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Debate about speakers

  1. Oct 18, 2006 #1
    Me and my roommate are having a debate about how speakers work... He says that speakers use ohms, he came to this conclusion after the guys at best buy told him that his speakers "didn't have enough ohms"

    I said that speakers use volts not ohms to work, and that the ohms are just a property of the speaker that transferes the energy into the energy in the sound wave...

    who is right? please be as thorough as possible...
     
    Last edited: Oct 19, 2006
  2. jcsd
  3. Oct 18, 2006 #2
    Speakers use current to operate.

    Because the speakers have an impedence (measured in Ohms) (and because you change some energy to sound) the speakers require a voltage to operate.
     
  4. Oct 18, 2006 #3

    russ_watters

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    Voltage is the force, current is the quantity of charge transferred, and impedence is the resistance to that flow - and it is a physical property of the speakers.
     
  5. Oct 19, 2006 #4

    Danger

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    As quinn and Russ said... speakers don't work on ohms; they create them due to their internal resistance. Tell your roommate that he has to do the dishes for the next month to atone for his blunder.
     
  6. Oct 20, 2006 #5

    Meir Achuz

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    The guys meant that the resistance (in ohms) of the speaker should be the same as the effective resistance of the amplifier for best performance.
    This is called "impedance matching". The standard amplifier impedance is usually 8 or 16 ohms, which the speaker should match.
     
  7. Oct 20, 2006 #6

    turbo

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    Yes, solid state amps can tolerate higher-than-optimum impedance loads (including running into an open no-load condition), but not lower-than-optimum, which can burn out the output transistors. In contrast, tube amps can run into dead shorts without crapping out, though their efficiency is best if you run them into the impedance for which they are designed. Years ago, I saw my neighbor (a young guy) taking a big Sansui integrated amp out of his car, and I asked what he had bought. He explained that this was his third amp - the previous two had failed right after he turned them on. Curious, I went into his apartment, and he had speakers in about every room. The problem was that he was making lots of parallel connections, reducing the effective impedance. The sales guys at the discount store should have known enough not to give him a second "replacement" amp without asking some probing questions.
     
  8. Oct 20, 2006 #7

    berkeman

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    Here's plenty more info from wikipedia.com

    http://en.wikipedia.org/wiki/Loudspeaker
     
  9. Oct 21, 2006 #8

    rcgldr

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    8 ohms might be common for cheaper receivers, but the better ones and power amplifiers can work with 4ohm speakers. Thre are power amplifiers that can work with 2ohm speakers.

    What wasn't made clear hear is that speakers convert electrical power (watt = volt x amp) into sound power, based on their efficiency. Power (watts) is also equal to voltage^2 / ohms or amps^2 x ohms.

    Although effeciency is desirable, some of the ways of improving efficiency sacrifice sound quality, like poorly ported systems. Most high end speakers are less efficient but more accurate and less power sensitive (many speakers respond to higher volumes by increasing base response more than mid and high range response) than medium quality speakers.
     
  10. Oct 21, 2006 #9

    DaveC426913

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    Speakers operate by electromagnets. The current applied to the electromagnet will cause the diaphragm to jiggle in and out, producing sound.

    The ohms are an indication of how well the electromagnets will resist movement - bigger magnets need more current to get them to move, smaller magnets need less current.

    If the speakers are low power, they have weaker magnets. A high-powered signal from a powerful amp will overwhelm the weak magnets and blow the diaphragm.

    So, you need speakers with "more ohms" - enough to resist the output of your amplifier.
     
  11. Oct 21, 2006 #10

    turbo

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    Actually speakers do not use electromagnets, but permanent magnets and very lightweight coils. The most common type of speaker has a permanent magnet with a hole in it. Suspended inside the hole is a coil on a cylindrical core, often of paper or kaptan that is attached to the back of the speaker cone. The AC signal from the amplifier energizes that coil (called the voice coil) causing it to oscillate in the field of the permanent magnet. Since the voice coil is on a core attached to the back side of the speaker cone, when the coil moves, it causes the cone to vibrate, creating sound waves. The most common power-related failure mode of such speakers is not damage to the speaker cone, but heat-related failure of the voice coil or mechanical damage to the voice coil windings due to the coil rubbing the magnet. Speakers are very inefficient motors, so most of the energy spent in driving them is radiated off as waste heat. Having repaired and restored tube-type guitar amplifiers for many years, I have often had to use the services of speaker rebuilders. Often the frame, magnet, and cone are perfect, but the speaker either doesn't work or distorts badly. In this case the speaker rebuilder replaces the surround, the cone, and the voice coil and dust cap, keeping the frame and magnet and preserving the original appearance of the speaker. This type of repair is quite common with vintage guitar amplifiers.
     
  12. Oct 21, 2006 #11

    DaveC426913

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    And a coil of wire, when current is passed through it, becomes an ___________.
     
  13. Oct 21, 2006 #12
    Op-Amp? :rofl:
     
    Last edited: Oct 22, 2006
  14. Oct 22, 2006 #13

    rcgldr

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    The speakers won't be harmed by this, but the stereo will. If speakers don't have enough ohms, then they will draw too much current from the amplifier, causing damage to the amplifier (or at least blowing a circuit breaker or fuse). Most amplfiers base the gain on voltage, and expect a specific amount of resistance to this voltage, based on the ohms of the speakers. Some amplifiers have a switch to toggle between 8 ohm / 4 ohms, and in some instances, 2 ohms. If you're speakers are between the amplifier settings choose the lower number, for example, if your speakers are 6 ohms, then select 4 ohms on your amplifier.

    What damages speakers is excessive power, which results in excessive voltange and current through the speaker. You'll overheat or overdrive the speaker, causing damage.

    The general ratings for a speaker are it's impedance in ohms (sometimes shown as a curve, since lower frequencies can involve higher impedance), the power handling in watts, the efficiency, and the response (typically +/- 3db across the frequency range for the speaker at a specific volume). Higher quality speakers handle more power and retain a relatively flat response across a wide range of volume (power input). Generally, some efficiency is sacrificed in order to retain a flat repsonse across the full range of volume due to negative feedback for control, and/or accoustic suspension for dampening the speaker system to prevent over excursion.

    The popularity of home theater speakers which generally have loud but inaccurate base response, has reduced the market and increased the prices of good musically oriented speakers. I managed to find a pair of Energy Veritas 2.8 speakers (500 watts, 4 ohms, very flat response), at about half price ($1.5K per speaker), but these are no longer made. The next closest speaker system is $5k per speaker.

    Probably the most accurate speakers are true studio "far range" monitors, the ones that handle the most power, but these are very expensive.

    One other tidbit, some tweaters use piezo electric crystals to generate high frequency sound instead of a normal speaker setup. I've seen both 3/4" dome and piezo electric crystals used on good quality speakers, so I don't know if there's an advantage for one versus the other.
     
    Last edited: Oct 22, 2006
  15. Oct 22, 2006 #14

    turbo

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    A solenoid.
     
  16. Oct 22, 2006 #15

    NoTime

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    :rofl: :tongue2:
     
  17. Oct 23, 2006 #16

    DaveC426913

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    Not quite, you skipped a step. But solenoids do make use of electromagnets.:tongue:
     
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