Beyerdynamic Opus 55 Mk II review

I need to give you a disclaimer, the Beyerdynamic Opus 55 Mk II is my favorite microphone for recording speech for analysis. So I guess this review might be biased a bit, but then again, this is a personal web site, so most of the things I write are biased in one way or another. There are a few different variants of this microphone; the one I am reviewing is Opus 55.18 Mk II BLK, which is terminated with a 4-pin mini-XLR connector. I also use the CV 18 in-line pre-amplifier.

Construction and design

The microphone has a rugged and water-resistant construction. It comes with a neckband and a detachable boom. The neckband makes it great for unobtrusive stage use, but problematic for field recording. However, because the boom can be detached easily, it allows for mounting the microphone on other headbands (see more on that below). I have been using the microphone since 2004 and have never had a problem with its reliability or performance. Table 1 below contains a list of technical specifications.

Frequency response

The Opus 55 Mk II is an omnidirectional condenser microphone. It has a very wide and flat frequency response. In my post on speech acoustics, I talk about the difficulty of capturing low frequencies of speech (approximately below 300 Hz) in an unbiased fashion. Cardioid directional microphones suffer from proximity effect, so they're out. Omnidirectional microphones are immune to the effect, but they are often "tailored" to influence the sound of the low frequencies in order to filter out low-frequency rumble and hum (e.g., Sony ECM55B, AKG HC 577). There are, therefore, very few close-speaking microphones with a flat low-end. The Opus 55 Mk II is one of them. For me, this is a crucial feature because I am interested in studying acoustic features that show up in low frequencies (e.g., nasalization and spectral tilt). The frequency response of the Opus 55 Mk II is flat where it matters most (see Figure 1).

Sensitivity

Head-worn microphones typically have a lower sensitivity (e.g., Shure Beta 53) because they're designed for stage use where speech is produced with a high vocal effort (i.e., it is loud). However, in a typical interview situation, people rarely speak up. Therefore, a low-sensitivity microphone requires the pre-amplifier to be turned up, which may introduce unnecessary noise and distortion, especially in lower-end, inexpensive devices. The Opus 55 Mk II has a medium sensitivity (4.5 mV/Pa), which makes it perfect for interviews, at least for me and my equipment. It may not be equally well-matched with your device.

Power requirements

The Opus 55 Mk II requires power between 1.5 and 9 V. In order to be able to use standard phantom power supplies (48 V), the microphone must use a specially de singed, in-line pre-amplifier. I use the MJ-53 (Figure 2), but CV 18 will also work, and I am very happy with it. It looks like a slightly oversized XLR connector and has a convenient belt clip. It also provides an interface between the mini XLR and standard XLR connectors, so the microphone can be connected by means of standard, balanced XLR cables.

What I like

I like almost everything about this microphone. It has just the right acoustic and electrical performance for my needs.

My wish list

Battery-powered belt-pack

I realize that this microphone is primarily used with wireless transmitters. However, I would really love a battery-powered belt-pack that would provide phantom power and a mini-to-standard XLR interface. Audio-Technica AT831b, which is another one of my all-time favorites, is a great example of that kind of design. It can be powered by a battery or regular phantom power. This is perfect in the field if you want to use a recorder that doesn't have on-board phantom power.

A headband

I make my own headbands, but it would be great if the microphone was offered with a traditional headband, such as those used in telephone headsets. That would be so nice!

DIY headband

I have designed my own headband that is easy to use for my interviewees (Figure 3). It is small, extremely lightweight, and adjustable. You can use the stock Shure accessory Boom Holder (RPM570) and glue it onto a standard telephone headset. Pick a headset that you like and one that doesn't cost too much. Mine was under $12 at RadioShack

Audio tests

I have a lot of audio recordings with this microphone. They're also available on this web site. Let me just include a few that are representative of the microphone's performance. In each case, the microphone shows a very flat response (results in a realistic speech envelope) and neutral low-end (harmonics close to the fundamental). Figure 4 shows a spectrogram of a phrase "their good clothes are old" recorded with the Opus 55 Mk II at 48,000 Hz, 24-bit. I used a state-of-the-art Tucker Davis microphone pre-amplifier and my USBPre A/D converter. The recording was made inside a sound-proof recording room. It is so luscious. This little mic is just great. The detail is so good, so clean. Figure 5 shows a narrow-band spectrum of the vowel /o/ in the word "clothes." The envelope is very natural, just as expected. There's no bias in the low, mid, or high frequencies. DOWNLOAD ORIGINAL FILE.

Figure 4. Spectrogram of a phrase "their good clothes are old" recorded with Opus 55 Mk II, a Tucker-Davis pre-amplifiers, and USBPre A/D converter

Updated! Interview with Klaus Kirchhöfer of Beyerdynamic

As we look for the best technology for our research, we often find ourselves walking across a mine field of poor advice and vested interest. My goal behind bartus.org is to provide speech and hearing scientists with honest, unbiased, lab-tested, and field-tested reviews of some of the most interesting audio and video technologies available. There are only a handful of manufacturers that specialize in research equipment (e.g., Tucker-Davis and Kay Pentax), but we can sometimes find appropriate equipment in the offerings of companies that specialize in pro audio equipment for musicians and recording studios.

Beyerdynamic is a German company dating back to the 1920s. Over the years, it has consistently provided some of the most innovative, reliable, and enjoyable pro audio equipment. Based on my experience, the Opus 55 MkII omnidirectional, headset microphone is one of the best microphones for recording speech currently available. I was, naturally, curious to find out more about the product line. I have recently had the pleasure of interviewing Mr. Klaus Kirchhöfer, Produktspezialist kabelgebundene Mikrofone ProAudio, from beyerdynamic GmbH & Co. KG, in Heilbronn, Germany. I include fragments of the interview below.

BP: "The Opus 55 Mk II is one of the best speech-recording microphones for speech and hearing researchers. Can you tell me a little bit about the engineering philosophy behind the microphone? What motivated the design of the capsule and the neckband?"

KK: "We wanted to offer an unobtrusive, easy to handle and versatile headworn microphone. It´s predecessor, named Opus 55 already sounded good, but was physically larger and some users had problems adjusting the expandable neckband. "Easy to handle" meant staying with an omnidirectional polar pattern, which doesn't´t show a proximity effect and is far less sensitive to small changes in position in comparison to a directional microphone. Also, an omnidirectional capsule can be built smaller than a directional one, reducing the physical size any further would have led to more self noise, less robustness - or a significantly higher price."

BP: "What is your primary audience for this line of microphones?"

KK: "For dancers, sports applications (or similar ones with lots of moisture), we wanted it - well, not totally water proof but protected against spreading water. I have to admit, we didn't´t have scientific applications in mind ;-) And finally, we gave it a quite flat amplitude response to make it useful also for flute or violin players, who don´t want to attach microphones to their instruments or have to change them quickly."

BP: "Sometimes, using a headset microphone is not possible and a lavaliere microphone is preferred. Does Beyerdynamic have a lavaliere microphone that is similar to the capsule of the Opus 55 Mk II? If so, what is it?"

KK: "We offer the Opus 55 Mk II capsule as a lapel microphone, named MCE 55. Due to their position, they may need different external equalisation, but their transducer elements are identical."

BP: "Those of us who record speech in the field, often use small digital recorders. Does Beyerdynamic have any battery-power options for the Opus 55 MkII? Having a self-powered microphone helps save the recorder's battery power, and eliminates potential phantom power noise issues that inexpensive recorders can produce."

KK: "Opus 55 Mk II (and MCE 55) cannot be powered by phantom power directly. It needs the additional CV 18 (or a similar) unit which converts phantom power from mic preamp to some kind of AB-powering for the microphone capsule. Many portable recorders, which just offer unbalanced microphone inputs offer a, sometimes called "Plug-In" power in their 3.5mm mini jack sockets. Exchanging Opus 55 MK II´s (or MCE 55´s) plug to a mini jack (or building an adapter), you can use this "Plug-In" power to feed the microphone(s) directly, the needed current is very low. We do not offer a battery powering unit for these electret microphones."

BP: "A lot of hearing researchers use headphones to deliver auditory stimuli. Flat and broad frequency response is highly desirable. Which Beyerdyanmic headphones would you recommend for researchers?"

KK: "DT 880 Pro (semi open) and DT 250 (250 ohms, closed) will work fine for the described application. Headphones can never have a technically linear amplitude response as they mask the listener´s individual head related transfer function and try to simulate it. Many users describe these two models as very neutral sounding."

Finally, Mr. Kirchhöfer assured me that Beyerdynamic has a strong interest in developing relations with scientists and will gladly welcome feedback from us. I believe him. I have worked with several manufacturers before, and Mr. Kirchhöfer impressed me greatly with his professionalism and commitment to providing the best product possible. Thank you!