The Test Principle

Room modes — standing waves — arise when the dimensions of a room create a resonance path at specific low frequencies. Once excited, the trapped acoustic energy takes time to dissipate. You hear this as a bass bloom, a tonal coloration that persists after the source stops, or a specific note that always sounds louder or longer than its neighbours.

The test tool exploits this resonant behaviour deliberately. By sending a rapid, continuous stream of tone bursts at a known mode frequency, you force the room to sustain that resonance. When the time between bursts is shorter than the room's natural decay at that frequency, the energy accumulates: each burst reinforces what the previous one left behind. At short enough intervals, the mode never has time to collapse between excitations, and the result is a near-continuous sine tone — not from the speaker, but from the room itself.

This is your test condition. The room is now acting as a resonator, storing and radiating energy at the problem frequency. When you then activate your AVAA, it senses the particle velocity at the room boundary and generates a precisely timed counter-reaction that opposes the mode. The standing wave collapses — and the sustained tone you built up disappears. This near-instant before/after transition is the clearest possible confirmation that the unit is absorbing energy at the right place and at the right frequency.

Why the room resonance accumulates

At 63 Hz with 10 oscillations, a burst lasts approximately 159 ms. If the room's modal decay time at 63 Hz is 800 ms (a typical value for an untreated small room) and you set the burst interval to 300 ms, each new burst arrives while the previous reverberant tail is still at around 70% of its original level. The energy from each successive burst adds to this residual, and within three or four cycles the room reaches a quasi-steady state where the sustained tone level is maintained. Reducing the interval to 150–200 ms drives the room even deeper into saturation.

Burst Generator — Step by Step

The burst generator sends periodic sine tone bursts at a frequency and repetition rate you control. Work through the following steps in order the first time you use the tool for a given room mode.

1. 1

   Set the frequency to your room mode

   Enter the frequency of your identified problem mode into the Frequency (Hz) field, or drag the slider. Common first-order axial modes range from 30 Hz (a 5.7 m room length) to 120 Hz (a 1.4 m room length). For typical studio and listening rooms, expect problem frequencies between 40 Hz and 100 Hz.

   Precision matters

   A few Hz of offset can significantly reduce the excitation of a narrow resonance. Set the frequency as close as possible to the measured mode peak — use the numeric input field for exact entry rather than the slider.

2. 2

   Set the number of oscillations

   The Number of oscillations control sets how many complete cycles each burst contains, which determines burst duration: duration = cycles ÷ frequency. At 63 Hz, 10 cycles produces a 159 ms burst. At 40 Hz, the same 10 cycles lasts 250 ms.

   For AVAA verification, 8–15 cycles is the recommended range. More cycles deliver more energy per burst and make the modal buildup faster and more pronounced. Fewer cycles produce a sharper, more click-like burst that is easier to time but less effective at driving a resonance.

3. 3

   Start with a long interval to hear the room's natural decay

   Set Time between bursts to 1.5 s and press Start. With a long interval, each burst is clearly separated. Listen carefully to what happens after the speaker goes silent: the room continues to ring at the burst frequency for a noticeable period before decaying away. This is the modal decay you are about to control with the AVAA.

   The longer the ringing persists, the stronger the mode. An untreated room with a significant mode at 63 Hz may ring for 0.8–2 seconds after a single burst. Note the character of this decay: it may sound like a sustained musical pitch, a low thump with a tonal tail, or a warbling presence that takes time to settle.

4. 4

   Shorten the interval until the tone becomes quasi-continuous

   Gradually reduce the Time between bursts: try 0.8 s, then 0.5 s, then 0.3 s, then 0.2 s. At each step, listen for the change in character. At some interval — usually between 200 ms and 400 ms depending on the mode's natural decay — the room stops recovering between bursts. The signal transitions from a series of distinct pulses into a sustained, continuous tone at the mode frequency.

   This is your test condition. Leave the interval at the lowest value that produces a clearly sustained tone. You have now built up the resonance to its maximum useful level.

5. 5

   Enable the AVAA and observe the change

   With the quasi-continuous tone playing, switch your AVAA unit to active mode. Within one to two seconds, the sustained tone should diminish noticeably or disappear entirely. The room is releasing the stored resonant energy faster than the bursts can replenish it because the AVAA is actively removing it.

   What a working AVAA sounds like

   The effect is not a sudden mute — the tone fades over roughly one to two seconds as the room relaxes to its new, lower equilibrium. Once the AVAA has established control, the burst tone should sound significantly quieter and drier at your listening position. The "sustained room tone" should become either absent or much reduced.

6. 6

   Compare AVAA active vs. inactive repeatedly

   Toggle the AVAA off while the bursts continue playing: the sustained tone will rebuild within a few seconds. Switch it back on: it collapses again. Repeat this toggle several times from different positions in the room to build a clear picture of the unit's effect across the listening area. If a second person is available, have them operate the AVAA toggle while you listen at your primary position.

CEA Burst Mode

Enabling the CEA burst (windowed) checkbox applies a Hann window to the burst envelope. Instead of switching on and off abruptly, the burst ramps up from zero over the first 25% of its duration and fades back to zero by the end. The waveform display on the burst generator canvas shows the shape of the active mode.

For AVAA verification, leave CEA mode unchecked. The rectangular burst is more effective at charging the room's resonance because it delivers energy at the full amplitude from the very first sample, giving the mode less time to begin its decay before the next reinforcement arrives.

Pink Noise and White Noise Generators

The noise generators provide a broadband alternative for situations where the exact mode frequency is uncertain, where multiple modes are present in a frequency region, or where you want a more intuitive, music-like reference for evaluating the room's bass behaviour.

Pink noise

Pink noise has equal energy per octave: each doubling of frequency contains the same amount of power, resulting in a spectral slope of −3 dB per octave from low to high. This closely matches the long-term spectral distribution of most music and programme material. Pink noise in a room with a prominent mode will sound coloured — a particular bass frequency will appear louder and more sustained than its neighbours. Enabling the AVAA should reduce this coloration, making the noise sound more balanced and tighter in the low end.

White noise

White noise has equal power at every frequency (a flat power spectral density), which means the upper octaves of the audible range receive far more energy per octave than the lower. In practice, white noise sounds noticeably brighter and harsher than pink noise. It is most useful when working alongside a measurement microphone for absolute frequency response analysis, or when you specifically want more energy in the upper part of your test band.

Setting the cutoff frequencies

Both generators include a bandpass filter formed by a highpass filter at the low cutoff and a lowpass filter at the high cutoff. These allow you to focus the noise energy on the frequency region of interest and avoid the discomfort of broadband noise outside your target range.

1. 1

   Set the low cutoff below your lowest mode of interest

   Set Low cutoff frequency to approximately 5–10 Hz below your lowest problem mode. If your lowest mode is at 40 Hz, set the low cutoff to 30–35 Hz. The highpass filter rolls off below this point at approximately 12 dB per octave.

2. 2

   Set the high cutoff above your highest mode of interest

   Set High cutoff frequency to approximately 20–30 Hz above your highest problem mode. If your highest mode of interest is 100 Hz, a high cutoff of 130–150 Hz gives clean attenuation above the region without cutting into the mode. The lowpass filter has the same 12 dB/octave slope.

3. 3

   Press Start and listen

   The band-limited noise will play through the filters you have set. Listen to the character of the bass in the room. With a strong mode in the band, certain frequencies within the noise will appear to "jump out" as louder, more resonant, or longer in duration than others. Enable and disable the AVAA to compare: a working AVAA should reduce this unevenness and produce a smoother, more uniform bass texture.

Reading the Frequency Response Curve

Each noise tab displays a theoretical response curve showing the shape of the combined highpass and lowpass filter applied to the noise source, drawn on a logarithmic frequency axis. This is a computational display — it represents the mathematical transfer function of the filters at their current cutoff settings, not a live measurement of the room or the audio output.

How to read the axes

The horizontal axis runs from 10 Hz (left) to 1 kHz (right) on a logarithmic scale, so each decade (10→100, 100→1000) occupies the same physical width. Vertical gridlines mark the decade boundaries. The vertical axis shows relative magnitude in dB, with 0 dB at the top (the passband reference) and −48 dB at the bottom. Horizontal gridlines appear at 0, −12, −24, and −36 dB.

What the curve tells you

For pink noise, the in-band region of the curve is not flat: it carries the inherent −3 dB/octave spectral tilt of the pink noise source, sloping gently downward left to right. For white noise, the in-band region is flat. In both cases, the curve rolls off steeply on either side of the passband, following the 12 dB/octave attenuation of the second-order Butterworth-equivalent highpass and lowpass filters.

The curve updates instantly as you move the cutoff sliders, giving you a precise visual preview of the frequency band you are targeting before you begin playback. The portion of the curve between the two cutoff frequencies represents the energy you will be sending into the room.

Parameter Reference

Burst duration reference

Burst duration in milliseconds = (number of oscillations ÷ frequency) × 1000. Examples:

Interpreting Results

Signs the AVAA is working correctly

Understanding the AVAA's operating range

The AVAA is most effective at frequencies where passive panel absorbers and foam have very limited impact — typically from approximately 15 Hz to 150 Hz, with peak effectiveness in the 30–100 Hz range. This is exactly the region where room modes are most problematic and hardest to control with conventional materials.

What a partial result looks like

Troubleshooting

Tips for Best Results

• Test each mode frequency separately. Different modes may respond differently depending on AVAA placement and the geometry of the room. Spending two to three minutes on each identified mode frequency gives a much clearer picture than sweeping through multiple frequencies simultaneously.
• Use headphones to verify the source signal first. Before evaluating the room response, confirm the tone burst is audible and at a reasonable level in headphones. This isolates the source from the room and verifies that the tool is working correctly before you begin the comparison.
• Build the resonance fully before toggling the AVAA. Let the room reach its quasi-steady-state sustained tone — usually three to five seconds after shortening the interval — before switching the AVAA on. Starting the comparison too early may give a misleading result if the room has not yet reached full saturation.
• Test from multiple positions in the room. The spatial distribution of a mode means the subjective improvement varies by location. Move to different positions — front-left, centre, back-right of the listening area — and note where the AVAA effect is most and least pronounced.
• Eliminate background noise during testing. HVAC systems, computer fans, and street traffic can produce low-frequency content that overlaps with the test range and makes it harder to hear the burst signal and its room response. Test with HVAC off if possible.
• Match playback level to your normal listening level. Room modes are partly level-dependent in their perceptibility. Testing at a level similar to your normal working level gives the most representative result. Excessively high levels may introduce compression or speaker distortion that confuses the evaluation.
• Use the long-interval decay as a diagnostic before and after AVAA installation. Record (mentally or with your measurement software) the approximate decay time of each mode at long burst intervals before enabling the AVAA. This becomes a qualitative before/after benchmark that you can return to at any time.
• The effect at the mix position is what matters. If the AVAA is working mechanically but you cannot hear the difference from your mix chair, evaluate whether the unit's placement is coupling to the mode in a way that reduces energy at your specific listening position. Room mode pressure distribution is three-dimensional, and the optimal AVAA position depends on both the mode shape and your listening geometry.