Understanding REW Playback Capabilities
You cannot natively make Room EQ Wizard (REW) play through all speakers and subwoofers simultaneously using a single test signal without external routing configurations. REW is designed to output a sweep signal to one channel at a time to maintain measurement integrity. However, by using an ASIO driver or an HDMI multi-channel interface, you can route signals to specific speakers or utilize a “summed” approach for subwoofer integration. To achieve a full-system response, you must calibrate channels individually and verify integration via the REW Alignment Tool.
TL;DR: Quick Summary for Audio Calibration
- Native Output: REW sends signals to one output channel (e.g., L, R, or SW) at a time by default.
- The Workaround: Use an HDMI connection to an AV Receiver (AVR) to address each channel individually via WASAPI or ASIO.
- Multi-Sub Integration: Use the REW Alignment Tool to time-align subwoofers before measuring the “all speakers” response.
- Best Practice: Measure channels independently to avoid phase cancellation artifacts during the sweep.
How to Route Audio in REW for Multi-Channel Systems
To get the most out of your room analysis, you need to understand how to bypass the standard stereo limitation. Most users struggle because they attempt to use a basic 2-channel USB DAC.
Prerequisites for Multi-Speaker Testing
- Hardware: An AV Receiver that supports HDMI LPCM input from your PC.
- Drivers: Install ASIO4ALL or the specific driver for your multi-channel interface.
- Connection: Connect your PC via HDMI to the AVR and set the Windows sound settings to “7.1 Surround.”
Step-by-Step Configuration
- Open REW and navigate to Preferences > Audio.
- Select your Output Device as the HDMI interface connected to your AVR.
- Click Output Channels and verify that you can see all available channels (e.g., L, R, C, LFE, SL, SR).
- Run a sweep on a single channel to verify the signal hits the correct speaker.
- Repeat for each channel to build your Acoustic Measurement Data.
Can REW Play All Speakers and Subs at Once: The Limitations
It is important to clarify that “playing all speakers at once” is rarely ideal for acoustic measurement. If you send a sweep to every speaker simultaneously, the comb filtering and phase interference will make the resulting graph nearly impossible to interpret.
Why Individual Measurements Outperform Simultaneous Sweeps
- Phase Correlation: Simultaneous sweeps cause overlapping sound waves, resulting in deep, inaccurate dips in your frequency response.
- Isolation: By measuring one speaker at a time, you can identify specific room modes (standing waves) associated with that speaker’s physical placement.
- Time Alignment: You must measure individually to calculate the delay settings required to align your subwoofers with your main speakers.
Comparison of Measurement Approaches
| Method | Accuracy | Difficulty | Primary Use Case |
|---|---|---|---|
| Single Channel Sweep | High | Low | EQ, Room Mode Identification |
| Summed Subwoofers | Medium | Medium | Aligning multiple subs |
| All-Channel Simultaneous | Low | Very Low | Checking master volume levels only |
Practical Tips for Subwoofer Integration
If your goal is to ensure your subs are playing correctly with your speakers, focus on the Alignment Tool rather than trying to force a simultaneous sweep.
- Measure Mains: Take a high-resolution sweep of your Left and Right speakers.
- Measure Subs: Take a sweep of your Subwoofer channel.
- Use the Alignment Tool: In REW, open the Alignment Tool, select your main measurement and your sub measurement.
- Adjust Delay: Use the Add Delay function in the tool to see which millisecond value creates the flattest crossover region.
- Apply to AVR: Manually input the calculated delay and crossover frequency into your AV Receiver settings.
Frequently Asked Questions (FAQ)
Can I use a Y-splitter to measure all speakers at once?
While you technically can, it is highly discouraged. A Y-splitter will degrade your signal integrity and prevent you from adjusting individual channel gains or delays, which are critical for accurate room correction.
What if my AV Receiver doesn’t support HDMI input from a PC?
If you are restricted to analog inputs, you will have to use a multi-channel USB interface. Without a direct digital link to your AVR, you may be limited to simple stereo (2.0 or 2.1) measurements.
Does REW automatically fix my speaker phase?
No, REW provides the data and the visualization tools (like the Impulse Response graph), but you must manually apply the corrections to your DSP, AVR, or pre-amplifier settings.
Is it necessary to measure every surround speaker?
For a standard 5.1 or 7.1 setup, it is highly recommended to measure every speaker. Each speaker interacts with the room’s unique boundaries differently, and individual EQ can significantly improve the “envelopment” effect of your system.
