recordinghacks

A classic mic design returns with a modern spin

The ribbon microphone is a natural figure-8 microphone; it’s a thin ribbon of metal foil suspended between some magnets. Air moves the ribbon back and forth and a current is induced in it by the magnetic field. It’s sort of like a one-turn dynamic microphone.

There are a lot of different variants on the ribbon design, from the small high-tension ribbon mics beyerdynamic makes to the aluminum-on-mylar printed ribbons Fostex used to make, but most of the time when people think about ribbon mics they think of the traditional line that RCA made popular in the 1920s and kept making well into the 1970s with constant technical innovation.

Back in the 1930s, the ribbon was very popular because its low mass meant it was the only available microphone design that could handle high frequencies and reproduce transients well. Today in 2010, the reason most people grab a ribbon is the exact opposite; the ribbon tends to smear over transients and mellow out the high end more than modern condenser designs. The old RCA ribbons had a wide variety of sounds but all with the same basic character, and it’s one you’ll hear on a lot of older recordings.

The Cloud Microphones JRS-34-P was designed by Stephen Sank, whose father Jon R. Sank (hence the initials) was the designer of many of the later RCA ribbon microphones, including the BK-11 that was probably the pinnacle of ribbon microphone technology for RCA. The “P” stands for “passive”, meaning this isn’t a modern active design with a built-in phantom-powered head amp that lets the mic run with a wide variety of preamps. Cloud makes such a mic, the JRS-34, and its head amp is available separately as the Cloudlifter. I had a chance to work with all three products; most of my tests were done on the JRS-34-P, which gets most of my attention below.
Now, somewhere I had got the idea that this Cloud microphone was a BK-11 copy internally, and when I plugged it in and listened, I was very surprised to find that it wasn’t. Then I opened it up, and looked inside, and it didn’t look anything like a BK-11 in there either. So if it wasn’t a BK-11 copy, what was it? Well, it was its own thing, and it was a good thing.

How it sounds

This mic does sound like an early RCA ribbon mic. More like a RCA 77 DX or a 44B than anything else, but it doesn’t really sound like either. The top-end response on it is ragged in the same general way that the early RCA mics are. It’s mellow, but it’s not exactly smooth. It clearly has a very recessed top end, which is characteristic of the older ribbons.

Turning it around, you find that the null on it is pretty good. Not as good as some figure-8s, but better than a 77DX. It’s certainly good enough to record a singer-songwriter without getting vocal leakage into the guitar mic.

The off-axis response is a little rough… it definitely changes tone quite a lot once you get off the center line, and that starts to make problems for distant area miking. Mind you, it’s not as rough as a 77DX, but it’s rougher than a BK-11.
I tried it as an area mic on a string section and that was kind of pushing it because the room tone was not as clean as I’d have liked. But close-miked on a single violin it was excellent.

It also made for a great mic on trumpet and saxophone. On sax you can tilt a figure-8 mic around and get some of the bell sound and some of the body sound with a single microphone and the results doing that were great.

On vocals it did quite well, like a brighter version of the 77DX but just as mellow. Some people want that 1960s “Gary Owens Laugh-In Announcer Voice”; this mic won’t make you sound like that, because Gary Owens sounds like that without any microphone at all. But if you sound like Gary Owens already, this is your mic.

As a PA microphone, the gain before feedback on this mic isn’t as good as a BK-11 or BK-5, but it’s better than a 77DX in figure-8 mode. That would seem consistent with the off-axis response being less even than that of a BK-11 but more even than on a 77DX. I used it on massed violins at a concert with relatively low stage levels and it had that mellow ribbon sound.

What’s inside

Opening it up, the first thing I noticed is that the ribbon assembly is made of stamped metal, and I am thinking that a lot of the top-end roughness comes from resonances off the flat surfaces in there. This is similar to some of the earlier RCA designs, although the Cloud designers have clearly made the magnet assembly smaller thanks to modern materials. The later RCA models used rounded magnet assemblies so that sounds reflecting off the magnet are diffused rather than reflected right back, and I’m told that the very newest Cloud mics now feature this.

The ribbon itself was much larger than the BK-11 ribbon and was more like the ribbon you’d see inside an RCA 44 microphone. Clearly some work has gone into reducing internal reflection problems, however, in a way that you do not see in any of the cheaper Asian-made ribbons.

Unlike the RCA ribbons, the magnet assembly here is suspended on a shock-mount frame, using springs which have been rubber-damped to reduce boinginess. Since I didn’t hear any boing, and since handling noise was pretty low, I can only conclude that this was very effective.

Because the output impedance of the ribbon is much less than one ohm, and it needs to drive a microphone preamp with an input impedance a thousand times higher, the ribbon mic transformer is very difficult to make and in many cases it’s the main sound-quality bottleneck in the microphone. I did a quick square wave test on the Cloud’s very small Cinemag output transformer, and it’s not as clean as the old RCA or modern Lundahl or Royer transformers, but it’s a substantial improvement over the transformers that the Chinese folks are using — and Cloud reports it was chosen for its sound, which the engineers liked better in this mic than the Lundahl’s. I can’t argue with that.

The wiring from the motor assembly to the transformer is twisted together for low inductive pickup, but it’s still flexible which is definitely a problem; any movement of that wiring is going to be a source of distortion. On the other hand, the way the body is designed, using a stiffer wire would reduce the effectiveness of the internal shock mounting, which on this mic is a big plus. Again, I’m told this is something Cloud has addressed in their newest shipping models, which have stiffer wire and a slightly reworked shock mount to counter its negative effects.

How does it measure?

It’s difficult for me to do detailed measurements on figure-8 microphones because I have only a small hemianchoic chamber, so I sent it off to a friend with a full chamber.

The on-axis frequency response is very much how you would expect, a fairly flat line up until about 7 Khz and then a dropping, somewhat ragged response above that. Approximately what you’d see if you looked at a large ribbon mic like a 44 or 77… the mass of the ribbon is the main contributor to the top-end drop-off, which is how it’s supposed to be.

The front and back responses were absolutely identical, which is a good thing, but one thing I noticed was that the null on the right side was about 10 dB better than the null on the left side. Both nulls were very good, but I think there is some asymmetry involved, possibly the result of sound bouncing around on the bottom part of the case where the transformer is; packing this part of the mic body with cotton wool would help a lot to remove that and make it more symmetric. Cloud’s latest mics have sound-absorbing lining that reportedly helps this.

Sensitivity was lower than an SM57 but really quite respectable for a ribbon mic. The microphone passed the usual RF test (2 watts at one foot on 146 MHz) without any problem, although the accompaning Cloudlifter pre-preamplifer (see below) did not.

I did expect to see a divot in the top end resulting from reflections off the surface of the magnet, but honestly I didn’t see anything at all. That’s a nice sign… some careful work has gone into this microphone.

Ribbon mics have low output… live with it

This mic is a little more sensitive than most of the older classics, but it still has very low output compared with a modern condenser or a lot of modern moving-coil dynamics.

Now, all the time I hear from people “I can’t use this microphone because I have to turn the gain on my expensive mic preamp all the way up.” This is foolish. The reason you buy an expensive mic preamp in the first place is so it sounds good, even at high gains. Just turn it up and it’ll sound fine.

If you’re limited to one of those inexpensive console preamps where the bass response changes when you adjust the gain trims, you probably won’t be happy with any conventional ribbon microphone because the preamp just won’t sound good with the gain up all the way. Don’t blame the mic, blame the console.

This mic does work just fine into inexpensive solid-state input preamps like the Symetrix 302, and into better console preamps. So do old RCA mics. Just turn the gain all the way up and relax.

The Cloudlifter

If you have a console preamp with an input transformer, you may have too low an input impedance for a ribbon mic to be happy. Likewise, some console preamps may just not have enough gain. For this, Cloud makes a neat gadget called the Cloudlifter Pre-Preamplifier. It’s a box containing a phantom-powered four-FET balanced amplifier that goes between the mic and preamp and gives you not only a very high-Z balanced input (so the mic sees very little load, but still has good noise rejection from the balancing), but also gives you about 20 dB added gain.

The Cloudlifter seems to add little noise and while the common mode input rejection isn’t as good as in some preamps, it’s respectable enough unless you are working in high-RF environments. While being tested at one location, it did pick up an odd squealing from a targeting radar at a local military base, but so do guitar amps out in that area as well.

The Cloudlifter is also a reasonable device to use with any ribbon mic that wants to see a higher input Z, like in fact all the old RCA ribbons. If you’re using ribbon mics on stage or in a situation where you are often moving from one studio to another, the Cloudlifter will help you get the best sound out of the ribbon in a very wide variety of environments.

The JRS-34 active ribbon mic

As I mentioned before, Cloud also makes the JRS-34, which has the same PC board that the Cloudlifter uses, built inside the microphone. Interestingly, the asymmetric nulls were a little bit worse inside this mic than on the JRS-34-P, which reinforces my belief that the asymmetry is the result of sound bouncing around down at the bottom of the case. But in terms of actual sound quality, I couldn’t tell the difference between the JRS-34-P with the external Cloudlifter and the active version of the mike.

The active version of this mic is a little more convenient if it’s going to be your primary (or only) ribbon, but the Cloudlifter is a tool that you can use on any ribbon microphone (and even some dynamics), so if you intend on having a good closet of different ribbon mics it would cost about the same and give you more flexibility if you take the external route and buy the passive mic with the Cloudlifter.

Conclusion

This mic isn’t a 44B or even a 77DX…. but it’s a lot less expensive and will probably be more reliable than one of those, and it will give you a lot of the sound of those mics. It’s clearly designed out of the old RCA tradition with some sacrifices to bring costs down.

AEA will sell you an absolute copy of the 44B, and it will give you more of that traditional RCA sound, but its cost is an order of magnitude higher. This Cloud mic will give you a substantial part of that sound at a reasonable price.

This is not one of the cheap Asian-made ribbon microphones flooding the market right now, and actual engineering has gone into the acoustical design. Some folks set out to make a mic with a particular sound, and these folks did, instead of starting out with a bunch of mic parts and seeing what kind of sounds they can get from them like the Asian folks do. The world needs more of this kind of vision.

Prices (as of June, 2010):

• JRS-34-P, $1499
• Cloudlifter, $329
• JRS-34, $1799

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