Minimum wire AWG for 4 ohm speakers

Question

I am planning on building a Bluetooth speaker using two of these speakers:

They will be hooked up to a Bluetooth CSR8645 board. The length of the cables is smaller than 10cm. I have wired them up used some speaker cable but the cable is too thick and not flexible and it broke one of the pads from the CSR board at a more sudden movement. My plan now is to solder a 4 pin JST connector to the board and hook the speakers using that connector to the board to prevent anymore damage to the board and also add modularity to the whole project. My question would be what AWG wire should I use for the JST connectors? I found one with 22AWG wires. Would that be enough? Speaker wire is too thick for that kind of connectors. Or do you have any other connector suggestions that I could solder the female one directly to the CSR board?

Thank you!

Answer 1

Loudspeaker damping is largely dependent on the ability of the amplifier to control the voltage at the loudspeaker. Any series resistance degrades the ability to drive the speaker voice coil.

I haven't seen any recommended figures on this but I would expect that if you keep your cable resistance to less than 10% of the loadspeaker's impedance that you should not have any deterioration in sound reproduction quality.

Use one of the many online calculators to calculate the required gauge of cable for a given distance. Remember to account for the return wire as well.

Answer 2

With 5W and 4ohm and 10cm length I think you can wire what you want. You should consider thermal dissipation and voltage drop.

The current is I = 1.12Arms. You have a JST connector; they usually go with cross sections up to 0.5mm2 or 1mm2, that correspond to 20 and 17 AWG.

This I current will dissipate P=22mW/m (22mW per 1 linear meter of length). With 1 mm2 cross section, voltage drop is 20mV/m one way, so including return is 40mV/m. You have 10 cm so it's not a problem, and even with 1 m length that will not be an issue.

You should worry about mechanical constraints, so I thing 0.5 mm2 fits and is flexible enough. If in the future you want to deliver more power, or increase the length, you will change the 0.5mm2 (20AWG) to 1mm2 (17 AWG, or 18 or 16, as you prefer, if they are compatible with the connector).