Review: Audio-Technica BP40

I’m usually quite partial to the look of Audio-Technica’s microphones. While it typically doesn’t wheel out the super-fine mesh work and gold inlay — the gorgeous AT5040 aside — I’ve always found its condensers struck a healthy balance between wanting to use them and admiring their looks. 

I’m not so sure about Audio-Technica’s latest mic: the large diaphragm dynamic BP40. It looks like the first thing I ever turned on a lathe in high school woodworking class. There’s eight concentric gouges in the body with only two having an intended use — one to locate the ringmount and the other to hide the low-cut filter switch. On the plus side, it certainly gives you something to hold onto, which is handy for a relatively heavy mic like this.

The BP40 is technically designed to be a broadcast vocal microphone, like the Shure SM7 or the (equally ‘ugly duckling’) Electrovoice RE20. But will the BP40, like the SM7 and RE20, be versatile enough to escape life on a spring-loaded boom arm from time to time?

The first thing I noticed when plugging in the BP40 alongside a Shure SM7B, was the difference in output. It was around 10dB more than the Shure when right up against the grille, depending on what was feeding it. The Shure’s lower output helps it handle the occasional Howard Stern-esque outburst but it does require a decent preamp to gain up the quiet bits. There aren’t any rules dictating which mics you can and can’t use in a radio station studio. These days you’ll find presenters spitting into everything from low output dynamic mics to sensitive large diaphragm condensers. The quieter, more controlled the studio, the more sensitive the mic you can have. A studio with less acoustic treatment or if you’re likely to have a bunch of guests all talking at once, might lend itself to having a dynamic where you have to be ‘on mic’ to be truly heard. Presumably, that’s what Audio-Technica is trying to offer with the BP40, a mic with the robustness and control of a broadcast dynamic but with an output level closer to a studio condenser.

DIAPHRAGM DISPERSION

The two mics have a few similarities: the frequency response of both mics starts to dive pretty quickly beyond 15kHz and they both have a large diaphragm, switchable high-pass filter, humbucking coil, built-in pop filter and rugged metal construction.

From there, things start to diverge pretty quickly. There’s roughly the same amount of foam between your mouth and diaphragm on both the SM7B and the BP40. Probably slightly more on the Audio-Technica, with the SM7B’s being of a finer grade. But the difference is in the spacing. The cage around the SM7B’s diaphragm puts a substantial air gap between the foam and the diaphragm — about an inch and a half. The BP40 barely has any gap. When you place your mouth against the screen of the Audio-Technica, compared to the Shure you get more proximity effect, more level and more power from plosives.

Thankfully the internal pop filter on the BP40 works fine; you do get a little more power coming through, but you’re not going to distort the diaphragm.

What I did find interesting was the slope and corner frequency of the high-pass filter. It’s a 100Hz rolloff filter, with a 6dB/octave slope. It doesn’t make much of a dint in the low end boost of the proximity effect and functions more as a catchall for low-end intrusions, like air conditioning units.

The SM7B, on the other hand, has a high-pass filter that’s gentler in slope, but begins much further up; closer to a 3dB/octave, 200Hz rolloff. It provides more of a gentle roll out to counter proximity effect if required, though this is mostly controlled by the cage’s separation.

The SM7B also has a mid-boost switch, which gives a gentle boost centred around 3kHz. The BP40 has a more defined boost centred around 4kHz, but it’s built into the response; you can’t switch it in or out.

There are a couple of other major differences between the two: vibration transmission and polar pattern. Tapping the stand connected to the BP40 gave a healthy bump in the mic pickup, while the SM7B was virtually silent. It’s part of the beauty of Shure’s Unidyne design that no one’s really matched. Squeezing the BP40 into its optional AT8484 shockmount will kill any stand-borne niggles.

The BP40 is also hypercardioid, while the SM7B has a cardioid pickup pattern. Because the BP40’s diaphragm is so wide, if you stay in front of the mic and don’t talk into its side, you’ll still be in the sweet spot. It does pick up the room a little less, but the Shure’s lack of sensitivity has this effect anyway.