First, refer to this page:

index

Not a lot of info, but it shows "upgrade" speakers that Becker recommends for w123 cars that have their headunits.

Look at the images for the upgrade speakers and then take a look at these:

RetroSound R-525N 5-1/4" 2-way speakers at Crutchfield.com[rank399]Car+Speakers

RetroSound R-452N 4" 2-way speakers at Crutchfield.com[rank399]Car+Speakers

Sure looks identical to me.

So it seems to me that this is the best and lowest-risk approach to stereo speaker upgrading in a w123 or similar car.

Other speakers may or may not work for you and with or without some modification, no matter how slight. But this looks like a good route, especially if you are a purist and want to keep your HU.

The question then becomes to four-channel amp the OE HU output to feed the speakers or not?

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