X-R microphone capsule amplifier

Description

The X-R microphone capsule amplifier is a microphone “body” that supports the X-R series interchangeable microphone capsules. The X-R requires +9 to +48V phantom power.  The X-R capsule amplifier is available in mono, stereo, and three- or four-channel output.

The X-R amplifier includes a standard 5/8″-27 thread mount microphone clip.

Input configuration

The mono capsule amplifier may be supplied with a female, male, or right-angle male RCA input.  Right-angle, female-female, and male-male adaptors are also available.

The stereo and multichannel versions are supplied with permanently mounted capsule heads:

• stereo: 120º
• three-channel left-center-right:  90º
• four-channel 2D surround:  90º
• four-channel 3D (ambisonic):  120º

Stereo recording

Various stereo recording angles may be achieved by using RCA adaptor accessories between the capsules and capsule heads.  The capsule spacings and stereo recording angles with each adaptor are as follows (click on spacing for image):

* omnidirectional capsules do not resolve a stereo recording angle of less than 180 º at less than 55cm spacing.  However, when used with the equalization disc, the resulting polar response becomes subcardioid at frequencies above 3kHz.  Thus, the recording angles shown for the omnidirectional capsule with equalization disc are derived for a subcardioid polar pattern.

Two X-R capsules may be connected to a single input with the RCA Y adaptor, which will mix the two signals from the capsules.  When used with an RCA extension cable, the Y adaptor mixes two discrete sources into a single microphone channel.  Also, the Y adaptor may be used to blend an omnidirectional capsule with a directional capsule.  This technique is especially useful with the acoustic low-pass filter, yielding a hybrid pattern with a directional high-frequency response and an omnidirectional low-frequency response.

Ambisonic decoding

When used on the four-channel 3D head, the short cardioid capsules have 4cm radius from the center of the head.  The capsule head output given above is “A” format.  This output must be mixed to “B” format (bidirectional response on three axes, plus omnidirectional) for further processing, using the matrix:

W (omnidirectional) = FLU + FRD + BLD + BRU
X (front to back) = FLU + FRD – BLD – BRU
Y (left to right) = FLU – FRD + BLD – BRU
Z (up to down) = FLU – FRD – BLD + BRU

The resulting ambisonic frequency response requires correction.  The recommended filters (low-frequency shelving, notch, and high-frequency shelving) to decode to B format are as follows:

W filters: +9dB shelf @ 120Hz; -7dB notch (Q=1) @ 5kHz, +9dB shelf @ 11kHz.

XYZ filters: +9dB shelf @ 120Hz; -11dB notch (Q=1) @ 4.5kHz.

Note that the low frequency shelving boost is not recommended for recording distances of less than 1m.

Output configuration

The mono version has an XLR-3-M output; the stereo version is available with either XLR-3-M (unbalanced) or XLR-5-M (impedance- or electrically-balanced) outputs.  Three- and four-channel versions have an unbalanced XLR-5-M output.

X-R capsule outputs are inverse polarity.  For the mono XLR-3-M output amplifier, the capsule signal is round to pin 3 (negative polarity), with an impedance-balanced output on pin 2.  Thus, capsule amplifier will yield positive polarity when connected to a balanced input amplifier via a standard XLR microphone cable.  When used into an unbalanced input, pin 3 should be connected as the signal lead.

The X-R capsule amplifier is also available with a transformer-coupled (mono only) or electrically-balanced output (mono or stereo).  The electrically-balanced output will increase output level by 6dB, and has twice the current draw compared to the impedance-balanced output.

For the stereo XLR-3-M version, the left channel is routed to pin 3, and the right channel to pin 2.

The output pin configurations for XLR-5-M versions are as follows (inverted unless otherwise noted):

Custom output cables are available in a range of special formats to support stereo and multichannel output.  These cables are configured to route the X-R output pins to pins 3 of the XLR-3-M outputs, with impedance-balancing components on pins 2.  This will result in positive polarity when connected to balanced XLR input microphone amplifiers.

X-R microphone capsule amplifier specification:

Phantom Power Input: +9-52V (+12V minimum recommended)
Power supplied to capsules: +10V across 6.8KΩ

Current, per channel, with capsule, unbalanced, impedance-balanced, or transformer-coupled output: 1.0mA
Current, per channel (mono or stereo), with capsule, electrically balanced output: 1.6mA

Input Impedance: 6KΩ
Output Impedance: 75Ω (each pin); 150Ω (dual XLR stereo output cable)
Recommended Preamp Input Impedance: 1.5KΩ or higher

Maximum Input Level, 1kHz @ 1% THD: +10dBV / 138dBSPL (standard capsule)

Total Harmonic Distortion, 1kHz @ 0dBV: less than 0.005%

Frequency Response: 20Hz to 20kHz (-0.3dB @ 20Hz)
Noise: -124dBV unweighted, -127dBA

Weight, mono:  68g (2.4oz)
Weight, stereo or multichannel:  100g (3.5oz)

Dimensions. mono:  95mm x 19mmø (3 3/4″ x 3/4″ø)
Dimensions. stereo or multichannel:  125mm x 19mmø (5″ x 3/4″ø)