while ones with lower values could produce peakier ones that require additional power for similar volumes produced from both models.

Efficiency

The Q factor can have an enormous effect on subwoofer efficiency. A subwoofer with a higher Qes value is generally more efficient at higher frequencies; ones with high Qms values perform better at lower frequencies.

Qts values measure how electrical and mechanical components of the subwoofer interact, making one with high total Q factor values generally more energy-efficient across its frequency range.

Impedance

The Q factor can influence a subwoofer’s impedance as well. Subwoofers with higher Qts values typically exhibit greater impedance at resonance than subwoofers with lower values – this may affect how it interacts with an amplifier as well as overall sound quality.

Enclosure Design

The Q factor also has an impactful role to play when considering the enclosure design of subwoofers; those with higher Qts values may work better in sealed, while lower values might work best with porting or air flow systems. Design can greatly influence the sound quality and efficiency of subwoofers.

What Is A High Qts Subwoofer?

QTS stands for Total Q Factor of Speaker System and measures the electrical behavior of subwoofers within closed enclosures. It indicates how effectively subwoofers perform.

It is a measure of the sharpness of the driver’s free-air resonance. It is defined as (Fh-Fl)/Fs, where Fh and Fl are the upper and lower -3 dB points of the driver’s voice coil impedance in free air. The optimum enclosure volume is related to Qts but is not directly proportional.

It is accurate to say that the volume gets larger as Qts get larger. Likewise, F3 gets smaller as Qts gets larger, and for the sealed box enclosure, F3 is inversely proportional to Qts.

What is Subwoofer Q? (Qts, Qes, Qms Explained)

A subwoofer with a QTS value greater than 0.5 is tailored specifically for use in sealed enclosures, where bass response tends to be tight and accurate.

A subwoofer designed specifically to perform well within this type of environment has typically features such as stiff suspension systems and reduced mechanical resistance which enables it to perform optimally within this type of airspace.

High QTS subwoofers also tend to possess greater sensitivity as compared to their lower counterparts allowing less power consumption for similar output levels achieved from lesser QTS values subwoofers.

What Is the Q setting On The Subwoofer?

Q settings on subwoofers serve to adjust resonance frequency in its enclosure. They’re typically found either on an amp’s subwoofer EQ settings or home theater receiver crossover settings and enable damping adjustments – altering how quickly a subwoofer responds to different frequencies.

Low Q values will give rise to flat responses with minimal resonance, perfect for music playback applications. Conversely, higher values increase bass response with greater resonance – perfect for home theater purposes and fine-tuning the subwoofer’s response according to room acoustics and personal tastes.

The Q setting can also help fine-tune responses as needed based on personal tastes or environmental conditions.

What Is The Difference Between QES And QTS Subwoofer?

QES and QTS specifications of subwoofers provide useful insight into their performance by outlining various aspects of their characteristics.

QES stands for electrical Q factor in subwoofers. This indicator measures how effectively electrical energy is converted to acoustic energy by the subwoofer. A subwoofer with an increased QES value requires less power for sound production while producing lower impedance sound levels; however, it may produce inaccurate reproduction of low frequencies leading to boomy or muffled tones in its output.

QTS refers to the total Q factor of a subwoofer and takes into account both electrical and mechanical properties such as suspension and cone properties of its design. Subwoofers with higher QTS values will have a more damped response with tighter bass frequency response as well as additional power requirements to reach any given sound level.

Overall, QES measures the electrical efficiency of a subwoofer while QTS evaluates its overall performance when considering both its electrical and mechanical characteristics.

What Should I Set My Q Factor to? 

The Q factor or quality factor is an indefinable value that measures the damping of resonant systems. Its optimal value depends on individual applications and requirements for every system in use.

Higher Q factors often result in narrower bandwidths and sharper resonance peaks, making them suitable for applications such as radio frequency circuitry or musical instruments; however, longer ringing times and susceptibility to noise could potentially prove undesirable in audio systems or similar.

Subwoofer Q

Conversely, lower Q factors produce wider bandwidths and gradual resonance peaks that could prove advantageous in applications requiring smooth responses such as audio systems or mechanical damping systems.

Therefore, selecting an optimal value of the Q factor depends upon the specific requirements of a system and must take into consideration desired performance characteristics when making this determination.

Other Important Parameters

Research done in the study of loudspeakers has discovered methods that can predict the frequency response performance, and other characteristics of a loudspeaker system, based on its physical properties.

By understanding the relationship between these physical parameters and how to change them, we may alter the response of the system to fit the desired goal. Apart from the Q factor and related specifications, other nomenclatures for the physical characteristics of a speaker are:

  • Vas: The volume of air having the same acoustic compliance as the speaker’s suspension. Vas or compliance is a measure of the overall stiffness, or resistance to motion of the cone, the surround, and the spider. It is specified in terms of the volume of air having the same compliance as the driver. A small number corresponds to a small volume of air, which is stiffer than a larger volume of air. Thus, compliance and stiffness are inversely proportional. The optimum enclosure volume is proportional to Vas. It is usually measured in cubic feet, and generally is equivalent to the internal volume of the enclosure. This is the principal specification for the speaker cabinet.
  • Re: The static D.C. resistance of the voice coil measured in Ohms.
  • Sd: The surface area of the speaker’s cone.
  • BL: The magnetic strength of the motor structure.
  • Mms: The total moving mass of the speaker including the small amount of air in front of and behind the cone.
  • Cms: The stiffness of the driver’s suspension.
  • Rms: The losses due to the suspension.
  • Re: The D.C. resistance of the voice coil measured in Ohms.
  • Sd: The surface area of the speaker.
  • Fs: The resonant frequency of the speaker. The free-air resonance or Fs is the resonant frequency of the driver’s voice coil impedance with the driver suspended in free air (no enclosure). The -3 dB frequency (F3) of an enclosure is proportional to Fs.
  • Xmax: The width of the voice coil that extends beyond the front plate plus 15%. This relates to how far the speaker can move in either direction without appreciable distortion. The amount of power required to move a speaker to its maximum excursion is referred to as displacement-limited power handling. Please note that this number varies with enclosure size and type.

Conclusion

When purchasing a subwoofer, understanding its Q factor should be one of your main priorities. Measured through Qts, Qes, and Qms values respectively, its effects can have profound impacts on frequency response, efficiency, impedance, and enclosure design – key aspects to bear in mind for the successful selection of your subwoofer that fits best into your requirements and preferences.

Understanding the response parameters allows us to calculate the predicted frequency response of a given speaker system. The formulas that accomplish this are rather lengthy and complex and are best left to software for processing.

However, several high-quality computer programs on the market automate the design process of building an enclosure.

Final summary:

  • Q: The ratio of resistance to reactance, or vice versa.
  • Qes: The electrical “Q” of the speaker.
  • Qms: The mechanical “Q” of the speaker.
  • Qts: The total “Q” of the speaker.
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Norvan Martin is the founder of BoomSpeaker.com. He is a professional Electronics Engineer and is passionate about home theater systems and AV electronics. BoomSpeaker was created as an online hub to share his knowledge and experiences as it relates to home theaters and home audio electronics. My email: [email protected]  Connect on Pinterest and Linkedin