There are a few main parts that enable one to accurately do this experiment; a sound source, a sound recorder, and an acoustically balanced hall. For my sound source, a simple audio speaker will produce a tone, and for the sound stage, the Tualatin High School Auditorium will be used. The speaker mentioned will be one (1) Alesis M1 Active Studio Monitor. This speaker was chosen for its studio-grade signal to noise ratio, good frequency response, and also for its front-ported design, allowing for the majority of the sound to exit to the front. Because some of the signal will still exit from the sides and the back of the speaker, an additional enclosure will need to be constructed around the speaker, minus the front face, to minimize this loss. The signal to be sent through the speaker will be produced by a tone generator built into the ProTools Professional Hard-Disk Studio Recording System. The signal will have a bit-rate of 24 bit, and a sampling frequency of 48KHz. This is the optimum setting for this system to ensure signal purity. The signal from the ProTools system to the Alesis M1 Monitor will be transferred by Monster 1000 Studio Audio Cable to further preserve signal purity. The decibel measurement will be measured by use of a Neumann TLM 103 series condenser microphone attached to a Manley Voxbox. The Neumann microphone was chosen because a) it was the cleanest microphone available in regards to signal-to-noise ratio, b) it has a large diaphragm, therefore making it extremely responsive at even the quietest sound levels, and c) it has a flat frequency response from 60Hz - 5KHz, making it ideal for this experiment (Neumann). The Manley Voxbox was chosen for its clarity as a powered microphone preamplifier. At +/-1dB 20Hz - 60KHz, it cannot be beat for pre-amp purity (Manley). The response from the microphone will be measured by analyzing the output voltage from the mike-preamp output by a Fluke Multimeter. By using these combinations of ultra-pure signal generators and recording devices, the values for this experiment can be determined at a higher precision level.
To determine the sound pressure based on frequency, distance, and added insulation, the data will be measured in units called decibels. Decibels are the standard "unit for expressing the ratio between two amounts of electric or acoustic power, or for measuring the relative loudness of sounds" (Brit). Decibels originated from the measurement "bels" named after Alexander Graham Bell (1dB = .1 bel). Since the measurement coming from the output on the Manley Voxbox will be in Volts, the equation:
must be used (UCSC, Cirrus). Because background noise will be present; everything from line noise to random noises in the auditorium, the first measurement taken will be without any sound coming from the speaker/tone-generator. This will yield a "reference" voltage to be used for the variable "Voltage B." The measurement for "Voltage A" will be taken directly after the microphone preamp (Manley Voxbox).
Introduction
| Information | Procedure
| Data | Conclusion
| Links | Return to
Research 2001
© Don't even think about copying