David Bock: There are a couple of things that go into that. The bottom line is that the ’50s were really the golden age of audio design. Those guys really did know what they were doing when they designed a lot of the key gear that people are still using. They used a lot of the correct techniques, and they had the luxury of decent materials and the time to research things properly.
There is a tone to these things that is harder and harder to duplicate. Not impossible, just harder and harder. They had tubes back then that are harder to get now. The available selection of materials was a lot greater back then. Then there’s the element of chance. Why would someone pay $20,000 for a 251? Well, maybe that particular 251 really does sound unique because AKG’s production was so sloppy and the capsules were so poorly machined that you’re bound to get one that excels beyond everything else and the rest are just kind of average. Now we have CNC machines that can make these tiny little holes on the capsule backplate all the same, which AKG really couldn’t do at the time.
The sound comes first, but that’s not the whole story. The first thing I had to do was try to find what makes the microphone sound the way it does. There were at least 15 points that you have to look at, it turns out, if you’re going to emulate the sound of a microphone. The first large problem is, “I want to copy the sound of a 251.” Well, which 251? I rented about ten 251s here in town [Hollywood], and you know what? There’s no such thing as a common 251. They’re all totally different. I could hear it and I could measure it.