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Using Microphones

Recording the Bass

Recording the Bass - both acoustic and electric.


Figure 1. Miking up a bass cabinet.

Even more so than electric guitars, bass guitar is recorded simply by direct injection into the mixing board these days; or even replaced with a synth (heard the DX-7 yet?). Miking up the bass cabinet is still popular, however giving a touch of warmth and fullness to the sound. In fact, most recordings today use a deliberate mix between the DI'd signal and the microphone.

If you are interested in the latest sound and would like to record a double bass, here's the necessary mic technique. If it's an investment in microphones that will make you happy, I've prepared a few hints. And finally, continuing last month's phase switch project there is a short but important paragraph about correct wiring of XLR connectors.

Sound Projection



Sound sources radiate sound with a certain directivity which depends on the design of the source and the frequency. Bass frequencies below 100 Hz are generally radiated by all instruments and most speaker cabinets with very little or no directivity - rather uniformly in all directions. Higher notes, however, will be radiated over a narrower angle. They contain important components of bass sounds, such as harmonics and percussive 'clicks' such as the bass drum kick or popping sounds of a bass guitar.

To pick up a bass instrument satisfactorily, place the microphone within the instrument's main sound radiation area: in line with the speaker axis of a cabinet or the bell axis of a tuba and at right angles to the sound board of the double bass or the bass drum head. This ensures pick up of the instrument's entire frequency range.

Figure 2. Picking up the double bass.

Bass Cabinet

Placing the cabinet with its back to the centre of a wall is better than corner placement. Place the mic in front of a speaker's centre, close up, approximately 20 cm away. When combining this output with a direct injected signal try a phase switch to turn one of the signals out of phase with the other. This can often result in a 'fuller' sounding bass, with a very interesting sound being produced (Figure 1).

Double Bass

Position the mic between 5-20 cm in front of the f-holes, pointing directly at them. A combination of this mic's sound with the sound of a contact pick-up such as a C-ducer tape will add life and a natural sound quality to the feedback safety of the pick-up. See Figure 2.

Bass Microphones



There are a few microphones with an extraordinarily good bass response. Most of them have been around for more than 20 years and can be found in any studio in a variety of bass pick-up applications. Just like a pair of good condensers, at least one of them should be at hand for the ambitious home studio owner.

%image3% The AKG D12, for example, started out as a vocal mic until it became the bass mic. It has a strong proximity effect (bass rise at short working distances) and a special bass chamber lifts frequencies around 100 Hz, giving the typical warm and full-bodied sound. The main construction principle is its large diaphragm. Large diaphragm mics, though far away from a physically ideal microphone design, have a certain 'personal' tone quality to them. The D12 is perfect for all applications calling for a certain degree of 'bottom' or 'guts'.

The Electro-Voice PL20 (RE20, until recently) is a so-called Variable Distance design. A number of rear sound-entry ports at the side of the mic characterises this design and eliminates any proximity effect. It is also a popular mic for brass and reed instruments.

The Shure SM7 has a wide variety of applications including vocals. The Sennheiser MD421 (reviewed last month) is often used for bass drum, giving a lighter sound; good for guitar cabinets, too, especially for non-distorted sounds.

The AKG D202, a two-way microphone has a very neutral sound with no proximity effect at all.

All the above are dynamic mics. Finally I'd like to mention two condenser large-diaphragm types with switchable directional characteristics: the Neumann U87 and the AKG C414. They are standard studio all-round mics and will also give superb performance when picking up bass sounds.

XLR Wiring



Figure 4. XLR IEC/US wiring standards.
XLR Connector (viewed from rear of microphone).

IEC
Pin 1 Ground (Earth)
Pin 2 In-phase
Pin 3 Return

American
Pin 1 Ground (Earth)
Pin 2 Return
Pin 3 In-phase

Last month, I covered the use of the 'phase switch' as a useful tool in recording. But what does 'in-phase' mean regarding microphones? When a positive pressure is applied to the diaphragm (the diaphragm is pushed into the mic) the mic will produce a positive voltage on its 'in-phase' pin with respect to the 'return' pin. To check out a mic's internal wiring you need a polarity tester (available eg. from EMT) which will provide the pressure impulse. But you can also use one mic as your reference mic and check out the others following this procedure:

Connect both mics to your mixer, with only one mic's channel open. Hold the mics close to each other and, talking into both of them, bring up the other mic channel's fader. If the bass response becomes poor, the microphone or (much more likely) a mic cable is wired incorrectly, being 'out-of-phase'.

As far as microphones are concerned, all manufacturers wire them according to the IEC standard. For mixing desks, effects units etc. some brands use the American standard, with Pin 3 in-phase, Pin 2 return, but this shouldn't present any problems, as long as balanced lines are used (Figure 4). With single-ended (unbalanced) connections you may run into trouble. More about that next time.



Previous Article in this issue

Monitoring - Problems & Solutions

Next article in this issue

Mating Microphones


Home & Studio Recording - Copyright: Music Maker Publications (UK), Future Publishing.

 

Home & Studio Recording - Aug 1984

Donated & scanned by: Mike Gorman

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