Acoustics: boundary bass gain (wall / edge / corner loading) for the listener and sources #897

New issue

Closed

opened 2026-10-20 21:29:33 +00:00 by sky_line · 1 comment

sky_line commented

2026-10-20 21:29:33 +00:00

Owner

Part of the room acoustics work (#683, #857, #858, #892).

Today

Reverb is one diffuse tail per room or zone, so it doesn't depend on where the listener stands.
Bass: nothing models the low-frequency boost near hard boundaries.

Physics

A nearby hard surface reflects low frequencies nearly in phase with the direct sound, because the wavelength is much longer than the distance to it. Each close boundary adds up to about +3 dB:

Position	Boost
One wall	about +3 dB
Wall plus floor (an edge)	about +6 dB
A corner	about +9 dB

The boost fades once the distance passes about a quarter wavelength (roughly 0.5 to 1.5 m for content below about 150 Hz). It applies at both ends:

Listener: standing in a corner sounds bass-heavy.
Source: a speaker or subwoofer pushed into a corner gets more bass. This is why speaker placement matters, and why subs go in corners (#892).

Proposal

Distances:
- For the listener, read the distance to the nearest surfaces along the principal directions from the existing room rays.
- For sources, use the per-source room probes (#857).
Boost: compute a low-shelf boost from the nearby boundaries:
- each one's contribution falls off with distance relative to the wavelength;
- it is scaled by the surface's hardness (metal and stone give the full boost, soft and foliage less);
- it is smoothed over time.
Applying it: OpenAL EFX per-source filters can cut bass but not boost it. Options:
- a parallel bass-boost send: a low-passed send into an auxiliary slot that carries an EQ or pass-through effect, summed with the direct path;
- the EFX equalizer effect;
- doing it in the speaker feeder for #892 streams, where we own the PCM.
Cost: reuse existing rays, so it adds no new ray budget. It should cost nothing when acoustics is off.
Setting: a strength control, so the effect can be compared on and off.

Test

A large hard room, such as the gold reverb cube with metal prims. Compare the room centre, a wall, an edge and a corner, and a subwoofer speaker moved from the centre into a corner.

Part of the room acoustics work (#683, #857, #858, #892). ## Today - **Reverb** is one diffuse tail per room or zone, so it doesn't depend on where the listener stands. - **Bass:** nothing models the low-frequency boost near hard boundaries. ## Physics A nearby hard surface reflects low frequencies nearly in phase with the direct sound, because the wavelength is much longer than the distance to it. Each close boundary adds up to about +3 dB: | Position | Boost | |---|---| | One wall | about +3 dB | | Wall plus floor (an edge) | about +6 dB | | A corner | about +9 dB | The boost fades once the distance passes about a quarter wavelength (roughly 0.5 to 1.5 m for content below about 150 Hz). It applies at both ends: - **Listener:** standing in a corner sounds bass-heavy. - **Source:** a speaker or subwoofer pushed into a corner gets more bass. This is why speaker placement matters, and why subs go in corners (#892). ## Proposal - **Distances:** - For the listener, read the distance to the nearest surfaces along the principal directions from the existing room rays. - For sources, use the per-source room probes (#857). - **Boost:** compute a low-shelf boost from the nearby boundaries: - each one's contribution falls off with distance relative to the wavelength; - it is scaled by the surface's hardness (metal and stone give the full boost, soft and foliage less); - it is smoothed over time. - **Applying it:** OpenAL EFX per-source filters can cut bass but not boost it. Options: - a parallel bass-boost send: a low-passed send into an auxiliary slot that carries an EQ or pass-through effect, summed with the direct path; - the EFX equalizer effect; - doing it in the speaker feeder for #892 streams, where we own the PCM. - **Cost:** reuse existing rays, so it adds no new ray budget. It should cost nothing when acoustics is off. - **Setting:** a strength control, so the effect can be compared on and off. ## Test A large hard room, such as the gold reverb cube with metal prims. Compare the room centre, a wall, an edge and a corner, and a subwoofer speaker moved from the centre into a corner.

sky_line added the

feature

label

2026-10-20 21:29:33 +00:00

sky_line added this to the Slipstream project

2026-10-20 21:29:33 +00:00

sky_line referenced this issue

2026-10-21 23:01:24 +00:00

Acoustics: lying snow absorbs sound (snow-covered surfaces deaden reflections and reverb) #930

sky_line referenced this issue from a commit

2026-10-22 08:20:13 +00:00

#897 boundary bass: low-shelf boost near hard surfaces via an EQ send