We have all heard a recording that made us wish ours sounded that good. We wonder how it was possible for it to sound with such quality, definition, realism, dynamics and power. Making the best possible sound is the goal of every sound engineer, producer and artist. Of everything in the recording or live sound chain the signal passes through, from the microphone, the mic preamp, the compressor, the equalizer, the mixing console, the recorder, the reverb units, the delays and the special effects gear, all the way to the monitors, the most important element when it comes to achieving top-quality sound is undoubtedly the microphone, and second, or equally important, the preamp.
You could say the most important thing is the mic/preamp combination. If you manage to capture the sound in the best possible way, it is much easier to maintain that quality through the rest of the gear that follows the mic/preamp.
There are many techniques that have been used in the best studios for many years and that have been little known until now, because high-quality microphones with special characteristics, such as figure-8 microphones, were expensive.
The figure-8 microphone is one of these, and it has had very little exposure. As a result, most engineers have had few chances to learn about its extremely valuable characteristics, which make it possible to get recordings that are impossible with other microphones.
Quality Without Excessive Cost
Now there are good figure-8 microphones for every budget, and some are very affordable.
There are many microphone “techniques” with many different goals. Sometimes a technique is used to make a sound more defined. Other times it is to obtain a “special” frequency curve, one that is flatter or has some frequencies cut and others emphasized. There are techniques for special effects, such as stereo recordings that are more natural and at the same time have a greater sense of panoramic width. There are also techniques for getting more separation between one instrument or voice and the other instruments and voices.
All of these goals are possible with the microphones we’re discussing: figure-8s. For example, isolating the vocal from the instruments when they are all recorded at the same time. Or recording a singer-songwriter with maximum separation between voice and guitar. In this case, cardioid microphones achieve a separation that is a fraction of what we get with figure-8s.
The Characteristics of the Figure-8 Microphone
The figure-8 microphone picks up sound from two sides, with one side out of phase with the other. They are normally side-address mics, and both sides are “good.” At 90 degrees from the pickup axis lies the null axis, which rejects sound in a 360-degree plane. Unlike other directional microphones such as cardioids, which reject sound in a very uneven way depending on frequency, the figure-8 cancels 100% of the sound in that plane at all frequencies at once.
If we looked at the polar diagrams of a large-diaphragm multipattern microphone, we would see several interesting details in the figure-8 pattern compared with the cardioid:
First. On the figure-8 mic at ninety degrees there is a drop in pickup at all frequencies. This is the plane where the signal reaches both sides of the capsule at the same level and out of phase, so the sound is canceled 100% at all frequencies.
Second. With the cardioid microphone at 90 degrees, the attenuation is only between 4 and 8 dB across the indicated frequencies from 250 Hz to 8 kHz, and about 23 dB at 16 kHz.
Third. The cardioid has response curves with very significant peaks and dips at every pickup angle except zero degrees, where it is flatter. For example, if we study the curve at 180 degrees, we see a very irregular curve with an 18-decibel variation in just two octaves between 500 Hz and 4 kHz.
- 1. 250Hz - 17dB
2. 500Hz - 28dB
3. 1Khz - 23dB
4. 2kHz - 14dB
5. 4kHz - 10dB
6. 8kHz - 16dB
7. 16kHz - 17dB
At the high frequency of 4 kHz, it not only picks up up to 18 dB more level than at frequencies from 250 Hz to 2 kHz at 180 degrees (where it should be more directional), but it is also less directional than at almost any other angle.
Useful Conclusions:
1) First, the cardioid microphone has no angle that truly rejects well, and its rejection at 90 degrees is quite poor, which is where other sound sources often enter the microphone.
2) Second, a figure-8 microphone has a plane at 90 degrees where the rejection is excellent and can be put to very good use in different ways.
3) A third conclusion is that the figure-8 microphone has a flat response at any angle, so its off-axis sound is more natural and less colored. This can therefore be put to good use when we want to capture direct sound from several angles or pick up ambient sound off the pickup axis.
4) Another conclusion concerns the quality of the ambient sound entering a cardioid microphone like those in our example, which have large capsules. The frequency response curve is very irregular, with peaks and dips, at any angle other than zero degrees. The cancellations of different frequencies at each angle produce an ambient sound that isn’t good. For this last reason, the cardioid microphones used to hang in a concert hall to capture an orchestra and the room are always small-capsule models (as long as good cardioids are available).
The polar patterns normally shown (especially those of cardioid microphones) are an idealization of the polar curve. For a cardioid microphone, a polar pattern showing a single curve is in reality little more than a symbol and not an actual drawing of the polar pickup. To know the truth, you have to see the polar curve at a number of frequencies.
Practical Uses of the Figure-8 Microphone
We can use a figure-8 microphone to get sounds in recording and live sound that are impossible with other microphones.
One of the most interesting uses is the isolation you can achieve with a figure-8 microphone.
1. Getting more separation when recording two voices or instruments at the same time, with 2 figure-8 mics.
2. Isolating or reducing the sound of other instruments when recording a voice or instrument, with a figure-8 microphone. This can be done with the null plane in a vertical position (FIGURE 4) or with the null plane in a horizontal position.
3. Separating the voice and guitar of a singer-songwriter with two figure-8 microphones. In PHOTO 1 you can see how one figure-8 microphone is set up for the voice with its null plane aimed at the guitar, and the other figure-8 microphone is set up on the guitar with its null plane aimed at the voice. In this case the difference in isolation between a figure-8 microphone and a cardioid microphone is very large, because at 90 degrees from the pickup axis the figure-8 has its null plane, while the cardioid normally has only 5 to 10 dB of attenuation at frequencies below 10 kHz. This saves us a lot of time and makes changes easier, such as adjusting the level of or equalizing the voice or the guitar.
Another isolation use of a figure-8 microphone is to reduce feedback from monitors and from speakers aimed at the audience.
The other quality we’ve seen in the figure-8 microphone, and what makes it so interesting, is that its off-axis frequency response is really very good. This characteristic makes it very useful when it is moved away from the sound source and picks up a high level of ambient sound relative to the direct sound. This makes it possible to use a large-capsule figure-8 microphone at a greater distance from the source.
Stereo Techniques with Figure-8 Microphones
We will talk about stereo recording techniques in another article. However, since there are techniques well known among those who make stereo recordings with microphone pairs, such as MS and Blumlein, that use figure-8 microphones, we will mention them briefly here.
The MS Stereo Technique
(Mid-Side) with a figure-8 microphone is very curious and interesting. It is a stereo technique in which you can widen or narrow the stereo image after you have finished recording. It consists of setting up two microphones together (what is called “coincident”).
One mic (normally a cardioid, which picks up what will be a mono signal) captures the mid sound (M for Mid) and the other mic is a figure-8 that captures the side sound (S for “Side”) with its null plane facing the sound source. The two signals are passed through a matrix to create the left and right channels. The matrix sums the two mics into the two channels, L and R, inverting the polarity of the S signal in one of the channels. The MS technique requires a good-quality figure-8 microphone in which the two sides are very similar.
Blumlein Stereo Recording Technique
It uses a pair of figure-8 microphones. It is also a “coincident” technique, with the microphones together and crossed at 90 degrees, each at 45 degrees toward the sound source. This way, the null plane of each microphone falls right on the pickup axis of the other.
Another technique that uses figure-8 microphones is multichannel, developed by the manufacturer Schoeps for recording multichannel 5.1. This technique can be considered a variation or extension of the MS technique
