'96 Miata Headrest Speaker Improvement

The following article came in to the Miata.net Feedback mailbox. We asked Jeff Anderson, our audio expert, to review it. Jeff thought it made some sense. Be warned, however! That capacitor is not there to lower the level of sound - it is there to protect the small headrest speakers from low frequencies.

The low frequerncy sound would require more motion than those small cones can manage, possibly resulting in physical damage to the headrest speakers at high volume.

Also, the low frequencies involve significantly more electrical power, and without that capacitor protecting the speaker, the speaker voice coil could overheat (and delaminate) or burn out from the increased power being fed to it - especially at high volume.

Using a capacitor to limit low frequency energy to a small speaker is a well-recognized method of protecting those small speakers and usually actually results in an improvement in sound quality as the poor little speaker is no longer asked to try to reproduce low frequencies that it cannot (but using up all of its available cone travel trying).

(Also see Jeff's radio repair which improves the headrest sound in earlier Miatas.)

I have a '96 with the factory radio and was VERY disappointed with the sound of the headrest speakers - you could not hear them even with the fade set to full headrest.

After hearing about out of phase wiring problems, I opened up the headrests to switch the wires as a check for the in/out of phase condition. When I opened up the speaker boxes (with some difficulty) I discovered that the speakers had a capacitor wired into the positive speaker lead. When I bypassed the capacitor, the speaker volume and tone improved drastically!

I am not sure why Miata put this capacitor in the speaker, but I have bypassed mine and saved the cost of replacement speakers. (See note above. Ed.)

It is an easy modification to make and can be done in one of two ways - with or soldering.

When you look at the wire connectors on the speaker (from the back), you will find 3 male terminal posts. A closer look will show that the wires from the speaker to the male terminal posts go to the right and center posts. The wires coming up the seat back conect to the right and left posts, with a capacitor connecting the left and center posts. Thus, the capacitor completes the circuit, Since the capacitor lowers the volume, you need to eliminate it from the circuit. Bridging the left and center posts will bypass the capacitor. You can do this by soldering a short jumper wire between the left and center posts or by wrapping them with a piece of bare wire, twisted tightly. The soldering method is more permenant and professional. I did mine with the wrapped wire and they have stayed in place for 3000 miles with no problems.

A word of caution. DO NOT DO THIS WITH THE RADIO ON. Accidentally shorting the speaker wires (either the left or center terminal to the right hand one) can damage the radio itself.