Why does koto feel crisp and kiri feel soft? The answer lies in wood density, cell structure, and how vibration travels through each species.
# Module 3 — Wood Science: What Makes One Species Different
Every wood species has a unique density, fibre orientation, and cellular structure.
These physical properties directly determine how a blade responds to ball contact.
## Vibration Frequency — The Measurable Metric
When a ball strikes a blade, the entire structure vibrates. Researchers at
Institut National des Sciences Appliquées (INSA Lyon) have measured this in
peer-reviewed studies:
> "Vibration modes and frequencies can be modelled from ply construction —
> number of plies, wood species, and thickness. Carbon fibre has a higher
> vibration frequency than wood."
> *(Manin, Poggi & Havard, 2012; Yıldızbaş et al., 2022)*
### Hz Reference Scale (Approximate Community-Measured Ranges)
| Blade Type | Approx. Hz | Feel |
|-----------|-----------|------|
| Very soft defensive 5-ply | ~600–900 Hz | Maximum dwell, maximum touch |
| Standard 5-ply all-wood | ~900–1,100 Hz | Balanced, classic feel |
| Stiff 7-ply all-wood | ~1,000–1,200 Hz | Controlled power |
| Inner composite (ALC/ZLC inner) | ~1,200–1,500 Hz | Wood feel + speed boost |
| Outer carbon / TriCarbon | ~1,600–2,000+ Hz | Maximum speed, direct feel |
*TB ZLF (Butterfly): 1,400 Hz measured by player on Revspin.net — confirms this scale.*
## Why Species Behave Differently
Dense wood species (koto, walnut) resist deformation — they transmit energy directly,
giving that crisp surface feel. Low-density species (ayous, kiri) absorb more
energy through cellular compression, extending dwell time.
Hinoki is unique: despite being lighter, it has high elastic energy storage.
The ball compresses the wood slightly, then springs back — this is the "pingy"
resonance hinoki users describe. It is fast not from hardness but from
stored-spring rebound.
## Thickness is an Independent Variable
> ⚠️ Often overlooked: blade thickness affects stiffness *independently* of ply count and species.
> A thin 5-ply (5.5mm) and a thick 5-ply (6.5mm) of the same species will play differently.
> The thicker blade is measurably stiffer, faster, and has less dwell.
> *(Source: Tibhar Stratus Power Wood reviews, Revspin.net: "The thickness gives it umph")*
**Rule of thumb:** Same ply species + greater thickness = higher Hz = stiffer blade.
Natural wood variance also means two specimens of the same blade model can differ
meaningfully in weight and feel. DHS Chinese pro blades are specifically noted
for batch variance in the community.