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dbx® 231s

Dual-channel, 31-band graphic equalizer

Item #: 856231S

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Built to last

When the pros need an EQ, they turn to dbx. With a proven track record that spans four decades, dbx EQs are ideal for touring, studios, and audio installations. If you're putting together your first portable sound rig, or getting started on your home studio, dbx's Series 2 is a no-brainer. The 231's dual 31-band graphic equalizer retails at a reasonable price point, and it's versatile and durable. Don't be surprised if this workhorse is still one of your favorite pieces years down the road.

Easy to use

The user interface on the 231s is simple but elegant. Each channel has 31 nonconductive sliders at 1/3 octave intervals. Time-tested Constant Q technology allows the unit's sliders to maintain stable frequency characteristics at all positions. You can also set each channel's gain boost or cut range at ±6 dB or ±12dB via a convenient front-panel control. LED lights let you monitor output gain, EQ bypass and signal clipping at a glance. Each channel has separate XLR and 1/4" inputs and outputs for quick and easy connection to your gear.

Product Highlights:

  • 1/3-octave Constant Q frequency bands
  • switchable boost/cut ranges of ±6 dB or ±12 dB
  • dual XLR and 1/4" TRS inputs and outputs
  • frequency response: 10-50,000 Hz
  • low cut filter: 12 dB per octave at 50 Hz
  • front-panel bypass switch
  • input gain: ± 12 dB
  • 4-segment LED ladders for monitoring output levels
  • dynamic range: 112 dB
  • 19"W x 3-1/2"H x 6-1/2"D (2U rack space)
  • weight: 6.2 lbs.
  • warranty: 2 years parts and labor
  • Our 60-day money-back guarantee

Precise control of specific frequencies

When you're running a PA for a live event, you'll often need to pinpoint and control certain frequencies in order to put a damper on feedback and get everything sounding even and balanced. An EQ gives you precise control over frequencies across the whole audible spectrum.

dbx® 231s Reviews

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What's in the box?

Download owner's manual

  • Dual 31-band graphic equalizer
  • 7' AC power cord
  • 4 Pan-head rack screws
  • 4 Poly washers
  • User's Manual
  • Product Registration card

Product Research



Overview: The dbx 231s dual 31-band graphic equalizer is a versatile, professional-quality EQ with simple, straight-forward controls. It features two independent channels and 31 frequency bands, broken down in 1/3-octaves. Each non-conductive slider has approximately 1" of movement with a detent at the 0 (flat) position. The 231s fits neatly into a standard equipment rack (2U space required), and includes 4 rack mount screws and washers.

Input Gain: The 231s is equipped with a rotary input gain control to set the signal level to the equalizer. The input gain control has a range of -12dB to +12dB. You can monitor the input to the EQ through the 4-LED Output Level Bar Graph, which has green (2), yellow (1), and red (1) indicators. There is also a red LED to indicate if the input signal is clipping. The 231s has independent input gain controls for each channel.

Frequency Bands: The 231s includes the following frequency bands: 20Hz, 25Hz, 31.5Hz, 40Hz, 50Hz, 63Hz, 80Hz, 100Hz, 125Hz, 160Hz, 200Hz, 250Hz, 315Hz, 400Hz, 500Hz, 630Hz, 800Hz, 1kHz, 1.25Hz, 1.6Hz, 2kHz, 2.5kHz, 3.15kHz, 4kHz, 5kHz, 6.3kHz, 8kHz, 10kHz, 12.5Hz, 16kHz, and 20kHz.

Switchable Boost/Cut Range: The dbx 231s has a maximum boost/cut range of +/- 12dB. If desired, you can switch to a range of +/- 6dB. This gives you finer control within the range. The boost/cut range switch is located on the front panel. When the button is pressed in, the button lights up to indicate the range is +/- 12dB. When the button is in the out position, the range is +/- 6dB, and the button is unlit. There are Boost/Cut Range switches for each channel.

Low Cut: To instantly cut out low frequencies, you can engage the built-in 50Hz 12dB/octave high pass filter. The Low Cut switch is located on the front panel, and remains lit when pressed in and activated. There are Low Cut switches for each channel.

EQ Bypass: Each channel has an EQ Bypass switch, which bypasses the graphic equalizer section in the signal path, when activated. An EQ Bypass switch is provided for each channel, and remains lit when engaged.


Inputs: The dbx 231s is equipped with a 1/4" TRS (tip/ring/sleeve) phone jack and a female locking XLR (pin 2 hot) input connector for each channel. Each input can accept balanced or unbalanced input sources. The maximum acceptable input level is typically +22dBu (ref: 0.775Vrms).

Outputs: Each channel has a 1/4" TRS phone jack and a male XLR output connector. The outputs can be used with either balanced or unbalanced loads. The maximum output level is greater than +21 dBu balanced/unbalanced into 2 kΩ or greater, >+18 dBm balanced/unbalanced (into 600Ω).

AC Power: The 231s has a 3-pin IEC power cord receptacle, and accepts 100-240 VAC.


  • Frequency Response: <10 Hz to >50 kHz, +0.5/-3 dB
  • Bandwidth: 20 Hz to 20 kHz, +0.5/-1 dB
  • Dynamic Range: Typically >112 dB
  • Signal-to-Noise: Typically >95 dB
  • THD+Noise: <0.003%
  • Interchannel Crosstalk: <-90 dB, 20 Hz to 20 kHz
  • Input Impedance: Balanced 40 kΩ, Unbalanced 20 kΩ
  • Output Impedance: Balanced 100 Ω, Unbalanced 50 Ω

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Looking for more? Check out the next model in this lineup.

dbx Dual 31 Band Graphic EQ

dbx® 1231


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internal power and additional input/output options

The dbx® 1231 offers these features:

boost/cut range switch (±6 dB or ±15 dB)

inputs: XLR, 1/4" TRS and barrier strip with ground lift

magnetically isolated internal power supply transformer

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