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The 251 is THE vocal sound people ask for, but the original (vintage) versions are 50+ years old and sound very different from one another. Repairing, rebuilding and “nursing” original 251’s has been David Bock’s work spanning over 30 years. The risk for a modern studio or end user to depend on a vintage mic on a daily basis is increasingly problematic. The 251 is David Bock’s answer to the vintage mic dilemma of getting “that sound” without the headaches. It is a premier lead microphone for premier voices. It is built to last and provide the studio and user with many years of daily,

high end performance.

Patterns: Cardioid, Omni, Figure of 8 [ADJUSTABLE]

Frequency Range: 10Hz to 18kHz, +/-2dB
Sensitivity: 19mv/Pa


Equivalent Noise: 18dB [“A” Weighted] 32dB [Unweighted]
Distortion vs.SPL @1kHz: 
112dB = 0.5% THD 
118dB = 1% THD
129dB = 2% THD
(increasing distortion is non-exponential, nearly linear, primarily 2nd harmonic)


Impedance: 200 Ohms true transformer balanced
Recommended load: 1.2k Ohms
Dynamic range (maxSPL-"A"noise): 94dB
S/N (94dB-noise): 76dB “A”, 62dB unweighted


Capsule size: 1” diameter, dual asymmetrical backplate CK12 type
Tube type: New Old Stock 6201 
Dimensions: 2” dia x 8.5” oal (52x216mm)
Weight: 1lb 9.3oz (1.58lbs) =716g
Shipping weight: 12 lbs
Power Supply: P251 true linear, factory wired 115v or 230v operation


The 251 cardioid pattern shuts off the back of the capsule to deliver extraordinary vocals when worked very close. On less experienced vocalists, it is recommended to use a pop filter, enabling closer working distances to take advantage of the magical proximity effect. There is no low frequency filtering used on a 251 so you will hear low frequency content you’ve never heard before. 

At distance, the 251 delivers a level of definition that is amazing. The high end does not fade with distance like so many other condensers and the power and depth of the low end response is a joy to hear. The Omni and Figure 8 patterns prove useful in these non-voice applications.

The 251 provides the user with absolute confidence that this is the mic you put in the most critical situations. Bock Audio's 251 uses a proprietary hand-made German capsule, a proprietary hand-wound multisectioned audio transformer, 

NOS tube in the mic amplifier, a hand-built outboard power supply and a custom low capacitance audio cable. This is one of the best overall mic packages available on the market at any price. The 251 is the ideal microphone to choose when there is a variety of applications that must met with absolute top recording quality. With frequency response that extends well beyond the normal range of typical studio microphones, the Bock Audio 251 sets new standards. 

FOR VOCALS, the 251 instantly delivers that huge vocal sound you have wanted for years. It sounds equally impressive on females and males. It will capture the most intimate and subtle details of a vocal yet maintain integrity at high SPL’s. It holds up track after track, “sitting on top” in extremely dense mixes without EQ.


FOR INSTRUMENTS, this mic offers very high end performance on critical stringed instruments, orchestras, choirs and small ensembles. The outstanding transient response reveals elusive harmonic details that spell the difference between good... and GREAT in your recordings.