will different lengths affect sound

If you believe that one speaker cable has different sound from another then this sonic signature will be proportional to the length of the cable. Sonic difference will be very small and you can probably convince yourself that there is or isn't any difference - becomes issue of faith. Take into consideration that it is more difficult to sell uneven cables.

Much simpler explanation than transmission line analysis:

Inductance of straight wire runs in order of 400nH/ft. Inductive reactance of 10' of speaker wire (20' counting both ways) at 20kHz is Xl=2*pi*20e3*20*400e-9=1ohm.
Difference between 10' and 100' of speaker cable at 20kHz is
9 ohms. You can argue that tweeter has higher impedance at 20kHz but often there is also compensating network of capacitor and resistor across the tweeter to even it out. Let assume that we care only about 10kHz range - the difference is still 4.5 ohm. It is not even an issue of signal divider but phase shift. 4 ohm of inductive reactance with 4 ohm of resistive load would shift phase by 54deg.

Let's assume 10' and 20' cables. At 10kHz difference of reactance between them would be 1 ohm while difference of phase shift with 4 ohm resistive load would be about 3 degree. I'm not sure what kind of load different speakers present at 10kHz but all I'm saying - it might be audible.

I screw-up numbers in my last post - 54 deg should be 45 deg while phase difference between 10' and 20' cable comes to 12.5 degree (assuming resistive load of 4 ohms).

arctan(2/4) - arctan(1/4) = 12.5deg