In this application note, we will show you how to integrate a subwoofer with your existing loudspeakers by using a miniDSP 2x4 HD. You can use an existing preamp, or replace a preamp and a DAC with the miniDSP 2x4 HD. (In the latter case, you will need to program a remote control to adjust volume in the miniDSP 2x4 HD.)

• 1. What you will need
• 2. Get connected
• 3. Configure routing
• 4. Measure and equalize the subwoofer
• 5. Add the crossover
• Wrapping up

1. What you will need[Top]

• A miniDSP 2x4 HD (boxed or kit) together with the matching 2x4 HD1 plugin.
• Ability to run acoustic measurements. You will need a measurement program such as the freeware Room EQ Wizard (REW), and measurement hardware for which we recommend the UMIK-1.
• The subwoofer. In this app note, we will assume that the subwoofer is self-powered (has an integrated amplifier).

This is the block diagram of the 2x4 HD1 plugin. Outputs 1 and 2 will drive the two loudspeakers (via your existing power amplifier) and output 3 will be connected to the subwoofer. (Optionally, a second subwoofer can be connected to output 4.)

2. Get connected [Top]

This diagram shows how to connect everything up. (Please follow the procedure in the User Manual on initializing the miniDSP and familiarizing yourself with the 2x4 HD1 plugin before doing this.)

3. Configure routing [Top]

The 2x4 HD1 plugin allows any input to be routed or mixed to any output. This a key element of its extraordinary flexibility. To implement subwoofer integration, set up the routing as shown in this screenshot. (See the User Manual for how to rename the input and output channels.)

4. Measure and equalize the subwoofer [Top]

Measurements for subwoofer integration are done with the microphone at the listening position and pointed between the two speakers. That way, the in room response of the speakers and subwoofer are measured. See the app note Acoustic measurement with the UMIK-1 and REW.

To measure the subwoofer, mute output channels 1 and 2, and check that both crossover filters in the Xover block of channel 3 are bypassed. Set the subwoofer's crossover frequency control to maximum and set any phase control to the flat position.

Use REW's Auto EQ to generate a set of parametric filters to "flatten" the response. The procedure is described in the app note Auto-EQ tuning with REW.

Then load the generated filters into the PEQ block of channel 3 and run another measurement. Here is an example "before and after" measurement:

5. Add the crossover

In the Xover block of channels 1 and 2, add a high pass filter. There is no hard and fast rule about what frequency and slope to use, but here is a typical example:

(If your speakers are sealed and roll of naturally at 80 Hz, use a BW 12dB/octave filter instead.)

In the Xover block of channel 3, add a low pass filter. Here is a typical example:

Unmute all output channels, mute the right input channel, and run a measurement. Initially, you may not get a smooth combined response through the crossover region. In that case, you will need to make some adjustments:

• Adjust the frequency, type, or slope of the subwoofer low pass filter. If changing the slope, you can make it steeper but do not make it shallower!
• Adjust the frequency, type, or slope of the speaker high pass filter.
• Add delay to either the subwoofer channel or the speaker channel.

Then unmute the right channel and mute the left channel. Repeat the fine-tuning for the right speaker. (Note that if you added delay to the left speaker, you must add the exact same delay to the right speaker.)

Wrapping up[Top]

That's it for this app note! Have fun, and please let us know about your subwoofer integration experience in our forum.