Lectrosonics TM400 Wireless Measurement System

Typically several issues can present problems for using standard wireless systems in critical measurement applications. Amplifier self-noise, distortion, and companding circuitry in wireless systems can cause deviations in frequency and phase response while taking critical measurements. The Lectrosonics TM400 is a high-performance product that innovatively addresses these issues for all but the most critically demanding measurement situations.
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(click thumbnail)Developing the TM400The need for a wireless system capable of transmitting error-free signals from a calibrated test microphone to a computer running real-time analysis software is not new. In fact, many engineers have been willing to sacrifice a certain degree of signal integrity in order to "go wireless" by using existing analog systems. Although some of these systems have worked fairly well, various issues including audio companding artifacts, external phantom power or a battery in the microphone have kept many engineers away from doing this.

Lectrosonics developed Digital Hybrid Wireless in 2002 as a way to transmit high-quality audio signals wirelessly without the problems associated with companding or pre-and de-emphasis. One of the more recent products using this approach is the TM400 system for test and measurement.

The UH400TM transmitter is a locking plug-on type providing 5V, 15V or 48V phantom power. The 100mW RF power of the transmitter provides very long range despite its small size and robust construction. The R400A receiver is a desktop-type unit providing a balanced XLR and unbalanced 1/4-inch outputs. The output level is variable from -50 to +5 dBu, allowing connection to any standard analog sound card or measurement input. The receiver also provides a Smart Tune function, allowing for one-button scanning and frequency selection.The use of measurement microphones in applications for live sound, measuring loudspeakers while setting up sound systems, determining delay times, and measuring room acoustics issues such as reverberation, has become commonplace. Most engineers are familiar with SMAART, SIM or SprectraFoo products to measure and equalize sound systems for live concerts and installations. Typically several issues can present problems for using standard wireless systems in critical measurement applications. Amplifier self-noise, distortion, and companding circuitry in wireless systems can cause deviations in frequency and phase response while taking critical measurements. The Lectrosonics TM400 is a high-performance product that innovatively addresses these issues for all but the most critically demanding measurement situations.

Features

The Lectrosonics TM400 system consists of a UH400TM plug-on transmitter and R400 receiver. The receiver is compact at 5.5 inches wide, 6.25 inches deep and 1 RU high. Housed in a protective hard Pelican-style case, it includes two removable whip antennas and a power supply. The balanced XLR audio output level is variable from -50 dBu to +5 dBu. The receiver power supply uses an external wall wart that incorporates a locking-type chassis connector. I am not a big fan of wall wart-type power supplies because in my experience durability has always been an issue. The R400 receiver has a locking power connector to improve on the design, which is a good idea, but in my experience these types of fragile plastic receptacles do not hold up.

The price point of $1,890 may appear high at first glance when compared to the cost of a few high-quality cables. However, the TM400 is a wireless system that in addition to its use for wireless measurements can be used with any wired mic to convert it to a wireless.

The UH400TM transmitter includes frequency, audio level, phantom, and power controls. Phantom power is selectable at 5V, 18V or 48V. The operating frequency is selected by turning two small pots with a miniature screwdriver (included). The unit is small and durable, and includes a protective nylon Cordura case.

The Lectrosonics unit provides an ample 256 different frequency options in 100 kHz steps for its RF transmission. The TM400 uses Lectrosonics' "SmartTuning" feature for finding clear frequencies. It is a good design that is fast and straightforward with no external computer software required. The SmartTuning feature uses the unit's receiver as a RF spectrum analyzer so users can quickly locate a clean band for operation. It is quick and easy to set up the receiver and transmitter for trouble-free use.
Fast FactsApplications: Live sound, contracting

Key Features: UHF Digital Hybrid technology; Smart Tuning; 256 frequency option; true diversity reception

Price: $1,890

Contact: Lectrosonics at 505-892-4501, www.lectrosonics.com.
In Use

I had the opportunity to use the TM400 in several venues to analyze various speaker systems and set delay times for the various PA, balcony and front fill speakers used during concerts with Tony Bennett and his Quartet. I found the operating range of the TM400 wireless to be extremely good. Drop out was never an issue, even when using it throughout venues of up to 250 feet, or when traveling to the rear of some balconies without a clear line of sight to the receiver,. When setting delays, users will find that even with the stock antennas, the TM400's range will typically exceed the amount of delay that can be applied to the measurement signal.

I made a series of measurements using a B & K microphone connected to a Toshiba laptop utilizing SIA-SMAART with a "reference" high quality microphone cable that I normally use when performing system measurements. I then repeated the measurements using the TM400 to compare the wireless connection. The low-frequency response below 50 Hz appeared to be slightly different and there was a small 1 dB rise between 8 kHz and 16 kHz. In my applications of tuning, the difference was so slight it in no way compromised the results I was trying to achieve. Using the wireless to set delays in a balcony was the best, due to its obvious mobility and time saving feature.

The UH400TM transmitter uses a 9V battery and runs for 4.5 hours on a standard alkaline and 12 hours on a lithium battery. It would be nice if the unit had a digital output (S/PDIF/AES-EBU) to allow users to use the unit with a measurement system without the need for A/D conversion.

Summary

The Lectrosonics TM400 is a welcomed, convenient tool for tests and measurements in live events for theater, amphitheater, and arena setups where long cable runs can be time consuming. The complete TM400 package including a measurement microphone, laptop computer, cables, adapters, etc. easily travels in your carry-on bag or briefcase. In speaking with sound engineers on the road, I found several that have tried wireless before to do system measurements from other wireless manufacturers. Unfortunately, none of them could attest that the results were worth the purchase of the product. Lectrosonics has changed that with the addition of the TM400 to its product line.