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What is speaker Crossover Frequency?

Discussion in 'Home Cinema Speakers' started by The_Mole, Aug 27, 2005.

  1. The_Mole

    The_Mole
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    If a speaker has got a frequency of 40hz-20khz, what does it mean when it claims to have a crossover frequency of 3hz.
     
  2. Kobus

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    hi, welcome to av.
    the bass speakers handles all freq. below 3hz and the midrange/tweeters the freq. above that.
    go and read/surf, there are lots more interesting stuff to learn.
     
  3. Sniper

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    i would assume you mean 3Khz -

    any frequency below that point will be directed to the mid/mass driver, and anything over that to the tweeter!
     
  4. GaryB

    GaryB
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  5. Kobus

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    damn,I never get the chance to give answers & then still mess it up 3hz vs 3 f#* khz
     
  6. Sniper

    Sniper
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    hehe... well i was refering to 'The Mole''s post actually but yeah, just a typo i guess!
     
  7. swiftpete

    swiftpete
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    So if I have speakers in a home cinema setup with different crossover frequencies front and back(bigger speakers at front), is that an issue or does it not matter?
     
  8. ChrisAV

    ChrisAV
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    Different crossovers in front/rear speakers is fine, the same (full range) signal goes to each speaker, the internal crossover just dictates which go to the tweeter (high frequencies - treble) and which go to the woofer (low frequencies - bass).

    Also, in a home cimena set up (5.1, the .1 being the subwoofer) the amp will usually have a crossover setting. Assuming all speakers as set to 'small' then all frequencies below the crossover (usually around 80Hz) are sent to the sub, and all frequencies above sent to the remaining speakers. In this case the reduced range (say 80Hz to 24kHz) goes to the front/back speakers, and again is split by the internal crossovers in each speaker to woofer/tweeter.

    Chris
     
    Last edited: Jan 29, 2009
  9. BlueWizard

    BlueWizard
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    Expanding on what has already been said, it is extremely difficult to design a single cone speaker that uniformly covers a wide range of frequencies. Some makers try, and have fair results, but the speakers are always lacking in something.

    So, as we make speakers larger, they have much better bass response, but we start losing high frequency response. As we make speakers smaller, the high frequency response improves, but we lose low frequency response.

    So, why not just use a lot of medium sized speakers? Well, the problem there is you get neither good high nor good low response.

    So, the best alternative is to use one large speaker for bass, and one small speaker for highs. But how do we keep the lows out of the tweeter and the highs out of the woofer? Since neither of the speakers is capable of reproducing those frequencies, if we want to eliminate distortion and damage, we need to filter and separate the frequencies.

    Along comes the Crossover Network.

    Next, a quick intro to coils and capacitors.

    As fate would have it, at low frequencies a capacitor looks like a very high impedance. So, if we put a capacitor in series with a tweeter, at low frequencies where the capacitor impedance is high, all the voltage us consumed by the CAP, and very little is left over for the tweeter. In short, we have filtered out the low frequencies.

    Now as the frequency goes up, the impedance of the capacitor goes down until it is essentially a short circuit or zero, and all the voltage is then passed on to the tweeter.

    A coil does exactly the opposite. I high frequencies it has a lot of impedance, and at low frequencies is a very little impedance. So, if we put a coil in series with the woofer, it passes through all the low frequencies and blocks out all the high frequencies. Again, we filter just what we want to filter.

    So, we select a woofer and tweeter that overlap in their frequency response, and put the crossover frequency in the middle of that.

    For example-

    Woofer = 30hz to 3,000hz
    Tweeter = 2,000hz to 20,000hz

    The overlap is between 2,000hz and 3000hz, so, we put the crossover at 2,500hz and everybody is happy.

    The crossover frequencies can tell you something about the design goals of a speaker, but the speakers themselves set the correct crossover frequencies and there is nothing anyone can do about it. We simply have to trust that the designers made the right choice.

    Look at the example above, what if we tried to put the crossover at 4,000hz? That would be nice for the tweeter, but it would suck for the woofer. It would leave a big hole in the response between 3,000 and 4,000hz.

    To illustrate how knowing the crossover frequencies can tell you about the design philosophy, let's go through a couple of examples.

    Speaker #1 -
    -Crossovers at -
    -- 300hz
    -- 2500hz

    Speaker #2 -
    -Crossover at -
    -- 800hz
    -- 5,000hz

    Speaker #1, from a certain perspective, in not a true 3-way speaker. I has Low-Bass, Mid-Bass, and tweeter. So it is a 2-way (midbass & tweeter) with an extended Low-Bass speaker added.

    Speaker #2 is a true three way speaker in that, it has a woofer, true midrange, and tweeter.

    Today you frequently see hybrid speakers. As a real world example, look at the Wharfedale Diamond 9.6 -

    Wharfedale

    Frequency: 28-24k @ -6dB
    Crossover: 150Hz, 1.0kHz, 6.0kHz

    The low 150hz crossover tells me that this is a 'half-way' system, as in a 3.5-way; a full 3-way with an additional 0.5-way added on.

    Below 150hz you have TWO 8" woofers working together. Between 150hz and 1,000hz, we have ONE 8" woofer working. Between 1,000hz and 6,000hz we have a true midrange speakers, and above 6,000hz, we have a tweeter.

    So, we have a true 3-way woofer, midrange, tweeter speaker system that has an additional woofer to support bass below 150hz. There is a reason for this type of system, but I won't get into it here.

    So, going back to my hypothetical examples, we see Speaker #1 with its Low-Bass, Mid-Bass, tweeter design, has a very different design philosophy than Speaker #2 which is a true woofer, midrange, tweeter design.

    As usual, that's pretty long winded, but hopefully there is some valuable information in there somewhere.

    Steve/bluewizard
     
    Last edited: Jan 30, 2009

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