Multiple Subwoofers: Optimize Them With Multi-Sub Optimizer Software

Introduction

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 minimizes the seat-to-seat frequency response variation in the bass region while simultaneously optimizing the response flatness at the main listening position. You can choose to have MSO perform this optimization on just the subs, or to include the main speakers in the optimization. In the latter case, it automates the process of integrating the subs with the main speakers, including delay/distance settings and EQ in the crossover region.

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:

Multi-Sub Optimizer Main Window

A screenshot of the Multi-Sub Optimizer main window with a typical project loaded is shown below. The graph shows the data before and after optimization in a room with drywall construction. Note the decrease in seat-to-seat response variation at 56.6 Hz.

Detailed descriptions of the user interface elements are given in the tutorial and the reference manual.

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

Multiple Subs Before and After Optimization (Brick Wall Boundaries)

Another example 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 minimize the seat-to-seat variation across listening positions while flattening the MLP response. The measured data imported into the program are from a user's room and system. In this example, equalization, gains and delays were only applied to the subs, not the main speakers, so there isn't much effect above about 120 Hz.

These frequency responses are especially rough, as they were measured in a home with brick construction and hard wall boundaries. Homes with drywall construction will yield smoother bass response, such as the results in the first figure above.

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 miniDSP device or Behringer DCX2496 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 miniDSP 2x4 and DCX2496 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.

MSO can be used effectively on systems with two subs or more. See How Many Subs are Needed? for more information.

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

System Software Requirements

MSO runs only on Windows. MSO requires Windows Vista or a later version of Windows.

Important: Measurement System Requirements

Your measurement system must be capable of using either an acoustic timing reference or a hardware loopback timing reference to achieve time-synchronized measurements. This means that USB microphones can only be used with Room EQ Wizard (REW) 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.

Before You Begin

Before using MSO, please do the following:

Tutorials and Online Discussion

License

Acknowledgments