Good room acoustics, whether in a control room, recording room or home studio, are crucial to any professional audio recording or music production. Whether you are a musician, sound engineer or podcaster, room acoustics play an important role in achieving optimal results. A poorly treated room can lead to unwanted sound colouration, resonance and inaccurate monitoring conditions that can cause you to make the wrong decisions when using an equaliser, for example.
Fortunately, there are software solutions that can help you analyse the acoustic properties of your recording studio room and plan improvements more accurately. One such software is the freeware Room EQ Wizard, or REW for short.
In this blog post, we’ll show you how you can use REW to measure your own studio room, gain a better understanding of its acoustic properties, and take targeted action to optimise the room’s acoustics.
1. Equipment requirements
To accurately measure your room, all you need is:
- A computer, running the free Room EQ Wizard software (Mac/PC)
- Studio monitors
- Audio interface
- Measurement microphone (even inexpensive models will do, e.g. Behringer ECM8000, Superlux ECM-999)
- XLR cables
- Level meter or mobile phone app
2. Set up REW and audio devices
- First, connect your speakers to the outputs of your audio interface that is connected to your computer.
- Connect your microphone to an input and activate phantom power for that channel.
- If your interface allows direct monitoring (the microphone input goes directly to the speaker output), make sure it is switched off. You can find this setting in your interface’s control software.
- Download and install REW on your computer.
- Open REW and go to Preferences to select the audio driver and interface. Depending on your version of REW and operating system (Mac or Windows), the screens may look slightly different. Then select the appropriate outputs for the audio output of the test signal (e.g. Output 1 and Output 2) and the appropriate input to which you have connected the test microphone.
- If your test microphone was supplied with a calibration file, you can load the file into the Preferences window.
3. Adjust the measurement microphone and loudspeaker
Leveling the measurement microphone and the loudspeakers is essential for accurate and comparable measurement results. Leveling ensures that the microphone preamplifier and the loudspeakers are always set to the same reference volume for consistent and comparable measurement results.
Place the measurement microphone at the listening position, approximately at ear level, and with both speakers having the same distance from the measurement microphone.
Now start the SPL Meter function in REW to set the volume reference so that all measurements will have the same volume reference point for comparison.
To do this, select the Z-weighting – everything else is predefined – click “Calibrate”, select “Speaker Signal” in the window that appears and click “OK”.
Now set the output volume at the interface to a level at which you would like to listen to (loud) music and use a sound level meter or app to check the volume in the room at a distance of about 1-2 meters from the speaker. Readings of 70 to 90 dB are good. If it is still too low, feel free to turn up the output volume on your interface. Trust your ears.
Enter the value you now read in dBC on the sound level meter into the dB field of the SPL meter in REW.
From now on, do not change the output volume on the interface!
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4. Make the measurements
Use the “Measure” button in the menu bar on the left to open the measurement window. Here you will find the final settings before you start measuring.
You can now use the “Level” and “Check Levels” settings to find the correct measurement volume. Do not change the output volume on the interface itself! We have just set this using the SPL meter. Instead, adjust the gain of the microphone preamplifier on the interface. Increase this until the dBFS value displayed in REW is around -20.
REW will indicate a proper microphone level by displaying “Level OK”. If no level is displayed, make sure that you have activated phantom power and that the correct input is selected in the settings.
You are now ready to make your first measurements using a sine sweep. Proceed as follows:
- Set the sine sweep length to 256k. This is enough for most measurement situations.
- In the “Repetitions” field, select the number 2 for two sweeps if you are using a microphone connected via an XLR cable. This gives a good signal-to-noise ratio.
- The number 1 and the correct sample rate are particularly important if you are using a USB microphone.
- You can also set a delay before the measurement starts and, of course, the output of your interface to which the measurement signal should be sent.
- Click “Start” to start the measurement and move away from the monitoring position.
Choose a place where you will stay during the measurement which will not distort the measurement result too much. For example, corners or first reflection points are unfavourable. If you are taking several measurements, make sure you are always in the same place in the room.
Obviously, you want to keep a good overview when taking several measurements, e.g. with different microphone or loudspeaker positions. You should always label the measurements clearly in the spaces provided.ungen immer eindeutig in den dafür vorgesehenen Feldern beschriften.
5. Your first measurement is done
You now have an impulse response of the room and REW will show you many different results. Although the initial results are a very important step towards effective acoustic measures, it is always advisable to consult an acoustician. Despite the measurement, the actions that will improve your room acoustics are still completely unclear at this stage. The correct interpretation of the results also requires a great deal of experience. This starts with the correct zoom setting of the measurement results to focus on what is really important.
The measurement is a very good basis for experienced acousticians to plan very precisely. The following aspects are of particular importance:
- Actions to bring the reverberation time into the desired range
- Correct number and positioning of bass traps
- Do I need diffusors and/or absorbers?
- Is there a lot of carpet in the room?
- Effect of room modes and early reflections on your listening experience
- Recommended speaker and listener positions
- Accuracy of measurement results
Talking of correct measurements: if you need assistance measuring your room from an experienced acoustician, you’ve come to the right place. HOFA-Akustik has been in business for over 15 years and acoustically optimized hundreds of home studios, control rooms and recording facilities.
We recommend our professional Room Acoustic Planning Service, where you can send us your measurement results along with information about your room. You will then receive a personalized proposal for optimizing your room acoustics.
If you have any questions, please do not hesitate to contact our HOFA-Akustik team.
