History
What is the big deal with ribbons? Ribbon microphones were popular because they were better than the moving coil microphones available at the time. In the 1950s, condenser microphones took over. Not only did condensers sound better but ribbon microphones presented many disadvantages. They needed huge magnets and were therefore bulky. Some of these magnets, like on the classic RCA 44, weighed up to six pounds! The ribbon microphone is fragile. The two micron thick ribbon is suspended between the two magnets and, if while capturing sound waves there is too much air movement or SPLs, the ribbon will tear. The inconvenience does not stop there however as you still needed a heavy transformer to convert the microphone signal to a usable voltage level. Even then the voltage output of the microphone wasn’t that high.
Today : the myths and reality
Ribbon microphones never really disappeared. In recent years the technological advances have allowed ribbons to come back more prominently on the microphone scene. Neodymium magnets (the size of a AAA batteries) allow for much smaller microphones. Audio transformers are now of better quality and less noisy. In addition, recent ribbon microphones are able to withstand more dBSPL (louder sounds) than those of yesteryear. Generally ribbon microphones do not need to be supplied with phantom power. Sending 48VDC won’t hurt most new ribbon microphones but can kill an older model. All these elements now help make the ribbon microphone a real option when recording and even for live stagework. Blowing air at the ribbon is still not a good idea but you can place the microphone in front of a guitar amplifier or use it on drums. You do need to be careful if you use it for a kick drum, but as John Jennings explained, tilting the microphone forward so the air is distributed along the ribbon, can help you get the microphone closer to the kick drum.
When should you use a ribbon microphone?
As you can imagine, the answer is: “It depends”. It is true that there isn’t a perfect microphone or perfect position for all recording applications. What is a ribbon microphone best used for then? A ribbon microphone has smooth high frequencies, is generally bi-directional and offers a good frequency response both on and off axis.
Frequency Response
The sound of a ribbon microphone is often described as silky, as if it puts a soft thin blanket over everything. The ribbon seems to slightly attenuate the highs when compared to a condenser microphone. This is due to the resonant frequency of the membrane and the fact that it physically absorbs the high frequency transients. Condenser microphones have a tight diaphragm with a resonant frequency around 1kHz. The ribbon in a ribbon microphone is supported in a more relaxed fashion and Royer’s have a resonant frequency at 40Hz. As a consequence condensers naturally boost the highs (sometimes aggressively) and the ribbons don’t. When you need a warm sound for vocals, a ribbon microphone can do that for you (it worked with Elvis Presley). Need a microphone that will smooth out a sound source with an aggressive highend like an electric guitar? A ribbon microphone can do that too. Eddie Kramer used a ribbon (Beyer M160) on Jimi Hendrix’s guitar amps. As a room microphone, a ribbon will provide a very smooth reverb. The use of the right microphone for a given situation or source can (should) mean there is less need to EQ.
Bidirectional
The classic ribbon microphone is, by definition, bidirectional (figure eight) although other polar patterns are available. Both faces of the ribbon are exposed to sound (0º and 180º) but the sound coming from the sides (90º) is greatly rejected. The most obvious application is picking up two sources (singers for example) or using the front of the microphone to record the source and the back to record the natural room reverberation. By extension, you can use a pair of ribbons for a stereo recording. The ribbon is the microphone of choice for the Blumlein stereo technique.
Off-axis response
The frequency response of a microphone is important and the aspiring engineer often only considers the on-axis (in front of the microphone) response while neglecting the off-axis response. The consequence of a bad off-axis frequency response is that any leakage from other sources (such as other instruments) into the microphone will not sound good and will interfere with the general sound in a negative way. As John Jennings said, “Bleed is good if you have good off-axis response”, and this is the case with most ribbon microphones. Being bidirectional, you expect the sound behind (180º) the ribbon microphone to be picked up with a flat response too. At 90º (and 270º) the sound is cancelled out. At 45º we are off-axis and the frequency response of ribbon stays unchanged making it ideal in a stereo XY (coincident) configuration. In XY, the two microphone capsules are angled so that a center stage source is actually 45º off axis for one microphone and 315º off axis for the other. Whether miking in stereo or mono, the flat off axis response can act like a reverb that glues everything together.
In order to give a context to these technical aspects, next time I will provide some audio examples so that you can hear the sound of a ribbon microphone for yourself and hear how they can be useful to you.
Questions and comments? k.blondy@musitechnic.net