U87ai vs. u87 what’s really behind the difference in sound

You know, it’s no so much the trade-off off noise/headroom that I am motivated by. It’s more to do with what I feel is the subjective sonic feeling of this voltage issue. The lower voltage I believe allows the capsule to sound more generous and round in the low-midrange…less tight and over-damped if I can put it that way. It reminds me of power amps with lower-damping factors and the way that slight "release" of control over a woofer, considered by some to be technically a step in the wrong direction, actually sounds more musical to listen to. It might not be something that shows up clearly on a frequency response plot, but it does affect the way the mic responds dynamically to a singer…the interaction of the mic with the changing dynamic of a performance.


Every single time I hear a comparison of an 87Ai to an 87, I hear the same thing. The Ai sounds somewhat clearer but in a non-musical way…too tightly controlled. Th lower voltage 87 breathes and swells in the meat of the vocal range and makes more of the "melody frequencies"…i.e. it carries the melody better I feel.

The difference in sensitivity between 60 V and 47 V capsule bias is only 20 log (60/45) = 2.12 dB. The more significant difference for achieving the higher sensitivity and lower self noise in the U 87A results from lowering the parasitic capacitance appearing shunting the transducer at the FET gate from 205 pF in the U 87 to 78 pF in the U 87A. A detailed description of the difference between U 87 and U87A can be found in the archives of the Neumann forum:

We can calculate the the unknown values for effective capacitance at rest from the known data. This does include the nominal capacitance Cnom of the transducer and how much additional capacitance causes a 10 dB reduction in sensitivity. We shall cleverly deduct the value of CP by rearranging the sensitivity formula in such a way as to eliminate the unknown delta C. We know the only change is in the additional 10 dB-padding capacitor Cpad, thus:

From the circuit diagrams we learn that the rear transducer is NOT burdening the front of the capsule in the U87A! It is this difference in parasitic capacitances which accounts for most of the difference in sensitivity. Now we have the 2.1 dB boost as a result of the bias increase from 47 V to 60 V and 8.4 dB from the reduction in static capacitances:

A word of caution! Eliminating the 10 pF feedback capacitor in the U87 will NOT result in any benefit, since the inherently higher parasitic capacitance (mainly from the permanent parallel back element) is also responsible for significantly higher THD, which needs to be partially counteracted and compensated for by this feedback mechanism.

Quote from: usattler on April 16, 2013, 09:18:14 am The difference in sensitivity between 60 V and 47 V capsule bias is only 20 log (60/45) = 2.12 dB. The more significant difference for achieving the higher sensitivity and lower self noise in the U 87A results from lowering the parasitic capacitance appearing shunting the transducer at the FET gate from 205 pF in the U 87 to 78 pF in the U 87A. A detailed description of the difference between U 87 and U87A can be found in the archives of the Neumann forum:

We can calculate the the unknown values for effective capacitance at rest from the known data. This does include the nominal capacitance Cnom of the transducer and how much additional capacitance causes a 10 dB reduction in sensitivity. We shall cleverly deduct the value of CP by rearranging the sensitivity formula in such a way as to eliminate the unknown delta C. We know the only change is in the additional 10 dB-padding capacitor Cpad, thus:

From the circuit diagrams we learn that the rear transducer is NOT burdening the front of the capsule in the U87A! It is this difference in parasitic capacitances which accounts for most of the difference in sensitivity. Now we have the 2.1 dB boost as a result of the bias increase from 47 V to 60 V and 8.4 dB from the reduction in static capacitances:

A word of caution! Eliminating the 10 pF feedback capacitor in the U87 will NOT result in any benefit, since the inherently higher parasitic capacitance (mainly from the permanent parallel back element) is also responsible for significantly higher THD, which needs to be partially counteracted and compensated for by this feedback mechanism.

Apparently disregarded is the importance of dynamic range. Based on the experiences of the target audience for studio microphones, in the upgrade design the dynamic range was expanded slightly and shifted toward higher sensitivity, by lowering the self noise and increasing the output capability. This was achieved through the combination of marginally higher capsule bias and lower parasitic capacitive loading of the FET gate. This in turn reduces distortion and eliminates the need for the compensating feedback capacitor.

Arguably, few real world recording scenarios approach the threshold of pain (115 dBspl) at the microphone position, and the standard 10 dB pad should accommodate most exceptions. Furthermore, the distortion at the specified maximum SPL is less than 0.5% and increases gradually beyond this level, rather than causing hard clipping. For capturing of even louder events perhaps more suitable microphones should be considered, inevitably ‘featuring’ lower sensitivity and higher self noise, even if such microphone were to have the same dynamic range.

Klaus, I guess the argument boils down to our longstanding difference in emphasis on perfection VS tradition. Aside from my almost daily exposure to both versions, U87 and U87A, I am also an actual owner and user of both types. I mention this in the sincere hope you are not trying to imply that I may be just a poster or poser! [Just saw this inadvertently mangled sentence in the earlier post and have corrected it. My apologies! KH]

As to the marketplace as one source for information, we could look at the total sales for each version, which are overwhelmingly in favor of the U87A. I further venture the guess that at Neumann|USA we receive more contact and feedback about Neumann microphones than anywhere else, except at Neumann\Berlin. In our Service Department we get numerous requests for ‘upgrading U87 to U87A, but rarely, if ever, the other way around… (BTW, we do neither)

By focusing only on the top end of the dynamic range, you unfortunately overlook or dismiss the bottom end of self-noise. Most reputable microphone manufacturers have made great efforts to match the improvements made in recording media and elsewhere in the recording equipment, which exposed limitations in the self-noise of ‘vintage’ microphones.