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Sound Reproduction

  • H4-66: CROSSOVER NETWORK - LARGE ADVENT

    H4-66
    Show circuit and components of a passive crossover network and how the crossover network functions.
    A crossover network was taken from an old Large Advent loudspeaker system which was destroyed in a steam bath. The components have been mounted on a plastic base to which a loudspeaker can be attached and into which a signal may be input. A signal such as the sine wave from an oscillator is input into the network, its frequency adjusted, and the loudspeaker switched between the woofer and the tweeter position in the circuit, demonstrating how the crossover network directs various frequencies into the appropriate loudspeaker.
    H4, ME3

  • H4-67: CD WITH HOLE

    H4-67
    See if a compact disc will play even if it has a small hole drilled through it.

    According to the theory of the compact disc, the Cross Interleave Reed-Solomon Code (CIRC), in which the data are impressed on the disc, is coded so as to override certain types of localized damage to the disc, correcting for so-called burst errors. This is done so as to avoid playback problems as the disc ages and gets a bit scratched up.

    Being scientists, we decided to check this by drilling holes in a compact disc to see if it would still play. It did not take long to find a CD in which it was imminently worth drilling a hole: a bunch of hackneyed overtures by Rossini. Did it work?

    It sure did!! The CD played right past holes of 0.0083" (0.2mm), 0.0135" (0.34mm), 0.021" (0.53mm), and 0.032" (0.8mm), and only sometimes gave small clicks for a hole of 0.062" (1.55mm). A 0.118" (2.95mm) hole really did the job, causing large clicks and skipping. This can be heard on the CD, Track 2 (William Tell Overture) as repeated brief skips beginning at about 0:48, clicks at about 3:25, and major, repeated skipping just after 4 minutes.
    H4, FS1

    h4-67ah4-67b

  • H4-68: MP3 COMPRESSION

    H4-68
    Play and compare various MP3 compressions of a short musical CD excerpt.
    "Were diu werlt alle min," a 50-second piece from Carmina Burana by Carl Orff (1895-1982) has been compressed by an MP3 program to several bitrates: 224 kB/s, 56 kB/s, 40 kB/s, 24 kB/s, 18 kB/s, and 8 kB/s. A nice way to do the experiment is to play the samples in order of decreasing bitrate and ask your students to listen for any degradation in sound quality. The words of the piece, translated from medieval German into English, are: "If all the world were mine from the sea to the Rhine, I would give it up to have the Queen of England lying in my arms." Some things to look for as the sound deteriorates include: 1. trumpet tone quality in opening fanfare. 2. clarity of the voices. 3. full sound of the timpani. 4. fidelity of the crashing cymbal.
    H4, FS1

    h4-68a

  • H4-81: AUDIO CART - COMPLETE AUDIO SYSTEM

    H4-81
    Show the various components of a reasonably modern audio system.
    This audio cart is a permanent Lecture-Demonstration setup consisting of : (1) a 60 Watt per channel integrated audio amplifier, an audiocassette deck, a compact disc player, and a pair of Large Advent loudspeakers. Use it to show what these components look like, or obtain some of our vast library of recordings to play, and illustrate what it sounds like. Play a recording of Tuvan throat singers and really baffle them. A number of standard demonstrations make use of this audio cart systen.
    FS1

  • H4-92: AUDIO RECORDING - DIGITAL DOMAIN DEMONSTRATION CD

    H4-92
    Examples of early digital sound reproduction.
    Compact disc with audio system.

  • J7-24: BARKHAUSEN EFFECT

    J7-24
    Demonstrate flipping of magnetic domains in iron.
    A soft iron wire is positioned in the core of a large coil. The coil is attached across the microphone input of an audio amplifier, which in turn is connected to a loudspeaker. Hold the iron core fixed as you bring a small magnet near one end of the wire. Magnetic domains flip into alignment with the applied magnetic field as the magnet comes closer and the field increases. When a domain flips, it emits a short electromagnetic pulse which is picked up by the coil as a spike and heard as a click on the loudspeaker. To make the experiment more convincing, do it with a piece of copper wire and without any wire at all in the coil.

  • K5-02: PIEZOELECTRIC CRYSTAL - AUDIBLE

    K5-02
    Demonstrate that a piezoelectric crystal converts electrical impulses into physical vibrations.
    An audio frequency electrical oscillation from an audio oscillator (in this case a 3 KHz sine wave, generated by the oscillator shown at left above, and fed through an audio amplifier) is converted into a sound vibration by the piezoelectric crystal in the center of the mechanical apparatus at right above. This is a commonly technique commonly employed for creating ultrasound.