Please exlpain the audio term "roll-off"

Discussion in 'Audio Hardware' started by dogpile, Oct 4, 2007.

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  1. dogpile

    dogpile Generation X record spinner. Thread Starter

    Location:
    YYZ - Canada
    I have yet to experience it. Perhaps it doesn't exist in my system?? Just curious... what are the signs??
     
  2. Curiosity

    Curiosity Just A Boy

    Location:
    United Kingdom
    Roll off:
    The expression stems from the notion of plotting the audio frequency range of a component in the form of a graph.
    You place the audio frequency range along the horizontal axis and the output along the vertical in decibels (db's).

    Ideally the component should not exhibit a deviation in its output from the lowest to the highest frequencies. When plotted this is said to be a 'flat response' but this does not always occur, particularly with transducers and when you plot this you'll see a 'roll off' where the response ceases to be 'flat'.
    In such instances there is therefore less of the particular frequencies being reproduced.
    The steepness of the roll-off plays an important role too.
    Generally it's is held a flat response from 20hz to 20khz is desirable for HiFI components.

    Does that help?
     
  3. Claude

    Claude Forum Resident

    Location:
    Luxembourg
    Treble roll-off:

    [​IMG]
     
  4. Fedot L

    Fedot L Forum Resident

    “Primarily” desirable for any HiFI component, it’s no more the case for the whole system's frequency response for imperfect listening place acoustics conditions, and especially rare for full range loudspeaker units. Both needing a multi-channel equalization in order to obtain an acceptable resultant flat response from 20hz to 20khz.
    If not to mention specific cases of deviation from a resultant “system’s” flat response:
    1. The “loudness compensation”, whenever wished, while listening at sound pressure levels lower or higher than the same sound source listened “naturally”, by “loudness correctors”.
    2. Spectral losses in listened programs due to poor spectral quality of many programs, to compensate by multi-channel equalization or, for simple cases, be “bass” and “treble” knobs.
     
  5. Green Tea

    Green Tea Sweet Soulful Sounds

    Location:
    ϟ
    Courtesy of J. Gordon Holt (Stereophile)

    Rolloff:

    "A frequency response which falls gradually above or below a
    certain frequency limit. By comparison, the term cutoff (often
    abbreviated to "cut," as in "bass cut") implies an abrupt loss of
    level above or below the frequency limit."
     
  6. fjhuerta

    fjhuerta New Member

    Location:
    México City
    Example: a stock T-amp has a bass roll-off, starting at 200 Hz, unless you mod it. :(
     
  7. Black Elk

    Black Elk Music Lover

    Location:
    Bay Area, U.S.A.
    It exists in all hi-fi systems, but some systems are more extended than others (i.e., the frequencies at which roll-off begins are lower [for the bass] and higher [for the treble]). The only way you would know whether your system is bandwidth limited (and rolling off too soon) is to compare it to a known wide bandwidth system.

    What are the signs? Lack of deep bass extension if you have low-frequency roll-off and a lack of treble extension if you have high-frequency roll-off. While the roll-off can also be a function of the source and amplifier, it is easier to think in terms of speakers. Imagine listening to a speaker with a 3" woofer compared to one with a 15" woofer. The larger driver should provide deeper bass, and one can say that the 3" driver rolls off (i.e., its output level falls) earlier, let's say 100 Hz, than the 15" driver, let's say 20 Hz (since we are talking about bass frequencies an earlier roll-off occurs at a higher frequency, for tweeters the situation is reversed and the earlier roll-off occurs at lower frequency).

    If your system is able to provide bass and treble to the limits of audibility (typically referenced as 20 Hz to 20 kHz) then it can be termed wide bandwidth, and the low and high frequency roll-offs occur outside the audio band.
     
  8. As far as high frequencies go, another term is "muffed"
     
  9. Steve Hoffman

    Steve Hoffman Mastering Engineer Your Host

    "Roll-Off":

    A song by the LA Surf/Soul Instrumental group THE RUMBLES as featured on their DCC compact disk.
     
  10. Fedot L

    Fedot L Forum Resident

    Incorrect as a rule to follow without taking into consideration the type of the cabinet used and the “cabinet volume / driver diaphragm’s surface area / driver diaphragm’s mass” ratios! Needing an acoustical calculation.
    There are many contrary cases.
     
  11. dogpile

    dogpile Generation X record spinner. Thread Starter

    Location:
    YYZ - Canada
    Awesome :righton: Thanks all for the comments, explanations & song contributions (Steve) - very helpful and appreciated :wave:
     
  12. whiskerbiscuit

    whiskerbiscuit Forum Resident

    Location:
    SoCal

    Hey, I've got that one! Now I'm gonna have to give it another spin.
     
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