D12VR Testing and Comparisons - UPDATED Oct 2020
The AKG D12VR was released a few years ago, and since I started working on the original D12s I've wanted to see how the D12VR performed in comparison. I remember reading somewhere that the D12VR was based on AKG's last NOS D12, but can't find the source now.
Here goes. We'll start with some pictures.
It's worth noting that comparison between the D12VR and a D12 is difficult: any D12 you may find (with the exception of a NOS one I worked on recently) will have been kicked around various stages, studios, etc for the past few decades. The conditions will vary hugely, as will the sound. It might be the case that there's a D12 whose frequency response perfectly matches that of a D12VR, but there will be many more that don't match at all.
Here, I'll be sharing the on-axis frequency response curves of these mics, measured fairly close to the test speaker - a typical position for these mics. These curves aren't the ultimate comparison between these mics: I don't have the anechoic chamber required to pull off full polar data, nor did I investigate the effects of high SPLs: AKG mentions the D12VR uses the transformer from a C414, which might show up some saturation effects at high levels.
All that said, I do find frequency response measurements give a good idea of how a mic will sound, and it's an easy way to compare a few different mics.
Setup & Calibration
This section will explain the test setup, the choice of equipment, and how the equipment was calibrated. It's mostly included for completeness - feel free to skip to the results further down.
The test speaker was a KEF HTS3001SE with the bass reflex port blocked. This is a 4.5" coaxial speaker which is a good approximation of a full-range point-source. This is preferable to using a conventional multi-way speaker, where the woofer and tweeter will be physically separate - those require some distance for the different drivers to acoustically sum, which would mean the room would have much more influence on the measurements. The speaker was facing straight upwards, and I added some foam to cut down on reflections from my desk. I don't know how much difference that will have made, but it's unlikely to have a negative effect.
The mic-to-speaker distance was fixed at 60mm from the front edge of the tweeter waveguide. I decided to keep the mic-to-speaker distance fixed, rather than aligning capsules, as I find this to be more representative of real-world use.
The USB interface is a Behringer UMC404, which is adequate.
To calibrate REW, I used a Beyerdynamic MM1 to measure the frequency response:
Which can then be exported as text, and then imported as a calibration file. With that calibration file in place, I got this:
Which shows the calibration has worked well - only in places with extreme corrections do we have some wiggles, of the order of a couple of dB, and the phase response stays at zero degrees across the range.
The frequency response curves for each mic are presented below, and I included some comparisons which I thought would be particularly pertinent. The images should be self-explanatory, but I'll include some discussion at the end.
The curves below are from another two D12s, which have both been sent to their new homes. The mics were at a different distance to the test speaker, but the same calibration routine was used. As a result, the curves are still comparable with the ones above, although the proximity effect will be subdued a little.
There are two things I'd like to highlight with this graph: first, that there's considerable variation between the two D12s. They came to me from different countries, in different conditions, and while I'm certain they hadn't been previously modified, they had different diaphragms. That makes three different diaphragms I've seen installed on AKG D12s (the other looked like a D25 diaphragm).
I'll leave it to the reader to compare the graphs with the passive D12VR.
Even after going back and looking through the frequency response curves for the D12s I've restored over the past few years, I couldn't find a D12 that matched the D12VR. I can, however, see some similarities if I cherry-pick specific bits of some of the D12s. For instance, the blue curve just above this text has a similar 70Hz bump, but the D12VR appears to reach lower into the bass. That could be the different operating distance, though.
The kHz range of any D12 has some lumps and bumps, and so does the D12VR. D12s have been around for decades, and will have been subject to a lot of use/abuse since then. As a result, the variation between them is large, even after restoration. As a result, if I saw the 1-10kHz range of a D12VR, I could easily believe it was an original D12 that was being measured.
While I couldn't find a D12 that matched the D12VR, there are enough similarities that I'd consider the D12VR (operated in passive mode) to be a direct replacement for a D12. The kHz range is about right, and the much-talked-about extended low-frequency pickup is present. The only niggle for me is the dip around 500Hz. I suspect, though, that some D12s out there do exhibit this dip.
Used in the default passive mode, and the D12VR has a nice vintage flavour. Engage the filters and you get a selection of curves, which can be useful when EQ options are limited, or the engineer is looking for a more "finished" sound straight from the mic. I prefer the passive mode, but some engineers like the Audix D6 and the like, which have some extreme boosts and cuts built-in. I expect the right filter selection would make those engineers happy, too.
The D12VR looks and feels like a premium dynamic microphone, and I'll look forward to using it in the future.