Neumann large diaphragm condenser microphone capsules.

While sending some condenser capsules to my trusted workshop for restoration, I realized I had in my hands the history of studio microphones:

An original M7 and various editions of the K87 and K67, all genuine Neumann/Gefell specimens, the reference sound of music production from the '50s to today.

Fascinating, inimitable, beautiful even just to look at. These capsules are the result of meticulous and distinctive research by German engineers, and if they have had no rivals for over 60 years, the reason is simple: they sound damn good.

Each capsule characterizes a condenser microphone according to its distinctive tone, and although the design of the amplifier circuit continues to change (tubes, transistors, back to tubes, with and without transformers, etc.), our favorite large-diaphragm capsules survive this constant evolution. It's now more a son of marketing than real technical needs.

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This is an M7 capsule, a large-diaphragm condenser from Neumann/Gefell dating back to around 1957.

The design is the work of engineer Georg Neumann himself, who, perhaps somewhat unwittingly, revolutionized the way we record and listen to music with this project.

The double membrane is made of PVC (Poly-Vinyl-Chloride), a liquid polymer plastic deposited on a glass support to create an extremely thin membrane, approximately 8 - 10 micrometers thick.

Unlike modern Polyethylene membranes (such as Mylar and Hostaphan), which also come in thicknesses of 3 or 6 microns, PVC is much more challenging to work with and is more prone to degradation over time. For this reason, it's very difficult to find an original M7 capsule that has retained its characteristic tone.

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In the 1960’s a new capsule was introduced, called the K67, the beating heart of the new Neumann condenser microphone, the U67.

As Telefunken ceased production of the VF14 tube (Neumann was the sole buyer, and the costs for the factory were no longer sustainable), engineers set to work to launch a new condenser microphone model, the U67, which quickly became the reference microphone in recording studios worldwide.

The transition to Mylar had already occurred between the M7 and the K47, as well as the membrane mounting system (screwed instead of glued). Additionally, unlike the K47, which shares the same drilling pattern with the M7, the new backplate has an innovative design. These features give the microphone a sound very different from its predecessors. The K67/K870 is the same capsule found in modern U87 Ai studio microphones.

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At the end of the 1960s, with the advent of transistor technology, a new studio condenser microphone, the famous U87, was introduced.

For various design improvements, a new capsule called K87 was introduced. It shares the same drilling pattern as the K67, but this time divided into 2 electrically isolated backplates. In fact, it's the only capsule with 4 contacts instead of 3 (2 membranes and two fixed electrodes). In essence, the K87 is exactly a K67 with the two backplates isolated (this means that if the two electrodes of an 87 are electrically contacted, a 67 is obtained, but the reverse is not achievable).

Missing from the lineup are the K47 and K89, mounted respectively on U47/M49 and U89.

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The capsule is the beating heart of a microphone, being largely responsible for its tonality and often the component that determines its final cost, at least for the handmade condenser microphones we design and produce at the Braingasm laboratory. For more refined tastes, we choose M7 capsules (Thiersch Red Line in Mylar or original Microtech Gefell PVC) for projects in the style of the U47, or Tim Campbell for projects in the style of Elam or C12.

Some of these K67 and K87 capsules that will be restored are part of an ambitious project in collaboration with a highly talented sound engineer with whom we are designing custom signature models. Stay tuned!
 

The fine art of building a ribbon microphone - Pt.1

'The tool is half the master'... always true, whether you're a carpenter, a farmer, or a surgeon. In our case, the right tools are indispensable, and the ribbon microphone doesn't forgive.

We're working on a micrometric scale; the aluminum ribbon is 1.8 microns thick. To give you an idea of what we're talking about, here's a list from Wikipedia that illustrates the order of magnitude in question with some examples:

1-10 µm: Typical diameter of a bacterium

1.55 µm: Wavelength of light used in optical fibers

6-8 µm: Diameter of a human red blood cell

6 µm: Anthrax spore

7 µm: Thickness of a spider web thread

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Cutting a bacterium in half is already a difficult concept to visualize, let alone being careful not to damage its edges, crumple it, or make it fly away with a sigh, and so on.

For an easy-to-imagine comparison, consider that household aluminum foil has a thickness ranging from 40 to 80 microns, which is almost 50 times greater than our microphone ribbon.

But cutting is just the beginning of the work. Once the ribbons are cut correctly (4 mm wide and 100 mm long), the next phase is corrugation. This system allows the ribbon to expose more surface to the sound field than a flat ribbon. It also increases its elasticity and resistance.

We proudly present our super vintage (and, above all, artisanal) machine for corrugating the ribbon, built with used Meccano parts.

The next phase, once the ribbon is cut and corrugated, is its placement inside the structure, called the motor.

The ribbon motor is a simple mechanical system consisting of two permanent magnets glued to a metal structure.

We'll cover the housing and tuning phase in another post. For now, let's conclude our beloved scientific talk.

The ribbon microphone exploits the physical law of electromagnetic induction, the same wonder of physics that brings dynamic microphones and loudspeakers to life. In practice, the aluminum ribbon is suspended in a strong magnetic field and vibrated by the surrounding sound field. Due to this physical law, a tiny electrical current is generated at the ends of the ribbon, consistent with the incident pressure wave. This current is then extracted, converted through an output transformer, and made available on the microphone's balanced output.

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Tube 47 - Braingasm Custom

My Neumann U47 needed functional restoration, and once it returned back, shining like the sun, it gave us an idea: a Braingasm-branded valve U47.

Aware that we were stepping onto the field for the Champions League final, we got to work for many months, studying the original schematics and various "clone" projects, testing the Neumann in all its aspects to discover its versatility, and soldering away. Finally, we are ready to present it.

Like other handmade microphones born in the lab, this is not just another U47 clone or replica in circulation. We aim to create something innovative, inspired by the genius of our predecessors. Always keeping in mind that the Braingasm Lab’s mission is to offer high-quality sound at an affordable price for everyone. We seek to move forward, not sideways.

Before diving into the usual technical details, we are publishing the beta test of the finished microphone, compared to the original Neumann and a Braingasm Deluxe with a Gefell M7 capsule, the flagship model of our transistor series. The microphones are positioned as close as possible to each other, about 3 meters from the drum kit. The preamp used is a Tubetech. Check out the sound:

We have a long testing session planned where we aim to be as comprehensive and precise as possible, appreciating the performance of our new tube microphone on vocals, electric, and acoustic instruments. For now, we'll settle for these three tracks. Follow us to hear the rest.

After treating your ears with some snare and kick, let's finally move on to our beloved technical details:

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Let's start with the body, made in Europe with CNC machines. Like the original model, the grille has three levels of mesh, the basket is made of copper, and the body is anodized aluminum. We experimented with other models, shapes, colors, and materials, but the nuclear torpedo has always been the hands-down winner.

Braingasm Tube 47 - Long Body

Neumann U47 Short Body (1960)

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We've maintained the original layout and point-to-point wiring on the sides of the transformer, ensuring that the high-impedance area is as close as possible to the capsule and valve. Our electronic design differs from the original in many aspects, including the capsule biasing circuit and the tube’s power supply voltages. Among various options, we've chosen a Telefunken EF800, powered according to specifications.

NOS Telefunken EF800 tube, AMI BV8 transformer, MKP film capacitors

VF14 M tube, BV8 original transformer

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Finally, the capsule is a Thiersch STW7 transducer (M7 Red Line). Soon, we'll also test fitting a vintage M7 Gefell. The original Neumann U47 mounts a KK47.

Thiersch M7 Red Line capsule

Neumann K47 capsule

Decca Tree 47

Three identical microphones in cardioid/omni versions for Decca Tree recordings. With this matched trio of 47s, we've raised the bar even higher, implementing a subminiature switch on the circuit for polar pattern selection.

The directivity and slight emphasis on high frequencies (typical of pressure gradients in omni configuration) nod to the behavior of the M50s, absolute protagonists of the traditional Decca Tree setup.

Another special feature is the very strict matching (the capsules were selected from a stock of 20 transducers).

Microphones for singers and songwriters- In studio with Pino Marino

The 47 and 12 capsules are two complementary transducers, very different in character and intended use, and they adapt well to both vocals and instruments.

The first is a rather neutral capsule across the spectrum, with its natural emphasis on the high-mid range, displaying the typical mid-focused timbre of the 47. On the other hand, the second has a more 'loud' attitude, more pronounced at the extremes of the audio band thanks to a greater proximity effect and a bell curve shifted towards 8-10kHz.

When it comes to vocals, my advice is to choose the Deluxe 47 for rock vocals (vintage tone) and the Deluxe 12 for softer productions (modern tone).

This approach promotes the correct placement of the vocals in the mix without many artificial adjustments, as a rock song will naturally be very 'loud' due to the presence of distorted guitars and prominent drums, leaving the upper midrange open for our vocal track recorded with the 47 to comfortably sit without hindering or being hindered. On the other hand, in a pop production (or any softer genre), the vocal recorded with the Deluxe 12 will have its space within the spectrum and can be the reference instrument for the entire arrangement—full, present, and pleasant.

P.S. Pino chose the Deluxe 12.

The purchase of a studio microphone often relies on habit, sometimes on reading (controversial) technical specifications, and almost never as a result of an awareness derived from in-depth listening tests.

The opportunity to test a microphone on your own instrument (in this case, the voice) is a rare commodity in the global 'add to cart' market. However, it is an immense resource when dealing with the boutique market.

I met Pino Marino, an evergreen figure in Italian singer-songwriter music (as well as a keen ear), to record a song in the studio and conduct tests on our Braingasm Deluxe 12 and 47 large-diaphragm microphones.

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