I've been lucky enough to have a pair of Neumann KM 184 small diaphragm condenser mics for the last few weeks. These are mics I've used a lot in the past and I've always wanted a pair. While it's not exactly breaking new ground to suggest that these mics are an excellent choice for acoustic instruments they are still my first choice, not because there aren't other mics which can do a similarly good job but because I know these mics and they always deliver. In much the same way as an SM57 is popular on electric guitar cabinets because it is a known "first call" mic for many, the KM 184 is my first call mic for acoustic guitar, but that isn't to say that there aren't other mics which could do an excellent job, particularly in light of the fact that being Neumann's they are at the top end of the market in terms of price.

Sennheiser e614

To offer some basis for comparison I've borrowed a pair of Sennheiser e614s. These mics were new to me. I've used the e604, the e602 and the e609 many times in the past, all excellent mics, but I've never used these.

The 614s are hypercardioid, small diaphragm condensers and as the KM 184s are cardioid this presents a dilemma because the difference in the polar pattern could contribute significantly to the differences. In short, the distance factor, the distance from a source at which the ratio of direct to indirect sound is similar, is 1.7 for a cardioid and 2.0 for a hypercardioid. What this means in practice is that the hypercardioid mic should be used from slightly further away to yield similar results.

One of the first things which struck me is purely practical. The mic clip which comes with the KM 184 is a thing of beauty, precisely engineered its hard plastic clip snaps into place with a positive action and grips firmly without any possibility of slip but not so tightly as to make removal difficult. The thread adaptor is metal and the adjustable pivot tensioner is a metal thumbwheel with a firm grip. By contrast the e614 ships with a standard rigid plastic clip which is by no means poor quality but grips the e614 so tightly that removal was really difficult. Because of this in practice I would leave the e614s in the clips permanently.

My friend Guy Fletcher, a busy pro folk musician, was visiting me and as a "just for fun" exercise we recorded him playing a traditional tune on fiddle. The thinking being that if a mic has a tendency towards harshness, a fiddle will reveal it! I wouldn't usually use a small diaphragm condenser in a violin, I prefer ribbons in this application, but in this example it's useful for showing potential issues. This was a very quick recording and in a less that ideal space, tucked into the corner of my loft studio, in fact you might notice that Guy is wearing headphones in the guitar take but not for the fiddle, that's because there were no click tracks involved, he just overdubbed guitar over his fiddle. Thanks to Guy for permission to use this warts and all recording. The recording was made via the preamps in a Focusrite Red 4 Pre without AIR engaged without HPF filters engaged and no EQ or dynamics.

The Neumanns and Sennheisers change together, you never hear a mixture of a KM 184 and an e614 together. The change is indicated by the titles in the video. I'll leave the conclusions up to you but my thoughts are that in this less than perfect environment the differences are very minor indeed. So minor that once the video was edited I went back to check I hadn't mislabelled my audio files. I can confirm that they are different but not that different. Considering the difference in price between the Neumanns and the Sennheisers, the Neumanns retail for around £590 each in the UK and the Sennheiser closer to £170 each, this is the perfect illustration that unless everything else is right, a top flight microphone isn't going to be enough on its own.

To investigate this further a recording under more controlled conditions was required. 

Using The Sennheisers And Neumanns In Stereo

To give a chance to examine the differences between these two mics I recorded a short acoustic guitar example with both sets of mics in an XY array. Again this wasn't taking the difference in polar response into account as I wanted to compare like with like and changing two variables at the same time would have made things more complicated.

Both recordings were made with a stereo XY array with a mutual angle of 90˚ from a distance of 30cm with the array aimed at the neck/body join. To minimise the effect of position I arranged the two arrays one on top of the other (see image). The recording was made via the preamps of a Focusrite Red 4 Pre without AIR engaged and without the HPFs engaged. No compression or EQ is used.

The differences are clear, the e614 being both brighter and lighter through the midrange. The Neumanns sound much fuller and the top end, while not at all hyped, is sweet never harsh.

Which do you prefer on this guitar?