This is a simple retrofit for a set of Nakamichi speakers. The original Nakamichi speakers in the front and back of my SC400 were broken because the foam around the speaker had disintegrated and so they needed to be replaced. The rest of the Nakamichi system (the component tweeters in the front, the sub, the head unit and the Nakamichi amp in the trunk) were still ok so I just wanted to simply replace the four broken 4" speakers.

I replaced them with a set of four Infinity Reference 4012i 4" 2-way Speakers which are high efficiency speakers comparable to the originals. For the front 2 speakers I modified them by adding a capacitor in series with the co-axial tweeter to de-emphasize the high frequency so that they work well with their companion component tweeters still mounted above on the door.

The original Nakamichi speakers for the front and back are similar except that the front ones have a smaller co-axial cone. This modification tries to replicate that difference to get the same audio balance that the Nakamichi engineers sought for the Lexus SC400 interior.

The wiring of each 4012i co-axial tweeter has a capacitor soldered in series on one side with the other end of the capacitor soldered to one of the connection post. To modify 2 of the speakers for the use in the front, I wire another capacitor in series to the return wire going to the other post. The effective capacitance of two capacitor in series is reduce by the formula Ceff = (C1 * C2)/(C1 + C2). I selected a 10uf 50 volt non polarized capacitor for this purpose.

The 2 rear speakers need no modification.

The Infinity 4012i mounting holes line up with the original mounting holes so no mounting modifications were needed. To adapt the new speakers to the mounting plates, I cut a gasket to seal the tiny air gap between them. I initially did this with some gasket material I found on Ebay but finally decided to use the rubberized Dynamat material instead. The latter has the advantage of dampening out any mechanical audio resonances.

The result is a musically balance system almost identical to the original such that I didn't even have to adjust the original tone settings on the head unit. The modification allows the component tweeters on the door to continue to project a stereo image in front of the driver while the 4" speakers on the door provides some higher frequencies to fill in the image. I'm am very happy with the sound from this retrofit.

This is a fairly easy retrofit compared to the much more complicated ones needed for many high end aftermarket speakers. It may be the way to do a restore for anyone who is satisfied with the sound from the original Nakamichi sound system.

The retrofit involves the following items:

4 - 4" speakers
2 - capacitors and some small shrink tubing for insulation
4 - mounting gaskets cut from Dynamat material.
- Electronic solder and solder gun.

New Speaker Installed in a Front Box

 

This gasket is made with gasket material. I later replaced this with a Dynamat material.

 

I added a capacitor to the tweeter circuit.

 

Capacitor insulated with shrink tubing.

 

Rear speaker with Dynamat gasket.