IoSR Blog : 13 January 2014

Microphone of the month - December

It's microphone of the month time again (the microphone that has been booked the most in the month of December - see here for more). As a change from the previous two months, the microphone of the month for December is the AKG C414 B-XLS No. 1.

The AKG C414 has been around since 1971 in various guises (almost as long as the Tonmeister course), and in that time it's become very widely used. It's a large diaphragm condenser microphone with variable directivity, and (depending on the model) switchable high pass filter and attenuation (pad). Its popularity is most likely to be due to the flexibility of the variable directivity, together with specifications that are reasonably good in all areas.

It's certainly not a perfect microphone though. As can be seen from the frequency response below, there is some mid-range unevenness and a slight high frequency boost.

Frequency response of the AKG C414 B-XLS set to omnidirectional, taken from

Also, due to the fact that it uses a large diaphragm, the directivity deviates at high frequencies. For instance, when set to an omnidirectional pickup pattern the directivity is almost figure-of-8 at high frequencies, as shown below.

Directivity of the AKG C414 B-XLS set to omnidirectional, taken from

Of course, the advantage of a larger diaphragm is a lower noise floor, and the C414 B-XLS is claimed to have an equivalent noise level of just 6dBA. This, coupled with a claimed maximum SPL of 158dB (including a pad), means that it should cope with most things put in front of it, from an electric guitarist given musical notation (probably the quietest musical sound ever) to something a bit short of a thermonuclear explosion.

414s in many forms

We've collected a large number of AKG C414s over the years: four C414EBs, four C414B-ULSs, and six C414B-XLSs. All of these have had a similar retangular shape, variable directivity and a large diaphragm, but with different electronics and slightly different features.

The EB was one of the earliest versions, and was the first to introduce the 3-level pad (0, 10 and 20dB attenuation), and the high pass filter (flat, 75Hz, and 150Hz cut-off frequency).

The EB was replaced by the B-ULS, which was black rather than silver, but more importantly had a different circuit design. The ULS acronym stood for "Ultra Linear Series", which was intended to denote a "completely linear transfer characteristic of all transmission parameters". Quite what that really means is unclear, but the circuitry is significantly more complex than the EB.

Our B-ULS models are the less common transformerless version (as indicated by the "TL" above the directivity switch as can be seen in the picture above). This model is often referred to as a B-TL model, but still carries the B-ULS indication on the rear of the microphone. In theory, the removal of the transformer should improve the technical performance of the microphone, though some argue that this has caused the loss of some of the character of the B-ULS.

The B-XLS was a fairly significant redesign of the C414. Rather than a boxy metal body with physical switches, the B-XLS has rounded edges and push-buttons with LEDs to indicate the status. Whether you think the latter is a good idea or not depends on how much rigging in large venues you do. In order to change the settings of the B-XLS, it needs to be phantom powered; this is easy to arrange in a small studio, but could be a pain if you need to walk a long way to find a handy phantom power source just to change the directivity pattern before you rig it. OK, with a bit of forward planning it's fine, but there's always that one time when you're suspended upside down in the Royal Albert Hall and you remember that you haven't checked the settings ...

The addition of LEDs also makes them a little less useful for work with video: as you're not able to turn the LEDs off they're just that bit more conspicuous. One more thing about the LEDs - the directivity pattern LED turns red if the microphone clips. A cunning idea, although slightly compromised when you think that this LED is usually pointed at the performer rather than the engineer.

The B-XLS also included changes to circuitry, extending the dynamic range of the microphone by lowering the self noise by 8dB and increasing the maximum output by 6dB.

The microphone model specifications are summarised below.

C414 EBC414 B-ULSC414 B-XLS
Equivalent noise17dBA14dBA6dBA
Maximum SPL (no pad)138dB134dB140dB
High pass filterNone, 12dB/oct at 75Hz or 150HzNone, 12dB/oct at 75Hz or 150HzNone, 12dB/oct at 40Hz or 80Hz, 6dB/oct at 160Hz
Attenuation (pad)0, 10, or 20dB0, 10, or 20dB0, 6, 12, or 18dB

Overall then, the AKG C414 is a flexible microphone with lots of uses, and I think it's probably best summed up by this quote from Sound on Sound magazine:

"I haven't found anything they do badly, and I've found lots of things they do well"

by Russell Mason

Have a look at, which includes specifications of wide range of microphones, and allows searching based on almost any parameter. It also includes a library of useful articles.