Review of the DPA 4006-TL and 4090 omnidirectional microphones (for linguists)
Introduction: About DPA
Although DPA has technically only been in existence since 1992, the company draws on more than five decades of world-class microphone design experience going back to the first range of measurement microphones created by DPA's progenitor, Brüel & Kjær, in the 1950s. Brüel & Kjær is obviously a well-known brand in the world of speech and hearing sciences, highly renowned for its sound level meters and other precision research and clinical tools. DPA has recently increased its number of employees to over 100 and is now represented by professional audio distributors in more than 40 countries around the world. In the past five years alone, DPA has experienced an average annual growth of 25 percent, and, in 2007, was presented with the prestigious King Frederik IX's award for outstanding contribution to Danish export.
DPA's ultimate goal is to provide "the absolute finest possible microphone solutions for your tasks." DPA engineers are driven by the idea of providing the cleanest, most faithful sound reproduction for a variety of recording scenarios, including voice and acoustic instruments. DPA prides itself on taking no shortcuts in their designs and running a very stringent quality manufacturing process. DPA products are usually praised for their exceptional clarity and transparency, reliability and, above all, pure, uncolored and undistorted sound.
About DPA microphones
In my review of the DPA 4066 headset microphone, I detailed DPA's commitment to producing a very versatile microphone system. The DPA 4006-TL and 4090 are no exception. They are both manufactured to a very high precision standard and should withstand the daily laboratory use for many years. DPA publishes a very useful website called "DPA Microphone University" which offers a wealth of useful information about microphone technologies, recording techniques, etc. I strongly encourage you to visit the site and explore its educational materials.
I would like to thank DPA Microphones, Inc., and in particular, DPA President, Bruce Myers, for their help with this review. They are a really good group, with brilliant engineers and a very helpful technical support crew. DPA has a strong interest in developing productcs for the scientific community.
I typically recommend head-mounted microphones for both field and laboratory use. However, stand-mounted microphones are a very viable alternative, especially in sound-treated laboratories and anechoic chambers. Stand-mounted microphones, including the 4006-TL and 4090, require perfect recording technique. They must always be mounted on a stand, preferably, with a shock mount (DPA has an impressive selection of mounting accessories). The stand should be isolated from the surface with acoustic foam to further avoid low-frequency vibrations reaching the microphone housing. The microphone should be positioned about 2 inches from the mouth, off to the side. One should try to advise the talker to not move their head during the recording session so as not to unpredictably change the acoustics of the recording. I sometimes receive questions of whether one can mount a measurement microphone on the ceiling of a sound-treated booth. Of course, you can do that, but if the subject is farther from the microphone than, say 5-10 inches, you are going to lose a great deal of spectral detail and allow much of the room's acoustics to shape the spectral characteristics of the recording.
Design and specifications
DPA 4006 (Figure 1) is one of the most popular types in the DPA microphone range due to its precise, detailed and natural reproduction. This is achieved by a low-noise, high-sensitivity, omnidirectional design, with a broad and flat frequency response (Figure 2).
Figure 1. The DPA 4006-TL microphone (image courtesy of DPA)
In striving to achieve an even cleaner sound, the 4006-TL is equipped with a state-of-the-art transformerless preamplifier and is powered via a standard 48 V Phantom Power supply. This design increases the sensitivity and provides an extended low-frequency handling capability (15 Hz to 20 kHz ±2 dB). All components in this construction are carefully selected to fulfil the demand for optimal neutrality, accuracy and extremely low distortion even at very high sound pressure levels. The microphone is fairly resistant to popping but I do recommend that you use the supplied windscreen.
Figure 2. DPA 4006-TL microphone frequency response with the near-field grid fitted (according to the manufacturer)
Table 1. Specifications for 4006-TL Microphone, P48, Transformerless
|Principle of operation:
|| 16 mm (0.63 in) pre-polarised condenser
|Frequency range, ± 2 dB:
|| 15 Hz - 20 kHz
|Sensitivity, nominal, ±2 dB:
|| 35 mV/Pa; -29 dB re. 1 V/Pa
|Equivalent noise level A-weighted:
|| Typ. 15 dB(A) re. 20 µPa (max. 17 dB(A))
|Equiv. noise level ITU-R BS.468-4:
|| Typ. 27 dB (max. 29 dB)
|S/N ratio, re. 1 kHz at 1 Pa (94 dB SPL):
|| 79 dB
|Total harmonic distortion (THD):
||<0.5% THD up to 129 dB SPL peak, <1% THD up to 135 dB SPL peak
|| Typ. 120 dB
|Max. SPL, peak before clipping:
|| 143 dB
|Cable drive capability:
|| Up to 100 m (328 ft)
|| Phantom P48
|| 2.60 mA
|| 3-pin XLR-M (Standard P48)
|| 150 g (5.29 oz)
|| 16 mm (0.63 in)
|| 165 mm (6.5 in)
|Operating temperature range:
|| -10 to +70° C (+14 to 158° F)
The DPA 4090 (Figure 3) is a high quality omnidirectional condenser microphone. Due to its uniquely natural and open sound, the 4090 is designed primarily for instrument amplification in the studio or on the stage. Due to its linear frequency response in the 20 Hz to 20 kHz range (Figure 4), speech researchers can also use these microphones for sound presentation alignment, testing and tuning. The 4090 can also be used as a less expensive alternative to the 4006-TL in a speech laboratory. The rugged and compact design features a 5.4 mm diameter pre-polarized condenser capsule in a tapered body measuring just 12 cm (4.75 in).
Figure 3. The DPA 4090 microphone (image courtesy of DPA)
Figure 4. The DPA 4090 microphone frequency response
Warranty and service
The DPA 4006-TL comes with an impressive five-year warranty which covers the microphone, its mechanical functionality, and performance within documented specifications. If you need your microphone serviced, you need to contact the dealer from which you purchased the microphone and they will send it to the nearest authorized DPA service center where it will be tested and repaired. It will be returned to you "clean and buffed." I always point out that it is important to buy from reputable dealers only.
The DPA 4006-TL performed wonderfully in all of my tests. It is, without a doubt, the best laboratory (stand-mounted) microphone I have ever tested. It lives up to its reputation as a very quiet and clean microphone. It handles more easily than the Earthworks M30, partly due to its superior resistance to popping, with proper technique, of course.
Due to its high sensitivity and superb electronic design, the DPA 4006-TL has extremely low self-noise (Figure 5). You can be certain, that the microphone will give you an extremely clean recording. It is a perfect choice for recording speech in an anechoic chamber.
Figure 5. DPA 4006-TL self-noise
By comparison, the DPA 4090 has a slightly higher self-noise, but still rather low (Figure 6). Again, it does appear to be a good lower cost substitute to the DAP 4006-TL.
Figure 6. DPA 4090 self-noise
The DPA 4006-TL has exemplary low-frequency response (Figure 7). It is pancake-flat and limited only by the performance of your microphone pre-amplifier. 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 DPA 4006-TL 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 DPA 4006-TL microphone. The spectrum in Figure 7 shows the low frequency response of the DPA 4006-TL microphone. The microphone reproduces each center frequency really well, with no appreciable attenuation or amplification above 50 Hz. There is, however, a slight dip around 50 Hz, but it is very slight, indeed, and should not negatively influence your recordings. From my point of view, the DPA 4006-TL passes the low-frequency test with flying colors.
Figure 7. The DPA 4006-TL microphone low frequency response
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 8 shows a rather successful LPC analysis/re-synthesis of the English word "love" with a 100 Hz decrease in F1 and a 200 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 appear to be properly resolved, with no dropouts (at a 0.01 s time step). Once again, I must stress the importance of recording technique, particularly that of close (and constant) placement.
Figure 8. The DPA 4006-TL microphone LPC analysis / re-synthesis formant tracks of the vowel /uh/ in "love"
The DPA 4006-TL microphone delivers excellent spectral detail and a very natural spectral envelope (Figure 9). Transient response shines, as evident by the initial consonant bursts at the beginnings of each word in the phrase. The microphone is impressive at capturing even the slightest detail in the release burst spectra of /cz/ and /k/.
Figure 9. The DPA 4006-TL microphone; spectrogram of the Polish phrase "czarna krowa"
Figure 10 shows a spectrogram of the American English phrase "buy a large barrel of good beer" showing superb spectral detail.
Figure 10. The DPA 4006-TL microphone; spectrogram of the English phrase "buy a large barrel of good beer"
Figure 11 shows an FFT of the vowel /I/ and Figure 12 shows an LPC of the vowel /ai/. Both vowel spectra are beautifully defined, showing properly resolved formant frequencies, narrow bandwidths, and a natural frequency envelope. You can be confident that the DPA 4006-TL will give you accurate formant data.
Figure 11. FFT of the vowel /I/
Figure 12. LPC of the vowel /ai/
I have been thoroughly impressed with DPA products. Their entire line of microphones and related accessories makes it one of the more appropriate systems for speech and hearing research. The 4006-TL is the best laboratory microphone I have ever tested. It is simply superb. The 4090 is not far behind. I would compare it to the Earthworks M30 in terms of handling and performance.
In short, if you can afford it, simply buy it and enjoy it. You will not be disappointed.
The flagship DPA 4041-SP large diaphragm microphone
I believe this review would not be complete if I did not mention the DPA "flagship" microphone, the 4041-SP. The 4041 series a large-diaphragm omnidirectional microphone that has the lowest noise, highest precision, and highest resolution of all DPA microphones currently in production. It has been used for long-term preservation purposes of historic instruments (e.g., Stradivarius violins) and the greatest operatic voices. DPA claims that the microphone comes very close to the absolute lowest theoretical noise floor. If your project requires the ultimate quality, you may want to give the 4001-SP a serious try.
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