FM Plus Large-area Dual FM and Wi-Fi ALS with 4 FM R37

The Williams AV FM 557 is a complete large-area assistive listening system built around an FM+ transmitter and four R37 receivers. It combines 72.1–75.9 MHz FM transmission with Wi-Fi audio streaming, providing two listening delivery paths from one system. Its 17-channel FM platform, four included receivers, Ethernet management, and rack-ready transmitter make it suited to managed installations requiring documented technical performance and ADA compliance.

Ideal Use Cases

The FM 557 is designed for large-area applications where clear assistive audio must reach listeners throughout an established coverage zone. Traditional FM delivery supports the supplied R37 receivers, while Wi-Fi audio streaming adds another way to distribute the program audio. The system is particularly appropriate when an installation needs four FM receivers from the outset, selectable channels, remote monitoring, and integration with professional microphone or line-level sources.

Why Choose This Model

This package combines an FM+ transmitter with four R37 receivers as a complete assistive listening solution. The transmitter offers 17 selectable wideband FM channels and a specified transmission range of up to 1,000 feet when used with an ANT 005 coaxial antenna mounted on the rear chassis connector. Each R37 receiver accesses the 17 channels through a seek button in its battery compartment. The receivers operate on two AA alkaline or NiMH batteries, with approximately 50 hours of operation specified when using two BAT 001 non-rechargeable alkaline batteries.

Installation and Integration

The transmitter measures 8.45 inches wide by 8.25 inches deep by 1.72 inches high and weighs 3.2 pounds. It occupies half the width of a standard 19-inch rack and is one EIA rack space high. One or two units can be installed in a single rack space with the optional RPK 005 single-unit or RPK 006 dual-unit rack-mount kit.

A combination three-pin XLR and 1/4-inch TRS input accepts balanced or unbalanced line-level audio and balanced or unbalanced microphone signals. Selectable 14.4 VDC phantom power is available at the analog combo jack. The rear RJ-45 Ethernet connection supports 10/100 Base-T IEEE 802.3 networking and CAT 5e cable runs up to 328 feet. A hosted web page provides remote control and monitoring, while the front-panel 3.12-inch high-resolution OLED display and buttons support direct operation.

Performance Highlights

The FM transmitter operates from 72.1 to 75.9 MHz with frequency accuracy specified at ±2 ppm from 0°C to 50°C. RF output can be set to Full, Medium, Low, or Off, and a green On Air LED indicates active transmission. Compatible antenna options include the ANT 005, ANT 021, ANT 024, and ANT 025.

DSP-based audio processing provides selectable compression ratios of 1:1, 1.5:1, or 2:1, plus high-pass and low-pass filter frequency control. With the Music audio preset, frequency response is 31 Hz to 16,000 Hz at ±3 dB. Typical transmitted-RF signal-to-noise ratio is 67 dB, while total harmonic distortion is less than 0.25% at 1 kHz at the RF output. A ten-LED input array displays levels from -18 to +9 dB, using green, amber, and red indicators to identify normal peaks, near-overload peaks, and overload peaks.

What Makes It Different

The defining feature of the FM 557 is its combination of established FM reception and Wi-Fi audio streaming. The four supplied R37 receivers provide immediate access to the 17-channel FM service, while the transmitter’s network interface adds browser-hosted control and monitoring. The transmitter also supplies dedicated 1/4-inch headphone and RCA line outputs, adjustable audio input gain, selectable phantom power, configurable RF power, and menu-controlled RF timeout settings of 30 minutes, four hours, or Always On.

Final Assessment

The Williams AV FM 557 brings together dual FM and Wi-Fi audio delivery, four R37 receivers, professional analog audio connectivity, Ethernet administration, and flexible rack integration. Its specified 1,000-foot maximum FM range with the ANT 005 antenna, 17 selectable channels, DSP audio controls, and approximately 50-hour alkaline receiver battery life provide a clearly documented foundation for a large-area assistive listening installation. The system carries a two-year parts-and-labor warranty and FCC, RoHS3, WEEE, and Industry Canada approvals.