If you need a driver for a small enclosure, then you’ll want something with a fairly low Qts value to hit a critically damped target Qtc around 0.65 to 0.7. Why might you want an over-damped driver? If you are using it in an enclosure, the compliance of the air in the enclosure combines with the compliance of the cone to create a new Q value – Qtc. A low-Q driver (Qts < 0.65) is considered mechanically overdamped, but this helps to bring the cone back to rest quickly after a signal is removed. A higher-Q speaker (Qts > 0.85) will store and release more energy, which causes the woofer cone to continue to move after the current is removed from the voice coil. We can sum it up in a few short statements. The two values create a “total Q” value called Qts.Ī while back, we wrote a detailed article on why you would want to choose low-Q woofers for your door speakers. The electrical Q is defined by Qes and is the ratio of the driver’s reactance to its resistance. The Qms value is the mechanical Q of the suspension. In the context of Thiele/Small parameters, speakers have three Q values: Qms, Qes and Qts. If you’ve been following the articles we’ve published about speaker specifications, then you’ll recall that a speaker includes two springs (the spider and the surround) that work to bring the cone back to rest after the electrical current is removed from the voice coil. When a technician is working with an equalizer to calibrate the output of a speaker, they will look at the frequency response measurement with an RTA, then choose a filter frequency and Q to boost or cut the signal to compensate for variations in the acoustic response. Three EQ filters are set to add 6 dB at 500 Hz: blue has a Q of 20, yellow is 4.31, and pink is 0.1. Here’s the same graph, with the second band set with a Q of 0.1 and the third band set with a Q setting of 20. The ARC Audio software is quite flexible, allowing for Q values from 0.1 to 20. Three EQ filters are set to add 6 dB at 500 Hz: blue has a Q of 8.6, yellow is 4.31 and pink is 2.2. I’ve overlaid two additional plus 6 dB filters on this equalizer response graph, one with a Q of 2.2 and a second with a Q of 8.6, to demonstrate the change in bandwidth. However, you need to know this: High Q values result in a narrower bandwidth and lower values in broader bandwidth. It’s unlikely that we will take the time to calculate Q values. Looking at the screenshot of the ARC Audio PS8 Pro software’s frequency response plot, we can see that boosting 500 hertz by 6 dB using a filter with a Q of 4.31 gives us -3 dB values of about 442 and 558 hertz. Frequency response of a +6 dB boost at 500 hertz using a filter with a Q of 4.31 For example, you might want to boost or cut frequency content at 500 hertz but not affect the output at 400 or 630 hertz. ![]() If you had a 30-band graphic equalizer in your vehicle, you’d want each band of adjustment to not overlap with an adjacent band (by default, at least). ![]() So if we divide the center frequency (F) by the bandwidth (B), we get the Q. Two values are important to the calculation of the filter Q: the center frequency of the filter and the bandwidth of the waveform at the point that it’s 3 dB down from the peak. Let’s look at the frequency response chart of a single band of equalization. ![]() ![]() A graphical representation of how equalizer filter Q is calculated. Yeah, I know, more gobbledygook, right? The chart below helps to make everything much clearer. So, in this context, what exactly does Q mean? In short, it’s a unitless comparison of the -3 dB bandwidth of the filter to the center frequency. We call this a parametric equalizer when frequency, cut/boost and Q are all adjustable. Your installer can dial in a certain amount of boost or cut at a specific frequency and turn the Q knob or enter a value that defines the frequency range the level adjustment affects. Many car radios and equalizers include adjustable bandwidth settings. When talking about equalizers, the Q of a filter describes its bandwidth. For speakers, proper cone control requires carefully calculated damping. The Q factor describes the damping characteristics of a resonant system. Car audio enthusiasts will run across the term Q, Q factor or Quality factor when discussing car audio speakers, subwoofer enclosures or parametric equalizer configuration.
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