Get The Best From Condenser Microphones

Andrew —  April 13, 2011 — 6 Comments

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If you already own a selection of mics, or you’ve been able to borrow some mics off friends then you will already be on the right path to keeping your costs down for running a cheap multitrack recording session. The mics that you have will probably include some dynamic mics and maybe a few others, which are most likely to be condenser mics. There are other types of mics you might come across of course such as contact mics and boundary mics, but these are much more specialised and are unlikely to be sitting in the back of a mate’s cupboard. They are easy to recognise because they don’t often look like conventional microphones. You might be lucky and come across some ribbon mics, but the chances are slim so we’ll cover those in a later post when we look at buying new mics.

So, back to condensers and a quick overview of how they operate;

A condenser mic works by sound waves changing the air pressure immediately next to the diaphragm, causing it to move a small amount. The diaphragm is placed very close to a metal backplate and a DC voltage is applied across the two (which is why they require phantom power). The diaphragm and backplate become the two plates of a capacitor. As  the diaphragm is moved further away from or closer to the backplate, the capacitance changes and a current flows that is proportional to the movement of the diaphragm. Hey presto, you’ve got a condenser capsule!

This is a much more delicate arrangement than the capsule you will find in a dynamic microphone, and so they need to be treated with care. If you drop it and the two plates are knocked or moved, then that’s probably the end of the capsule, whereas if you just drop an SM58 (which I’m not advising) the grill might dent but should still work fine!

Condenser mics generally come in two different flavours; those with large diaphragms and those with small diaphragms. I’m not going to go into great detail as to how the technical differences between the two affect their response, because DPA have already written an excellent page with all the info on it here that would take some doing to surpass.

Small Diaphragm Condensers

These tend to have a diaphragm diameter of maybe 1 to 1.5cm, and have a superb wide frequency response, in particular their hf response is generally better than large diaphragms. This is really useful when you want to pick up something with a lot of high frequency content like cymbals, so try them out as drum overheads! Generally they can handle higher sound levels too and have a good dynamic range, i.e. loud stuff = no problem. (see the DPA link above)

Their high frequency response makes them a very popular choice in the classical recording world, because without that nice flat top-end a recording can easily become dull-sounding. So if you are recording a piano or acoustic guitar, a small diaphragm will give you a nice crisp and bright high end.

Large Diaphragm Condensers

These typically have a less even high frequency response, as the physical size of the diaphragm means that high frequencies will ‘break up’ across the diaphragm rather than moving it all in one go, like a piston. So high frequencies usually drop off pretty quickly beyond about 10kHz. That might sound pretty high and maybe not worth considering, but to get the high top-end back, manufacturers often put in a little hf boost, which will extend down much lower than 10kHz, probably down to about 2kHz. This isn’t a bad thing, in  fact it can be really useful on something like vocals to bring out the singer’s tone and can sound very flattering. They are also more sensitive than small diaphragm mics, and are less noisy i.e. very quiet stuff = nice and clean, again useful for things like vocals.

Most large diaphragm condensers will come with a -10dB pad on them, because if they are subjected to high sound level they distort more easily than small diaphragms. So if you decide to try them out on something like drums then put the pad in. They are also more likely to have a switch-able directivity pattern, so you can for example put them in cardioid to reject some of the room if you want them on an acoustic guitar, or in omni if you want a nice deep low end on an upright bass.

So, once again, it would seem the key to getting the most out of the mics you have available, is to have a bit of an understanding of how they work and what they are likely to work well with, and of course a whole lot of experimentation. You will probably find that auditioning the mics before you use them to be a useful trick, more info on that with the page on dynamic microphones.

[image via recordinghacks]

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