Multiple Subwoofers: Optimize Them With Multi-Sub Optimizer Software


Multi-Sub Optimizer (MSO) is a free Windows-based software program for optimizing the bass response of audio and AV systems having multiple subwoofers. It optimizes the flatness of the combined frequency responses of main loudspeakers and multiple subwoofers at multiple listening positions simultaneously. Although it's possible to use it for identical equalization (EQ) of all subs at once, it does not depend on a global EQ approach like commercial "room correction" systems do. Such systems cannot reduce the seat-to-seat variation of the bass response. Instead, MSO performs optimization of EQ, gain and delay parameters individually for each subwoofer. This individual EQ optimization for each sub causes the variation of the bass response from seat to seat to be reduced, and the bass response at each listening position to be flattened.

MSO can be used to perform tasks that include:

  • Optimizing subwoofer integration with main speakers through delay, gain and EQ adjustments
  • Reducing seat-to-seat frequency response variation of the combined sub outputs through optimized EQ of each sub individually
  • Achieving optimum subwoofer time alignment via individual sub delay adjustments
  • Improving response flatness of the combined sub outputs at all listening positions
  • Creating, specifying and achieving your desired target frequency response curve to shape the bass response to taste
  • Plotting your data in a variety of ways
  • Computing filter information for manual entry or as text files containing biquad coefficients for import into miniDSP EQ hardware

Multi-Sub Optimizer Main Window

A screenshot of the Multi-Sub Optimizer main window with a typical project loaded is shown below. Detailed descriptions of the user interface elements are given in the tutorial and the reference.

Multi-Sub Optimizer Main Window
Multi-Sub Optimizer Main Window

Multiple Subs Before and After Optimization

An example set of frequency responses at multiple listening positions before and after optimization is shown below. Each trace corresponds to a listening position. The response at each listening position is computed by combining the measured results of four subs plus main speakers at that position, taking phase into account (complex summation). The top traces are before optimization and the bottom ones are after. A display offset separates the groups of traces for clarity. In the case of the "after optimization" results, the overall response at each position is computed by applying the response of a set of filters to each individual sub measurement prior to their complex summation. The parameter values of these filters are computed by MSO to optimize the performance at each listening position. The measured data imported into the program are from an actual user's room and system. Equalization, gains and delays were only applied to the subs, not the main speakers, so there isn't much effect above about 120 Hz.

Multiple Subs Before and After Optimization
Multiple Subs Before and After Optimization

System Hardware Requirements

A multi-channel DSP device or equivalent software using IIR filters, such as a Behringer DCX2496 or a miniDSP device or similar is assumed to be present in your system. All the subs must be driven by a mono signal derived from the sum of the signals to the main speakers, as is the case with traditional bass management used by AV receivers and preamp-processors in home theater applications. This mono signal must be split as is done internally to the DCX2496 and miniDSP 2x4 devices, and separate EQ, delay and level adjustments provided for each sub individually. Some two-channel and even multi-channel systems operate the subs in stereo mode. For such systems, MSO is not an appropriate tool for optimization and its use will likely cause unpredictable results.

If your system uses two subs, the improvement in using MSO may be limited. You'll get best results with three or more subs. Despite this caution, one user who reviewed MSO has reported improvements in a two-sub system.

Many of MSO's filter types are compatible with those of the popular and low-cost Behringer iNuke amplifiers.

System Software Requirements

MSO runs only on Windows. MSO requires Windows XP Service Pack 3 or a later version of Windows.

Important: Measurement System Requirements

Your measurement system must be capable of using a loopback timing reference or the equivalent acoustic timing reference to achieve time-synchronized measurements. This means that USB microphones can only be used with Room EQ Wizard version 5.15 or later in conjunction with the acoustic timing reference feature. If you are measuring a two-channel system using a USB microphone, REW 5.15 versions prior to beta 6 had the restriction that the speaker used for the acoustic timing reference could not also be measured without some special workarounds. You must use REW 5.15 beta 6 or later when measuring a two-channel system with a USB microphone. For more information, see the measurements section.

  • Program: The software is free and can be downloaded here. Unzipping gives you install_mso.exe, which you run to install the program.
    Most recent update: Version 1.22, uploaded 1 July, 2017. See the revision history.
  • Tutorial Files, Samples and Help: A tutorial is contained within MSO's .CHM help file. A standalone version of this .CHM file is available for download. If you have problems displaying the .CHM file, see the readme.html contained within the zip file for instructions. You'll also need to download the tutorial's sample files and projects. For detailed help information, see the Help Contents.

Where To Start

Online Discussion and Application Notes

The main discussion thread about MSO is at AVS Forum. This is the most active discussion thread, where updates and other news are posted.

MSO was written and is maintained by Andy C (andyc56 at AVS Forum).

There is also some MSO discussion on reddit.

miniDSP now have an application note called "Optimizing multiple subwoofers with the DDRC-88BM and Multi-Sub Optimizer".

AVSForum user rumpeli has created an MSO presentation and tutorial in German in the forum.

Before You Post to the AVS Forum MSO Thread

The AVS Forum MSO discussion thread is for discussion of MSO usage, theory of operation, feature requests, bug reports and so on. It's not an REW or miniDSP support thread, nor is it an acoustical consulting thread. Before posting, you should read the MSO documentation and the documentation of your DSP hardware. You should also be very familiar with your measurement software, and have a general grasp of the theory of measurements, including at least a qualitative sense of the meaning of the frequency response and impulse response measurements and their relationship to one another. For more information about interpreting various types of measurements, see the "Signals and Measurements" section of the REW documentation. See the Status of MSO Support page for current information about MSO support.


Multi-Sub Optimizer is freeware (software gratis) for non-commercial use only. Commercial use is a violation of the license agreement.

This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License. To view a copy of this license, visit


Thanks to Earl Geddes, whose video about multiple subwoofers and its associated PowerPoint presentation inspired the creation of this software.

Thanks to C├ędric Moonen for the High-speed Charting Control used for MSO's graphs.

Thanks to Nemanja Trifunovic for the UTF-8 CPP library used for UTF-8 text conversion.

Thanks to Jag768 from AVSForum and DIYAudio for beta testing, providing data and many helpful suggestions for program features.

Thanks to markus767 and AV_mike from AVSForum for finding and reporting bugs.

Thanks to AVSForum user Svenibaer for posting many interesting optimization results.

Thanks to AVSForum user rumpeli for posting some interesting optimization results and creating an MSO tutorial in German.

The optimization algorithm used is from the following article:
J. Zhang and A. C. Sanderson, JADE: Adaptive Differential Evolution with Optional External Archive, IEEE Transactions on Evolutionary Computation, 13(5): 945 - 958, October 2009.