Review of the Nady HM-10 omnidirectional headset microphone (for linguists)

July 2010

Acknowledgments

I would like to thank Nady Systems, and, in particular, Ms. Toby Nady, for help with this review.

Introduction: About Nady Systems

Nady Systems has been designing, manufacturing, and marketing wireless microphones since 1976. I remember, back in the late 1980, in Poland, while I was working as a sessions musician, Nady wireless guitar systems were the performing musicians' most desirable gadget. I have no idea how Nady got their products across the Iron Curtain, managed to popularize them, and turn them into a status symbol. I do not believe that it was because of genius marketing à la Apple. Rather, I think that Nady wireless products were designed and engineered very well, and they were available at affordable prices. I think that this would still be a fair characterization of Nady as a professional audio company: they make innovative, high-quality products that have the unique quality of becoming musicians' favorite tools. In 1996, John Nady, the founder and CEO of Nady Systems, was recognized for his achievements by the National Academy of Television Arts and Sciences with an Emmy for Outstanding Technical Achievement in pioneering wireless microphone technology.

Nady has a respectable line of microphones including vocal and instrument microphones for both live and studio applications, including dynamic microphones, large-diaphragm condenser microphones, tube microphones, drum microphones, USB microphones, and the HEADMIC™ Series. Currently, the series includes five head-mounted microphones available both for wired and wireless applications.

The Nady HM-10 microphone: Design and specifications

The Nady HM-10 microphone (Figure 1) is an omnidirectional electret condenser microphone, available with a mini-XLR (3 pin) or a 3.5mm plug for wired and wireless applications. The version reviewed here is supplied with the 3-pin mini-XLR connector and the 9~52V adapter (the XM-10) for wired use with standard phantom power. Table 1 summarizes the microphone's specifications.

Figure 1. The Nady HM-10 microphone and supplied accessories

The headband

At first glance, the Nady HM-10 looks similar to other microphones reviewed on this website. The headset consists of a miniature capsule, a slim-profile boom, and a flexible, behind-the-ears headband (Figure 2). The headband, a crucial aspect of a speech-recording microphone, is designed rather well. It is virtually weightless, fits comfortably behind the ears, and, most importantly, holds the microphone close to the talker's lips, at the recommended distance of about 2-4 cm. The headband design is very similar to that of the DPA4066 (review), the YPA (review), and the Sennheiser HSP2 (review).

Figure 2. The Nady HM-10 microphone showing the front of the headband

Headbands are a frequent subject of discussion (and controversy) among those of us whose research relies on high-quality, spectrally rich, unbiased field recordings of speech. The headband must provide a close microphone placement. It must hold the microphone close to the talker's lips, off to the side of the mouth (as shown in Figure 2). One of the most important advantages of head-mounted microphones is that the capsule is kept at a constant distance from the mouth, thus allowing the recordist to set and maintain appropriate signal levels throughout the recording session. In addition, a properly designed headband provides a shock mount for the capsule and, if coated, adds some resistance to handling noise.

I receive a lot of questions via this website regarding the use of head-mounted microphones. While most people seem to recognize the purely acoustic advantages, many have reservations about their interviewees being comfortable wearing a headworn microphone. My usual answer is that, yes, we do need to choose a headband that is as unobtrusive as possible, but that most people, if asked, have no trouble putting a headset microphone on. I have been using headset microphones in the field for about ten years now, and not a single subject has ever refused to put one on. I cannot guarantee that they were not made shy or self-conscious about it, but I am not sure whether the feelings would be any different towards a lavalier or hand-held microphone.

Figure 3. The Nady HM-10 microphone showing the back of the headband

Having said that, headset microphones vary greatly in terms of ease of use and comfort. In fact, I make my own headbands, which I design specifically for the purposes of field interviews. The Nady HM-10 is among my favorite headband designs, though it could benefit from better coating to help reduce handling noise. Looking at the photos of the microphone you might conclude that the headband is flimsy and fragile, but, in everyday field use, this type of headband has proven to be dependable and sturdy enough to withstand the rigors of most field recording scenarios. It is just a simple, yet effective design. Figure 3 shows the back of the head to show you how the headband rests on the back of the neck, hooked comfortably behind the ears. To use the Apple cliché, "it just works." The added advantage of the headband is that it folds flat for easy storage. Finally, should you want to adapt the microphone to a third-party headset, you can do so easily with the HM-10 by detaching the boom from the headband.

The capsule

The Nady HM-10 is built around an omnidirectional, miniature electret condenser capsule (Figure 4) with a wide and flat frequency response . The idea behind this type of design is to provide a clear and crisp recordings of speech for many live applications, including theater, vocals, lectures, sermons, TV, and others.

Figure 4. The Nady HM-10 microphone capsule

The microphone has the medium-to-high sensitivity of about 7.9433 mV/Pa and the maximum sound pressure level limit of 130 dB SPL. In my experience, the slightly increased sensitivity works perfectly well with conversational speech (50-60 dB SPL) and helps minimize the overall levels of self-noise in the recording chain. The frequency response is mostly flat, with one presence peak around 10,000 Hz, which is rather commonplace in microphones of this type (Figure 5). The microphone does not overload easily and should be perfectly adequate for most loud speech sounds and relatively resistant to popping due to plosives. The windscreen goes a long way toward ensuring that, of course.

Figure 5. The Nady HM-10 microphone frequency response according to the manufacturer

The XM-10 phantom power adapter

The microphone cable is terminated with a 3-in mini-XLR connector (Figure 6), which connects to the XM-10 phantom power adapter (Figure 7). The adapter provides an interface between the microphone and a 48 V phantom power source. Due to the industry-standard XLR connector, the adapter makes the HM-10 compatible with most professional wired microphone applications. In addition, the phantom power adapter has a built-in high-pass filter (aka "low-cut filter," Figure 8), but it lacks a mute switch or a belt clip attachment, neither of which are indispensable, but would, nevertheless, be useful on this type of microphone.

Figure 6. The Nady HM-10 microphone 3-pin mini-XLR connector

While the XM-10 phantom power adapter works really well, I would very much like the option of a battery-powered adapter, such as the one supplied with the Sanken COS-11D xBP microphone (review). Battery-powered microphones help save your recorder's precious battery life, and, more importantly, supply the microphone with just the right amount of voltage for low-noise operation. You may have noticed that other microphone systems also use the 3-pin mini-XLR connector (e.g., Audix HT5, reviewed here), however, the wiring is different so the power adapters are not interchangeable.

Figure 7. The Nady XM-10 phantom power adapter

Figure 8. The Nady XM-10 phantom power adapter; a close-up of the low-cut filter

Audio tests

Low frequency response

Low frequency response is one of the critical features of a speech recording microphone. I must admit that I am somewhat biased in this regard because the bulk of my own acoustic analysis and synthesis lives below 500 Hz. However, if you are interested in the analysis of pitch, phonation, spectral tilt, F1, nasalization, breathiness, laryngalization, lateralization, and other articulatory features with low-frequency correlates, you will need a neutral low-end. I tested the Nady HM-10 microphone with my usual setup. I generated a waveform with peaks of equal amplitude at the frequencies of 50, 100, 200, 300, 400, and 500 Hz. I then played the signal out of a flat-response loudspeaker and recorded it with the Nady HM-10 microphone about 1.5 inches from the sound source (a typical headset distance). The spectrum in Figure 9 shows the low frequency response of the Nady HM-10 microphone. The microphone reproduces each center frequency really well, with no appreciable attenuation or amplification below above 100 Hz. There is, however, a slight dip around 50 Hz, but it is very slight, indeed, and should not negatively influence your recordings. In fact, I am quite impressed with the HM-10's performance below 500 Hz. From my point of view, the Nady HM-10 passes the low-frequency test. If used with a flat-response microphone pre-amplifier, the Nady HM-10 will deliver rather respectable low-frequency response.

Figure 9. The Nady HM-10 microphone low-frequency response

Self-noise

Since we record speech at relatively low sound pressure levels (50-60 dB SPL), we require the entire recording chain to be as quiet as possible (to have a low noise floor). Microphones of medium-to-high sensitivity (such as the Nady HM-10 or the Sanken COS-11D) may require your recorder's pre-amplifier gain to be turned up to perhaps 50-75% of its range, which, depending on the recorder, may or may not generate appreciable levels of self-noise. You can read more about testing equipment for self-noise in this post. The idea is to measure real-world inherent noise in the recording chain. I use the same methodology in all of my microphone reviews, so you can compare the present results with those obtained in the other tests.

Again, the Nady HM-10 does not disappoint and delivers very respectable self-noise performance. Figure 10 shows a spectrum of self-noise generated by a recording chain consisting of the Nady HM-10, a Tucker-Davis microphone pre-amplifier, and the Sound Devices USBPre (reviewed here), calibrated to the peak level of -12 dB SPL, and normalized to the RMS of 70 dB SPL.

Figure 10. The Nady HM-10 microphone spectrum of self-noise

One word of caution: watch out for low-frequency hum. As you can see in Figure 10, there is a 60 Hz peak of around 50 dB. Low-frequency rumble is virtually unavoidable in any industrialized urban environment. In addition, your own equipment may generate 60 Hz (or 50 Hz outside of the US) hum due to ground loops or induction from power lines. This is especially true when using any of the popular USB recording interfaces with a laptop computer. The hum may come both form the interface and the laptop itself. Check your laptop's A/C adapter, as many of them are "dirty," generating high levels of noise that leak into your precious recordings. You may want to try the Ebtech Hum X hum eliminating device (reviewed here). It does work wonders for hum originating from ground loops.

I was really impressed with the HM-10's noise performance, I decided to test it against Beyerdynamic Opus 55 MkII (review), one of the quietest head-mounted condenser microphones I have tested. You can read more about the comparison at the bottom of this page.

Spectral detail

The Nady HM-10 delivers rather respectable spectra detail. There is ample detail in the entire speech-specific range of frequencies. Transient response appears to be very good, and there is no evidence of any significant phase distortion. As you can see in my test recording in Figure 11, the spectrogram shows enough data to satisfy even the most demanding analysis. Similarly, the LPC response in Figure 12, shows sharply defined formant peaks and a natural spectral envelope.

Figure 11. The Nady HM-10 microphone spectrogram of the Polish test phrase "czarna krowa"

Figure 12. The Nady HM-10 microphone LPC of the vowel /o/ in "bordo"

One of my favorite practical (and rather demanding) tests of spectral detail is LPC analysis/re-synthesis. For the synthesis to be successful, the recording must have exceptionally high degree of spectral detail and a very favorable SNR. Of course, a lot of that is accomplished due to close placement, but the microphone capsule must be able to capture the detail in an unbiased, distortion-free manner. Figure 13 shows a rather successful LPC analysis/re-synthesis of the Polish word "bordo" with a 50 Hz decrease in F1 and a 100 Hz increase in F2 (both marked in red) throughout the ten-frame range. The processing was done with the synthesis tools available in Akustyk 1.8.1. All frames, including the voiceless /r/ in the middle, appear to be properly resolved, with no frame dropouts (at a 0.01 s time step)

Figure 13. The Nady HM-10 microphone LPC analysis/re-synthesis of the Polish word "bordo"

I also resynthesized the English word "add" to try to provide a more practical application of the processing (Figure 14). The resulting pronunciation (formant tracks marked in red) shows an example of the /ae/ influenced by the Northern Cities Chain Shift. Again, the synthesis is of very high quality, with no frame drop-outs, or audible artifacts (at the time step of 0.001 s). You can listen to the comparison by clicking the PLAY button below.

Listen to MP3 at 128 kbps (the first token original; the second re-synthesized):

Figure 14. The Nady HM-10 microphone LPC analysis/re-synthesis of the American English word "add"

Finally, Figures 15 and 16 show an example of American English speech data (you can record the entire recording at the bottom of the page). The detail is rich and unbiased. You should obtain excellent results with such recordings.

Figure 15. The Nady HM-10 microphone spectrogram of the American English phrase "buy a large barrel of good beer"

Figure 16. The Nady HM-10 microphone LPC and FFT of the vowel /uh/

Comparison of Nady HM-10 and Beyerdynamic Opus 55 Mk II

Throughout my review, I really got to like the Nady HM-10 microphone. It has a really good subjective sound quality, the recorded speech is very easy to post-process with compression and EQ, and the actual acoustic performance on most tests turned out to be quite good. I wanted to make a direct comparison between the Nady HM-10 and my favorite Beyerdynamic Opus 55 Mk II. The Opus definitely wins in terms of build quality and headband design, but I wanted to see how self-noise and spectral detail compared across the two. I used my Fostex FR-2LE recorder with onboard phantom power in order to make the test more consistent with a real-world field recording scenario. The talker wore both the microphones on opposite sides of the face, at the same distance from the mouth. The microphone trim levels were identical, as the microphones proved to closely matched in terms of actual sensitivity. I recorded the test phrases simultaneously, with the HM-10 in the left channel, and the Opus in the right channel.

In terms of self-noise (Figure 17), the Beyerdynamic wins quite convincingly. It has much better immunity to 60 Hz hum and has a significantly lower overall noise floor (with both signals normalized at the RMS of 70 dB SPL)

Figure 17. A comparison of self-noise spectra of the Nady HM-10 (left panel) and the Beyerdynamic Opus 55 MkII (right panel)

I also tested each recording with LPC analysis available in Akustyk (Quick LPC), which is one of the most common types of acoustic analysis of speech used in sociolinguistics. The LPC values are nearly identical (Figure 18 and Table 2), with the Beyer turning out slightly narrower bandwidth values, possibly indicative of slightly better spectral detail and signal-to-noise ratio. The differences are so small that I would consider them insignificant for most purposes.

Figure 18. A comparison of HM-10 and Opus 55 MkII LPC spectra

The Beyerdynamic Opus 55 Mk II retails for about $200 plus $75 for the CV 18 phantom power adapter. The Nady HM-10, including the HX-10 adapter, sells for less than the price of the CV 18 alone. The Beyer does win acoustically, but only slightly so, for most purposes, anyway. It also wins in terms of build quality, lower handling noise, and lower inherent noise. Neither manufacturer provides a battery-powered adapter for their respective microphones. If you need an inexpensive microphone for your or your students' projects, the Nady is going to save you over $200.

Conclusions

As we saw throughout the review, the Nady HM-10 produced consistently good recordings of speech. It has an affordable price, low self-noise, medium-high sensitivity, a nicely designed headband, and an effective phantom power adapter.

On the other hand, the Nady HM-10 does not offer a battery-powered adapter and lags behind the likes of Beyerdynamic Opus 55 MkII in terms of build quality and acoustic performance.

Having tested the HM-10, I am convinced that it is the best speech recording microphone under $100 currently available, and it is surprisingly close in terms of acoustic performance to microphones costing several times as much. The decision, of course, is yours, as always. It is possible that the Nady microphone might not even be available in your market. Check with the Nady website to see if it has distributors and technical support in your part of the world.

Download audio files

	Description	Quality	Comments
	With Tucker-Davis pre-amplifier and Audio-Technica CP8506 48VDC 4-Channel Phantom Power Supply	48,000 Hz; 24-bit; mono	Captured with USBPre in a sound booth
	With the USBPre; test recording in Polish	48,000 Hz; 24-bit; mono	Captured with USBPre in a sound booth
	With Fostex FR-2LE and onboard phantom power	48,000 Hz; 24-bit; mono	Captured with Fostex FR-2LE, calibrated to peak level of -12 dBFS, in a quiet room A comparison between Nady HM-10 (left channel) and Beyerdynamic Opus 55 MkII (right channel)