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Atlas EQM131

31-band graphic equalizer

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Item # 978EQM131

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Our take on the Atlas EQM131

The Atlas EQM131 is designed to provide basic graphic equalization for sound masking and public address systems. Its 31 bands at 1/3-octave steps give you precise control, so you can make music and announcements easier to hear in a busy environment. This versatile rack-mounted unit has balanced and unbalanced input and output options.

Product Highlights:

  • rack-mounted graphic equalizer with 1/3-octave frequency bands
  • balanced XLR and 1/4" TRS inputs and outputs
  • unbalanced RCA input and output
  • frequency response: 20-20,000 Hz (±5dB)
  • 19"W x 1-3/4"H x 8-1/2"D (1U rack space)
  • weight: 4.9 lbs.
  • warranty: 3 years parts and labor
  • Our 60-day money-back guarantee

What's in the Box:


Hands-on research

Product Research


Overview: The Atlas EQM131 is a single channel, 31 band, graphic equalizer designed for both professional and consumer applications. It includes both High- and Low-cut filters, Clip indicator, Bypass, and a Range switch that changes the range of the faders for either 6 or 12 dB of boost/cut. Inputs include balanced XLR and TRS jacks as well as unbalanced RCA jacks. Atlas's ISO centered 1/3 octave bandwidth-constant Q filter design minimizes interaction between filters yet is still wide enough for creating correction curves. When used with an Atlas amplifier and sound masking module, the EQM131 can also be used to create a 1/3 octave masking spectrum.

Front Panel:

  • Power Switch
  •  Faders: Each of the 31 front panel 1/3 octave faders has 20 mm of travel with a center detent indicating the zero position. The range of the faders can be set with the Range button which gives the faders either 6 or 12 dB of boost/cut. The 31 bands range from 20 Hz to 20 kHz and include bands for: 20 Hz, 25 Hz, 31.5 Hz, 40 Hz, 50 Hz, 63 Hz, 80 Hz, 100 Hz, 125 Hz, 160 Hz, 200 Hz, 250 Hz, 315 Hz, 400 Hz, 500 Hz, 630 Hz, 800 Hz, 1 kHz, 1.25 kHz, 1.6 kHz, 2 kHz, 2.5 kHz, 3.15 kHz, 4 kHz, 5 kHz, 6.3 kHz, 8 kHz, 10 kHz, 12.5 kHz, 16 kHz, and 20 kHz.
  • Range: Switches the range of the faders between 6 and 12 dB of boost/cut. Two LED indicators will display which Range the EQ is in.
  • Bypass: This switch allows the signal to pass through the unit unaffected. When activated, a red LED below the switch will illuminate.
  • Clip Indicator: This LED indicator will light if the input level exceeds +22 dBm.
  • Variable Low Cut Filter: Provides a 12 dB/octave shelving filter with a range from 10 Hz to 250 Hz. The Low Cut filter allows frequencies above the filter frequency to pass through (high-pass). Filtering is done pre-faders.
  • Variable High Cut Filter: Provides a 12 dB/octave shelving filter with a range from 3 kHz to 40 kHz. The High Cut filter allows frequencies below the filter frequency to pass through (low-pass). Filtering is done pre-faders.
  • Level: This is the master output level control. The dial has a center detent at 0, which is unity gain when using a balanced line-level signal. If wired for unbalanced operation, the output signal may need to be boosted. From center 0 the signal will be attenuated when turned to the left and can go all the way to -∞ (no sound). When turned to the right of 0, the signal will be boosted, with the range going up to +6.

Rear Panel:

  • Inputs/Outputs:
    • Balanced: The balanced section includes a female XLR and 1/4" TRS jack for the Input section, while the Output section has a male XLR along with a 1/4" TRS jack.
    • Unbalanced: The unbalanced section includes 2 RCA jacks, one for the Input and one for the Output.
  • Ground Lift Switch: This switch makes or breaks the electrical connection between circuit ground and chassis ground. If an audible hum occurs, the switch gets set to whichever position eliminates the hum.
  • Line Voltage Selector: Sets the power supply to work with either 115 or 230 volt input power.
  • AC Mains Fuse: 500 mA 250V fuse.
  • AC Power Cord


  • EQ Type: Mono, 1/3 Octave
  • Bands (Filters): 31
  • Filter Type: Constant Q
  • Maximum Input Level: +22 dBm
  • Output Impedance: 150 Ω
  • Maximum Output Level:
    • Balanced: +22 dBm
    • Unbalanced: +18 dBm
  • Frequency Response: 20 Hz - 20 kHz (+/- 5 dB)
  • Signal to Noise Level: 94 dB
  • THD: 0.01%
  • Power Requirement: 115/230 V, 50/60 Hz
  • Fuse: T500mA/250V (100-120 V)
  • Dimensions: Width - 19.0", Height - 1.75", Depth - 8.50"
  • Weight: 4.9 lbs.

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