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> Bruel & kjaer b&k 4135 ¼" microphone capsule - tested
Bruel & kjaer b&k 4135 ¼" microphone capsule - tested
This is one of B&K's finest standard (as in reference) microphones with legendary stability and accuracy. The some information from the datasheet are shown below:
Type 4135 free-field and random responses for high-level, high-frequency and for small scale model work.
* Pressure variation measurements
* Dynamic Range: 30 - 165 dB
* Artificially aged for long term stability
* High resistance to humidity
Depending on the type, the insulator is made of either silicone treated quartz or a synthetic ruby to give dimensional stability. The diaphragm consists mainly of nickel and the backplate and housing are made of high nickel alloys. This minimizes variations in sensitivity with temperature.
During production the microphone cartridges are subjected to a high temperature (150C), forced ageing process which ensures long-term stability.
Special care has been taken in the design of the system for equalisation of the static pressure between the inside and the outside of the cartridge to give a low and well-defined lower limiting frequency.
* Frequency Response Characteristic: Free-field & Random
* Open Circuit Frequency Response ( 2dB): 4Hz to 100kHz
* Open Circuit Sensitivity (mV/Pa): 4
* Lower Limiting Frequency (-3dB): 0.3 to 3Hz
* Cartridge Thermal Noise (dB(A)): 29.5
* Open Circuit Distrotion Limit, 3% @ 100Hz: >164dB
* Resonance Frequency: 100kHz
* Polarisation Voltage: 200V
* Polarised Cartridge Capacitance @ 250Hz: 6.4pF
* Mean Tempoerature Coefficient (@ 250Hz, -10 to 50C): -0.01dB/C
* Influence of Static PRessure @ 250Hz (dB/mBar): -0.00007
* Influence of 1m/s2 Axial vibration (dB): 59
* Typical Influence of 50Hz, 80A/m magnetic field (dB): 30
* Influence of relative humidity: <0.1dB (in the absence of condensation)
I took the protection grid off and the diaphragm looks in perfect condition though covered in dust (which I've now cleaned off!)
It looks in perfect condition and I mounted it on one of my 2669 pre-amplifiers and it calibrated about 1dB under the nominal value with my 94dB calibrator (my calibrator always reads a little low) but the behaviour and noise level on the mic. lead me to bewlieve this is functioning correctly.
