Guenter Villnow
Guenter Villnow

In this application note, we will show you how to integrate a subwoofer into a stereo system using a 4-output miniDSP processor and REW (Room EQ Wizard). This app note is applicable to the miniDSP 2x4 HD, DDRC-24, miniDSP Flex (with or without Dirac Live) and SHD Series processors.

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 application notes UMIK-1/2 setup with REW and Auto EQ with Room EQ Wizard.

If your processor has Dirac Live and you don't want to learn how to use REW, try instead the simpler procedure described in the app note Subwoofer Integration with miniDSP and stereo Dirac Live.

Getting connected[Top]

Connect the system as shown in this diagram:

SHD subwoofer integration - system connections

Start miniDSP Device Console and connect to your processor. Change the displayed labels on the output channels. In the example below, we have used "Left Spkr", "Right Spkr" and "Sub". Then set up the Routing like this:

SHD subwoofer integration - routing matrix

Note: if your subwoofer has a built-in low pass filter, set it to the highest possible frequency. This is because we will be doing the crossover in the miniDSP processor.

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 speakers (output channels 1 and 2).

  2. Bypass the subwoofer low pass crossover filter (the Crossover block of output 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. For information on how to do this, see the app note Auto EQ with Room EQ Wizard. Be sure to choose the correct Equalizer option (and therefore sample rate) for your processor.

There is no need to get the response exactly flat, as an additional step later will perform additional correction. The purpose here is just to get a clean crossover to the speakers.

Figure 2 shows our EQ 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

3. Enable crossovers[Top]

Click on the Crossover button for output 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 Crossover button for output 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. This can be done by adjusting the level control on the subwoofer (if it has one) or with the gain control on output channel 3. Then re-measure. 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 time delay (optional)[Top]

If you wish, 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 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 output channel. Gain and delay will need to be copied manually. In the Crossover and PEQ blocks, use the linking feature:

miniDSP SHD: linking Crossover 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 output channels, they must both be the same – do not set different delays on the left and right speakers.

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 left and right.

6a. Tailor final response with PEQ (units without Dirac Live)[Top]

If you are using a processor without Dirac Live, perform additional EQ using the PEQ blocks on the input channels. There are two key things to do here:

  1. Use a low shelf filter to add some bass boost. Most people prefer a slight boost. Here is a typical example:

    miniDSP subwoofer integration - bass boost

  2. Perform additional room correction, particularly at low frequencies. For example, if you take multiple measurements around the listening area, then take an average, you can improve the overall result around the listening area.

6b. Tailor final response with Dirac Live[Top]

If your processor has Dirac Live, run your Dirac Live calibration now.

When you get to the Volume Calibration tab, note that there will be only two channels shown. This is because the miniDSP SHD Series/Flex/DDRC-24 are stereo Dirac Live processors. They treat each speaker combined with the subwoofer as a single channel. There is no separate Dirac Live channel for the subwoofer.

Volume calibration for stereo Dirac Live

On the Filter Design tab, 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

Dual subs and more[Top]

For smoother response across the listening area, you can use more than one subwoofer. A simple approach is to connect a second subwoofer to output channel 4 of your miniDSP processor and enable it in the Routing matrix:

SHD subwoofer integration - routing matrix

Link the PEQ and Crossover blocks of output channels 3 and 4. When measuring, measure both subs at the same time.

A more advanced approach is to use separate equalization on each subwoofer. This can be done using the Multisub Optimizer program, as described in our app note Dual-sub integration with miniDSP and MultiSub Optimizer.

For more than two subwoofers, a simple approach is to just "Y-connect" them to output channels 3 and 4 and proceed as above. More advanced approaches using a separate miniDSP processor are described in the app note Tuning multiple subwoofers with miniDSP.

Wrapping up[Top]

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


Related Products - Typical multi-sub processors