Studies using the music of Mozart are mixed. If you want to use music to improve your intelligence, look into the recordings that are based on the theories of Alfred Tomatis. Regardless of the type of music, it is the distribution of the frequencies especially the higher frequencies.
Check out the Sound therapy system developed by Patricia Joudry or the SAMONAS (Spectrally Activated Music of Optimal NAtural Structure) CD recordings.
"The Samonas system is a powerful and sophisticated tool for auditory intervention based on the findings and experience of classic music therapy, neurobiological research and understanding of brain functioning.
Somonas combines and represents the knowledge of Nature, Physics of Acoustic Sounds and the development of Psycho-Acoustic Structures relating to all parts of the human organism.
Samonas Sound Therapy comes from the "Klangstudio Lambdoma" of Ingo Steinbach. Steinbach's highly original work should be seen in the tradition of the great Alfred Tomatis, but it extends Tomatis' ideas in several important ways.
Tomatis and Steinbach agree that music's overtones (high-frequency tones that you may not even notice) can profoundly energize and invigorate our ears, brain and total body. But Steinbach stresses the importance of using enjoyable, euphoric, audiophile quality CD recordings, because he found that the brain is more responsive to pleasant sounds.
Feed the brain and body through the ear Steinbach's Sound Therapy entails listening every day - for four weeks to seven months or more - to classical music that is specailly recorded and specially activated via a Steinback Envelope Curve Modulator to include a complex overtone frequency matrix ranging from 5 to 20,000 Hz. Steinback's special CDs feature his own hand-selected musicians, instruments and recording environments, and meticulous production. Heard through high-quality headphones and top-quality equipment, the music has a startling richness. It provides a micor-massage to the middle ear and stimulation to the inner ear, resulting int he specific input the brain needs to process the full range of sound necessary for the brain's development (rather than the limited range in our normal environment). This in turn stimulates full functioning of body and nervous system."
"The astounding effect of this therapy is due to a special treatment of classical music with the newly developed envelope shape modulator of the SAMONAS principle. This process is called Spectral Activation. This ensures that the healing effect of this special music reaches the psychological level of human hearing in the body. The body's own memories are naturally awakened.
Sound Therapy establishes a connection to the echo of the past in which the vibrating energy of sound simultaneously signifies vitality, life energy, and immediate presence. For the individual who wants to use Sound Therapy, it is an instrument for the stimulation and harmonisation of vitality, life energy, and the ability to concentrate. In addition it stimulates creativity and productivity.
The therapeutical applications of SAMONAS Sound Therapy have been practiced for many years. It affects the brain and nervous system directly through the sense of hearing and can be used to improve hearing. It can be used to improve psychological and physical conditions such as hearing, learning difficulties, voice problems and behavioural disturbances which are causally associated with the area of acoustic perception. Some problems, especially by Tinnitus and Stress are helped by listening to the CDs. Spectral Activation of Sounds in the SAMONAS Sound Therapy and the concept of syn-energy"