Blue Note’s Unsung Heroes: The Microphones

A change from record reviews, I decided to take some time out to explore one of the reasons, possibly the main reason, why vintage Blue Note recordings sound as good as they do. Yes, brilliant musicians, yes, Van Gelder at the dials, his Ampex tape-recorders, his Scully lathe, yes, Plastylite pressing, but the audio-fidelity chain starts with moving air, from acoustic instruments captured by . . .  the microphone, eventually to be re-created as moving air, from your speakers, and to your ears. The long journey through mixing mastering and amplification starts with the quality of the capture. So a guided tour of the world of Blue Note and vintage microphones. Trust me, it will be fun.

Vintage condenser (valve) microphones from the golden era are rare and much sought after The most famous of them all is the Neumann U47, microphone of choice of Frank Sinatra, Michael Jackson, Elvis Presley, Nat King Cole, The Everly Brothers, Roy Orbison, David Bowie and countless others, even today, Beyoncé, and the sadly departed “Amy House-wine” (apologies, poor taste)

 

 

 

 

You may not know it by name, but you have been listening to the Neumann U47 for decades. Wind-back the clock sixty years, Blue Note late ’50s, recognise the mic in the picture? The U47. What it does for the human voice, it does for the jazz front-line musical voice. Without this valve microphone you would not be hearing the sparkling quality of the golden era.

 

 

 

 

What is special about the U47 is it’s exceptional high-mid response, the territory of the human voice, 2-5kHz, , and the area of brilliance above 6kHz (air, sibilance, cymbals). There were microphones before the Neumann U47, there were many others after, but the U47 is sufficiently iconic that it sells for up to $10,000, more than a premium original copy of Mobley 1568.

But where to start? First some basics, I’ll keep it short, skip if you know it all

 Basics: The Microphone

A microphone measures the sound pressure variations at its diaphragm within a range of audible frequencies. As the sound waves cause varying pressures around the mic diaphragm, the microphone produces a coinciding electrical audio signal, which is sent to the engineers mixing desk and tapes.

Basics: Volume

Volume (loudness) is measured in “decibels” across the range of human hearing from inaudible (0) to intolerable (150) . Next time your better half tells you are playing music “too loud”, refer her to this chart. How many decibels is “too loud”, sweetheart?” Hint: this tactic generally rarely works. “Too loud” is an opinion, not a measurement. 

The absolute measure of loudness, decibels (linear) is one thing. What matters for microphones is their relative sensitivity at different frequencies across the audible spectrum, between a 30Hz sub-bass to upper thresholds of hearing around 20kHz and beyond. This is reported in +/- decibels variation from a “flat response” (“flat” 0dB,  meaning equal sensitivity at all frequencies) 

Basics: Frequency (Hz)

Sound is a traveling longitudinal wave which is an oscillation of air pressure. A sound’s volume is measured in decibels (dB), its pitch is measured in hertz (Hz), a number of cycles per second: the faster the oscillation, the higher the pitch.

All instruments in the jazz spectrum have a different frequency range, and benefit from microphones  with the best sensitivity to their characteristics.

An engineer’s cheat-sheet below  follows the conventional wisdom that hearing effectively stops at 20kHz, though there is plenty of evidence that instruments can generate frequencies far in excess of this, even if not all microphones can record it, and that the presence of higher frequencies is preferred.

The trumpet (not included above) is more or less the loudest jazz instrument, which generates a massive 90dB volume at peak,  and pitch that stretches up to 100kHz.

The ideal microphone is one with a “flat response”, equally sensitive at all frequencies, but that was not how things work. Microphones exhibit different sensitivity to different parts of the frequency range, measured in decibels above or below the flat response  level.  The sensitivity template below is an engineer’s view where  these fall (there are no  agreed definitions)

For commercial applications, TV and radio broadcast –  sports commentary and news readers, microphones were designed to perform well in the 2-5kHz range. The bottom end and top end of the frequency spectrum is more  important in music, and prey to reducing microphone sensitivity at either end, roll off. Some microphones excel in the area of brilliance, inhabited by cymbals and hi-hat,  others in the bass and sub-bass frequencies, and some have raised sensitivity in the vocal range.

Early Days: late 40’s early 50’s: the US ribbon microphone

Exemplified by American RCA ribbon microphone. Produced from 1932 – 1955, the brick-shaped  RCA 44-BX is perhaps the single most recognizable ribbon microphone in broadcasting history, along with its sausage-shaped successor, the  77-DX. The 44 BX uses a 2″ long corrugated aluminium ribbon just 1.8 microns thick, roughly 1/20th the thickness of a human hair. These collectable vintage microphones, often from the final inventory of closing radio stations,  sell today for $3-6,000

The pattern of directional sensitivity became switchable – omni-directional, cardioid– heart shape sensitivity , or bidirectional, front and back only, according to intended use. These patterns determined how far an instrument’s microphone would also pick up other instruments, background noise and ambient room reflections, or just the facing  instrument’s voice.

The frequency graphs of these ribbon microphones show the roll-off of bass frequency to compensate for the proximity effect – an increase in bass sensitivity due to close proximity to the sound source, in this case a radio announcer’s voice. Switched to music, the microphone’s sensitivity remains flat.

A 44DX or BX is seen here suspended horizontally above Herbie Nichol’s  piano – apparently this angular position caused the internal ribbon to “sag”, improving bass responsiveness. Also sneaking into the shot, a Neumann U47, multiple sources. (Van Gelder’s piano-recording technique has been a subject of some debate, though generally I find no fault with it) 

German valve microphones Arrive!

The early ’50s saw the arrival of highly sensitive German-manufactured valve/ condenser tube microphone, replacing the ribbon technology with a vacuum tube – large diaphragm, separate power supply – exemplified by the iconic Neumann U47:

Particularly sensitive to the mid-band voice of the alto and tenor saxophone, seen frequently in Francis Wolff’s studio  portraits, the substantial U47, also  seen below left, Zoot Simms. 

Next generation: small diaphragm pencil condenser microphones

The early 60s saw the arrival of more compact valve microphone designs, the small diaphragm pencil condenser microphone, pictured below centre and right, Dexter Gordon and Eric Dolphy

A range of mics aimed at specific tasks emerged, for the upright bass in particular. These benefited from the proximity effect, a phenomenon in which moving the microphone closer to the sound source improved its bass sensitivity.   

The small diaphragm pencil condenser microphone became popular with Van Gelder, especially the German Shoeps M221b destined for drum-kit overheads, and another small diaphragm pencil condenser microphone, the Neumann KM54a addressed by Tina Brooks,  pictured below right.

With stereo in the ascendant, engineers had to equip themselves with multiple sets of microphones, four to six mics for the drum kit alone, a not inconsiderable outlay.

The Art Director butts in

Many Francis Wolff studio portraits feature the most visually provocative accessory to the simple microphone tube – the shockmount – an elasticated suspension cage which holds the microphone body, insulating it from vibration and rumble, and looks rather other-worldly. 

The slim pencil condenser microphone itself is visually the least impressive element, but embraced by the large angular shockmount, and the sensitive capsule end capped with a large ribbed globe to attenuate airflow from the instrument, it’s an object of beauty: uniting both form and function. 

 

West Coast, Roy Du Nann, and the AKG C12

Meanwhile, back on the West Coast . .  .

Art Pepper Meets The Rhythm Section (1957): 

Contemporary Records  are among the best audiophile vintage recordings, frequently attributed to the C12 – a microphone which deserves equal billing to the U47, though not found in the Van Gelder microphone armoury.

Nine different directional characteristics could be selected from the remote control unit, and it claims a range from 30Hz to 20kHz. The C12 was introduced in 1953 and about 2,500 of them were produced in its ten year run.  Its capsule was the first to have  an acoustic “fingerprint” in its frequency response, a well-judged rise in the brilliance zone of air and sizzle.

One of the most famous ’60s Brit-pop vocalist, Dusty Springfield – high maintenance in the hair lacquer and mascara department –  I only Wanna Be With You, recorded all her hits with the C12.  

Original AKG C12’s today are rare and typically sell at an extraordinary premium of $15-20,000, a dollar a hertz, even up to $30,000.

FET : the transistor arrives!

In the early ’70s, to reduce cost, and improve on the wastage rate of vacuum tube manufacture, original tube microphone designs began to be replaced by a transistor-based model, signified by the suffix letters FET – Field Effect Transistor, So you have a Neumann U47 FET, valued today at about a tenth of the original tube model. Valves good, solid state not so good.

Some of the photos in this post are respectfully borrowed from the RVG Legacy site, where you will find lots more information. 

Collector’s Corner

Here my exploration of vintage microphones ends, many competing manufacturers, competing models, incrementing model numbers, Ela 251, U67, TLM 102, all too much for me What I understand better is why original vintage recordings make such fine vinyl records. 

At least now you can look at a vintage LP cover photo with a microphone featured, and can casually toss into conversation: “Interesting, a U47, I believe“, leaving your fellow collectors at a loss for words, having previously thought a U47 was a wartime enemy submarine. Hopefully you have gained some information that may be useful to you at some future date, if only your local pub quiz-night. Good luck, and mine’s a pint,.

Any engineers out their, feel free to correct any mistakes, probably many, I learned a lot in discovery but I am not an engineer, just a fan of what engineers do. To comment engineers must first complete this Captcha test: :

Tee Hee

More on music soon.

 

 

LJC