As concerns about global warming increase, carbon emission reduction has become an important task facing mankind [1, 2]. In 2015, The Paris Agreement was reached at the United Nations Framework Convention Climate Change (UNFCCC) in Paris, hosted by UN Secretary-General Ban Ki-moon. The Paris Agreement proposes maintaining the average global temperature rise below 2 °C and strives to not exceed 1.5 °C .
In line with this, the Korean government announced that it would move forward to become ‘carbon neutral’ by 2050. As an interim goal for carbon neutrality in 2050, Korea submitted its Nationally Determined Contribution (NDC) to the UNFCC, aiming to reduce greenhouse gas emissions 40% by 2030 compared to 2018. .
Expanding the use of wood is a crucial task in moving toward carbon neutrality. Wood requires low energy to manufacture and process, and discarded wood can be used as an energy source. Thus, wood is a sustainable, cyclical resource that can be used indefinitely [4, 5] and has been a popular eco-friendly material in construction, furniture, and musical instruments from the past to the present [6,7,8,9,10,11].
Recently, noise pollution has haunted as a weighty environmental problem. Raising recognition of the health effects of noise has accelerated the widespread interest in sound-absorbing materials [12, 13].
Among the various uses of wood resources, there are various studies on the use of solid wood and wood by-products as sound-absorbing materials. Thin wood panels have a plate vibration-type sound absorption effect . Perforated wood paneling acts as a resonant sound absorber. It is possible to absorb sound according to the noise frequency by adjusting the diameter and frequency of the perforations and the size of the air back cavity [15, 16].
Also, wood cross-sections can be used as porous sound-absorbing materials. Sound absorption effects are better in a broadleaf tree cross-section with developed vessels than in a conifer cross-section made of tracheids . As for the effect of pore structure on sound absorption, diffuse-porous wood with high through-pore porosity without large pore size is more advantageous than ring-porous wood [12, 18, 19]. Depending on the area, sapwood has better sound absorption than heartwood. The reason is that heartwood has developed tyloses, which interfere with the absorption of sound waves [17, 20,21,22].
Ring-porous wood also has sound-absorbing effects. A cross-section of ring-porous wood is not a very good sound-absorbing material; however, it can be used as a resonance sound-absorbing material if used concurrently with a backside air back cavity. The longer the distance of the air back cavity, the better the sound absorption capability at low frequencies [23, 24].
Forest by-products, such as tree bark, wood chips with sawdust, and bark panels, can be excellent sound-absorbing materials. In addition, many researchers have recently studied the sound absorption capabilities of natural cellulose materials, such as kenaf, coconut, hemp, straw, granular cork, broom fibers, and date palm waste [25,26,27]. Among them, this study focuses on forest by-products as eco-friendly, sound-absorbing materials.
Kang et al.  investigated the sound absorption capabilities of wood bark particles with different thicknesses and densities by crushing wood bark from five types of conifers and 1 type of broadleaf tree. It was shown that the sound absorption coefficient increased as the thickness of the impedance tube containing the wood bark particles increased. The most effective sound absorber was made of Hinoki (Chamaecyparis obtusa (Siebold & Zucc.) Endl.) bark particles (100 mm thickness) and had an average sound absorption coefficient of 0.90 at 100–6400 Hz.
Boubel et al.  reported the sound absorption capabilities of wood chips and sawdust depending on the particle size. The results showed relatively better absorption coefficients at 1.25–2.5 mm, 0.63–1.25 mm, and 0.31–0.63 mm, whereas 5–8 mm and above and 0.16–0.315 mm grades had the lowest sound absorption efficiencies. Redwood particles sized 1.25–2.5 mm showed the best sound absorption capability.
Tudor et al.  manufactured larch bark panels by adjusting density, particle size, and particle orientation (perpendicular and parallel) parameters and investigated their sound absorption capabilities. The noise reduction coefficients (NRCs) of the larch bark panels were 0.1–0.3 (for 30 mm particle thickness) and 0.15–0.5 (for 60 mm thickness).
Jang  examined the sound absorption capability of pine (Pinus densiflora) pollen corns using ISO 10534-based impedance tubes. Their optimum sound absorption coefficient was 0.586 at 740 Hz, found at 12 cm particle thickness. Their NRC reached 0.305 at 6 cm thickness and 0.517 at 12 cm thickness.
Pine cones are the fruit of a pine tree and are the shell after the pine tree seeds have been blown away. Recently, there have been various studies to utilize them, such as using them as flocculants for water purification , biocarbon , and anti-inflammatory agents . However, there are few studies on the use of pine cones as sound-absorbing materials. This study may outline a new approach to utilizing pine cone particles as an eco-friendly sound-absorbing material.
So, this study investigated the sound absorption capability of pine cone particles. In order to contribute to the creation of high added value forest by-products, this study intends to propose pine cones as one of the candidates for eco-friendly, sound-absorbing materials.