The construction of an acoustic guitar's top is the single most important aspect in determining the quality of the sound the guitar will produce. Acoustic guitar tops are made either of solid pieces of wood or of laminated wood, with several thin plies of wood glued together.
Spruce Top Guitars
Usually the term "spruce top" means that the top of the guitar is constructed of laminated plies of wood. Often, only the top layer is spruce, with less costly woods making up the layers underneath. Advantages of laminated top guitars include their lower cost and relative durability. Since laminated top guitars are sturdier than solid top guitars, they may be a better choice for younger players or for outdoor use. Laminated guitar tops are less sensitive to potentially damaging changes in humidity than solid tops are.
Solid Top Guitars
Higher-end acoustic guitars tend to be of the "solid top" variety. Solid top guitars vibrate much more freely and thus have better tonal quality over a wider dynamic range than guitars with laminated tops do. Solid top guitars also have the desirable characteristic of sounding better the more they are played since the top vibrates more and more freely over time if it is played on a regular basis.
Determining the Type of a Guitar's Top
Probably the best way to determine whether a particular guitar has a laminated top or a solid top is to angle it so that you can see the wood grain on the edge of the soundhole. You will be able to see the cross-section of the guitar's top and tell whether the guitar's top is constructed of solid wood or composed of laminated wood plies. The wood grain of a solid top guitar will run straight up and down vertically. Laminate tops will have seams between each layer of wood that are parallel to the top.
The Buying Decision
Several considerations will influence a buyer when deciding whether to buy a spruce top or a solid top guitar. Higher-end solid top guitars usually cost $500 or more. They will usually sound better and be easier to play. Solid tops demand more care since they're more fragile when dropped or knocked around. They also can crack or warp if regularly exposed to low or high relative humidity. Spruce top guitars vary in the quality of tone they produce. Folks on a budget can find a relatively good-sounding spruce top guitar at an affordable price if they shop around.