Rock Sounding is a method of underground exploration used by the inhabitants of
Understone. An operator sets up a large device that sends a series of vibrations into the rock, then listens for return signals using a set of sound receivers. The returning echos mean a number of things: rock joints, changes in material, voids in the rock, and so forth - combined, it makes for a rather confusing mess. It takes decades of training for even the most promising student to learn.
Tools of the Trade
There are two tools needed to take a rock sounding: a rock drum and a receiver. A rock drum consists of a large weight suspended from a tripod, and is enchanted such that the weight swings like a pendulum, only faster than it naturally would and not slowed by impact forces. This is placed such that the weight beats against the rock at a steady frequency, creating a consistent vibration in the rock.
The receiver consists of a helmet connected to a set of listening cones akin to the
ear horns made in the
Sleeping Lands through a set of long flexible pipes. The pipes are all about 8 feet long, and the cones mounted on the end magically amplify the sounds without distorting them, making the faint returning signals easier to discern.
Principles of Use
When taking a reading, an operator will first tune the drum to produce vibrations of a specific frequency, and will return to change this frequency several times throughout the process of a full reading, which helps determine the depth of a detected feature as well as providing more information about what it might be. Before using the receiver, the operator has to wait 10-20 minutes to allow the drum to remove any material that the vibrations will knock loose, ensuring a clear signal is being sent out. Then, they move to a position at least 30 feet away (often much further), where a section of wall is smoothed out. The separation minimizes interference from hearing the drum directly, and the smooth wall improves the ability to pick up clear echoes.
When using the receiver, the operator positions the listening cones on the wall in a variety of configurations, providing a complex set of sound signals for them to interpret. A minor enchantment on the cones allows them to stick to the wall when released, which lets the receiver set up several cones for each ear and compare signals - an important step for determining the orientation of the feature indicated by the echoes they listen to.
The full process of taking a sounding ranges takes at least 2-3 days of patient work, depending on the skill of the operator, and for complex signals, often takes much longer.
Social Impact
The development of rock sounding greatly improved the ability to construct artificial passages by indicating portions of weak rock that might collapse as well as natural caverns to be avoided. This allowed for the construction of long, safe
tunnels, connecting cities and other important locales directly, bypassing the dangerous trek through the wilds of the Depths entirely. This made trade and cooperation between cities much more common, and made for easy access to areas rich in valuable minerals and gemstones. It did, however, lead to a steady decline in importance of martial training, as the skills needed to survive in the wild caverns away from the cities became less valuable. The eventual collapse of their civilization, caused by the failure of the
High Magic wardstones, may have been less catastrophic had the martial traditions of their ancestors remained an important part of the community.
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