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Guenter Villnow
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Guenter Villnow
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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.

Note: This application note requires the use of Room EQ Wizard (REW) to measure the speakers and subwoofer and to generate correction filters for the sub. If you are not familiar with REW, refer to the following application notes:

To integrate a subwoofer without using REW, instead use the procedure in the User Manual, which uses only the Dirac Live app.

Getting connected[Top]

Connect the system as shown in this diagram:

SHD subwoofer integration - system connections

Start the SHD plugin and click the Connect button. 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

1. Decide where to put the sub[Top]

The location of the subwoofer can make a big difference. If you can, move the subwoofer to a few different locations and measure it. To measure the sub:

  1. Mute the speaker channels (channels 1 and 2).

  2. Bypass the subwoofer low pass crossover filter (the Xover block of channel 3).

Figure 1 shows the measurements we obtained with a subwoofer in two different locations. For this example, we chose the one in green despite the notches in the response, because it has more output down low. Each room is different and you will need to experiment in your own room to find the best compromise.

Two subwoofer locations

Figure 1. A subwoofer measured in two different locations

2. Equalize the subs[Top]

Use the REW Auto-EQ feature to flatten the subwoofer response around the crossover region. There is no need to try and get the response exactly flat, because Dirac Live will do that correction later. The purpose here is just to get a clean crossover to the speakers.

Figure 2 shows our equalization window in REW. Blue is the target, the darker green curve is the original measurement and the lighter green curve is after EQ. We used one-third octave smoothing.

Equalization of the subwoofer

Figure 2. Equalization of the subwoofer

Here are the key settings we used in REW:

  1. Equalizer: miniDSP 2x4 HD

  2. Target type: Full range speaker

  3. Target level: 72 dB (this will depend on your own measurement)

  4. Match range: 20 to 300 Hz

  5. Allow narrow filters below 200 Hz: Off

3. Enable crossovers[Top]

Click on the Xover button for channel 1. Here you will set a high pass filter to remove low frequencies from the left speaker. For example:

SHD subwoofer integration - high pass filter

Click on the Xover button for channel 3. Set a low pass filter to remove high frequencies from the subwoofer. For example:

SHD subwoofer integration - low pass filter

With the speaker still muted, run a measurement sweep. This will give you the response of the subwoofer with the EQ and low pass filter in place. Now mute the subwoofer, unmute the left speaker, and run another measurement sweep. This will give you the response of the left speaker with the high pass filter in place. Use the Overlays screen in REW to display both measurements.

If necessary, adjust the level of the subwoofer so that it aligns with the speaker near the crossover. You can do this by adjusting the level control on channel 3 and then re-measuring. Figure 3 shows the result we obtained:

Subwoofer with low pass filter and speaker with high pass filter

Figure 3. Subwoofer with low pass filter and speaker with high pass filter

4. Set and adjust time delay[Top]

Set the time delay between the speakers and the sub. As a starting point, use the difference in the distance of the speakers and the sub to the listening position. 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

Now unmute both the left speaker and the subwoofer and run a measurement sweep. Overlay this new graph with the highpass and low pass measurements from above. You should see that the new measurement has a reasonably smooth transition between the subwoofer and speaker. If it does not (for example, there is a dip at the crossover frequency), then adjust the time delay up or down by 1 or 0.5 ms at a time until you obtain a better result.

Figure 4 shows the result we obtained in mauve. In our case, the speaker was about a meter closer to the microphone than the subwoofer, but we got the best result with a time delay of 1.5 ms on the speakers.

Final integration of speaker and subwoofer

Figure 4. Subwoofer integrated with speaker

5. Check the right channel[Top]

Copy all your settings to the right speaker channel. In the case of the Xover and PEQ blocks, you can do this by using the linking feature:

miniDSP SHD: linking Xover or PEQ

Measure the right speaker and subwoofer together. If the result is not comparable to the left channel, you may need to adjust the time delay and try again. In this case, you will need to find the best compromise between the measurements for the left and right channels.

Note: if you have delay on the speaker channels, they must both be the same – do not set different delays on the left and right speaker channels.

Another method of adjusting the response near the crossover frequency is to change the frequency or the type of high pass filter on the right speaker. This will change the phase relationship between the speakers. Choose the best compromise between the two channels.

6. Run Your Dirac Live Calibration[Top]

You can now run your 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:

SHD subwoofer integration - after optimization

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. Using two or more subs can also help eliminate or reduce notches in the response such as shown in Figure 1.

A simple approach is to just connect a second subwoofer and follow the procedure described above in this app note again. For more advanced approaches, refer to the following app notes:

Wrapping up[Top]

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