|
|
Tutorials
Akustyk
Linguistics
Audio technology
Field recording
Recommendations
Reviews
Film Processing
|
Sennheiser HMD 25 (a.k.a. HMD25-1) Microphone Review
Before we go into the details of the microphone's design and performance, let me just say that, based purely on the spec sheet, I would not consider this microphone appropriate for speech research. However, having used the microphone for a number of years, I have grown to love it. It's performance is nothing short of extrordinary, especially in adverse acoustic conditions.
Figure 1. The Sennheiser HMD 25-1 microphone; you will often see it used by sportscasters, such as Marv Albert HMD25-1 SpecificationsSpec sheet, according to the manufacturer
Frequency responseThe HMD25-1 (in fact the HMD414, which is the microphone unit that is part of the headset) has a frequency response that is far from flat. This is typically really bad for speech analysis, but, somehow, the frequency response "evens out" with close microphone placement (at least at the low end). If you have no choice but to record in really noisy environments (e.g., in a college cafeteria, on a factory floor, in a busy street, etc.), the HMD25-1 is an excellent choice.
Figure 2. Sennheiser HMD 25 frequency response, according to the manufacturer What I like a lotImpressive signal-to-noise ratio (SNR)The microphone is capable of achieving a remarkably good SNR. It is designed to do that. The favorable SNR is accomplished by both close microphone placement and its hypercardoid polar pattern, which effectively rejects off-axis noise. Resistance to pop and hissThe microphone capsule and the included pop filter make the HMD25-1 resistant to pop and hiss. The pop and hiss are likely to occur with cardioid microphones during the articulation of plosives. The HMD25-1 is practically immune to this, especially if placed slightly off to the side of the mouth. Also, the microphone has good immunity to handling noise and wind. Excellent sound qualityYes, I do realize that the subjective "sound" of a microphone is irrelevant for speech research. However, this microphone really does sound great! It has a big, crisp, and detailed sound, reminiscent of large coil dynamic microphones, such as the Heil PR 40. No, not as good, but certainly close. Surprisingly good headphonesThe headphones have a very good, flat and broad frequency response and offer a surprisingly good sound. They're closed, sound-isolating headphones, but do not use and of the usual noise cancelling trickery. I like these headphones a lot. No need for phantom powerThe Sennheiser HMD25-1 is a dynamic microphone, so it does not require phantom power, which simplifies its operation and lowers power consumption in the field. One word of cautionThe Sennheiser HMD25-1 is truly a professional microphone. It is designed to be interfaced with professional-grade pre-amplifiers. It is a relatively low-sensitivity dynamic microphone and it therefore requires a high-gain, low-noise pre-amplifier. ConclusionI might be arguing against my own convictions here, but the Sennheiser HMD25-1 is a winner. No microphone I have tried is better at recording detailed speech signals in noisy environments. Audio testsExamples of recordings made with the Sennheiser HMD25-1 microphone are ubiquitous on this site. Figure 3 shows a spectrogram of the phrase "czarna krowa" in Polish. The spectral detail is outstanding. By the same token, the FFT in Figure 4 shows a really well-defined peaks and a natural spectral envelope, with just a touch of low-frequency roll-off. Below, you will also find a few audio files that I recorded with the microphone. You are welcome to download those and test them for yourself.
Figure 3. Spectrogram of the Polish phrase "czarna krowa"
Figure 4. FFT of the vowel /o/ in "bordo" Download original files
|
The 
