Coupling aluminium electrolytic bipolar capacitors
There are several ways to use a pair of polarised capacitors as a non-polar capacitor







simulate this circuit &ndash; Schematic created using CircuitLab

The first one relies on each capacitor not being damaged by being reverse biassed, and that any leakage when reverse biased serves to 'pump up' the common node to a higher voltage, so that after a while, each capacitor is forward biassed. I wouldn't recommend this for the health of the capacitors, or for the audio artifacts that would occur during use when the amplitude suddenly increases beyond the bias level, causing more charging.

The second one uses diodes to limit the reverse bias to a diode drop, and to provide a fast charge for the mid point. It's kinder to the capacitors, but I still wouldn't recommend it for audio coupling.

The third one uses an external bias circuit to ensure both capacitors are forward biassed. Some applications may not tolerate these bias resistors, but audio coupling will. Use a bias well above your audio amplitude to ensure forward bias. 

Note that many 'golden eared' audiophiles reject polarised capacitors anywhere in the signal chain, but I would use them as coupling capacitors, and most professionals do as well. Any modulation of impedance with voltage will be small, probably unmeasurable. When that's turned into a distortion measurement through interacting with much larger impedances in the amplifier, it's going to be irrelevant. Note that any distortion will be low order, that is, the same type that's present at measurable percent levels caused by loudspeakers and headphones, not the dreaded high order distortion caused by old bad class-B amplifiers. While low order distortion does cause intermodulation, if you can't measure it in the amplifier with a spectrum analyser, it's going to be inaudible, and dwarfed by the intermodulation from your speakers.