A sound investment is an investment that will yield a good return. It can refer to a variety of investments, such as a MICROPHONE (10 letters), STEREO (6 letters), amp (3 letters), YACHT (5 letters), RECEIVER (8 letters), and hifi (4 letters). A MICROPHONE is a device used to capture sound waves and convert them into electrical signals. A STEREO is a device that produces sound from two or more independent audio channels. An amp is an electronic device that increases the power of a signal. A YACHT is a large, luxurious boat. A RECEIVER is a device that receives and decodes signals from a transmitter. Finally, a hifi is a high-fidelity audio system that reproduces sound with a high degree of accuracy. All of these investments can be considered sound investments, as they can provide a good return on investment.