# Simple "Q factor" explanation

Hi folks...quick question...what comprises the "Q" equation(.70 ?) speaker makers frequently discuss...such as Dunlavy,etc...is this a combination of tuning and enclosure reasonances(?)...and is it obtainable in port designs? I have heard this more in relation to sealed designs...thanks...
3 responses
 .707 is said to be the correct "Q" with respect to damping. A higher Q indicates a woofer that is underdamped (loose) while a number lower than .707 indicates an overly damped woofer. I don't have the scientific background to tell you what the number means but .707, 1.41, 2.82, etc. are numberscommonly seen in physics along with 3.14 (pi). My guess is that with a Q of .707, the woofer cone moves when it should and stops when it should. A Q of .5 is better--lower tighter. .707 is maximally flat and more common. Its maximmaly flat because its the highest you can go without getting any resnonat peaks and getting the most hz extensions. Higher Q are less accurate. To get the Q lower the box volume has to go alot bigger. "It [Q] represents the degree to which the electrical, mechanical, and pneumatic circuits of the woofer/box combination interact to control resonances.""and is it obtainable in port designs?"Yes, its one of many things one designs around. I will try to fill in the gaps. Q has to do with filtering for the crossover points. The Q equation has two forms: Q=sqrt(2)/(4-K) where K is the passband gain. The second is Q=fo/BW where fo is the crossover frequency and BW is the bandwidth. For a Butterworth response (maximally flat), K=2 because the feedback and input resistors are equal (K=(Ri+Rf)/Ri in the active case). When k=2, you get the 0.707 Q factor you speak of. If K is lower than 2, you get an overdamped Bessel response. If K is greater, you get an underdamped Tschebychev response. The designer must decide which he wants and this depends largely on the box volume as stated above. Don't know if this is what you wanted but there can never be too much information IMO! Take care - Arthur