Home Theater Multi-Subwoofer Setup

Basic System Setup plus REW & Dirac Live


This white paper will walk you through the setup of a home theater multi-subwoofer configuration using the miniDSP 2x4, 2x4 HD or DDRC-24 (herein referred to as miniDSP). This process will help optimize the performance of your subwoofers and their integration into your home theater system.


Once you finish the initial setup below, your system is ready to go. To take your home theater to the next level, we outline the Room EQ Wizard (REW) semi-automated room correction capabilities. Finally, if you have a DDRC-24, we will cover running a Dirac Live project.

You can complete the basic setup without using REW and the UMIK-1 and substituting a sound dB level meter on your iPhone or Android.


Throughout the text we’ve included references to technical resources for more in depth information on specific topics.


Overview


  1. Basic System Setup

    1. System Architecture Concept

    2. Hardware Configuration

    3. miniDSP Basic Plug-in Setup

      1. Subwoofer Routing

      2. Delay Setting

      3. Crossover Setting

      4. Relative Amplitude Setting

      5. Final Steps

  2. Using Room EQ Wizard (REW)

    1. Choosing Your Correction Strategy

    2. Setting up for Measurements

    3. Making Measurements and Averaging

    4. Creating and Loading Room Correction Filters

    5. Tuning to Taste

  3. Using Dirac Live

    1. Choosing Your Correction Strategy

    2. Running a Dirac Project

    3. Tuning to Taste


Basic System Setup


System Architecture Concept


This method takes multiple subwoofers  and combines them into a single virtual, corrected subwoofer. We calibrate the single virtual room corrected subwoofer Independently of the audio video receiver or processor (AVR). After this is complete, your single virtual subwoofer reconnects to the AVR and appears as a single monaural  subwoofer. Then you can apply your home AVR correction process (Audyssey, ARC, YPAO, Dirac, etc.) to your entire system with its ideal virtual subwoofer attached.


Diagram 1.  Home theater with single virtual room corrected subwoofer


Hardware Configuration


Subwoofer placement will be driven by the number of subwoofers in your system, listening room configuration and aesthetics. In general, spatial diversity is preferred. 



Diagram 2.  Required connections and cables for system setup, measurement and correction.


Be sure that all of the subwoofer cables are of good quality, adequate length and securely connected. At this time you can check that the built-in level, equalization, inversion and crossover frequencies of the subwoofers are either bypassed or set to maximum.


REW signals generated in your computer can be sent to the miniDSP via analog RCA or USB.  Analog will be required for the 2x4, and are recommended for AVR inputs for simplicity, as opposed to HDMI. (see Resources #2, 3, 4)


Nominal Subwoofer settings


The settings in your subwoofer will be set so as to not interfere with the crossover and parametric equalization (PEQ) parameters that will be set up in the miniDSP.




Crossover

Max Hz / off

Phase

Gain

0 dB / mid level / 12 o'clock

EQ / Parametric

Off / bypassed

Parametric EQ

Off / bypassed

Power Mode

Always on


Diagram 3.  Baseline subwoofer settings


miniDSP Driver and Plug-in Setup


Follow the miniDSP User Guide instructions on downloading the required plug-in, drivers and Dirac Live as appropriate. This is a good time to remove any old miniDSP software and perform updates (see Resources #2, 3 and 4).


Diagram 4. Signal flow through the miniDSP showing routing, crossover and parametric equalization (PEQ).


Subwoofer Routing


We recommend that all the subwoofers be connected as a single monaural group, as shown in the following routing matrix example. These adjustments are made on the input page of the miniDSP. Also note that the input is set to analog and the master volume is set to 0 dB (maximum). 


The exception to this is for ARC calibration, when you have dual or quad subwoofers you can split them to the left and right sections of the room.


Diagram 5. Virtual monaural subwoofer routing matrix setting


Delay setting


From the plug-in output page, enter the individual subwoofer delay settings as follows:


  1. Measure the distance of the subwoofers from the center listening area.

  2. Calculate the difference in distance of each subwoofer from the farthest subwoofer in feet.

  3. Find the delay in milliseconds by dividing the distance in feet by 1.11.

  4. Enter the resulting value in the delay section for each respective channel (1 ms = ~1 ft).



Diagram 6. Delay Table for Basic Multi Subwoofer Setup



Diagram 7. Delay calculation table


Crossover Setting


Setting of the optimal crossover frequencies is critical to achieving the best overall system performance. Here are the things you need to take into consideration:


  • Depending on the size of your main speakers, determine the frequency and slope of the high pass filter your AVR will be applying to your main speakers.

  • You can choose a matching low pass frequency and slope for your subwoofers and then later experiment with different slopes and overlapping or underlapping frequencies.

  • We also recommend adding a 10 Hz or greater high pass filter to the subwoofers to eliminate unnecessary load on the amplifiers.

  • If your subwoofers have differing frequency response ranges, you can set high and low pass filters as shown below to limit amplifier power to their useful frequency range. 

 


Diagram 8.  Multiple subwoofer crossovers with high and low pass filter settings


Relative Amplitude Setting


You can complete the Basic Setup with a sound dB level meter on your iPhone or Android, or by using REW and a UMIK-1. If you’re planning on moving onto REW or Dirac, now is a good time to begin using the UMIK-1. 


Set the relative levels of the subwoofers equally. If you are new to REW, see Resources #5 and 12. 



Diagram 9. Three subwoofer relative amplitude overlay plot


Final Steps


At this point, the basic setup is complete and your virtual subwoofer is ready to be connected to your AVR or home theater processor.


We also suggest you reset your home theater correction software and begin a new system correction session. If you need more gain from the subwoofer setup, you can increase the input gain and output gain settings. It’s important to adhere to good gain structure practices (see Resources #13).


Using REW


Choosing Your Correction Strategy


At this point in time you need to decide if you want to apply REW room correction filters to the input channel and / or output channels (see Resources #5 and 8). In this example we will apply the room correction filters to the input channel only, which will allow you to tune to taste in the output channels.


Setting Up for Measurements


Audio Output


Connect audio output from your computer to the 2x4. 


REW signals generated in your computer can be sent to the miniDSP via analog RCA or USB.  Analog will be required for the 2x4, and are recommended for AVR inputs for simplicity, as opposed to HDMI. (see Resources #2, 3, 4)


When using the analog audio outputs from your computer, either line out or 3.5mm headphone jack. You will need an adapter cable from stereo 3.5mm to RCA plugs. Connect the RCA plugs to the 2x4.



Diagram 10. Headphone jack to RCA for analog REW calibration signal to miniDSP


Set Sample Rates


Set the input and output devices to the sample rate that you want to use.


If you are using a UMIK-1, set the output device to 48 kHz. (The UMIK-1 can only be set to 48 kHz.) If you are using a UMIK-2, set both the UMIK-2 and the output device to the sample rate that you want to use, between 44.1 and 192 kHz.


Windows


Open Control Panel, then Hardware and Sound, then Manage Audio Devices. On the Playback tab, click on the output device and then Properties. Drop down the selector to set the sample rate.


Mac


Open the Audio MIDI Setup application. Click on the output device and drop down the menu to set its sample rate.


Set up Room EQ Wizard (REW)


  1. Download Room EQ Wizard from REW - Room EQ Wizard Room Acoustics Software.  If you are using a UMIK-2, get the most recent beta version from AV NIRVANA. (You will need to register for a free account to download.) This will ensure that you get a version that supports the UMIK-2.

  2. Once installed, start REW. You will see a screen asking if you want to use the UMIK-1 or UMIK-2. Click on Yes.

  3. Answer Yes to the next question about the calibration file. You can download your unique UMIK calibration file at Acoustic Measurement Tools: UMIK-1.

  4. Use the dialog box that appears to locate one of your calibration files.

  5. Open the REW Preferences window. Select your output device and input device accordingly


Making Measurements and Averaging


Begin by making multiple measurements with the UMIK pointed to the ceiling, using the 90-degree calibration file. We recommend a measurement area similar to this:


Diagram 11.  Three dimensional space and recommended microphone positions


After making at least four measurements, average them to find the composite as shown below.



Diagram 12.  Averaged multi subwoofer room measurements


Creating and Loading Room Correction Filters


After completing the measurements, set up REW to generate filters for your miniDSP. Once the appropriate filters are created, download them to your miniDSP. The following images illustrate that process.


Diagram 13.  Setting parameters for REW inverse filter generation


Set the parameters for generating the correction filters. Shown in the screenshot above are the values we found to work best for our example. You should experiment with these values to get the best result.



Diagram 14.  Measured (purple), predicted (pink) and calculated inverse filter (turquoise) responses



Diagram 15.  Inverse filter downloaded and displayed in the miniDSP plug-in


Tuning to Taste


After you have completed this process and you're satisfied with the results, you can go into the individual output channels and adjust the PEQs manually for tuning by taste.


Using Dirac Live 


Choosing Your Correction Strategy 


Before you begin your Dirac project, be sure that you have completed all of the steps in the Basic Setup section above.


You have the option to run individual REW correction curves for each of the multiple subs in each of the output sections of the plug-in. For this example, we are going to leave those flat so you can tune each of the individual output PEQs to your taste.


Running Dirac Live


This is just a very brief overview for running the Dirac Live process. We suggest referring directly to the Dirac Live User Manual for a more detailed description of the procedure (see Resources #4). 


We recommend setting the Routing Matrix as follows, prior to running the Dirac project calibration and measurement process.



Diagram 16.  Routing matrix used during monaural subwoofer Dirac calibration and project


After loading the Dirac Live software in accordance with the miniDSP manual, you will perform the following steps: 

  1. Verify you have all the proper USB connections in place, with adequate room to see your computer and be able to fully move the microphone around the rectangular cube defining the listening area

  2. Initiate Dirac Live from the miniDSP plug-in

  3. Confirm that you have logged into your Dirac Live account 

  4. Verify that you have no error messages before you proceed to level calibration 

  5. Perform level calibration combining both Dirac channels (see Diagram 17)

  6. Select either narrow or wide focus listening area

  7. Perform specified measurements (please note that the character in the Dirac diagram is facing the sound stage)

  8. Proceed to calculating the Dirac correction waveform

  9. Export the Dirac project to the miniDSP unit

  10.  Save your Dirac project


Tuning to Taste


After you have completed your Dirac project and are satisfied with the results, you can go into the individual output channels and adjust the PEQs manually for tuning by taste. You can also have up to four tuning curves for different types of movies and music.


Making PEQ adjustments in the output section of the plug-in acts as an overlay to your Dirac project. This should be a real time activity using peak, high-pass and low-pass filters. For example, you can create a peak filter with either gain or loss and move it around real time to achieve your desired results.

 


Diagram 17.  Example of a tune to taste peak filter overlay used for adding some “punch”




Resources


  1. A Brief Overview of the miniDSP 2x4 HD

  2. miniDSP 2x4 User Guide

  3. miniDSP 2x4 HD User Guide

  4. miniDSP Dirac Live User Manual

  5. Multi-Sub Tuning Basics

  6. Sub integration for 2.1

  7. Driver time alignment

  8. Room EQ Wizard (REW)

  9. An Array Experiment with Magnetic Variometers Near the Coasts of Southeast Australia

  10. Low Frequency Optimization Goals The Crux of the Matter

  11. The Misunderstood 0.1 LFE Channel in 5.1 Digital Surround Sound - HomeTheaterHifi.com

  12. UMIK-1/2 setup with REW

  13. Gain Structure 101

  14. Acoustic Measurement Tools: UMIK-1

  15. miniDSP DDRC-24 User Guide


Support


Deer Creek Audio is here to help!  Please feel free to contact us with any questions:  email at staff@deercreekaudio.com or call (720) 726-9272.