01/07/09

LINE UP REVIEWS DPA 5100 MOBILE SURROUND MIC

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The DPA 5100 is a very interesting development from DPA, which extends the number and variety of microphone arrangements for the acquisition of 5.1 surround sound. The compact array resembles, in size and shape, a large bicycle saddle and provides six discrete outputs. The LFE feed is derived internally from the left and right microphones, and complies with the ITU specification of a -10dB signal level below 120Hz).There is no access to the inside of the unit for us nosy mic anoraks, as the acoustically transparent cover is intimately stitched in place!
By Mike Skeet, Line Up, Summer 2009

However, we are told that all the miniature capsules are pressure operated types (ie fundamentally omnidirectional), but that the required directionality is obtained through the use of DPA's development of a small interference-tube technique - patented as the DiPMic or Directional Pressure Microphone. Pressure operated microphones have some inherent benefits over pressure gradient types, of course, including being less affected by wind and handling noise.The left and right microphones are angled outwards, either side of the centre capsule and the capsule diaphragms have been arranged to be as close as possible to maximise the coherence, localisation accuracy and to minimise comb-filtering effects when mixing down to stereo or mono.

The rear facing capsules are flush mounted and spaced 185mm apart (roughly 'ear' separation) and there are acoustic absorbing baffles placed between the microphones to improve directionality and separation between channels. This also provides some useful time-of-arrival difference de-correlation for the rear surround reproduction.

The d:mension™ 5100 Surround Microphone is remarkable light, and both the top and bottom surfaces are fitted with 3/8-inch threaded sockets (the bottom one is an insert for a 5/8-inch socket) to allow the mic to be mounted on a stand or from a boom. An optional suspension hook is also available. Audio connections are via a Lemo 2B-series I8-pole female socket, neatly angled at the lower rear, and a five metre cable is provided with a Lemo plug at one end and six male XLRs at the other. Ten, 20 and 50m cables are available as optional extras. Also supplied with the mic is an outdoor cover for more wind protection and water deflection.

Listening The internal arrangement may be invisible, but the sound staging is quite tangible. I plugged the d:mension™ 5100 Surround Microphone into a box of six phantom powered mic pre-amps, all with the same gain settings (although in fact, the LFE channel doesn't require phantom power). Checking each output was very encouraging with spoken voice, and so I moved straight on to comparing the 5100 with one of my own DIY surround arrays using B&K4006 omnis. I found there was around 8dB more output from the 5100 capsules, but once I'd compensated for that the new array and my old 4006 system were reassuringly similar in terms of tonal characteristics on spoken voice.

Trying a stereo mix derived from only the front left and right capsules, the width and imaging came over very well. Bringing up the centre feed obviously fills in the middle of the soundstage, and I found running it at about 4dB lower minimises any tendency to narrow the stereo width. The rear capsules can be used to add some 'space', again at a slightly greater reduced level. Having tried all this, I saw a suggested down-mix chart in the User's Manual, which suggests -3dB for the centre and -6dB for the surrounds!

Having experimented with a number of double MS and dummy head surround microphone rigs over the years, both for location music recordings and outside for capturing birdsong and steam trains, I managed to squeeze into the short review period a number of these practices. First there was a brass band at a local theatre concert. I slung the 5100 above and behind the conductor, using only the front pair for the stereo mix, with some spaced figure-8 mics over the back of the band, and an MS pair for the soloists to the side of the conductor.

For the surround mix, the d:mension™ 5100 Surround Microphone feeds were all separately laid down on a Deva V, with the spot mixon channels 7/8. I had no problem mixing these spot mics with the front pair. I ignored the 5100's LFE facility for this concert. Listening back at home, I found the usual enhancement of surround over stereo. Down in Surrey, The Aiden Woodcock Trust assists talented young musicians with its concert room and a loyal local audience. It is quite an intimate acoustic in which I recorded violin and piano on a raised stage, with the 5100 slung from a convenient beam above the audience. Audience applause obviously needed reducing relative to the performers, but you do feel that you are sitting amongst them at the playback.

Next, I went off to one of the preserved steam railway lines, but unfortunately with only diesels in service! With my DIY dummy head array, you can hear a passing train from well outside the width of the front left and right loudspeakers. At the old Great Central Railway line in Leicestershire, the 5100 mic rig produced the same widened passing effect with its surround playback.

It was also interesting to record some birdsong. Aiming the 5100 at a prominent bird, the interference tube front mics really seemed to fix that bird to the centre speaker on playback. You can move to the sides of the sweet spot and it stays in that position.

Outside use of the level on the Deva's meters for the rear channels, which I haven't seen before with the Holophone (or my DIY version). I deduce that this must be due to the more omni-directional pick-up of these flushmounted mics, compared to the front three. Just how you then relate to this in post production, to optimise the overall surround, is for aural interpretation!

This new d:mension™ 5100 Surround Microphone rig suits all the different sound sources I tried, and is now a fine addition to my microphone collection. For outside 'roaming' use, a one metre connecting lead would be a worthwhile accessory, along with a screw-in handle. Secretly, I would also like to tryout a version with the directionalized rear channel mics - are you listening over there in Denmark?

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