Williams Sound FM 557 PRO FM plus assistive listening systems

72.1-75.9 MHz - 17 wideband channels (selectable) - Up to 1000 ft (304 m)

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What's in the box:

  • Williams Sound FM 557 PRO
  • (1) FM T55 transmitter
  • (4) PPA R37N receivers
  • (4) EAR 022 surround earphones
  • (2) NKL 001 neckloops
  • (2) BAT KT6 two-bay chargers and rechargeable batteries
  • (1) ANT 005 remote coaxial antenna
  • (1) IDP 008 ADA wall plaque
  • (1) RPK 005 rack panel kit
  • 2-year Limited Warranty


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Industry-first choice

Williams Sound's FM 557 PRO (WLS-FM557PRO) FM plus assistive listening Systems is a groundbreaking, industry-first choice of using traditional FM receivers or personal listening devices for Wi-Fi hearing assistance. Developed for hearing assistance in public venues, the FM + includes a complete audio processor optimized for the needs of hearing impaired people and are easily integrated with an existing sound system, or used with a microphone as a stand-alone system. FM + supports the iOS and Android WaveCAST Apps and the Wi-Fi Receiver in addition to all of the current and legacy Williams Sound FM receivers operating on the 72-76 MHz bandwidth.


  • FM receivers or using personal electronic Devices over Wi-Fi for hearing assistance
  • Exceptional Audio quality
  • Built on a Professional Digital Audio (DSP) platform
  • Users can use their own smartphones or headphones
  • Venues NO longer need to choose between providing FM or Wi-Fi assistive listening Systems

Serving professional communication needs worldwide since 1976, Williams AV offers digital, FM, infrared and induction loop wireless audio, as well as video annotation, presentation and conferencing systems.

Specifications for the Williams Sound FM 557 PRO

{ "ANT 005": { "Use with": "", "Connector type": "F-connector", "Cable type": "RG 59 coax", "Nominal Impedance": "75 Ohm", "Total Cable Length": "22 ft", "Active Antenna Length": "80 in" }, "EAR 022": { "Style": "", "Plug": "3.5mm mono", "Cord": "39"", "Driver Size": "23 mm", "Nominal Impedance": "32Ω", "Freq. Response": "20 - 20k㎐", "Weight": "15g", "Max Power Input": "30 mW", "Sensitivity": "118 dB @ 1k㎐" }, "FM T55": { "Dimensions": "8.45" W x 8.25" D x 1.72"H (21.5 cm x 21 cm x 4.4 cm)", "Weight": "Transmitter: 3.2 lbs (1.45 kg)", "Color": "Black/Silver with silver legends on the front, white legends on the back", "Rack Mount": "Standard 19” Rack, one EIA rack space high, 1/2 space wide1–2 units can be mounted in a single rack space with optional RPK 005 (single) or RPK 006 (double) Rack Mount Kits", "Power Supply": "Desktop Style Transformer (TFP 062); Input: 100-240 VAC, 50/60 ㎐. IEC Line Cord; Output: 24 VDC, 750 mA, 18W. 2.5mm ID center positive barrel connector", "Power ON Indicator": "Push On/Push Off latching power button, backlit green indicates power ON, backlight off indicates power OFF, fading from bright to dark indicates Sleep Mode.", "Temperature Range": "Operating: +32° F to +122° F (0° C to 50° C); Storage: -4° F to +158° F (-20° C to 70° C)", "User Interface": "3.12” High Resolution OLED display with selections via buttons. Hosted Web page. Remote control and monitoring.", "Dante": "Only available on FM T55 D", "Ethernet": "RJ-45 on back of unit supports CAT 5e cable lengths up to 328 feet (100 meters); 10/100 Base-T IEEE 802.3 compliant, unique MAC address", "RF Section": "", "Operating Frequencies": "72.1-75.9 M㎐ , 17 wideband channels (selectable)", "Frequency Accuracy": "± 2 ppm stability, 0-50˚ C", "Deviation": "± 75 k㎐ maximum", "Pre-Emphasis": "75 microsec", "RF Field Strength": "Does not exceed 80 mV/m at 3 m", "Compatible Antennas": "ANT 005, ANT 021, ANT 024, or ANT 025", "Transmission Range": "Up to 1000 ft (304 m) with ANT 005 coaxial antenna mounted on rear chassis connector", "RF Outputs": "(1x) #10-32 stud connector in center of unit (pcb mounted)(1x) F-connector on rear chassis", "RF Transmit Indicator": "1 Green LED On Air Indicator", "RF Power": "Full, Medium, Low or OFF indiacted by menu icon.", "RF Time Out (sleep mode)": "30 min. duration, 4 hr. duration, or Always On selected via menu. Starts when audio is below -18 dB level with no button pressed for selected duration.", "Audio Section": "", "Audio Processor Functions": "DSP based; Compression: 1:1, 1.5:1 or 2:1; High-pass and Low-pass Filter Frequency control", "Frequency Response": "31-16000 ㎐, ±3 dB (re: 1 k㎐, ±3 dB) (“Music” Audio Preset)", "Signal-to-Noise Ratio": "67 dB (typical) Transmited RF", "Total Harmonic Distortion": "Less than 0.25% @ 1 k㎐ (RF output)", "Common Mode Rejection": "Greater than 57 dB @ 1 k㎐, Mic or Line", "Audio Inputs": "(1x) Combination 3-pin XLR, 1/4" (TRS) jack for balanced or unbalanced line level, or balanced or unbalanced microphone with selectable phantom power", "Audio Input Gain Adjust": "In menu, adjustable to 0 to -50 dB, in 1dB steps", "Phantom Power": "14.4 VDC applied through 2.2 kΩ resistors to analog combo jack: Pin 2 and Pin 3 on XLR jack, or tip and ring on 1/4" TRS jack", "Audio Level Indicators": "10-LED array that reads -18 to +9 dB at 3 dB intervals. 7 Green, 2 Amber, and 1 red LED. Green LEDs indicate normal operating audio level peaks, Amber LEDS indicate close to overload peaks, Red LED indicates overload peaks", "Headphone Output": "1/4" TRS stereo jack, mono signal, 14.85 mW at +9dB, maximum in 33 Ω (level adjustable in menu 0 to -40 dB in 2 dB steps)", "Line Output": "RCA jack (black), -10 dBV (.32 VRMS); Output impedance 100 ohms at +9dB", "Input Levels (Bal or Unbal) (at Audio Input Gain = 0dB)": "Nominal (1st Amber + 3dB LED)Overload Warning (Displayed on Screen)Absolute Max. Rating*", "Nominal (1st Amber + 3dB LED)": "Overload Warning (Displayed on Screen)", "Microphone": "-55 dBV (1.7 mV RMS)-22 dBV (80 mV RMS)+20 dBV (10.0 V RMS)", "-55 dBV (1.7 mV RMS)": "-22 dBV (80 mV RMS)", "Line": "-25 dBV (55 mV RMS)+16 dBV (6.3 V RMS)+20 dBV (10.0 V RMS)", "-25 dBV (55 mV RMS)": "+16 dBV (6.3 V RMS)", "Approvals": "FCC, RoHS3, WEEE, Industry Canada", "Warranty": "2-year parts and labor", "NOTE: Specifications are subject to change without notice.* Stresses above these ratings may cause permanent damage or degrade reliability.": "" }, "IDP 008": { "10-3/8" (L) x 6-¼" (W) x 1/8" (H)": "" }, "PPA R37N": { "Dimensions:": "4.1" x 2.85" x 1.38" (104 x 72 x 35mm)", "Weight:": "4.6oz (130g) with batteries. 2.6oz (73g) without batteries", "Color:": "Black", "Battery Type:": "(2) AA Alkaline or 2 x AA NiMH", "Battery Life:": "Two (2) AA non-rechargeable alkaline batteries (BAT 001), approx. 50 hrs", "": "(2) AA rechargeable NiMH batteries (BAT 026), 1500 mAh, approx. 32 hrs", "Current Consumption:": "52mA nominal", "Temperature Range:": "– 0 to 50C", "Channels": "17, accessed via seek button in battery compartment", "Operating Freq.:": "72.1, 72.2, 72.3, 72.4, 72.5, 72.6, 72.7, 72.8, 72.9, 74.7, 75.3, 75.4, 75.5, 75.6, 75.7, 75.8, 75.9 M㎐*", "Intermediate Freq.:": "75 k㎐", "FM Deviation:": "75 k㎐", "De-Emphasis:": "75 µS", "LED Indicator:": "Power:  Green; Low Battery:  Flashes Green", "AFC Range:": "± 120 k㎐", "Sensitivity:": "2 µV at 12 dB Sinad with squelch defeated", "Input Overload:": "100 mV", "Frequency Response:": "200 – 15 k㎐", "Modulation:": "FM, +/- 75 k㎐ peak deviation", "Signal-to-Noise Ratio:": "65 dB min @ 100 uV", "Receive Antenna:": "Integral with earphone/headphone cord", "Audio Output:": "35 mW max, peak into 16 ohms", "Output Connector:": "3.5 mm stereo/mono phone jack", "Earphone:": "Earbud-type with foam cushion, 3.5 mm plug, 32 Ω", "Auto Shut-off": "Enters sleep mode after approx 6 mins of no RF signal", "Approvals:": "FCC, Industry Canada, RoHS, WEEE", "Warranty:": "Lifetime PLUS Limited Warranty, 90 Days on most accessories." } }

Research Materials for Williams Sound FM 557 PRO (WLS-FM557PRO)

We've added technical materials to help with your buying decision. Even if you're technically inclined, you may want to consider talking to our sales techs to make sure this item is the right fit for your particular use. 800.562.6006

FM 557 PRO (WLS-FM557PRO) Specifications

FM 557 PRO (WLS-FM557PRO) User Guide

FM 557 PRO (WLS-FM557PRO) Workflow Diagram

FM+ Overview

Williams AV FM+ Assistive Listening System

FM Plus Short

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