Surface Materials
Introduction
Different surfaces will have different effects on a sound. Certain ones are more reflective than others, and some surfaces will absorb much of the sound produced inside a room. The quality of sound absorption of different materials is measured using a standard called the Noise Reduction Coefficient (NRC).
A material's NRC rating is an average of how absorptive it is at the frequencies of 250, 500, 1000, and 2000 Hertz. The ratings are given from 0, being perfectly reflective, to 1, being perfectly absorptive. Any decimal rating is rounded to the nearest 0.05.
Below are a few common materials often found in rooms, and a few reasons why or why not they would be condusive to music from a harpsichord.
Fabric
NRC rating: 0.05
Contrary to our initial thought, fabric actually has a low Noise Reduction Coefficiency, and would be perfectly acceptable for a concert hall, as it would modulate the musical sound.
Glass
NRC rating: 0.05-0.10
Glass is not actually as reflective as it might seem. It is able to absorb some of the sound, but may not be condusive to a harpsichord in terms of its psychological effect on the ambiance of the room.
Plaster
NRC rating: 0.05
Plaster has traditionally been used in châteaus and palaces on the walls of rooms in which the harpsichord was originally played. This material has some absorption, and was decorated with gilded detailings and cornices, as well as paintings and statues. These decorations would not only lend a regal ambiance, but also modulate the sound to provide an even better overtones than one would think.
Wood
NRC rating: 0.05-0.15
Wood is another material that has been used and tested, particularly in the small parlour rooms of the 1800s during the Victorian times. It was here that chamber ensembles played their music for small audiences. Perhaps they knew what was best for the sound empirically, without the benefit of scientific evaluation.
Tile
NRC rating: 0.00
A song sung in the shower may sound good, but for a musical instrument the tile walls would be too reflective, bouncing the notes back without absorbing or modifying any of the sound. This creates too much reverberation in the room and for music creates a microsecond echo of the initial sound, which is not optimal for instrumental music. This eliminates the bathroom as an ideal location for the harpsichord.
Seating
NRC rating: 0.60 (Unoccupied fabric seating)
NRC rating: 0.80-0.85 (Occupied seating)
While unoccupied fabric seats can absorb more than half of a musical sound, occupied seats will absorb almost all of the emitted sound. Ironically, the best venue for a harpsichord would be one with the fewest number of people, even though most musicians would prefer to play to a full house.
Dispersion
"Sound is more pleasing if it is evenly dispersed, with no prominent echoes, no significant "dead spots" or "live spots" in the auditorium. This even dispersion is usually achieved by avoiding any focusing surfaces and avoiding large flat areas which reflect sound into the listing area. Sometimes it is desirable to add some anti-focusing surfaces."
-http://hyperphysics.phy-astr.gsu.edu/hbase/acoustic/arcaco.html#c5
© 2007 Teddy Wing
