Vocal Microphone and Capsule Testing

Time for another round of studio tests.  I have been working on a developing variety of microphone projects lately and have come to discover that good, actionable information about various microphone components is actually quite scarce on the internet.  Usually tiny gems of data are scattered all over the internet and buried hundreds of posts deep in often un-related web forum topics.  To compound the problem, egos, chest thumping, marketing hype, "trade-secrets", and general online drama often cloud discussions or turn into useless drivel.

Also, due to the infinite range of recording environments and monitoring systems, the often-provided lone audio sample can only describe a condition to a certain extent.  One mic is "open". . . well, compared to what?  Another one could be "opener".  Because of this,  I have found relative data to be more helpful, but that requires repetitive, structuring testing in a reasonably controlled way different from regular music production.  Even then,  concrete conclusions are hard to find and it is difficult to establish a "baseline", but in the end, these devices must be judged and improved by listening and meaningful comparison.  So, even if messy and imperfect, we must try.

With that as a framework, I entered the studio earlier today with a trunk full of DIY microphones and prototypes to test and attempt to provide some actionable information for people looking to build recording microphones.

More after the jump.





Truth be told, a few of these microphones have been kicking around the studio for some time now.  Setting up a test at this point in time was somewhat by design.  I wanted to make sure to a reasonable extent that the microphones were stable and operating properly.  Also, every microphone has a different sweet spot and way it "likes" to be used, so a little bit of knowledge about how to place them is important for efficient testing.  Because of this, we did have some ideas going in about which microphones had outstanding potential, but these initial impressions needed to be confirmed or disproved by tests.

In music production, everything hinges on the strength of the performance.  We bend over backwards to create the vibe and environment conducive to having some magic in the room to actually capture!  For a test session, it becomes even more difficult to find someone with a nuance and dynamic that can push a wide range on the microphones as well as consistency and stamina to repeat over and over again.

I was lucky Margo Leduc came into Studio 1225 a few months back to track a few jazz standards.  My long-time friend Jon Uhland who owns and operates the small production studio played some of the tracks for me when I was visiting.  She instantly came to mind when I was thinking about setting up a test session.  We contacted Margo, and she graciously agreed to let us use some of the tracks for samples, and we selected two short song sections to use.  We will inevitably tire of them completely and the songs will then be ruined in our minds, but we had to pick something!

"The best laid plans of mice and men often go awry". . . and awry they went.  A few days before the test, I found out I would have my toddler daughter with me for the session.  Some of the tests I had planned involved changing components mid-session between takes.  Likelihood of succes on those configurations suddenly became very low.  Also, one microphone that had proven to be stable prior to testing developed a catastrophic failure.  But despite those setbacks, we had enough configurations stable to still get some good information, and moving forward, I am hoping we will be able to schedule more sessions and add more high quality audio samples that can be directly compared.  I am hoping we have established a reasonably repeatable framework to do this.

Tests scheduled for today:

1) U87 capsules - Peluso, early variant Eric Heiserman HK87 (Success)

2) U87 transformers - AMI T13, Cinemag 13113, new prototype, vintage original  (failed due to toddler maintenance and time spent diagnosing other failures)

3) MK47 (U47 clone) capsules - Thiersch Blue Line, Beesneez M7, Eric Heiserman HK47 (Success)

4) C12 capsules - Tim Campbell CT12, Eric Heiserman HK12 (failed due to mic failure)

5) MK67 (U67 clone) - function test and general evaluation (Success)

A few notes about the test method and setup.  We felt that for vocal performance, proximity effect and a lot of other microphone positioning variables cannot be properly tested when putting multiple microphones up simultaneously.  Small position shifts as small as half an inch can make huge sonic differences, and I feel it is impractical to crowd everything into such a small area.  Also, a good singer will adjust performance and distancing to the mic's sonic feedback in the cans.  So, if you put up 5 microphones simultaneously, which one is the performer monitoring?  We opted to find a performer who can make reasonably consistent takes and to optimize the microphone placement for each individual mic like we would in a normal session. . . then, record the microphones one at a time.

Our signal chain for the vocal is as follows. . .

- Great River MP-1NV preamp
- Line input on MCI JH-630 console
- Apogee Rosetta A/D converter (24bit 48K)
- RME Digiface
- Logic Studio 9

The mixes generated are analog through the console.  No EQ was added to the vocal and very slight compression was used.

First up was the U87 clone detailed in a previous blog post.  This mic has become one of the go-to microphones for vocals in studio and it has proven to sound good on most singers that come through.  In fact, Margo's original track for her record were done on this microphone.  The emphasis in session was likely speed and efficiency, and to be honest, Margo sounds good on any decent microphone, so it makes sense that Jon just threw the "known" mic up.

Mic specs: DU87 PCB set, Peluso P-K87i capsule, AMI T13 transformer

U87 Clone - Love (WAV)
U87 Clone - Love (MP3)

U87 Clone - Summer Time (WAV)
U87 Clone - Summer Time (MP3)

Next, we have another U87 clone with the same build specs except with an early iteration of Eric Heiserman's HK87 capsule.  This early iteration of the capsule was based on measurements taken from an old vintage K87 capsule and is no longer his "standard" product which is closer to the new production K87 capsules.  There are two key differences.  1) drill holes are smaller in the older Neumann spec.  2) Eric has reduced the mylar tension in his current spec.  The microphone sits in a bare brass factory sample body, so we refer to it as the "brass" U87 in studio.

Mic specs: DU87 PCB set, 1st Gen Eric Heiserman HK87 capsule, AMI T13 transformer

Brass U87 Clone - Love (WAV)
Brass U87 Clone - Love (MP3)

Brass U87 Clone - Summer Time (WAV)
Brass U87 Clone - Summer Time (MP3)

A note about Eric Heiserman and why we test so many of his capsules.  In DIY land, and specifically in capsule development, there is a lot of secrecy, and many makers are very closed about specifications and processes.  It is completely understandable, and I respect the way each vendor chooses to operate their business, but it is refreshing to find a capsule builder who is open to development and is eager to collaborate and make spec adjustments and share the details about those changes and product specifications.  For DIY, this "open source" sort of approach in the long run will result in better capsules for all and a more educated/informed buyer.  Eric also does not take offense when we flatly tell him "its not good enough".  In this instance, we did not think the early production HK87 capsules were up to par sonically with some of his other models, and I am glad the original build thread featured the Peluso P-K87i capsule which may have a certain stigma associated with it in DIY community based on the well-known fact that the backplates are manufactured in China.  Disregarding the country of origin, it has proven to be a fantastic capsule and based on long-term use in studio, slightly superior to the 1st gen. Heiserman HK87.  The brass microphone will likely re-visit the workbench and receive a current production HK87 capsule which has undergone significant changes in backplate machining and diaphragm tensioning specs.  It may also end up being the test platform for transformers and get retrofitted with a way to quick change transformers.

Our next microphone is a vintage Neumann U87i retrofitted with a Peluso P-K87i capsule.  When Matador diagnosed this microphone originally and isolated the problem to the capsule, the most expedient solution to get the mic back online quickly was to use the capsule that we had on hand which happened to be the Peluso.  This mic shares primary vocal duties almost equally with the first microphone in general use, so we have not had reason to change the configuration again.  It just works for us.

Mic Specs: Vintage U87i, Peluso P-K87i capsule

OG U87i - Love (WAV)
OG U87i - Love (MP3)

OG U87i - Summer Time (WAV)
OG U87i - Summer Time (MP3)

The next microphone is a U67 clone using the ioaudio MK67 kit designed and produced by Max Kircher in Austria which includes BV.12 transformer that he winds himself.  This is the first test drive of this new microphone kit.  I also wanted to test drive Eric Heiserman's current spec HK67 capsule which is the same as the HK87 capsule except without isolated backplates.  The holes have been slightly enlarged from the 1st generation ones, but are not quite as big as the current production Neumann units, so it splits the difference a bit.  Membrane tension has also loosened a bit.  The tube was sourced from Christian Whitmore.  His recommendation was either Telefunken EF86 or the Amperex EF86 as excellent choices for U67 application.  At the time of purchase, I went with the Amperex because it was slightly cheaper and as new clones are sometimes prone to being a bit "harder" sounding than well broken-in vintage ones, we opted for the slightly softer tube.

Mic specs: ioaudio MK67 kit, Eric Heiserman HK67 capsule (2nd gen),  Amperex EF86 tube

U67 Clone - Love (WAV)
U67 Clone - Love (MP3)

U67 Clone - Summer Time (WAV)
U67 Clone - Summer Time (MP3)

This is a starting point for U67 clone testing, and there are several things we want to test in future installments.  The most important being original Neumann capsule (still in production) and original Telefunken EF86 tube to establish our baseline.  I am also interested in hearing some of the alt-tubes that people recommend like Valvo E80F tube and Shannon Rhoades skinned K67 capsule.  We are also looking for an opportunity to get hands-on a premium condition vintage original U67 to test against.

The next series of tests are U47 clone capsules.  There has been significant interest in U47 clones since Max Kircher released his ioaudio MK47 kit some time ago.  Recently, he also released a premium MK-U47 kit which has been quite popular.  Good comparative information about the capsule choices available is hard to come by.  I focussed in on three popular premium options.  It seems the "gold standard" capsule currently is the Thiersch Blue Line PVC M7 capsule.  It is the most expensive of the current options but there does not seem to be a single negative report about the Thiersch capsule I can find.  Most opinions from people who have tested various other high end capsules against the Thiersch Blue Line also concur.  It usually wins.  The 2nd test capsule is the Beesneez M7 capsule.  The purchase of the M7 was based on a raving review of the Beesneez K7 capsule by Klaus Hein floating around the internet, and the assertion by Ben and Veronica Sneesby that the current M7 is now the company's flagship U47 capsule offering.  The next capsule is the Eric Heiserman HK47 capsule which is a hybrid construction capsule.  This is assembled like a K67 with dual backplates as opposed to the original single backplate K47 and M7 capsules, but the hole patterns are modelled after the flat response M7/K47 capsules.

We will be testing these capsules on ioaudio mk47 kit microphones.  One inconsistency in the test is in the test bodies.  I originally wanted to test all configurations on the Alctron GT-2B donor body, but the mount that I ordered with the Thiersch Blue Line capsule (suitable for original dimension bodies), did not have a detachable saddle, so I was not able to adapt it easily to the GT-2B body which requires a lower post height.  So the Thiersch microphone was built on the 3 frame rail Alctron "MK47" (no relation to Max's kit) donor body.

The next mic is the Thiersch microphone.

Mic Specs:  Thiersch Blue Line capsule, Western Electric 408a tubes, mk47 kit

U47 Clone Thiersch - Love (WAV)
U47 Clone Thiersch - Love (MP3)

U47 Clone Thiersch - Summer Time (WAV)
U47 Clone Thiersch - Summer Time (MP3)

The next mic is the Eric Heiserman HK47 capsule.  Note, this test microphone is built on the short GT-2B body as detailed in my build thread on Groupdiy.com.

Mic Specs:  Eric Heiserman HK47 capsule, Western Electric 408a tubes, mk47 kit

U47 Clone Heiserman - Love (WAV)
U47 Clone Heiserman - Love (MP3)

U47 Clone Heiserman - Summer Time (WAV)
U47 Clone Heiserman - Summer Time (MP3)

I am usually very reserved about observations, but when we first put this capsule up on speakers, we were stunned by how good it was.  I immediately called up Eric and told him not to touch anything on his spec, and honestly, this was the reason I had to buy a Thiersch Blue Line to compare against "the best" and confirm its pedigree.  For this test session, this was the one that the singer kept coming back to and talking about.  This capsule really was the standout surprise in the test especially considering the price of entry.

The next mic is the Beesneez microphone built again on the short GT-2B body.

Mic Specs:  Beesneez M7 capsule, Western Electric 408a tubes, mk47 kit.

U47 Clone Beesneez - Love (WAV)
U47 Clone Beesneez - Love (MP3)

U47 Clone Beesneez - Summer Time (WAV)
U47 Clone Beesneez - Summer Time (MP3)

To us, the Beesneez somewhat disappointed and just did not seem to have "magic" and range that the other 2 capsules exhibited.  We did comment that somebody out there is really going to love it perhaps with really treble forward monitors.  For our uses, this microphone got "voted off the island", and it has been returned to my workbench.

Our final microphone is our Tim Campbell point to point C12 clone.  A well-loved mic for acoustic guitars and specific singers in our recording environment.  A more extensive battery of comparisons for C12 development were planned, but our other C12 microphone had a catastrophic failure that I could not resolve mid-session.  So, for now, we just have a single C12 sample from this test.

Mic specs:  Tim Campbell CT12 capsule, 1956 JG GE 6072 tube, AMI T14 transformer, Matador C12 kit

C12 Clone PTP - Love (WAV)
C12 Clone PTP - Love (MP3)

C12 Clone PTP - Summer Time (WAV)
C12 Clone PTP - Summer Time (MP3)

The Heiserman equipped C12 had what I believe to be a capsule failure.  The initial prototype capsules had a potential weakness in the backplate screw connection.  The problem did exhibit itself earlier in pre-testing, but was resolved by slightly tightening the terminal, but unfortunately during our session, the problem recurred and this time permanently.  Satisfaction is guaranteed on these capsules and Eric was helpful over the phone and will fix this or any other problems immediately, but it did set us back and a much anticipated data point is missing from this test session.  The capsule was sounding exceptional in pre-testing and I had high hopes for it.

I left the test session a bit disappointed that I failed to complete about half of the testing I had set out to accomplish.  Our singer Margo Leduc was top tier to work with and one of the most efficient singers I have worked with.  We had very, very few retakes and just cruised right through.  She certainly had more capacity in session to make a few more samples.  So, next time I will need to be better prepared.  On the up side, I think we now have a framework to add additional samples in subsequent sessions that can compare directly with the audio samples we were able to gather here.  So, we can build on our data set in a meaningful way to track our progress.

In general, I am quite pleased with the improvements these clones have made to the studio's production quality.  They certainly have raised the bar, and by building a few clones, I feel we are a few steps closer to having a top tier mic selection for production.  Everyone's tastes are different, and I hope these clips and future tests will help microphone builders select their expensive build components based on informed alignment with their sonic preferences without as much stabbing in the dark.