This app note explains how to use the acoustic timing reference feature of Room EQ Wizard (REW) with a miniDSP UMIK-1 or UMIK-2 to time-align the speakers in your home theater.
- Introduction
- Set up for measurement
- Measure the speakers
- Tabulate your results
- Set distances in the AVR
- Wrapping Up
- Digging deeper
Introduction[Top]
REW can use an acoustic timing reference when doing measurements. This can be used to measure time delay between speakers so you can time-align them. A typical home theater setup is shown in this diagram:
As indicated in the diagram, the front left speaker is used as the acoustic timing reference. Each speaker will be measured for its time delay relative to this timing reference.
Set up for measurement[Top]
Use your AVR controls to:
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Disable bass management (typically by setting all speakers to "large").
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Turn off any up-mixing or down-mixing. This ensures that one measurement channel from REW goes to just one speaker.
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Set all speaker distances to the same value. This makes it easier to calculate the delays between the speakers.
Set up REW for measurement through the AVR. For information on how to do this, refer to our app notes on HDMI measurement for Windows or Mac.
Measure the speakers[Top]
Click on the "Measure" button (top left of the main window). Check the frequency sweep range and level. Set Timing (towards the top right of the window that pops up) to "Use acoustic timing reference."
Set both Output and Ref. Output to "L":
Run a levels check and then the measurement sweep. You will hear a short "peep" sound from the left speaker, shortly followed by a full frequency range sweep. Rename the measurement to "Front Left".
Click on the "Measure" button again. This time, set Output to "R" but leave Ref Output at "L":
Run the measurement sweep and label it "Front Right."
Repeat this procedure for the remaining speakers, including the subwoofer, by setting Output to each speaker in turn. Label each measurement as you go.
HDMI supports 8 channels of audio over linear PCM, so a 7.1 system can be directly measured by setting Output. (REW is not able to output audio using bitstream formats.) If you have more channels, you can physically connect each remaining speaker to the front right channel of your AVR and set Output to R. If you do this, be very very careful not to short any wires to any other channels or to each other.
When done, save all your measurements to a file.
Tabulate your results[Top]
On the REW main window, click on the Front Left speaker measurement and then on the Info button:
Locate the parameter "System Delay" on the window that pops up. This shows the time delay of the speaker being measured relative to the timing reference. It also shows the equivalent distance in meters and feet. For the front left speaker, these values should be at or close to zero:
Other speakers will have a different delay. For example, this is our subwoofer:
If the relative delay or distance is positive, it means that the speaker being measured is further away than the timing reference. If the value is negative, it means that the speaker being measured is closer than the timing reference.
Click on each of the measurements and write down the relative distance shown next to System Delay. For example, here are the relative distances in meters reported by REW for our test system:
Front left: 0.00 Front right: 0.007 Subwoofer: 0.922 Center: -0.093 Surround left: -0.799 Surround right: -1.043
Set distances in the AVR[Top]
Measure the distance to the front left speaker, as this is the reference. The distance to the other speakers is that distance plus the relative distance recorded above. For example, with 2.6 meters distance to the front left speaker, our subwoofer distance is 2.6 + 0.922 = 3.52 meters. Our surround left distance is 2.6 – 0.799 = 1.8 meters.
Use your AVR controls to set the distance of each speaker and the subwoofer. If there are small differences between left and right as with our front speakers, this simply indicates that the microphone was not exactly in the middle of the listening area and can be ignored.
If you want to double-check your work, run all the measurements again – this time, all of the delay values shown by REW should be close to zero.
Wrapping up[Top]
Turn bass management back on and run additional measurements with REW and your UMIK-1/UMIK-2 to check integration of the speakers with the subwoofer. Have fun, and please let us know how you go in our forum!
