diff --git a/specs/16-audiobook-production.md b/specs/16-audiobook-production.md
index 712bc95..65a1411 100644
--- a/specs/16-audiobook-production.md
+++ b/specs/16-audiobook-production.md
@@ -108,6 +108,26 @@ voices/narrator_ref.wav  (voice for new narration) ─▶ 1. synth opening/annou
 | `umbraaudio/web/templates/index.html` | "Build Final Audiobook (MP3)" card + stats table + download links |
 | `tests/test_ar_export.py` | Unit tests with mocked TTS + ffmpeg |
 
+## 5a. Scene breaks (`<<<>>>`)
+
+A scene break is a segmentation row whose `text` is exactly `<<<>>>`. It renders as
+**2.000 s of silence**, never as speech.
+
+- **Author rule:** every scene-break utterance must carry `speaker_name = 'Narrator'`.
+  The system requires a speaker on every utterance row, and `Narrator` is the correct
+  value. A `speaker_name` of `scene_break` is **not** valid data — it was a transient
+  artifact of the generator, not an authorial choice. Normalized book-wide on
+  2026-09-26 (74 rows changed; 81 total).
+- **The speaker value is inert for rendering.** `is_scene_break(text, utt_type)`
+  (`umbraaudio/generation/scene_break.py:31`) keys off the `<<<>>>` text and the
+  `scene_break` type only, never `speaker_name`. Both generation paths short-circuit
+  before voice resolution — `generate_all_audio.py:167` and
+  `chapter_builder.py:514` (`write_scene_break_audio(out)` then `continue`, ahead of
+  `_resolve_voice_ref` at `:520`). So the value is required by the schema but cannot
+  affect the audio.
+- **Duration constant:** `SCENE_BREAK_SILENCE_MS = 2000` (`scene_break.py:26`).
+  Verified 2026-09-26: 62/62 existing scene-break WAVs are exactly 2.000 s.
+
 ## 6. Quality gates before upload
 
 - All tracks: 44.1 kHz, mono, 192 kbps CBR MP3 (ffprobe report in manifest).