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Loudspeakers What is Frequency Response?

Discussion in 'Sound, Music, and Intercom' started by lieperjp, Dec 4, 2008.

  1. lieperjp

    lieperjp Well-Known Member

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    New Ulm, Minnesota, United States
    To put it simply, what is frequency response?

    I was reading an article in the Nov. 2008 Live Sound about subwoofers and for the subwoofers listed it gave something called

    What does that mean?

    Note: The +- is supposed to be a plus-minus sign but I couldn't figure out how to type it in Firefox.
  2. AndrewWebberley

    AndrewWebberley Member

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    Lighting Programmer
    Burbank, CA
    Frequency Response in speakers is simply what frequency range the speaker can produce. The +- part is the variable amount from speaker to speaker. If they list the frequency response as 100 - 300 hz +-3db then the speaker can produce sounds between 100hz and 300hz but the actual volume/amplitude of these signals may vary by 3db. The db decibel and that is how sound loudness is measured. So you may have a speaker that is a little louder then another or you may have speakers that produce certain frequencies at a louder or softer volume. I hope this helps.

  3. mbenonis

    mbenonis Wireless Guy Administrator

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    Radio Engineer
    Washington, DC
    Essentially, the idea is that nothing can produce a perfectly flat output across the audio spectrum. That is to say, it's not possible (or very difficult) to make a device that has the exact same volume at 30 Hz that it does at 100 Hz. Thus, we have the concept of frequency response.

    Usually, we will pick a convenient frequency (say, 100 Hz or 1 kHz) and then determine the loudness of the device at other frequencies relative to that baseline frequency. We convert that to decibels, and then make a plot of the frequency v. the amplitude. Generally speaking, better devices have a flatter line across the frequencies they are designed for.

    it is worth noting that the better a product, the more likely you are to find a plot (or multiple plots) instead of a line that says "Frequency Response: 20 Hz to 20 kHz, ±3dB" This doesn't tell you much at all - a plot would show you exactly where you have peaks and dips in response. 'Course, for electronic devices you also need to know what the source, input, output, and/or load impedances are too for the frequency response plot to make any sense, but impedance is another topic altogether.
  4. anonymous381

    anonymous381 Member

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    AKG however has gotten very good at it!! :grin:

    EDIT: I'm pretty sure they only make headphones
    Last edited: Dec 4, 2008
  5. museav

    museav CBMod CB Mods Departed Member

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    Acoustical, audio and audiovisual consultant
    Marietta, GA
    Frequency response is simply amplitude (level) compared to frequency. As already noted, speakers do not output the same level at all frequencies and when a specs says "A Hz to B Hz (+/- XdB)" it is saying that given a constant input containing all frequencies at the same level (or a swept sine wave input of constant level), then the output of the speaker varies within the dB limits given over the frequency range noted. +/-3dB is the traditional limit to be used although some specs may use -6dB, +/-6dB, -10dB or not state any limits at all, making it a virtually useless spec.

    The frequency response is usually measured at a single point on the vertical and horizontal axis of the speaker. This measurement is typically in the far field (far enough from the speaker so it behaves as one device rather than being affected by each driver) and under free field (an environment free of reflections) conditions. While it is definitely useful data, it is also really only valid at that one point and under those specific conditions.

    Mike is absolutely right that most simplified ratings not only do not necessarily tell the whole story, they are unfortunately sometimes also less than accurate. Be it coverage/pattern, sensitivity, impedance or response, all of which vary with frequency, charts and graphs usually provide a much better picture of what is really happening. For example, it is not unheard of to find a subwoofer spec that states a sensitivity that turns out to be the peak sensitivity at a frequency much higher than a subwoofer would normally operate and that in the frequency range it will actually be used the sensitivity is several dB lower. There are also some speaker specs that show the frequency response after applying the recommended processing rather than just the speaker response itself. So read specs carefully, they are pretty easy to manipulate.

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