ALL PAIRED UP

An important aspect of how we evaluate equipment is to ask how the product is relevant to us within our workflow. Let’s find out if these mics are your bag of chips. The ZPC-1 is very susceptible to wind noise, even when using the supplied windshield. This clip-on attachment features a foam ball that covers the mic diaphragm, but it doesn’t seem to offer enough protection, even against a gentle wind. This sensitivity makes them much better suited to a studio environment.

As a matched pair, capable of handling high SPL, the ZPC-1 begs to be used in the studio on piano, drums, and other acoustic instruments. I can also see these mics being useful in studio sound design and foley applications. In a pinch they could be used to capture a choir, but the nature of the diaphragms will see much better outcomes in closer mic’d scenarios.

While recording my piano I casually held both mics in a ‘V’ type pattern with my left hand and played the keys with my right. This may seem lazy, but it was intentional. When I test or review pieces of equipment I put them through their paces in adverse settings. I may test a microphone without using its intended windshield or suspension system, and often with no microphone stand because under these less-than-optimal conditions weaknesses can be exposed, and hidden strengths can be revealed.

As such, I found that the piano sounded clean and clear, with a really nice tone, and almost no handling or cable noise. This suggests to me that with an optimal setup they’d be capable of capturing a truly lovely sound.

ZOOM CERTIFIED

Zoom has entered an already crowded marketplace with this offering, but has managed to produce a paired set of condensers for about the price you’d expect to pay for popular dynamic microphone models — and then made them sturdy enough to comfortably knock around in the studio and at live performances. At this price-point I suspect that there will be plenty of musicians and producers who will see the ZPC-1 as an attractive option. For Zoom it is a natural extension of its range, with these microphones matching up perfectly with the F3 and F6 recording devices.

FACTORS AFFECTING TONALITY

Condenser microphones commonly used for professional audio come with diaphragms varying in diameter from under 5mm to over 25mm. The diaphragm’s diameter affects the performance in numerous ways. From a tonality point of view, however, the most significant affects are on the high frequency performance and the self-noise.

DIAPHRAGM DIAMETER

The high frequency limit of a condenser microphone with a circular diaphragm is primarily determined by the relationship between its diameter and the wavelength of the frequency being captured. At frequencies where the wavelength is considerably larger than the diameter, the diaphragm is too small to have any affect on the tonality of the captured sound. At frequencies where the wavelength is considerably smaller than the diameter, the diaphragm is big enough to be an obstacle and therefore have a significant affect on the tonality of the captured sound. And at frequencies where the wavelength is the same size as the diameter, a situation can occur where the diaphragm is receiving equal amounts of energy from both halves of the waveform (positive and negative), which cancel each other out and create a null (i.e. zero output). This frequency – where the wavelength is equal to the diameter of the diaphragm – theoretically determines the upper limit of a condenser microphone’s frequency response because it defines the first null point, but it’s not that straightforward…

Unlike the simple maths for determining a ribbon microphone’s high frequency limit [as shown in the second instalment], the high frequency limit of the condenser diaphragm is also affected by the angle of incidence and the way the diaphragm is mounted. For any given diaphragm, the high frequency limitations will be different in a side-address configuration than in an end-address configuration, and different again if mounted in a diffraction sphere or fitted with an equalising ring or diffusion grid.

It gets complicated when trying to define the upper frequency limit of a condenser microphone with a simple formula or rule. It is, however, worthwhile putting the concept of ‘wavelength’ into perspective with diaphragm diameter. The range of human hearing is considered to exist between 20Hz and 20kHz. Assuming a room temperature of 21°C, 20Hz has a wavelength of 17.2m – that’s how long one cycle is in the air. It’s significantly bigger than any practical microphone. At 20kHz, however, the wavelength is only 17.2mm long. It’s significantly smaller than the 25mm diaphragms commonly seen in dual-diaphragm microphones and is therefore affected by them.

Based on this knowledge, we’ll use 17mm (close enough to the wavelength of 20kHz) as a threshold point for differentiating between small and large diaphragms. There are no hard-and-fast rules for this, but condenser microphones with diaphragm diameters less than 17mm are generally described as SDCs (Small Diaphragm Condensers) while microphones with diaphragms of 20mm or more are generally described as LDCs (Large Diaphragm Condensers). Condenser microphones with diaphragm diameters less than 17mm usually exhibit extended high frequency response and better off-axis response when compared to those with diaphragms larger than 17mm.

Due to the very light weight of the diaphragm and the potential to make it very small, it is not difficult to make a condenser microphone with a frequency response extending up to 20kHz – the upper limit of human hearing. Maintaining a consistent response beyond 20kHz becomes more of a challenge, but is important for those who need to record sounds with content above the range of human hearing; whether to slow it down to create sound effects for movies and games, pitch-shift it down to analyze bat calls and insect sounds, or make ‘high resolution’ recordings for the audiophile market.

OFF-AXIS RESPONSE & TRANSIENTS

A sound arriving from directly in front of the microphone, perpendicular to the diaphragm, is considered to be on-axis, and is said to be arriving at the diaphragm from an angle of 0°. For the purpose of this discussion any sound arriving from an angle other than 0° can be considered to be off-axis because it is no longer coming directly on-axis. (This is discussed in a later instalment where we look at microphones’ polar responses and acceptance angles.)

As the diaphragm gets larger it becomes more directional at higher frequencies. As a result, sounds arriving significantly off-axis will be duller than sounds arriving on-axis. This is generally referred to as a poor off-axis response and results in a reduction of overall high frequency energy relative to low frequency energy captured by the diaphragm. Poor off-axis response at high frequencies is a characteristic of all large diaphragm mics and fuels the myth that large diaphragms have better low frequency performance than small diaphragms, when the reality is that they have worse high frequency performance (as discussed in the previous instalment, see ‘Subkick microphones’).

As the diaphragm gets smaller its off-axis response improves. This is one of the reasons why small diaphragm condensers are often preferred for main stereo pairs when making distant-miked recordings of orchestras, choirs, pipe organs and chamber music – all situations where sounds arriving from all directions (including early reflections, reverberation and audience reaction) need to be captured with a consistent tonality. If not, the sounds arriving off-axis will be duller than those arriving on-axis and result in a sound that could be described as ‘muddy’ or ‘roomy’.

A microphone’s off-axis response is not much of an issue when close-miking a single instrument, but it can be an issue if you are close-miking a number of instruments playing together in the same space. After doing what you can to minimise spill by the strategic use of instrument placement, baffles and polar response rejection (as explained in later instalments), you’ll want the remaining spill to be captured clearly so it doesn’t muddy up the sound when all the mics are blended together in the mix. The better off-axis response of smaller diaphragms can have a cumulatively positive effect in this situation.

As a generalisation, the large diaphragm condenser’s reduced high frequency capture and accompanying slower transient response means it tends to sound mellower and potentially smoother than a small diameter condenser, but with inferior off-axis response. Regardless of the diameter, however, the condenser microphone’s diaphragm is always going to be significantly lighter than a similarly-sized dynamic microphone’s diaphragm/coil assembly and can therefore move much faster, giving it excellent high frequency performance and transient response in comparison.

EQUIVALENT NOISE LEVEL

In ribbon and dynamic microphones the primary source of noise is thermal noise, as explained in the previous two instalments of this series (1) (2). This form of noise is rarely mentioned in their specifications because it is very low and will be insignificant compared to the noise from the preamplifiers they are connected to – which tend to be used at higher gains than they would be with condensers due to the lower outputs of ribbons and dynamics.

In condenser microphones the term equivalent noise level usually refers to the combination of the diaphragm’s self-noise and the noise from the microphone’s electronic circuitry. Self-noise refers to noise caused by air particles randomly striking the surface of the diaphragm. This form of noise is not a problem with dynamic microphones because their considerably heavier diaphragms are less sensitive to the random impacts of air molecules. It’s also not a problem with ribbon microphones because their ribbon elements are not held under enough tension to make them sufficiently responsive to random impacts of air molecules.

Self-noise and equivalent noise level are explained in detail in the following instalment of this series. For now, the important thing to know is that with all other parameters being equal, a large diaphragm will have less self-noise than a small diaphragm. It will also have greater sensitivity than the small diaphragm (meaning it provides a higher output level from the same sound source) but with a lower maximum SPL. So if you need to make a very quiet recording or if you need to record something that has very low volume, a large diaphragm condenser is a better choice than a small diaphragm condenser; it is quieter due to its lower self-noise, and its higher sensitivity requires less preamp gain and associated noise. If you need to record something very loud, a small diaphragm is a better choice; it can handle higher SPLs with ease, its lower sensitivity means less chance of overloading your preamp, and its higher self-noise won’t be an issue with a loud sound source. There’s more discussion about this kind of decision making in a later instalment of this series…

The noise from the electronic circuitry inside the microphone also needs to be considered. All active electronic circuits create noise – especially when that circuit has to work with the very small signals coming from a microphone capsule. (For many years this form of noise was unique to condenser microphones, but nowadays it also exists with active ribbon mics, active dynamic mics, USB mics and any other mic that has electronic circuitry in it.)

A presentation by Neumann’s Martin Schneider compared the frequency spectrum and amplitude of the diaphragm’s self-noise and the internal electronics’ noise for a large diaphragm condenser with a very low equivalent noise level. When averaged across the audible spectrum from 20Hz to 20kHz, the noise from the microphone’s internal electronics was approximately 3dB lower than the diaphragm’s self-noise. The large diaphragm microphone used in this example has an equivalent noise level of only 7dBA, therefore the noise from the microphone’s internal electronics (being on average just 3dB lower than the diaphragm’s self-noise) could be considered significant. Microphones with very small diaphragms (i.e. 6mm or less), such as Earthworks’ QTC30 or DPA’s 4060, have equivalent noise levels of 20dBA or more, most of which is self-noise. In these examples the noise of the microphone’s internal electronics is probably insignificant.

RESONANCE

Because the diaphragm is usually a circular membrane held under tension, it behaves like a tiny drum (imagine a miniature roto tom) with a strong primary resonant frequency, or note, of its own. Any sound that contains frequencies at or near the diaphragm’s resonant frequency will cause the diaphragm to resonate, emphasizing those particular frequencies above others and thereby adding to the microphone’s characteristic tonality.

The condenser microphone designer tweaks the diaphragm’s diameter, mass and tension to determine its resonant frequency – which typically ends up somewhere between 5kHz and 9kHz – and then decides how much damping should be applied to control the resonance. Increasing the damping reduces the strength of the resonance (which is equivalent to lowering the amount of boost on a peak/dip equaliser), but also reduces the diaphragm’s overall sensitivity (which is like lowering the fader). There is always a compromise between resonance and sensitivity, hence the market is full of condenser microphones with a characteristic boost in the upper midrange or high frequencies – often engineered and marketed as a feature to provide enhanced detail or to compensate for the loss of high frequencies through the air when distant miking. This balance of resonance and damping is another factor that determines how the condenser mic affects the tonality of the captured sound.

Most condenser diaphragms are ‘edge terminated’ which means the electrical connections (or ‘terminations’) to the diaphragm and backplate are made at the edges, leaving the diaphragm free to move. Some are ‘centre terminated’, which means the electrical connection is made to a terminal in the centre of the diaphragm – as seen in Neumann’s classic U47 and U67 mics respectively. This is like lightly placing your finger in the centre of a drum skin and listening to how it affects the resonances and therefore the tonality; it changes the balance of the diaphragm’s resonant modes, but in the case of the U47 and U67 it’s just one of many things that affect or determine their tonality. Another is, of course, their tube circuitry…

INTERNAL ELECTRONICS

Every circuit that an audio signal passes through imparts its own sonic fingerprint on that signal (typically as a combination of its inherent harmonic and intermodulation distortions), and every condenser microphone includes an impedance converter circuit that the signal must pass through in the process of becoming useable. That circuit will contain numerous electronic components, but the primary component will be an amplifying device of some kind (tube, FET, transistor, etc.) that imparts its own sonic fingerprint, contributing to the microphone’s overall tonality.

As with ribbon and dynamic mics, for many years a transformer was used to give the condenser microphone a balanced differential output suitable for sending a signal down a microphone cable and into a preamp. Contemporary designs use a solid state electronic circuit and don’t require an output transformer, although many still use one. The acronym ‘TLM’, used in the model names for many of Neumann’s contemporary microphones, stands for ‘Transformer Less Microphone’. Similarly, when DPA made an updated version of their classic 4006, ‘TL’ was appended to the model number to indicate it was ‘Transformer Less’. According to DPA’s documentation, removing the transformer allowed the 4006TL’s low frequency response to be extended downwards another octave from 20Hz to 10Hz.

Some condenser microphone manufacturers have returned to using transformers primarily for their ‘old school’ tonal properties, or simply to take advantage of the transformer’s relative simplicity for providing a balanced differential output. When Audio-Technica designed the 5047 – a premium version of their 5040 – they added a transformer output to maintain a ‘constant load output impedance’ and provide a ‘smooth sonic character’. [The effect of a varying load impedance was discussed in the second instalment of this series; it is the reason why the tonality of a passive ribbon microphone can be affected by the preamp it is connected to.]

Released in March 2019, the SR314 delivered a boldly designed vocal microphone to the market with its precision-machined stainless steel chassis and retro-meets-futuristic design.

The SR314 is now available in three eye-catching combinations—stainless steel, black coated stainless steel with a black windscreen, and black coated stainless steel with a stainless windscreen.

Key features of the SR314 include rich open natural sound captured in a tight cardioid polar pattern that is consistent throughout the full frequency range. 145dB SPL handling and an extended 20Hz-30kHz frequency response are the footnotes on a vocal microphone as brilliant and striking as the rest of the instruments onstage.

The SR314, SR314-B, and SR314-SB ship with an MC4 microphone clip and 8.5-inch padded protective bag.