What Are First Reflections?
When your studio monitors emit sound, it travels in all directions. The direct sound reaches your ears first. Milliseconds later, sound that has bounced off a nearby surface — a side wall, the ceiling, the desk — arrives as a first reflection.
These early reflections (arriving within roughly 5 – 20 ms of the direct sound) are particularly damaging because the ear cannot separate them from the direct signal. Instead, they fuse with it, causing:
- Comb filtering — peaks and dips across the frequency response where the direct and reflected waves add or cancel.
- Stereo image smearing — reflections from asymmetric surfaces shift the perceived location of sources.
- Reduced clarity — transient detail is smeared when the reflection overlaps the direct signal.
The Mirror Trick
Finding first reflection points is straightforward with a helper and a flat mirror (even a small bathroom mirror will work):
- Sit in your normal mixing position.
- Have your helper hold the mirror flat against the side wall at speaker height.
- The helper slides the mirror along the wall. When you can see the face of one of your monitors reflected in the mirror, that spot is a first reflection point.
- Mark it. Repeat for the other monitor.
- Do the same on the other side wall, the ceiling, and (if untreated) the desk surface.
You will typically find 6 – 8 first reflection points: two on each side wall (one per monitor), two on the ceiling, and often the desk surface itself.
Which Surfaces to Treat
Priority surfaces for first-reflection treatment:
- Side walls — the most critical. Side-wall reflections are the strongest source of comb filtering and stereo image degradation.
- Ceiling — a ceiling cloud (suspended panel) or directly mounted absorber at the reflection points addresses vertical reflections.
- Desk / console surface — the console bounce is often overlooked. Angling monitors downward slightly or using a sloped desk surface helps redirect this reflection away from the ears. An absorptive mat on the desk surface is also effective.
- Floor — a thick rug or carpet between the monitors and the listening position absorbs floor reflections. Hard floors are particularly problematic.
Panel Selection
For first reflection points, broadband absorbers are the standard choice:
- Thickness: 5 – 10 cm of rigid mineral wool or fibreglass (40 – 60 kg/m³ density). Thicker panels absorb deeper into the mid-range.
- Panel size: at least 60 × 120 cm to cover the reflection zone fully. Larger panels (120 × 120 cm) provide more uniform control.
- Air gap: mounting with a 5 – 10 cm air gap behind the panel significantly improves low-mid absorption without increasing panel thickness.
- Absorption vs. diffusion: at first reflection points, absorption is preferred over diffusion. Diffusers require distance to work properly, and first reflection points are usually close to the listener.
Use the Absorbers tool to compare how different thicknesses and densities perform across frequency bands. Combine with the Placement tool to model your specific monitor-to-wall geometry and the SBIR calculator for front-wall reflections.
Verifying the Results
After installing treatment, measure the impulse response at your listening position using a measurement mic and software like REW. Compare the before-and-after energy-time curve (ETC). You should see a clear reduction in early reflection peaks. A well-treated first-reflection zone typically yields 10 – 15 dB of reflection attenuation.