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Earthworks Audio QTC30

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  • MSRP: $1,099


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QTC30 Documentation

OmnidirectionalEarthworks Audio QTC30

Omnidirectional Condenser Microphone

The QTC30 is an omnidirectional (pressure) electret condenser microphone with a wideband, low impedance preamplifier.

Like all of Earthworks’ “High Definition” microphones, the QTC30 meets all these criteria:

  • Fast transient response (aka “impulse response”) … “The impulse response is the single best measure of the overall sonic accuracy and fidelity of a microphone. “

  • Fast diaphragm settling time … “If the diaphragm is still vibrating from the sounds it picked up previously, it will tend to mask or color many or all of the subtle sounds that follow.”

  • Extended frequency response … “Studies have shown that acoustic sounds and overtones of musical instruments extend to beyond 100kHz.”

  • Minimal signal path … Pattern controls, pads, and filters can degrade the sonic qualities of the mic; therefore, the QTC mics have none.

  • High SPL handling … Low distortion up to and beyond 140dB.

  • Low impedance … The mic must able to put its signal through a long cable run without signal loss.

  • Consistent polar pattern … maintain a consistent pickup pattern over the mic’s full frequency range, to reduce phase cancellation at the edges and “spotlighting” of higher frequencies.

The QTC30 requires a standard 48V phantom power supply, with a high current level. The mic draws 10mA.

As an omnidirectional microphone, it exhibits no proximity effect.

The QTC model name prefix means “Quiet / Time Coherent.” The “Quiet” nomenclature distinguishes the QTC mics (self-noise ~22 dBA) from the TC series (~27dBA).

“Time Coherent” is Earthworks’ means of distinguishing the tiny omni capsule design from all the directional and larger-diaphragm condensers on the market. According to David Blackmer, other designs “smear the signal in the time domain” due to inadequacies of their design:

  • larger diaphragms resonate like drumheads when excited, coloring the recorded sound.
  • most mic capsules are mounted inside of a “cage” that causes resonances and reflections, introducing phase cancellation to the signal.
  • Directional mics “[sample] the sound at multiple points,” reducing the mic’s accuracy.

In contrast, the tiny (~6mm) omni capsule used in QTC mics avoids all these problems, producing a very accurate, realistic, and uncolored sound.

The QTC30 ships with its own calibration chart, providing the individually measured frequency response curve. A mic clip is also included.

The QTC30 is also available in a matched pair (model number QTC30mp); these ship in a padded wooden case.

Permalink: Earthworks Audio QTC30

The mic was released in 2003.


Frequency Response - OmnidirectionalClick Graph to Compare!
QTC30 Omnidirectional Frequency Response Chart
Pickup Patterns Pads & Filters
Omnidirectional (30 mV/Pa; 6 Hz - 30,000 Hz)
Capsule Dimensions Impedance SPL/Noise
Capsule diameter: 6mm
100 Ohms (Low) Max SPL: 142 dB
Self-noise: 22.0 dB(A)
Weight Length Max Diameter Interface(s)
160g (5.64oz) 165mm (6.50'') 22mm (0.87'')
  • 3-pin XLR male (1)
Power Specifications
  • Requires phantom power
  • Phantom voltage: 48 V, 10 mAv

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