The Blumlein Pair

Over the years, we’ve seen the development of many different recording techniques. While some may take it for granted, proper miking methods are of great importance for quality audio recordings, and they have pretty much changed the way that we listen to music. No matter the type of recording that you’re doing, whether it’s for music or audio for a film, you should be aware of different miking techniques that will take your work to a new level. In this brief guide, we’ll take a closer look at one of the oldest techniques called the Blumlein pair, which engineers still use to this day.

What is a Blumlein Pair?

An audio engineer named Alan Blumlein developed and patented this technique sometime in the 1930s. Back then, the method was pretty groundbreaking. It allowed the audio to have a spatial feel when replayed through two-channel stereo devices like speakers or headphones. The Bluemlein pair is a common practice these days and arguably the best way to record quality stereo audio.

The Blumlein pair technique requires two factory matched microphones, both of which have the same sensitivity as a function of position, also called the mic pickup pattern.These two microphones are then positioned facing the source at a 90-degree angle from one another and at a 45-degree angle off the central axis in opposite directions.

Since these microphones are supposed to have a bidirectional pickup pattern, the back lobes of each microphone face 225 degrees off the central axis. This allows you not only to record direct sounds from the source, but also the reflections of the room that you’re recording in. For this reason, the resulting recording appears to have more life to it. The use of unidirectional microphones would make the recording sound somewhat sterile in comparison, and it would sound as if the source is being suffocated. Of course, as with any creative profession, you’re free to experiment. But the proper Blumlein pair technique requires bidirectional polar patterns.

The whole idea is to record audio information that’s as realistic as possible. It’s probably the closest thing that you’ll get to being there and hearing the sound source. However, you also need to bear in mind that the overall quality of the audio really depends on the room’s acoustics as well as the size of the room.

Using the Blumlein Pair

Even though the technique is old, there are still many uses for it. First off, compared to spaced stereo microphone techniques, the Blumlein pair usually has no problems with phasing. It relies more on amplitude differences rather than the waveform phase to get that solid stereo image. At the same time, mono compatibility is also pretty good with the Blumlein pair.

This technique comes in handy for recording live ensembles, most of the brass sections, and stereo recordings of individual instruments. It’s especially useful for acoustic instruments like guitars and pianos. You can also implement the Blumlein pair for electric guitars, where you’d place the two microphones in front of one speaker of a combo amp or a cabinet. However, in many cases, engineers record electric guitars using cardioid pattern mics such as the Sure SM57. Cardioid mics are unidirectional.

Going back to acoustic instruments, the Blumlein pair can be deployed for drum recording, too. The pair of microphones is placed right above and slightly behind the drummer’s head. If you’re doing a professional drum recording, then these two microphones will just be an addition to all the individual miked up components. However, it can come in handy in case you don’t have enough channels on your audio interface or a mixer and just want to record a decent quality drum recording for a demo.

Mic Requirements

You can’t just use any type of microphones for this technique. The first and the most important requirement is that you need to use two identical microphones. They must be the same exact models matched from the factory. Secondly, you’ll need to think about the pickup pattern. As we already explained, these microphones need to have a bidirectional figure-8 pickup pattern. With this pattern, you get a stereo picture of the source, along with the room tone and reflections from the rear lobes. This creates a more realistic audio recording.

You can use any quality mic with a figure-8 pickup pattern for this technique. Both ribbon mics and condensers work well. For instance, a pair of Royer R-121s or Warm Audio WA-47Jr mics will do a fine job in a Blumlein arrangement. Just make sure to have the same exact models in a pair.

Pros, Cons, Alternatives, & Limitations

Overall, the Blumlein pair is a beneficial technique to use if you want to record a stereo image of one single source. In some cases, ye can even record a whole ensemble or band. We can also use it for an additional overall stereo image in combination with individually placed mics.

One of the downsides to using this technique is the potential cost. Bidirectional figure-8 pattern mics can be very expensive, although there are some decent ones out there if you know where to look. And of course, you’ll need a matched pair to do it right, adding to the cost. If they’re not matched, you may not a consistent stereo image, and the channels in the mix will feel unbalanced.

There are some other techniques that we can use for an additional room recording, and they usually include more spacing between the paired microphones. Overall, the Bluemlein pair is a great solution for stereo recordings. It will not only record the source but some of the room reflections.

It’s mostly limited to indoor recording where there will be some room reflections involved. It wouldn’t make much sense to record something outside using the Blumlein pair. You’ll pick up on the surrounding noises. But if that’s the goal or you want to experiment, go for it!