RECORDED MUSIC THE VINYL RECORD ALBUM I. Overview One of the first successful, mass-produced methods of storing and playing-back music is the vinyl record. Developed in the early 1900 s they are a direct descendent of the work of Thomas Edison (1877 recording on tinfoil cylinder!) and Emil Berliner (1887Gramophone = flat discs with spiral grooves!!). We have been discussing these vinyl records in class, observing their size, design and performance. In this lab experiment you and your partner will attempt to measure just how long, in meters, the wobbling Data Spiral Groove really is on an LP (Long Playing!) record album. II. Materials and Procedure Obtain the following materials from your instructor: Sample LP vinyl Record Album Sample (small piece) of the wobbling groove data spiral Microscope Slide Small piece of clay Metric Ruler Stereo Viewer Microscope Follow the procedure outlined in Part A and B. PART A As discussed in class, the sound data is recorded into the vinyl plastic as a wobbling Data Spiral Groove from the inside of the record to the outer rim. As you inspect the record notice the small gaps in the groove pattern. This is simply a space between songs. If you wanted to play a particular song (rather than just start from the beginning) you had to visually place the needle (be careful!!) onto the record in the correct location. The narrow gaps gave the user at least a reasonable chance to hit the start of the chosen song! Also notice you can feel, with a gentle touch, the actual Groove and to a good pair of eyeballs, you can see the Grooves themselves. The Grooves, however, are too narrow and too close together to see and measure accurately without magnification. Measuring the Data Area Using the Metric Ruler, measure the distance, in centimeters, from the center of the album to the place where the spiral groove starts. Record this as R s = cm. Now measure the distance, in centimeters, from the center of the album to the place where the spiral groove finishes. Record this as R f = cm. 1
The difference in the areas of these two circles represents the total area of recorded data on the Album. Use the pre-lab notes to calculate the total data in cm 2. Show your calculations with units here: Measuring the Groove Width, Depth and Pitch Place the small piece of clay onto the microscope slide. Then place the small sample of Vinyl Record on edge (@ 90 to the microscope slide) so that you will be looking at the side-view (called cross-section) of the Record Album. In this orientation, it is much easier to see the features of the data Groove. Position the slide/sample under the Stereoviewer Microscope and focus for clarity. Using the internal measuring scale and referencing the pre-lab notes, measure these three dimensions: Groove Depth, Z = cm Groove Width, X = cm Groove Pitch, P = cm Make these measurements carefully and repeat them several times until you and your partner are confident that the numbers you are writing down are correct. Be especially careful in measuring the Pitch, P. Pitch is not the width of the Groove. Pitch is the distance between successive Grooves!! Best technique would be to measure the total distance between, say, 10 Grooves in cm, then divide your measurement by 10 to get the actual Pitch distance in cm. Since this Pitch measurement is going to be used in a later calculation, measure it as carefully and accurately as you can. 2
Calculations Referencing the pre-lab notes and your data, calculate the Total Length, in meters, of the Spiral Data Groove on the Record Album you are studying. Show all your calculations with units here: Follow-up Questions 1. List some problems you see with this technology, i.e. given the way these records are designed what are some practical problems you see? 2. What is going to happen over time as the record is played over and over, each time dragging a diamond-tipped needle through the grooves to pick up the data vibrations? 3. What do you think will happen if this record gets damaged with a scratch particularly one that cuts across (i.e. perpendicular to) the grooves? 4. Can a CD or DVD be made to skip? How? How is it prevented in modern CD/DVD systems? 5. This Record Album is to be played at (an angular speed of) 33-1/3 RPM (and that speed does not change during the playing of the album!). What does RPM stand for? So what does this speed actually mean for the rotation of this Record Album? 3
6. TRUE or FALSE: (circle one) All parts of the Record Album rotate with the same angular speed. 7. TRUE or FALSE: (circle one) All parts of the Record Album rotate with the same linear speed. 8. Given the answers to questions #6 & #7, is the tracking speed (i.e. the actual linear speed in m/sec of the Needle in the Groove) faster at the beginning of a song or at the end of that song? Error Analysis Briefly comment on possible error sources in PART A of this lab and what you and your partner did to minimize their impact on your results. PART B Design a simple experiment in which you and your partner can calculate the Total Length of the Spiral Data Groove, in meters, in a different way. Here are a few clues to guide your thinking: Angular Speed of Record = 33-1/3 RPM ( it is constant!) Tracking Speed (speed of Needle in Groove in cm/sec, and it varies!) Total Playing Time of Record Album = seconds Prepare a short outline of your method/intended calculations and show them in the space below: Be prepared to explain your method to your instructor in class tomorrow. After your method is approved by your instructor, proceed with the: 4
Measurements/Calculations and Compute 1. The linear speed, in m/sec, of the Needle when the Album begins to play. 2. The linear speed, in m/sec, of the Needle as the Album finishes playing. 3. The Total Length of the Spiral Data Groove, in meters. 4. How close is #3 to your answer in PART A? Compute meters and % difference as compared to PART A. Follow-up questions 1. If it is indeed true (it is!) that the Record Player (sometimes called the Turntable or Phonograph ) Needle actually does increase in linear speed continuously as the song plays, why does the song not sound speeded up the longer it plays? 2. The manufacturers of the Record Player Needle used extremely hard metals like Stainless Steel or Tungsten Carbide or even tipped the metal with a tiny chip of diamond to keep the Needle from wearing out too fast. Obviously this wore the heck out of the Album Grooves. List some 5
ideas that the Record Album and Record Player companies might try to keep the (vinyl plastic) Albums from wearing out too fast. 3. If a 33-1/3 RPM Album is played instead at an angular speed of 45 RPM, comment on what the resulting music/voices will sound like. 4. Now suppose and old 45 Record Single (i.e. a single song recorded at 45 RPM, not a group of songs like on an Album) is played at 33-1/3 RPM. Comment on what the resulting music/voices will sound like. 5. Does this old Vinyl Record Album technology bear any resemblance at all to the modern Digital Compact Discs (CD/DVD) technology we are surrounded by today? Error Analysis Briefly comment on possible error sources in this lab and what you and your partner did to minimize their impact on your results. {Your calculation in #3 (Total Length of Spiral Data Groove) should be similar to your results (but likely not exactly the same) as your results from PART A. Be sure to comment on what factors may have contributed to getting a (slightly?) different answer.} 6