The rate of decay is an important measure, as it depicts how fast energy is being ‘spent’, or lost. If energy is released more slowly then it is contained within the mass, which in turn produces a slower rate of decay, or a higher perception of sustain. The amplitude is usually lower when the lost of energy is slow, and higher when the loss of energy is faster. Piano designers are interested in how the mass of the soundboard affects amplitude and decay. The impedance, or resistance to flow of energy through the wood is associated with the capacity of energy to be stored or contained in the vibrating wood of the soundboard, which affects the amount or amplitude of movement, and how much movement occurs over a time which affects perceived sustain.
Soundboard Amplitude:
To maximize loudness, we need to maximize the amplitude of the vibrational response of the soundboard for a given force, a quantity that is described by the frequency response function. 222
That [Stuart] sound board is about 5mm in the centre and tapering out thinner at the edges. Steinway is around 8mm in the centre tapering out to 5mm at the edges in some places. Generally, a tapered board is better and all makers employ variations on this concept. Steinway ribs are massive compared to Stuart so the actual board thickness is only a small part of the soundboard design… Overall mass reduction with high elasticity can increase the dynamic range. Increased stiffness can reduce dynamic range and increase metallic sound. 223
Stuart Soundboard- King William Pine
This species is widely used by Australian luthiers for the construction of sounding boards in musical instruments, for example pianos and violins. King William pine transmits sound at 5,500 metres per second the same as spruce which is renowned as producing the best soundboards for pianos and violins. 224
| Wood type | Thickness | Length | Width kydb | Width | Bass Bridge to rim | |
| Steinway | Spruce | 9-6 mm | 2.69m | 1.52m | 950cm | 25.5 cm |
| Stuart | King William Pine | 7-5 mm | 2.88m | 1.63m | 960cm | 16 cm |
| Soundboard Dimensions Table 3.4 | ||||||
222 Barlow C. Y. 1997. “Materials selection for musical instruments.” Proceedings of the Institute of Acoustics 19: 69-78.1997.
Source: Ulrike G.K. Wegst, “Wood For Sound”American Journal Of BotanyAm. J. Bot93:1369-1378
http://www.amjbot.org/content/93/10/1439.full.pdf ,accessed October 1, 2006.
223 Wayne Stuart email interview with author, 4th April, 2012.
224 Australian Timbers and Musical Instruments,
http://fennerschool-associated.anu.edu.au/fpt/nwfp/musicaltimbers/musicaltimbers1.html,
Australian National University,1998. (accessed 27.11.13).
