I've had the DPA 4060 and loved the clarity of it, but it sounded a touch harsh in the end for me, and I'd like to dial things back a bit.
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Apparently the 4090 is smoother than the 4060, so that's why I'm considering it. It's also much cheaper than the MK2. Perhaps this would give me the clarity I'm after but be less harsh as the 4060.
4060 and 4090 use the same capsule, but the special 4090 capsule protection grid produces a flat, measurement mic-like response through the treble range. Unfortunately that grid is not available for the 4060.
The 4060 series has two interchangable grids, both of which produce a rising treble response. The longer, high boost grid is designed to compensate for chest worn vocal pickup and produces a peaking +10dB response centered around 10kHz, some people use that for music recording but I find it completely unusable. The short grid produces a more mild +3db shelf type response that approximates a diffuse-field eq. Some users record using 4060 series mics without any grid attached to achieve a flatter treble response. There is no question that the high frequency emphasis is less without the grids, but I have never seen a response graph of the naked capsule in the 4060 housing without a grid so I don't know how flat the response it that way. DPA does not recommend it as the mics are not designed to be used without the grids.
With few exceptions I almost always find that I can improve my recordings with some eq, regardless of the mics or other equipment used, and I'm not averse to doing so. When I use the 4060s I use them with the short grids. Sound is subjective, we all have pesonal biasis and I understand that people sometimes hear a harshness in the raw 4060 response, but I find it manageble with some careful eq. For me, doing so is an acceptable trade for the clarity I have not found in any other miniature omni regarless of what i do with the eq. Many times I'm actually eq'ing an additional broad shelf boost for general tone, along with a narrower (higher Q) notch to quell that perceived the ringing or resonance that can sound harsh. Every recording is different so there is no blanket formula that works every time.
I highly respect Righard's opinion and expertice and I've picked up 3 pair of Countryman B3 to do my own subjective comparisons. They are nice mics and though I've not used them enough to make any conclusive decisions yet, at this point I still prefer the 4060 clarity. Perhaps it all comes down to personal preference, or perhaps it's dependant on the required eq work I feel is necessary and am willing to do regardless of the mic used. I look forward to experimenting with them further and may well change my mind. The B3 is certainly more attractively priced than any other mentioned here.
All the mics mentioned are good quality and can produce excellent recordings. If you can, try them yourself and decide what works best for you, your recording style, your production chain, your ears and your ultimate finished recordings.
BTW, I second the notion of recording in stereo over mono at least for the ambient portions of your sonic constructions. Panned mono instuments can work well in combination with that, though it might help to use a touch of some appropriate stereo reverb to help place the mono bits in the same 'imaginary acoustic space'. That sense of space, of 'being there', is a big part of what it's all about for me.