Dielectric Absorption, Dissipation Factor and Q
What is Dielectric Absorption?
Dielectric absorption is also referred to as "soakage" or "voltage retention. After a capacitor is charged, it retains part of the charge, even after being discharged and even if the conductors have been shorted together. Cables, like capacitors behave as if they have an additional series of RC networks in parallel with the primary capacitance, and it is these small distributed capacitances that retain charge due to the high series resistance. To measure dielectric absorption, the capacitor or cable is charged to some voltage for one minute, and is then shorted for two seconds. After a one minute delay, the recovered voltage is read using a very high impedance voltmeter. In some instances, a significant voltage "rebounds" from the capacitor or cable. Dielectric absorption is calculated by dividing the recovered voltage by the charging voltage, and is expressed in percent. Teflon, polystyrene, and polypropylene dielectrics will yield the lowest dielectric absorption, while PVC and vinyl will yield the highest. To insure that the audio waveform is not altered by secondary "rebounds" of charge and the high-frequency "fine inner detail" is preserved, it is prudent to use dielectric materials that have low dielectric absorption in audio interconnects and speaker cables.
What is Dissipation Factor?
Dissipation factor is important for AC power applications, which includes audio power transmission to loudspeakers. Dissipation factor is approximated by dividing Equivalent Series Resistance (ESR) by the difference: capacitive reactance (Xc) minus inductive reactance (XL), and is expressed in %.
DF = ESR/(Xc-XL)
Capacitive Reactance is calculated by:
Xc = 1/(2*p *f*C) = wC
and Inductive Reactance is calculated by:
XL = 2*p *f*L = wL
Reactance can be thought of as "AC resistance".
Dissipation factor is a function of age, frequency, and temperature. Dissipation Factor is a combination of conductor losses and dielectric losses.
What is Q?
All capacitors (and cables) have an inductive and a capacitive component. At very low frequencies, the cable appears primarily inductive and at higher frequencies becomes primarily capacitive. Q or "quality factor" is a measure of how abruptly the change from inductance to capacitance takes place. At the point of transition, the cable is in resonance, so it appears like a pure resistance. Resonance is when it's resistance is equal to the Equivalent Series Resistance or ESR. Resonance will occur at precisely one frequency. Q can be calculated as:
Q = 1/DF
We believe that the Q of a speaker cable is important. If the resonance point can be "tuned" to the right frequency, the cable becomes more like an ideal resistance and the phase response becomes more linear as well. High-Q cables seem to sound better and have better focus and clarity in stereo.