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Royer SF2

Active Ribbon Microphone
Published September 2015
By Hugh Robjohns

Royer SF2

Does the sound of Royer’s flagship active mic justify the asking price? We put it to the test...

American microphone manufacturers Royer Labs brought their passive R121 and SF12 stereo ribbon mics to the market in 1998, and can fairly be credited with playing a major role in the resurgence of the ribbon microphone genre over the last decade or so. Both designs were heavily influenced by B&O’s ribbon mics of the 1970s, with the R121 being designed by Dave Royer himself and the SF12 being a licensed, ‘productionised’ and improved version of a mic originally designed by the late Bob Speiden — a true ribbon mic guru, and the man who inspired David to start manufacturing ribbon mics in the first place.

Royer’s product line has evolved and expanded in interesting ways since those early days, most notably with the introduction of a lower-cost version of the R121 called the R101 (reviewed in SOS Feb 2011, and active, phantom-powered versions of both the R121 and SF12, called the R122 and SF24, respectively. There are also active versions of the R122 and SF24 with valve-based gain stages (the R122V and SF24V).

Around the world many classical recording and scoring engineers enthusiastically adopted the SF12 stereo ribbon microphone because of its deliciously smooth and natural tonality, and the way it could be employed in either X-Y or M/S configurations. However, stereo microphones don’t suit every application, and Royer Labs were persuaded to produce a mono version of the unique SF12. The resulting SF1 ribbon mic quickly became a firm favourite with classical recording engineers and remained so until its recent discontinuation. However, the SF1’s era came to an end because Royer Labs has produced a new version named, logically enough, the SF2, which is essentially the same mic but with an active buffer and gain stage. In other words, it is effectively half of an SF24!


Physically, the new SF2 is larger than its antecedent although the ribbon is housed in the same 25mm (1-inch) diameter slotted matt-black tube. However, the electronics and custom transformer require a little more space than a 1-inch tube allows, so the lower portion of the mic slopes outwards to a fatter, 39mm (1.5-inch) diameter base section with the XLR output connector at the bottom. The SF2 measures 142mm (5.6-inches) in overall length (the same as the old SF1), and weighs 448 grams (15.8 ounces).

Although the review pair of SF2 mics were full production units, they arrived in pre-production packaging, parts of which turned out to add quite a lot to the retail price of the mic. Consequently the SF2 is being made available in two versions, differing only in the packaging and accessories (and thus overall cost!).

The standard version ships in an aluminium presentation case, and comes complete with a protective velvet ‘mic sock’, the brand-new bespoke SFS2 shockmount, and all the usual QC documentation and handbook. The alternative ‘deluxe’ version costs roughly 30 percent more, but its aluminium carrying/storage case includes a Padauk wood presentation box in which to store the mic, a Royer-made 20-foot microphone cable, and a premium RSM24 shockmount — plus the QC documentation and handbook, of course. In both cases, Royer Labs provide a lifetime warranty (repair or replace) to the original owner.

Exactly the same ribbon motor assembly is employed in the SF2 as its predecessor, and the new mic is intended primarily for the same kinds of classical and acoustic instrument recording applications. However, the new mic’s compact, phantom-powered active buffer/gain stage is essentially a single-channel version of that used in the SF24. This amplifier provides a significantly higher output level than the original passive SF1, of course, along with the ability to drive long cables without loss of quality. The main benefit, though, is enabling the SF2 to be used with a much wider range of preamps than was the case with the SF1 (which ideally required a fairly specialised, and thus expensive, high-gain preamp to obtain the best performance).

One of the (many) advantages of the ribbon microphone genus is an excellent transient response, completely free of HF ringing and resonances, thanks to the inherently low-frequency resonance of the ultra-lightweight diaphragm. Royer Labs’ R-series mics have large ribbons, like the RCA 44, with a resonance frequency below 20Hz. However, the SF-series mics employ shorter, narrower and thinner ribbons — a choice which is important for the sound character — but that raises the resonant frequency up to about 35Hz. Consequently, a good shockmount is essential to minimise audible excitation from mechanical vibrations.

The Deluxe kit includes the RSM24 shockmount, a  wooden mic box, and a  20-foot XLR cable.The Deluxe kit includes the RSM24 shockmount, a wooden mic box, and a 20-foot XLR cable.The 1.8-micron-thick aluminium foil ribbon sits within the company’s proprietary ‘cross-field’ magnet assembly, which comprises four powerful Neodymium magnets with Permendur iron pole pieces. This arrangement cleverly minimises the front-to-back audio path length, which is an important factor in extending the high-frequency response. As a result, the SF2’s response remains well within a decibel or two between 30Hz and 15kHz, tailing off very smoothly and naturally below and above those limits. In fact, the response is commendably flat, with only the barest hint of a mid-range lift (about 1dB between roughly 3-5 kHz, and a similarly mild dip around 11-12 kHz).

Like most traditional ribbons, the SF2 has a perfectly symmetrical figure-of-eight polar response — which means it can be used as the Side mic in a Mid/Side array, if desired. It also exhibits negligible off-axis coloration as the frequency response is remarkably consistent across the usable regions of the polar response, which is a great help when multi-miking sources in a large orchestra, for example. If the ‘spill’ sounds natural it blends in to the on-axis sound from other mics far more easily and transparently.

Active Electronics

The internal phantom-powered amplifier — which is a patent-pending design — uses a custom transformer to present an ideal (high) load impedance to the ribbon transducer, guaranteeing optimum sensitivity and frequency response. It also protects the ribbon from the potentially disastrous consequences of phantom power being applied directly across the ribbon element, of course. The SF2’s stated sensitivity is a healthy signal level of about 12.5mV/Pa, which is comparable with that produced by typical studio capacitor mics, and about 15dB higher than the original SF1 passive ribbon. So there is no need to use specialised high-impedance, high-gain preamps with the SF2, any standard mic preamp with a normal gain range will be absolutely fine. Also, lowish input impedances won’t affect the performance of the ribbon mic at all, and the specifications suggest the mic is happy with any load above 1500Ω, which covers pretty much everything!

Of course, the inherent risk with active electronics is internally generated noise and distortion, as well as a finite headroom limit (all amplifiers will overload at some level). However, the Royer Labs design has been carefully optimised to work with the SF2’s ribbon element, with the transformer providing 15dB of ‘free’ noiseless voltage gain to boost the signal level in advance of the fully balanced and discrete low-noise FET buffer stage, which provides the low output impedance. The design is derived from the well-proven amplifier in the SF24, and the result is an equivalent self-noise below 18dB SPL, negligible distortion, and a maximum SPL capability of 130dB, which is appropriate for the intended applications. The gain stage only requires a very modest 4mA from the phantom power supply, too, so it’s not going to tax a console’s power supply.

In Use

I’ve used ribbon mics regularly throughout my professional career, starting with the classic Coles 4038 at the BBC, and am a huge fan of the technology. I own several ribbons from various manufacturers myself, and use them often for choral, orchestral and acoustic instrument recordings where their smooth, natural-sounding high end delivers a sublime sonic character that provides both detail and clarity, but without that ‘zingy-ness’ I associate with many capacitor mics. The figure-of-eight polar pattern, too, can be incredibly helpful in controlling spill if employed thoughtfully and creatively.

Although I’ve never used the SF24 model, I have recorded with a (borrowed) SF12 often and I’ve reviewed the SF24V (the valve version) as well, so I am quite familiar with the sound character associated with this particular range of Royer’s high-end ribbon mics. As it happens, we also used an SF12 as one of the mic arrays for the preamp comparison in the October 2012 edition of Sound On Sound (, and a lot of people have commented very favourably on the SOS forum about the sound quality of that mic.

The SF2 retains the same lovely, detailed, but so natural familial sound of the SF12 and SF24, combining a realistic body and weight with precise transient attack and open-window mid-range clarity. Of course, the ubiquity of large-diaphragm capacitor mics means that most people have been programmed to associate transient detail with a bright, edgy and vaguely resonant character, and so it often comes as a shock when presented with a microphone that preserves the transient detail and yet sounds velvety smooth and oh-so natural at the same time — but that’s what ribbon mics generally do, and it’s what the SF2 does especially well. In short, it captures the true sound of the source in an effortlessly natural way without any of the slightly unnatural qualities that might be associated with typical capacitor mics.

Another strength of a good ribbon mic is a very linear dynamic range, and I wondered if the gain stage might compromise that in some way in the SF2. I shouldn’t have worried, though — the years of development Royer have invested in their active gain-stage design was well worth it, because I couldn’t detect any hint of compression artifacts at all until presenting the mic with really silly levels.

Versatility is the name of the game with the SF2, since it is equally happy to be employed as a main mic on orchestras and choirs with a relatively distant placement, or to serve as a closer spot or accent mic on sections or soloists. The built-in gain stage ensures that the output level is still quite manageable with distant placements, while its reasonably high maximum SPL still enables moderately close placement to loud sources — although I wouldn’t recommend using it on a huge Marshall amp stack! There is a significant proximity effect, of course, so you wouldn’t normally want to place the mic closer than about 12 inches from the source (and ideally a little further away still), but at least the consistent off-axis tonality means that the inevitable spill blends naturally and transparently with other mics.

During its final development stages the SF2 was apparently put through its paces by a number of very demanding studios and engineers, such as Leslie Ann Jones at Skywalker Sound and Michael Bishop (Telarc), both of whom were very enthusiastic about this latest Royer SF incarnation. Jack Vad, the chief recording engineer with the San Francisco Symphony Orchestra, was so impressed after hearing them at Skywalker Ranch’s scoring studio that he acquired some for the orchestra’s own mic inventory, and apparently they were used on four solo vocalists in the orchestra’s latest recording of Beethoven’s 9th Symphony!

There is no getting away from the fact that Royer Labs’ flagship ribbon mics are expensive, and the SF2 is certainly very costly even in the ‘standard’ packaging. But for those who can justify the expense, I’ve not found any other ribbon mics that match it in terms of pure sound quality, and the user-convenience and excellent technical specifications are cherries on the top of an already mouth-wateringly delicious cake! I’ve always coveted the SF12, but the flexibility of two SF2s is even more appealing — even if I have to give up eating and drinking for a year!


Keeping within the Royer family, the obvious lower-cost alternatives are the R122 or the passive R101. They have slightly different sound characters to the SF2, but retain the key strengths and qualities. The AEA A440 and A840 are high-quality active ribbons based on the company’s passive R44 and R84 models, and SE Electronics’ Neve RNR1 is another high-end active design. Other worthy alternatives include AEA’s R84, R92, Audio Technica’s AT4080 and AT4081, Beyerdynamic’s M130, Blue’s Woodpecker, Coles’ 4038 and 4040, SE’s Voodoo VR1, Shure’s KSM313 and KSM353, and Sontronics’ Delta, Sigma and Apollo designs — among many more.

Published September 2015