Bibliographic record
Abstract
This paper investigates theoretically how duct geometry and liner thickness affect the attenuation of fundamental-mode sound propagation in a lined duct.The study was done to satisfy the need for a greater understanding of interior naturalventilation openings and of silencers implemented to improve the acoustical performance ('ventilators'), and to provide engineers and architects with optimal-design guidelines.It assumed ventilators of the simplest formstraight, acousticallylined ducts of rectangular cross-section.An analytical solution is presented for the attenuation of the fundamental mode in such a duct.Duct-liner thickness does not affect high-frequency performance; however, it limits low-frequency performance.A 25-mm liner is likely not thick enough to be effective, but a 100-mm liner may be excessive.Increasing the duct height reduces the attenuation at all frequencies; in order to provide effective attenuation through the 4000-Hz band, the height should not exceed 100 mm.If the cross-sectional aspect ratio of a duct is greater than 10, or the duct is only lined on two opposing surfaces, the attenuation of its fundamental mode is in effect identical to that of a 2D lined duct.Provided that the duct liner and height are such that the silencer is effective at absorbing sound at a given frequency, reducing the aspect ratio towards unity will result in large attenuation gains.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.003 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.001 |
| Bibliometrics | 0.001 | 0.000 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.007 | 0.001 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".