Power ratings of a speaker

Discussion in 'General Electronics Chat' started by asadsultan, Dec 16, 2017.

  1. asadsultan

    Thread Starter New Member

    Apr 12, 2017
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    I have a speaker written 5W and 6 ohms, what is meant by power of 5W, is it maximum power or avg power?
    Thanks.
     
  2. wayneh

    Expert

    Sep 9, 2010
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    It’s conventional to quote the continuous average power rating.
     
  3. bertus

    Administrator

    Apr 5, 2008
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  4. asadsultan

    Thread Starter New Member

    Apr 12, 2017
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  5. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    I would consider the 5 Watts as maximum power.
    Did you read this piece from the page?
    I handles the power versus movement of the speaker and the thermal issues:

    Why Speakers "blow out"
    Most people have blown a speaker at one time or another. A typical scenario is a large party where the guests are drunk and someone says “crank it up!” The result is that the volume control is turned up as far as it can physically go (despite the offensive sound quality), and the next morning the house owner realizes that one or more speakers are no longer functioning properly. What happened?

    There are two major ways speakers can fail: mechanical failure (most often limited to woofers, resulting from too much cone excursion) and thermal failure (the voice coil overheated and melted or burned). The most common reason for blown speakers: driving them with too much electrical power! Quite often the person operating the equipment does not fully realize how much power is being sent to the speaker. Below are some photos of a medium duty woofer (disassembled) to show some of the parts we are talking about:

    [​IMG]
    Woofer with cone removed (click on the image to bring up a large image in a new window) This is a medium duty woofer with its cone removed. The frame is sometimes called the "basket". The tan item at the center is the spider, this holds the cone centered. If a woofer is overdriven with too much cone travel, the voice coil can rip free from the spider.

    [​IMG]
    Woofer with cone removed (click on the image to bring up a large image in a new window) This is the cone from a medium duty woofer. Note the voice coil at the center, this is a 1.5" coil rated for about 50 watts. Had this woofer been blown due to thermal overload the coil may be charred, melted or the windings might be coming apart (this coil is in good shape).

    [​IMG]
    Close up of Woofer Voice Coil (click on the image to bring up a large image in a new window) Here is a close up of the coil. This woofer had been suffering from severe foam rot (see discussion below). This caused the coil to rub against the magnet structure. This is evident from the lines and scratches on the inside of the coil former.



    Mechanical failure of a speaker (most often a woofer) occurs because the speaker's cone is being asked to move farther than it was designed to safely do. When this happens, parts of the speaker become stressed due to stretching and excessive vibration, and in severe cases the cone and/or parts of the voice coil structure can collide with the frame of the speaker. If operation of the speaker in this fashion is not ceased, sooner or later something will rip, break, rupture or come loose. If the woofer's spider (a component made of a mesh like material that holds the voice coil in alignment) comes loose, the voice coil will basically be allowed to flail wildly inside the voice coil gap, and the insulation on the coil will be damaged as it rubs against the metal parts of the magnetic structure. When this occurs, the sound quality will take on a very gritty tone, it should be very obvious (to a sober person anyway!); if left to continue in this fashion, the coil will eventually break (resulting in no sound at all). Mechanical failure of midrange and tweeter components can and does occur, but it is much less common than woofer failures. Almost all of the time, failure of a midrange or tweeter speaker is due to thermal failure.

    Thermal failure of a speaker occurs when the speaker is fed more power than it is designed to safely handle. This basically causes the voice coil to get too hot, and two main things can happen. First, the adhesives used to hold the voice coil together can soften, resulting in the coil coming apart (this is a partial mechanical failure). If the coil gets too hot, it will simply melt or burn the wires in the coil, most often resulting in an open circuit (in this case there will be no sound at all).

    In the majority of cases, a speaker blowing out is usually due to an accident or carelessness. An example of an accident is someone making cable connections to components (a CD player) at the back of the amp while unknowingly having the volume at full blast while the amp is on (the very loud hum that is generated could blow up a speaker). More often, carelessness is the cause (the drunken party example above). It should also be mentioned that it can sometimes be easier to blow a speaker with an amp that puts out less power than the speaker is designed to handle! The reason for this is that an amp that is being overdriven can generate a lot of distortion and the RMS level of the amplifier output will be a lot higher than what the operator thinks it might be, and the speaker can blow (clarification: distortion itself does not blow speakers, but amplifiers driven into distortion cause more power to go to the speaker than one realizes). You may sometimes hear the statement "speakers can take a lot of power if it is "clean" power". This is true to a point. However, if you try to drive a speaker rated at 100 W with an amp that puts out 1000W, chances are you could wreck the speaker even though the power was totally clean (no clipping or distortion)! So remember, most speaker failures are caused by driving them with too much power. This is most often caused by amplifiers being driven into distortion, however the distortion itself is not the culprit. Driving an amplifier into distortion causes signal compression which results in a significantly higher average power level being delivered to the speaker.

    Bertus
     
    Sinus23 likes this.
  6. MrChips

    Moderator

    Oct 2, 2009
    17,296
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    One solution I have seen to protect high powered speakers is to put an incandescent light bulb in series with the speaker.

    Once I had an mic/amp/speaker go into feedback mode and I saw a flash of light come out from the back of the speaker box. My first reaction was that the speaker was blown. As it turned out, the flash was from the light bulb and the speaker was ok. whew!
     
  7. BobTPH

    Senior Member

    Jun 5, 2013
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    Treat it as maximum power.

    Consider "average power":

    1 second at 100W
    19 seconds at 0W

    Average power 5W; blown speaker.

    Bob
     
  8. Externet

    AAC Fanatic!

    Nov 29, 2005
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    Chinese Watts are smaller... :rolleyes:
     
    recklessrog likes this.
  9. recklessrog

    Well-Known Member

    May 23, 2013
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    HA HA!
     
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