David Bock On Microphones

Bock Audio 241

There are a few people on the planet that know a lot about microphones and how they're made, but not many know as much and have the dedication of David Bock, the founder and owner of Bock Audio (formerly Soundelux Microphones). After all, how many people would go to the extent of teaching themselves German just so they could read the old Neumann service manuals? David makes some truly excellent mics, and you'll see a little of just how that came to pass with this excerpt from The Recording Engineer's Handbook.
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"After stints repairing microphones (among other things) at such prestigious facilities as the Hit Factory and Oceanway, Bock Audio (formerly Soundelux) founder and managing director David Bock went from repairing vintage microphones to manufacturing them.  David now utilizes his expertise to produce updated versions of the studio classic 251, Although he previously made versions of the U47, FET47, M49 and U67 in the previous Soundelux incarnation of the company.  David was kind enough to share some of his insights as to the inner workings and differences between classic microphones and their modern counterparts.

What actually makes a vintage microphone so special?
There are a couple of things that go into that.  The bottom line is that the 50’s 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.

As you were trying to build an updated version of a vintage microphone, were you trying to copy everything including the circuitry and trying to get it as close to the original as possible, or were you trying to just make it sound like the original?
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. 

Among some of them there is a common thread though. Frequency response is the primary guidepost because all microphones have their own signature. But frequency response curves don’t always tell you everything. You have to take frequency response measurements not only far-field but also proximity (near-field), which strangely are not published and are completely critical to what we believe a microphone sounds like in the directional world. That’s key and it’s somewhat of a disservice that most of the larger condenser microphone manufacturers have not been publishing those graphs for many years. That’s why most engineers will say “Those graphs don’t really mean anything”. That’s because you’re always looking at a 1 meter graph but you’re not always putting your microphone 1 meter away from the sound source. So of course they don’t mean anything because they’re not telling you what you’re hearing. If you saw a proximity graph and a 1 meter graph you’d have a much better idea of what the microphone sounds like. 

So the dissection process continued through a lot of substitutions. You might take a power supply and substitute a different circuit topology and see what it changes, for instance. There are also a lot of measurements that you have to do. Our ability to test things today is definitely better than back when the classics were built but it’s not completely conclusive and opens up a can of worms that says “If I can’t measure it then I can’t hear it” which I completely disagree with. If you worked only towards measurements you end up with something that actually doesn’t sound particularly good compared to things that were designed with listening in mind. 

Finally, there are listening tests. My primary listening test is to make a recording of a drum set in a large room. I’ve got a couple of key locations where I place the microphone to give me an idea about the close and distant pickup characteristics. That’s where you start hearing the differences. Microphone capsules are related to drums. If you took 10 DW [drum] kits and you tuned them all the same they’d still sound all different. There’s a parallel you could draw towards microphones. You could tune all the snare drums and toms the same and even use measurement devices to be sure that they’re the same, and yet the trained ear of an engineer can pick out the differences between them.  We can lock on to things that are different about each one.

What was the hardest thing to get right?
Always the capsule because it’s so small and if you make a tiny change it makes a huge result.  But that’s not to say that the capsule is 99% of the sound. An 87 and a 67 don’t sound that similar yet they use the same capsule.

What’s the biggest difference in the way microphones are made today from the way the classics were made?
Mass production and availability of quality materials. Also, the need for profitability on a corporate level seems to affect how things are made a lot. I’ve seen the way Neumann microphone are built and they’re very different from the way they used to be. The way they built their microphone in the 50’s and early 60’s, I’ll be able to keep those microphone running for a long time.  Not so with the newer microphone. They still make a great capsule but they don’t make the microphone the same in terms of construction. They’re built for ease of production and lowest cost. It’s true almost across the board.

So if we were to make a broad statement, microphones are not made as well today as they were 50 years ago.
No they’re not. If you had a “cost is no object” attitude, you still don’t even have the same metals available. The quality of brass is different now from what they used in the 50’s and 60’s, for instance, and an equivalent can’t be found. 

With the way the business seems to be going, with less and less emphasis on sonic quality, will there be enough people left to appreciate what you’re doing?
Anybody who is serious about the profession either evolves to a point where they say “I can use an SM57 for every track to make a record” or “I’d rather use a hi-quality microphone to make a record”.  You’re going to go one way or the other and most people, if they stay in the business long enough, will usually gravitate to the more exclusive side."

Do check out David's mics at Bock Audio.

You can read additional book excerpts at bobbyowsinski.com.

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