[jstobo]

It is a b*****d size. I know because I have an original Porsche NOS replacement speaker ( Bought in 1983). I just went and measured it. The speaker itself is 4 3/8 " x 9". The mounting holes are 3 1/8" x 8". I never found a US replacement that matched it. When I installed a modern radio/CD you need 4 speakers because of the resistance. The old Porsches like ours had a 3 speaker system(1 upfront-2 in back). I use an adapter plate and installed 2 4" diameter speakers in the front hole. Much better sound. The plate is a common one althgough I did have to make some small mods so that it fit in the hole. Go to a car stereo place and I am sure they'll have one. If you have the original radio you can try to fit a 4x9 speaker if you can find one. Good luck.