Thursday, December 15, 2011

Spring microphones

Scene from Amelia
 
The first time I really noticed a spring microphone was when I bought New Edition’s Under the Blue Moon LP, back in 1986. Ironically, when I look the LP cover today, it seems that the photographer didn’t even bother to get the real thing. It has two of the most famous Shure models, and what seem to be two props made to look like spring microphones. To be honest, I used to think that New Edition had done a pretty good job on the 50’s cover songs as well. They did sing very well on this album, and it did have Little Anthony as a special guest, today but today it just sounds too “kiddie pop” to me. You can certainly find better cover versions out there these days.

All Bowlly and a Western Electric mic
Although you sometimes find contemporary artists using these mics on photo shoots or videos, they are hardly good enough to record anything these days. Unless, of course, you want that “old record” sound. Nevertheless, back in the day, artists like Bessie Smith, Blind Lemon Jefferson, and Al Bowlly (who had that typical “sweet singing” of the 20’s), depended on these microphones to record and perform.
 
Even though a lot of people call them spring microphones for the obvious reason, they are also known as carbon or double button microphones. They were made during the 1920’s/30’s, and widely used in radio broadcasts. I’m not going to explain the full technical details of how it works because I had some trouble understanding it myself. The spring suspension is known to prevent feedback or undesired vibrations. The housing contains carbon granules between two metal “pieces”. One of the pieces acts as a diaphragm that is affected by voice or sound waves and pressures the carbon granules into changing the electrical resistance between the pieces. Ultimately, this change of resistance results in the change of the current, and the sound eventually turns into an electrical signal. I found the schematic below on Wikipedia, to ease the understanding of the process.


But the hardest thing isn’t understanding how it works. It’s testing these microphones to see if they actually work. You need a small electrical current going through these mics for them to function. If you have an amplifier from the same era, great! But these are extremely hard to find, let alone a working one. After I bought my Lifetime model 6 carbon microphone, I searched online on how to get it working. Even sellers that are specialized in vintage mics, had no clue on how to wire them. Some even had amplifier schematics, but never tried to put one together. Finally, after some time, I came across an article written by Chris on his Preservation Sound page. Not only did he manage to make a unit to make the same Lifetime mic work, but he also uploaded audio links so you can hear how it sounds. If you understand the principles of electrical engineering, you can also try to make a unit, since there’s a schematic on how to put one together on the same page. But after I contacted Chris, he told me that he didn’t follow the schematic to the letter. That’s just an example he found online. He will be starting to make these units to order. So, if you have a carbon mic that you always dreamed of making it work, get in touch with Chris at chris@preservationsound.com. This week, I ordered a unit with him and will post an update once I get it.
 

Justin Timberlake in the What Goes Around...Comes Around video

At a steep price, today you can still find some of these almost centenary mics on Ebay. Keep an eye out for companies that made them back in the day, such as Western Electric, Universal, American, Electro-Voice, and Shure.

1 comment:

  1. A real very cool post!!
    I found this explanation very interesting:
    "The spring suspension is known to prevent feedback or undesired vibrations"
    Abraços!!

    ReplyDelete