Dumb question of the day: Why make a speaker with a low sensitivity?

Discussion in 'Archived Threads 2001-2004' started by KeithH, Dec 2, 2001.

  1. KeithH

    KeithH Lead Actor

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    Whenever I read discussions regarding speakers with a low sensitivity (e.g., 86 or 87 dB), people are always quick to make sure that the owner or potential buyer has an amp that is powerful enough to drive them. Since there are so many speakers out there with sensitivities rated at 91 dB or thereabouts, it begs the question to my mind of why manufacturers make speakers with low sensitivity ratings. I have not studied speaker design much at all, so I don't understand what might be gained by designing a speaker with a low sensitivity. There must be a reason why this is done. Help?
     
  2. Saurav

    Saurav Cinematographer

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    That sort of makes sense. Talking completely off the top of my head, here's one way to look at it. Let's say that for a given amount of input power, you as a speaker designer can produce "so much sound". Let's say the "amount of sound" value is fixed, and is a product of sensitivity and frequency range. So, if you reduce the frequency range, you can play louder, which gives you higher sensitivity, and vice versa. I know this is a totally childish way of looking at it, but the idea illustrates the tradeoffs that are probably involved.
     
  3. Brett DiMichele

    Brett DiMichele Producer

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    Think of it this way..

    Take 2 identical speaker cabinents (dimensionaly)

    and make one of those cabinents a 4 way Tower

    (Sub,Mid,Tweet,Mid)

    Take the other cabinent and make it a 3 way with

    Mid,Tweet,Mid

    Assuming the quality of each driver is the same used

    in both setups one of these is going to yeild a higher

    efficiency. The cabinent with more drivers will yeild a

    lower sensitivity rating because it needs more power to

    drive the additional speaker per cabinent. Plain and simple.

    Then factor into the equasion the quality of the drivers.

    The larger the motor (magnet) structures, the more power

    that speaker will take to drive (less efficient) but will

    produce better sound (better construction)

    Make any sense?
     
  4. Rick Radford

    Rick Radford Supporting Actor

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    Brett, I was accepting your example.. until I thought of the mfgs who offer various speaker combos... from 2 drivers to 5 or more in an enclosure.. and sometimes the more drivers have a higher sensitivity rating than the 2 driver one.
    For example: http://www.axiomaudio.com/products.cfm?productID=M60
    Axiom M40Ti (2 drivers) rated at 93
    Axiom M50Ti (3 drivers) rated at 95
    Axiom M60Ti (4 drivers) rated at 95
    Axiom M80Ti (6 drivers) rated at 98
    Or is my thinking bassackwards here?
     
  5. Tyson

    Tyson Stunt Coordinator

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    Tweeters are usually much more sensitive than mids & woofers, so the woofers & mid/woofers will determine overall sensitivity for the speaker. For a 2 way bookshelf speaker with a 1 inch tweeter and a 6.5 inch woofer, it is the woofer that probably has a sensitivity of 87db or so. So the tweeter has to be "dialed down", probably from around 91db or so, to 87db in order to match the woofer (this is done in the crossover). If you use 2 woofers run in parallel (both cover the same frequency range), then you will get a 3db jump in sensitivity. You still have a 2 way speaker, but it is a more senstive system.

    On the other hand, if you have a tweeter for the highs, a midrange woofer, and then a seperate bass woofer (which would give you a 3 way system), you don't gain any sensitivity with the extra woofer. Whichever driver is the least sensitive in this speaker will determine the sensitivity of the whole system.

    On top of that, you will also usually lose a db or 2 when you pass your power signal through a passive crossover. . .
     
  6. KeithH

    KeithH Lead Actor

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    Thanks all. Good information here. I have noticed bookshelf speakers with just one driver that have low sensitivities. The Sonus Faber Concertinos are rated around 88 or 89 dB and the Vienna Acoustics Haydns are around 87 or 88 dB.
     
  7. Evan S

    Evan S Cinematographer

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    Another thing to consider for efficiency rating is the enclosure type. If the speaker is bass reflex (ported) it is always going to be more efficient than acoustic suspension speakers because when the woofers flex, the air can escape the chamber, limiting the backwards pressure on the driver. In an acoustic suspension design, as the driver flexes, the air has nowhere to go (trapped in the enclosure) and that pressure builds up. You need more power to drive this design because of the built up pressure. In the Klipsch designs, the horn loaded tweeter produces a very efficient speaker because of that type of design...the sound is almost amplified, so to speak, so Klipsch speakers are typically around 96db efficiency. The design type of the speaker is the most important in determining efficiency..number and size of drivers is secondary.
     
  8. Mike_A

    Mike_A Stunt Coordinator

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    evan,

    based on the previous discussions in this thread, it seems like the extra sensitivity klipsch gains with a horn tweeter would simply have to be dialed back to match the woofers anyway. so why are klipsch's so sensitive?

    it seems like more manufacturers would want to go the high sensitivity route in general, but they don't seem to, especially on the low end where power is less abundant.
     
  9. John Kotches

    John Kotches Cinematographer

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    Another item not discussed is some driver designs are inherently low sensitivity.

    Here, I mean planars in general. Because bass reproduction is dependent on moving a particular volume of air, most planars do not have high sensitivy -- hybrid planar/dynamics usually do much better in this regard.

    Sensitivity is usually one in a series of tradeoffs -- ATC speakers are quite well regarded, but are dreadfully low in sensitivity. Some of my favorite speakers are made by Eminent Technology -- again these are terribly low sensitivity.

    Regards,
     
  10. Jon_B

    Jon_B Screenwriter

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    Like many have stated above, think of it as a byproduct. If you buy a car with a V8 engine, you should have more power than a 4 cylinder engine....but at the same time you get worse gas mileage. Speaker designers have to deal with similar issues when they make a speaker. You, the consumer, have to choose what is most important to you.

    Jon
     
  11. KeithH

    KeithH Lead Actor

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    More good information. Thanks again. I'm glad I asked. [​IMG]
     
  12. Patrick Sun

    Patrick Sun Moderator
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    Just to reiterate, sensitivity doesn't translate into sound quality, but it can guide you in mating the speakers with your amp/receiver's power capabilities.

    Louder doesn't always equal better.

    Some speakers account for baffle step compensation, and that can affect/lower its "rated" sensitivity, but at the same time provide a more smoother/fuller sounding speaker (given the rest of the crossover handles the on and off axis response of the drivers, and produces good imaging and balance to the overall sound).
     

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