recordinghacks

A fascinating ribbon mic design, reborn

Back in July of 2006, I reviewed the Crowley and Tripp Studio Vocalist microphone in the pages of this magazine, and since then the Crowley and Tripp company has been sold to Shure.

Now, let me say first of all that Shure has a very long tradition of making ribbon mics, starting in the 1950s and going until the 1980s. The Shure SM33 was a classic design and could be seen on Johnny Carson’s desk. The Shure 300 turned up on a lot of record sessions in the Fifties and Sixties. But in the Seventies, Shure discontinued the last of its ribbons and later turned support of these mics over to Dick Gardiner from the Harmonicats, who had a long-lived second career rebuilding them.

The KSM313 under review (originally sold by Crowley and Tripp as the Naked Eye) is a totally different design. Like the older Crowley and Tripp mics, it uses some sort of foamed metal alloy they call Roswellite, instead of conventional Duralumin.

So — how does it sound?

The KSM313 sounds like someone tried to take a ribbon mic design and make it sound like a U87. It has a good-sized presence hump, and while the high-end response drops off, there are a lot of spiky narrow resonances in the top octave which makes it sound almost sparkly and bright compared with a typical older ribbon design.

It’s not anywhere near as sparkly and bright as a U87, mind you, but it sounds like this is an attempt to push the ribbon design in that path. It is a nice crisp sound on female vocals, but it’s not bright to the point where it starts exaggerating tonsil noise excessively. I think this is a great sonic compromise where you’re looking for brightness and punch to get through a dense mix, without being over the top for a pop music mix. This is certainly not the typical “ribbon mic” sound.

Using the mic on a number of vocals was very interesting; the sound was very forward and colored, but it seemed very versatile, working well on a wide range of different singers.

When pulled way back into the far field, the mic performed reasonably well. Some mics just turn into mush in the far field because the off-axis response is poor, but the KSM313 did pretty well considering the intended application. Pulled back six feet in front of a bel canto singer it seemed a bit thin but the room acoustics were not exaggerated in any bad way. Pulled back on stage in front of a singer-songwriter, it worked quite well as an ambient mic and remained very balanced.

I tried it very briefly on trumpet and found that the same characteristics that exaggerate the articulation of a vocalist also exaggerate the blattiness of brass instruments. It was a very in-your-face sound; for this application, I put it back and put up an Electro-Voice RE20 instead.

On acoustic guitar it worked well but it pushed the sound of the guitar very far forward, sounding almost like God’s own SM57 but with a little more finger noise.

Oh, yes, and this mic does require a lot of gain. I was regularly using 60 dB of preamp gain for testing. However, there are a lot of inexpensive preamps now that will perform well; the built-in pres on the Mackie 1202VLZ did not have enough gain, but my Symetrix SX302 was fine with it.

Asymmetry: pluses and minuses

Something that I don’t like about this microphone is that the polar pattern is asymmetric. It’s a figure-8 mic, so you have a lobe in front that picks up sound, a lobe in back that picks up sound, and nulls (angles at which there is significantly less sound pickup) around the sides… but the frequency response of the front lobe and the back lobe are slightly different from one another.

Now, a number of newer ribbon mics do this (including some other Shure mics and some of the Royer mics), and it provides a larger palette of sounds for close-miking. The problem with this is that when the lobes are asymmetric, the quality of the null is degraded. This mic does have a poorer-quality null than typical figure-8 mics like the RCA BK-11, and my attempts at using it for a guitar player (putting the guitar in the null of the vocal mic and the vocal in the null of the guitar mic) were not as successful as with either the BK-11 or the AKG 414B/ULS.
This is a little disappointing to me because one of the things that I find really useful about figure-8 ribbons is the quality of the null and the ability to use the null to block out individual signal sources when tracking multiple instruments together. If you’re more interested in having two different ribbon sounds from one mic than in making use of the nulls, then the KSM313 does just that.

The mount

The KSM313 is supplied with what Shure calls a “monocle mount,” which is a fairly long lever arm with the mic on one side and a 5/8''-27 screw for a mic stand on the other side. The good news about this is that it provides a very convenient mount for a singer. The bad news about it is that it provides an arm that bounces up and down and really exaggerates low-frequency noise conducted in from the mic stand. This is a serious problem on stage risers that may not be in good condition, especially with a bass amplifier nearby. It would be good to have a shock mount available in place of the monocle mount for many situations.

I took it apart

The microphone comes apart very readily, revealing an interesting toroidal transformer that seems to be a smaller version of the one used in the Studio Vocalist. The transformer is really the weak point in any ribbon mic because it takes a very low impedance (well below an ohm) and turns it into a higher impedance the mic preamp can deal with. Typical ribbon transformers have a ratio of 1:100 or more, and it is very difficult to make a transformer with such a high ratio. I didn’t do measurements on this one, but the original measurements on the similar-appearing Studio Vocalist transformer were very impressive.

The ribbon assembly itself is quite small and quite solidly and tightly mounted. There’s no internal shockmounting, but everything inside is very tightly supported so that shocks won’t be exaggerated by internal resonances. Consequently, handling noise is actually very good, aside from the problems with vibration pickup from the stand noted above.

Some careful thought has gone into dealing with grille problems in a way that wasn’t done on the Studio Vocalist. This is important, and it’s probably much of the reason why the mic works so well in the far field.

The aforementioned asymmetry turns out to be the result of a plate mounted behind the ribbon. Not only does this change the response and make it different between the front and the back, but it also may act as a blast filter; if you have a problem with p-popping it might help to try the rear lobe. This isn’t mentioned by Shure but it could be a useful side-benefit of the design.

Measurements

The measured frequency response looked more or less like the response in the datasheet of the mic, with a few narrow spikes here and there that don’t normally show up on smoothed datasheet plots. The spikes all moved around as the mic position changed, which makes me think they are acoustical things going on rather than mechanical resonances. This is a good thing.

The mic response is, as mentioned above, wildly different in front and back. Whether this is an advantage or a disadvantage is up for discussion but it’s clearly deliberate.

Conclusion

This mic is bright without being shrieky or gritty. It’s good when you want to exaggerate something like a vocal and bring it forward in a dense mix without it being too over the top and piercing. This would also be a really great microphone for voiceover and announcer work, and the fact that it does well with a wide variety of different vocalists makes it a good versatile performer.

Crowley and Tripp did a good job with their original microphone designs, and Shure did well to buy them out, finally bringing ribbons back into the Shure catalogue. Some of the improvements in this microphone may be the result of Shure’s engineering folks going over it. [Shure comments that the output level of the mic has been set up to be roughly equal to that of their popular SM58 dynamic design. — Ed.]

However — don’t think of the KSM313 as a classic ribbon mic at all, because it’s clearly not designed to sound like a conventional ribbon, and it’s clearly not designed to be flat and neutral; instead, think of it as a deliberately forward-sounding and versatile mic that happens to have a ribbon inside.

Price (as of April, 2010): $1619

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