Hmm. What I don't like about coincident techniques is you throw away phase information. I wonder if you could take Blumlein configuration and just split the mics by about 15cm, while leaving the directions the same. This might give you the best of all worlds: directionality, phase information, and each mic hearing both front and back.
..If a Blumlein array has a SRA (the Stereo Recording Angle of pickup in which your source is located) of around +/- 40 degrees, then spacing the mics without changing the angle between them would narrow that SRA further. To keep the same +/- 40 degree SRA while introducing some time difference information you'd narrow the angle between the mics as you space them further apart. For your 15cm suggestion, that angle would be about 62 degrees.. Continue on in that way and you'll eventually end up with two figure-8 mics spaced about 60cm apart facing directly forward and using only time differences for stereo pickup, acting like spaced omnis in that aspect. Of course they'll sound different for a number of reasons, a big one being that they will reject all sounds arriving from the sides (and form above and below) which might be useful.
Below are some visualizations of the spacing and angles above provided by
a great website applet someone posted a link to on TS a while back. It can be quite interesting to play around with.
You can either choose standard mic'ing setups in the drop-down on the right, or roll your own by selecting the
mic pattern on the left and entering values on the top right for
mic spacing,
mic angle and orchestra angle which is the apparent width of the source viewed from the mic position.
Orchestra angle determines the position of the colored lines in the arc in front of the mics. The applet then calculates the SRA and the level and time differences between mics for full left/right sources. Those values are displayed in the grayed boxes on the right and the SRA is also visually displayed in gray under the colored orchestra angle lines. It also displays two other useful pieces of information: the angular distortion of the source during playback using a typical 60 degree stereo setup is shown by the spacing of the colored lines between the two speakers at the top. Finally and importantly, the overall sensitivity to sounds in the horizontal plane around the stereo mic array is shown as a gray line surrounding the mics. For Blumlein the gray line is a circle, indicating equal sensitivity in all horizontal directions. As the angle between the mics is reduced (regardless of the spacing between them) the sensitivity to sounds originating from the sides of the array is reduced, giving the 62 degree angled example a bean shape. Once the bi-directional mics are facing directly ahead, their nulls are fully aligned and the overall sensitivity of the array looks like a single bi-directional mic facing forward.
In order below is-
1) Bi-directional mics spaced 0cm, angled 90 degrees (standard Blumlein)
2) Bi-directional mics spaced 15cm, angled 90 degrees (same angle just spaced some in Richard's conjecture)
3) Bi-directional mics spaced 15cm, angled 62 degrees (notice the same SRA and source distribution as Bumlein, but with two differences- time difference information introduced by the spacing, and reduced sensitivity to the sides of the array)
4) Bi-directional mics spaced 77cm, angled 0 degrees (full time based spaced technique, needed a bit more than the 60cm mentioned previously to approximate the same SRA, note the increased angular distortion on playback and the full null for sources to the sides of the array)
Topic: Why Blumlein sounds more spacious than other coincident or near-so arrays (Read 31914 times)