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:

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.

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 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 (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:

Online Discussion and Application Notes