Peer Review: Lectrosonics TM400
Peer Reviews: Lectrosonics TM400; Price: $1,890 MSRP
We found the operating range to be very good, operating cleanly at more than 300 feet through concrete and steel and much, much farther with a clear line of sight. Given the size of most venues, coverage of sound systems, and limitations of typical measurement systems, range shouldn't be a concern for most users. If more range is required, Lectrosonics recommends adding a more directional, higher gain antenna to the system. Interestingly, SIA-Smaart-users will find that even with the stock “whip” antennas, the wireless system's range will typically exceed the amount of delay that can be applied to the measurement signal.
To explore the performance of the TM400, we made a series of measurements using an Earthworks M30 microphone connected to an SIA-Smaart-equipped computer via a standard microphone cable and then repeated the measurements using the TM400 to provide a wireless connection. We found that the TM400's frequency response is very close to the manufacturer's published specifications.
However, our results revealed one minor difference between wired and wireless operation: The low-frequency response drops by 3 dB at 30 Hz, and we found a very small 1 dB rise between 8 kHz and 16 kHz, which could be attributed to the physical size of the transmitter attached to the microphone. Otherwise, it's flat between 30 Hz and 8 kHz. We also found up to 180 degrees of phase shift at the extreme low and high ends of the audio spectrum.
One interesting note is that the Lectrosonics system utilizes a hybrid analog/digital transmission system. In this design, the audio data is digitized and the digital data is transmitted over an analog RF format. Lectrosonics claims that, “Because the information being transmitted is digitally encoded, immunity to noise (in the RF transmission) is much higher than a compandor can offer. Because the encoded audio is sent in analog format, spectral and power efficiency and operating range are not compromised.” We found this claim to be mostly true. One byproduct of the A/D conversion, which is done in 24-bit, 88.2 kHz format, is that the system shows an overall delay of about 3.25 ms. Users making critical measurements such as crossover alignments should be aware of this latency.
While the TM400 frequency and phase responses could be better at the extremes of the audio spectrum (below 30 Hz and above 8 kHz), the response is more than acceptable for all but the most critical applications. Compared to commonly available existing wireless systems, the TM400 is uniquely well suited for test and measurements, and also makes an excellent general use, wireless microphone system.Value
The $1,890 MSRP may seem high at first glance, especially compared to the cost of a few high-quality cables. However, when working in union halls or other facilities where stringing lots of cable can be costly, and in relation to other wireless systems that may not offer a “measurement-quality” transmission path, the TM400 system is well priced. One feature we'd like to see in the future is a digital output, such as S/PDIF or AES-EBU, which would allow users to bring the signal into our measurement system without the need for an additional A-to-D conversion.
After testing the Lectrosonics TM400, we found it to be a very convenient tool well suited for general tests and measurements in the field. We recommend using the unit at live events such as theater, amphitheater, and sports facility applications where long cable runs can be time consuming. We found that any disadvantages of this system are small when compared to the practical considerations of working with large or complex sound systems or venues.
Sam Berkow is the creator of SIA-Smaart and principal consultant and founder of SIA Acoustics, an acoustical consulting firm in New York City. He can be reached at firstname.lastname@example.org. Steve Sockey is a partner and senior consultant at SIA Acoustics and former chief systems engineer for the United States Air Force Band in Washington, D.C. Steve can be reached at email@example.com