Guenter Villnow
Guenter Villnow

The miniDSP SHD includes not only Dirac Live® but also a full set of crossover functions on its four output channels. One use of this is as a flexible tool for integrating subwoofers into your system along with Dirac Live. This app note shows you how.

We will assume that you have already installed the SHD plugin and Dirac Live Calibration tool as per the User Manual. If this is your first time using a miniDSP for Dirac Live calibration, we recommend that you perform a calibration first using just the two speakers before attempting to integrate a subwoofer. This will familiarize you with the operation of the software. It will also give you a baseline that you can compare to the system with integrated subwoofer.

Getting connected[Top]

Connect the system as shown in this diagram:

SHD subwoofer integration - system connections

The diagram assumes that you are using one subwoofer. If you are using two subwoofers, connect the second to output 4.

Configuring the plugin[Top]

Start the SHD plugin and click the Connect button. (See the User Manual for more information.)

For clarity, use the Outputs tab to change the displayed labels on the output channels. In the example below, we have used "Left Sp", "Right Sp" and "Sub". Then set up the Routing matrix like this:

SHD subwoofer integration - routing matrix

If you are using two subs, turn on the routing from Dirac 1 and Dirac 2 to to output channel 4.

On the Outputs tab, click on the Xover button for channel 1. Here you will set a high pass filter, to remove low frequencies from the left speaker. Here is a typical example:

SHD subwoofer integration - high pass filter

Do the same for the right speaker (channel 2).

For the subwoofer (channel 3), set a low pass filter to remove high frequencies. Here is a typical example:

SHD subwoofer integration - low pass filter

If you are using two subs, do the same for the second sub connected to channel 4.

You can also set the time delay between the speakers and the sub using the output channels. As a starting point, use the difference in distance of the speakers and the sub to calculate the delay. For example, if the sub is 1 meter further away from the listening position than the speakers, set the delay on the speakers to 2.9 ms:

SHD subwoofer integration - delay on speakers

If the sub is 1 meter closer to the listening position than the speakers, set the delay on the sub to 2.9 ms:

SHD subwoofer integration - delay on sub

Note: subs in rooms are unpredictable. The above is just a starting point. You may need to make further adjustments after measuring (see next section).

Initial Measurement[Top]

We recommend that you perform a measurement to check for initial integration between the subwoofer and the main speakers around the crossover frequency. While Dirac Live will correct for frequency response anomalies, it can't fully correct if you have a large "hole" in the frequency response at the crossover.

You can use Room EQ Wizard (REW) or a similar program to do this measurement. To use REW with the UMIK-1, please refer to our application section on acoustic measurements.

If you don't wish to learn how to use REW, you can use the Dirac Live Calibration Tool to perform this measurement. Save your configuration to a file and quit the SHD plugin first. Then follow the normal calibration procedure described in the SHD User Manual, but only perform a single measurement (instead of the full set of nine) before proceeding to the Filter Design tab. The "before" measurement shows the combined response of the subwoofer and speakers:

SHD subwoofer integration - measurement with DLCT

If there is a large "hole" in the response around the crossover, you will need to make some adjustments and remeasure. Quit DLCT before starting the SHD plugin again. Adding a delay to either the speakers or the subwoofer will change the response, as will inverting the subwoofer. You can also adjust the low pass and high pass crossover frequencies and change the slope. If the subwoofer is much higher or lower in level than the speakers, adjust the gain on the subwoofer.

See the User Manual for information on how to make these adjustments. After making adjustments, quit the plugin, start DLCT, and repeat the measurement.

Run Your Dirac Live Calibration[Top]

You can now proceed to run the full set of nine measurements for the Dirac Live calibration. Adjust the target curve to suit your preference. For example, this screenshot shows a target curve with an elevated bass level, which many people prefer, and the "after" response:

SHD subwoofer integration - after optimization

Advanced multisub integration[Top]

For even better subwoofer integration, two or more subs can be used to reduce the variation in subwoofer frequency response across the listening area. While EQ can correct the response to be flat in one location in the room, it cannot correct for spatial variation. For example, if the level of 40 Hz in one seat is 10 dB different to the level in the next seat, the difference between the two seats will always be 10 dB.

We have an extensive app note on optimizing multiple subwoofer on our site here: Tuning multiple subwoofers with miniDSP.

  • If using two subwoofers, they can be connected directly to the miniDSP SHD (outputs 3 and 4).
  • If using more than two subwoofers, either:
    1. Use Y-connectors to connect two subwoofers to each output of the SHD. This will not give individual control over each sub but can be used to good effect with Methods A and B in the app note linked above.
    2. Use an external DSP such as a 2x4 HD or 2x4 Balanced. Up to four subwoofers can be independently controlled from each external DSP.

When optimizing your multisub setup, be sure to use a preset that does not have a Dirac Live calibration loaded, so that Dirac Live gains and delays are zeroed. When done with optimizing your multisub setup, then a complete Dirac Live calibration.

Wrapping up[Top]

That's it for this app note! Have fun, and please let us know how you go in our forum.