Lecture 27 Electricity & Applications toMusic

Probe the Class OP

Last time we looked at some electrical circuits We identified charge. We identified charge. Current is the charge per unit time that passes through a point of a “circuit”. Current is the charge per unit time that passes through a point of a “circuit”. The current increases with the voltage across a “resistor” such as a light bulb. The current increases with the voltage across a “resistor” such as a light bulb. –The brightness of the bulb depends on the current through it. We used OHM’S LAW We used OHM’S LAW –Voltage (volts) = Current (Amps) x Resistance (ohms)

Mr. Ohm’s Legislation

200 Watts 60 Watts

POWER Let’s move a charge q from one side to the other in a time “t”. Let’s move a charge q from one side to the other in a time “t”. V=work/charge V=work/charge Work we do = qV Work we do = qV Power = qV/t Power = qV/t i=q/t i=q/t Power = iV Power = iV ViVi Resistance = R

More on Power through a Resistor R is fixed, so more power = more current = more light!

The USA at night. LOTS OF BULBS!

Will the bulb in (a) be brighter, dimmer, or the same brightness as any one bulb in (b)? Which bulb in (b) is the brightest? What would happen if one of the bulbs in (b) burned out?

A Magnet S N +Q OP Survey

Magnets - Summary Magnets Do NOT attract chages. Magnets Do NOT attract chages. Magnets have N and S poles Magnets have N and S poles Like poles repel Like poles repel Unlike poles attract Unlike poles attract

Other Observations A magnet moving into a coil produces an electric current (and voltage!). A magnet moving into a coil produces an electric current (and voltage!). There is a “magnetic field” around a wire. There is a “magnetic field” around a wire. A loop of wire acts like a small magnet. A loop of wire acts like a small magnet. A wire moving near a magnet will have a current generated in it. A wire moving near a magnet will have a current generated in it.

The Dynamic Microphone V The VOLTAGE is passed on to the next part of the circuit

Dynamic Microphones The Voltage is the audio signal. Dynamic microphones are extremely rugged and may be the most widely used microphones in television production. They are relatively in­expensive (for professional ‑ quality microphones) and usually have good frequency response. They tend to be somewhat less sensitive to high ‑ frequency sounds than are condenser microphones

They Come in all Colors too!

Condenser Microphones Add a Resistor to get the Voltage

Electrets Both plates are electrically charged, and sound hitting the faceplate causes a change in voltage. Electret condensers are a popular type of condenser microphone. Electrets are manufactured with a permanent electric charge in the capaci­tor and therefore require the use of only a very small battery as a power source to boost the output signal of the microphone to a usable level. As a result, electret condensers tend to be significantly smaller than other con­denser microphones.

Different strokes …

Bigger is Lower! Frequency Response

Directionality

“Stereo” Microphone

The Process We Are Looking At Sound Production Microphone conversion to electrical signal Amplify the Voltage Loud Speaker of some type LISTENER

Amplifier IN out SLIGHT TURN

The Simple Transistor Amplifier (Bipolar)

The Voltages NOTE SCALE DIFFERENCES

Don’t push an amplifier too hard

The Speakers … all kinds

Exploded View

Comments A speakers maximum response is at resonance. A speakers maximum response is at resonance. The heavier the structure, the lower the resonance frequency. The heavier the structure, the lower the resonance frequency. –In order to cover the entire audio range we need multiple speakers.  Woofer/Sub-Woofer for low frequency  “Tweeter” for high frequency  Mid range speakers as well.

Frequency Ranges for different types of speakers.

Another Music Application

Multiple Sources of Sound

The Strings

The “Package” The Instrument A Combination Amplifier and Speaker

Next Step (If We Get To It) The “new Electronics The “new Electronics The Digital World The Digital World Compression Compression The CD to the IPOD The CD to the IPOD