1. Loudspeakers stuart.jones3@southwales.ac.u k www.stuartjones.org

2. Agenda 1. History 2. Basic Design 3. Acoustic Wave Propagation 4. Impedance 5. Power 6. Sensitivity 7. Distortion 8. Frequency Response 9. Speaker Positioning 10. Studio Classics 11. References 3. History 4. Alexander Graham Bell Oliver Lodge History 5. Basic Design 6. Basic Design Components Gasket Dust Cap Cone Spider Basket Top Plate Voice Coil Core Magnet Back Plate 7. Basic Design Components A loudspeaker works on the basis that like charges repel and opposite charges attract and when current flows through a conductor, a magnetic field is produced around it. There are two important components in a speaker that cause movement: 8. Basic Design The Voice Coil and Magnet Voice Coil MagnetCore 9. Basic Design Components The voice coil and a magnet. The voice coil is a long winding piece of copper than is rapped around a circular drum called a core. The voice coil is suspended above the centre of a large magnet with the end of the voice coil attached to terminals on the basket. 10. Basic Design The Voice Coil 11. How Stuff Works Deconstructed - How Speakers Work Basic Design The Voice Coil 12. Acoustic Wave Propagation 13. Uniform PipeDiaphragm at rest Pressure is uniform everywhere in the pipe Pressure Distance P0 Acoustic Wave Propagation 14. Diaphragm moves forward Pressure increases in front of the moving diaphragm Pressure Distance P0 Acoustic Wave Propagation 15. Acoustic wave propagates away from diaphragm at speed of sound, even though the diaphragm has stopped. Pressure Distance P0 X=ct c Acoustic Wave Propagation 16. The job of a loudspeaker is to set up vibrations in the air which are acoustic representations of the waveforms of the electrical signals that are being supplied to the input terminals. A loudspeaker is therefore an electro-mechanic-acoustic transducer. Acoustic Wave Propagation 17. Impedance 18. Impedance It is an electrical measurement of a loudspeaker's resistance; its opposition to the flow of electric current (the audio signals) from your amplifier through your speaker cables to the speaker drivers and the fine wire in the driver voice coils. Similar to the way water pressure (voltage) forces the water (current) through a hose. If you have a narrow hose (a high impedance), not as much water (current) flows. Use a larger diameter hose (lower resistance) and more water (current) flows. 19. Impedance Acoustic Impedance Acoustic impedance can be thought of as a quantity that expresses how difficult the air is to move. A low value of impedance tells us that the air moves easily in response to an applied pressure (low pressure, high velocity), and a high value of impedance tells us that it is hard to move (high pressure, low velocity). 20. Impedance Mechanical Impedance Mechanical impedance is directly equivalent to acoustic impedance, but with pressure replaced by force (pressure is force per unit area) A low value of impedance tells us that the current moves easily whereas a high impedance restricts the flow of current to the speaker. 21. Impedance Manufacturers Specification We measure impedance in "ohms," named after George Ohm, the German physicist. Manufacturers of loudspeakers give us a nominal impedance of 4,6,8 ohms as this is the dominant characteristic. 22. Impedance 1. Electrical impedance is the reluctance for alternating current to flow in a voice coil. 2. Mechanical impedance is the physical opposition of the speaker cone or diaphragm to move. 3. Acoustic radiation impedance which refers to how efficiently the speaker moves air. 23. Power 24. Power Manufacturers Specification Power is just the maximum power a loudspeaker can theoretically handle without damage. Rather more important to those doing live sound than studio sound. 25. Sensitivity 26. Sensitivity Speaker sensitivity is a measurement of the amount of sound output derived from a speaker with one watt of power input from an amplifier. 27. Sensitivity Measuring Sensitivity 1 Meter 1 Watt (2.83 volts) Speaker sensitivity will generally be given as a SPL measurement taken at 1 meter on axis with a 2.83 volt input (1 watt @ 8 ohms). dB SPL Meter Speaker Reference Microphone 28. Sensitivity Loudspeaker Specification 29. Distortion Total Harmonic Distortion 30. Distortion Total Harmonic Distortion When an audio signal is passed through a component, unwanted harmonic frequencies that were not present in the input signal are generated and added to the original signal producing what is known as harmonic distortion. 31. Distortion Total Harmonic Distortion THD is typically given as a percentage (1%THD). Distortion in frequencies away from those most sensitive to our ears (~1kHz) will be not nearly as evident to the listener as distortion in frequencies that are. This means that 1% THD could sound much less distorted than 0.01% if the distortion occurred favourably. 32. Distortion Manufacturers Specification With the speaker outputting 90dB @ 1 meter THD = 2nd harmonic 3rd harmonic 33. Frequency Response 34. Frequency Response Manufacturers Specification Often, Manufacturers give frequency response simply as two extreme high and low frequencies. 35. Frequency Response A simple claim of frequency response that cites two frequency extremes unqualified by a dB specification (as with the specification given regarding sensitivity) is meaningless. It may mean that although the speaker responds at 40Hz (the cone moves a bit, perhaps) nothing will be audible because the speaker's response at 40 Hz is at - 30 dB and inaudible! 36. Frequency Response On the other hand, if the frequency response is given as 40Hz - 24kHz +/- 3dB, this indicates that every tone that emerges from speaker will be within 3 dB of the entire frequency range. However, manufacturers often use different methods of measuring frequency response, because there are still no universally accepted standards. 37. Crossovers 38. Crossovers There are two kinds of crossover: passive and active. Crossovers separate the signal into component frequencies which are routed to individual drivers. Separating the frequencies allows the drivers to be more efficient and protects them from being overdriven. 39. Crossovers However they are implemented, crossovers have the same basic job to do. The audio spectrum must be split up into two, three or (rarely) four bands, with appropriate crossover frequencies and filter slopes so that they recombine properly in the air in front of the loudspeaker. The roll-off rates must be fast enough to avoid exciting response inaccuracies that occur outside the intended frequency range of the unit; for example the bass filter output must drop fast enough as frequency increases to avoid exciting the resonance of the mid- frequency drive unit. 40. Crossovers Passive Amplifier Passive Crossover Input HF LF Passive crossovers deal with the signal after it has left a single power amplifier, and must therefore be able to handle large voltages and currents. Cabinet 41. Crossovers Active Amplifier Active Crossover Input HF LFAmplifier An active crossover uses a separate power amplifier for each driver unit, and the division of the audio spectrum is done before these amplifiers, using circuitry working at preamp signal levels. Cabinet 42. Crossovers filters { { { Crossover region LF pass band HF pass bandknee crossover point crossover frequency dB Hz Crossovers filters 43. Speaker Positioning 44. 90 90 1.5m - 3m 50cm 50cm 50cm50cm Mixing/Listening Position Sweet Spot 30 30 45. Speaker Positioning Speaker placement depends greatly on the room geometry. For example, a rectangular room will require different placement from a room with more complex floor plan. Exact placement depends on room acoustics, speaker type, and listener preference. They should be placed no less that 50cm from a boundary wall (especially from a rear wall if the speakers are rear ported) 46. In their 1980 paper, Davis and Davis specified that there should be . . . an effectively anechoic path between the monitor loudspeakers and the mixers ears. Davis, D. and C. Davis, Sound System Engineering, 2nd ed., Howard W. Sams, pp. 168169, 1987. Speaker Positioning 47. The front speakers (particularly the tweeters) should also be placed at approximately ear level when seated and aimed at the listening position. Speaker Positioning 48. Speakers placed too wide will loose their centre image. Speaker Positioning 49. Studio Classics 50. The first compact monitor to see widespread use in recording studios was the JBL 4311, a 3-way design introduced in the late 1960s. Studio Classics 51. Auratone cube, has a single 5-inch speaker. Studio Classics 52. Yamaha NS -10M Studio Classics 53. Loudspeaker Specification Do I have stands? These will prevent bass from leaking out. Is my amplifier good enough or is it a weak link in the chain? Perhaps the most important factor of the quality of the speaker? Am I happy to have a crossover frequency in such a noticable frequency band? Does the impedance match with my amplifier? Is this large enough to move the air in front of my speaker? 54. References Books Self, D., Audio Engineering Explained, Focal Press, 2010, U.S Everest, Alton F. & Polmann Ken C., Master Handbook of Acoustics, Fifth Edition. Mc Graw Hill, New York Dickason, V., Loudspeaker Design Cookbook, Audio Amateur Press, 2006, U.S Borwick, J., Loudspeaker and Headphone Design, Focal Press, 2001. U.S Toole, F., Sound Reproduction. Loudspeakers and Rooms, Focal Press, 2008, U.S Davis, G & Jones, R., The Sound Reinforcement Handbook, Hal Leonard Publishing, 1989, U.S Ballou, G. Electroacoustic Devices: Microphones & Loudspeakers, Focal Press, 2009, U.S Web Rybak, James P, Oliver Lodge: Almost the Father of Radio, http://www.antiquewireless.org/otb/lodge1102.htm(accessed Feb 2012) Understanding Loudspeaker Sensitivity http://www.goodsound.com/features/2008_02_01.htm Total Harmonic Distortion http://www.bcae1.com/thd.htm What Is THD? http://stereos.about.com/od/stereoscience/qt/whatisTHD.htm Loudspeaker Specification Explained http://www.hifipage.com/loudspeaker-specifications-explained-11/ Speaker Impedance and Ohmshttp://www.ecoustics.com/electronics/products/articles/556241.html Historic Timeline http://www.emolabs.com/images/timeline.swf Good Reference, Brain Knave, Electronic Musician, 2001. http://www.drbraukmann.com/DESN385/reading/StudioMonitorsArticle.pdf 55. References (cont) Video and Animation How Stuff Works Videos Deconstructed How Speakers Work, You Tube http://www.youtube.com/watch?v=3qA5315XTb8 (accessed, Feb 2012) Woofer Animation. You Tube http://www.youtube.com/watch?v=3ZQqCyRQFB4 (accessed, Feb 2012) Papers Toole, F.E., Loudspeakers and Rooms for Stereophonic Sound Reproduction, Proc. AES. 8th Intl. Conf., Washington, D.C., pp. 7191, 1990. Davis, D. and C. Davis, Sound System Engineering, 2nd ed., Howard W. Sams, pp. 168169, 1987.