Frequency Response Meanings?

Discussion in 'Amps [BG]' started by jessicabass, Mar 29, 2014.


  1. jessicabass

    jessicabass

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    I admit i am a bad bass player for not knowing this.
    But when looking at bass cabs and seeing a variety of specs,
    If i see....
    40-18, 30-15, etc.
    What does this mean?
    Is there there better numbers to have over others?
    Is the greater the distance between them allow for more levels of highs and lows?
    Which one is the highs and which one is the lows?
     
  2. Linnin

    Linnin

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    Human hearing at best is 20Hz (very, very low) to 20,000Hz or 20KHz which is very very high.
     
  3. Downunderwonder

    Downunderwonder

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    Your numbers are not ringing any bells.

    If you're talking about frequency response numbers, some cabs come with an average sensitivity and -3dB and -10dB frequencies. Essentially the -10dB mark is where response is totally useless, between that and -3db point you can have "some" if you play quieter, but don't expect much at all until you're much closer to the -3dB mark.

    The numbers don't tell you the power handling in the low end. Often, boosting EQ at -3bB mark won't allow you to get very loud overall before you're farting out.

    I find the 2nd harmonic of the lowest note is pretty good if it falls at or above the -3db point. Ymmv.
     
  4. seamonkey

    seamonkey

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    The numbers equate to what you can hear, but you need a graph, not just point numbers at the low and high.

    Try some of the ear training sites, for example
    http://www.audiocheck.net/engineertraining_bands_difficult.php

    Or grab a PC, and an EQ plug in with some headphones or earbuds. Use and RTA like http://www.trueaudio.com/rta_abt1.htm or one of the free smart phone apps.

    Good makers of speaker cabinets will publish a curve of frequency response, you can match that curve with EQ, then listen to yourself, or music through the EQ curve. It will soon make sense that when you're listen to a low E string, the fundamental is of 41hz is not always there for the bassiest of sounds. A good example of this is Timpani drum sounds that do not produce low fundamental yet everyone hears it. You can look for cabs that do produce the fundamental but you don't always need it. You should look for cabs that have the flattest frequency response. You can always EQ flat to sound like anything you want, you can't always EQ peaky dippy cabinets to do the same.
     
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  6. bongomania

    bongomania Gold Supporting Member

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    If what you are seeing is like 40 Hz - 18 KHz, or 30 Hz - 15 KHz, those are "supposed" to mean the lowest and highest frequencies you can expect to hear well from that cab. Those numbers are usually fudged badly, and sometimes outright lies--but you can still use them to get a general idea of what to hope for. "Hz" is the low end, "KHz" is the high end. So theoretically, a lower number at the Hz end and a higher number at the KHz end mean a wider usable frequency range.

    If a cab says it goes down to 30 Hz or lower, they are usually lying. If a cab says it goes down to 35-40 Hz, they might not be lying, but you should still not take it as gospel.

    On the high end, on the one hand good ears can hear up to around 20 KHz, but on the other hand a lot of bassists like the speakers to roll off highs above 5 KHz or so.
     
  7. jessicabass

    jessicabass

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    Thank you all very much.
     
  8. AlexanderB

    AlexanderB

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    My advice:

    To get some practical understanding, try to find a bass amp with a graphical eq. Most models from Hartke, Trace Elliot, Peavey and many Ampegs and Marshalls also have them.
    Play your bass through it and notice below 150 Hz will thicken the tone, how the 500-800 sounds boxy, the bite around 2 kHz etc.
     
  9. will33

    will33

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    There is a handy phone app called True Tone that is a signal generator. It passes test tones throughout the range of human hearing. They're sinewaves, like the tones you hear in a hearing test.

    I use it for quick speaker checks. If you have truly widerange, flat response headphones, you could even give yourself a basic hearing test with it. When connected to something like your bass cab, you can hear where the lowend falls away as you move lower in frequency, and/or where the treble falls away at high frequencies.

    It's not purely scientific, but educational none the less. To get truly s ientific results, you'd need to be in a controlled listening environment, have precise control over the power of the input signal, have calibrated measurement mic's, etc.

    "Hertz" are cycles, like how many soundwave cycles per second. Frequency is just that, the frequency of these cycles. 50 cycles per second, or 50 hertz, if very low tone. 10,000 cycles per second, or 10 kilohertz (abbreviated khz), is very high tone.

    The scientists who figured this out had the last name of Hertz, so we call them hertz (abbreviated hz).
     
  10. will33

    will33

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    To get a better grasp of the the frequency numbers mean, they must be used in concert with decibels (abbreviated db). These are a measurement of loudness, originally developed by Bell Labrotories for use in the early telephone system.

    These are not on an "even" scale, example, 6db is not twice as loud as 3db. When quoting speaker frequency response, numbers such as -3db or -10db state how much quieter the speaker is at that frequency compared to it's average output.

    A difference of 3db is generally percieved by the human ear to be a "small but noticable" change in volume. A difference of -10db is generally heard as half as loud, or +10db being twice as loud.

    Some manufactures will quote this 10db number to on paper in an advertisement, it would appear their bass speakers can play really deep(low frequency), but, those 10db sounding only about half as loud as the average output, is pretty much useless in a band situation.

    It's easy to pick and choose data to make something look good, when if one could see a complete set of scientific measurements, the result may not look so good.
     
  11. will33

    will33

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    Sorry for the typos, I have bacon grease on my thumbs.
     
  12. jessicabass

    jessicabass

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    LOL
    Thank you sweetheart.
     
  13. michaelandrew

    michaelandrew The bass player is always right. Supporting Member

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    Best excuse ever!

    There's lots of good advice in this thread. Here's my 0.02 semitones (2 cents) worth: The 20 Hz - 20 KHz definition of the "audio frequency range" is used for engineering convenience. Few people over the age of about 12 can hear anything near 20 KHz well enough for it to be of any musical importance and, as we age, we tend to lose the high frequencies (I'm 58 and get nothing over about 14 KHz). Our low-frequency hearing is never very good below about 100 Hz (which, BTW, is one reason we bassists get to lug around those big heavy cabs and why our amplifiers have to deliver 10 times the power used by our guitard colleagues - the wimps!).

    For music, it may not matter as much as you'd think (let the flame wars begin! ;)); the highest note on a "standard" 88-note piano keyboard is about 4200 Hz (or 4.2 KHz, but I forget the exact frequency). Commercial FM radio broadcasts (the old-school analogue ones) cut everything above about 15 KHz and they sound pretty good. At the low end: The lowest note on that "standard" piano is about 27.5 Hz but much of what you actually hear is the "2nd harmonic" an octave higher at 55 Hz. On a 5-string bass, tuned BEADG (my Yammy RBX 765A, for example), the lowest note is about 30.9 Hz (1st harmonic at 61.8 Hz) and the highest (24th fret on the G string) is about 196 Hz.

    So far, I've been talking about the "fundamental", or "1st harmonic" frequency. Harmonics - I've mentioned the 2nd one already - are at integral multiples (1x, 2x, 3x, etc.) of the fundamental frequency, so the 2nd harmonic is an octave (twice the frequency) above, the 3rd harmonic turns out to be a the 5th above the 2nd, and so on. A musical note - what you get, hopefully, when you pluck a bass string, for example - consists of a mix of the fundamental and a series of harmonics. It's the way the harmonics are mixed that gives us all those wonderful variations in "tone" on the bass - and why it's important for bass amps and cabs to have good high frequency response - up to, say, 15 Khz - as well.

    Sorry if that was a little more than the 0.02 semitones I promised. To really get into this stuff can be a bit of a math minefield - Google "musical acoustics" if you're interested.
     
  14. will33

    will33

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    An octave is a doubling or halving of frequency. Example, 200hz is 1 octave higher than 100hz, 400hz is 2 octaves higher, 50hz is 1 octave lower than 100hz, etc.

    A note on your bass is made up of the fundamental frequency (the lowest one) plus lots of harmonics above that.

    Example, your open A has a fundamental of 55hz, but also has harmonics of 110, 220, 440 and so on. The relationship of all these harmonics with each other is what gives us tone. Playing the same A by fingering the E string at the 5th fret gives you the same 55hz fundamental, same note and pitch, but has different tone due to those harmonic relationships being different than the open A because you're then vibrating a thicker, but shorter length of string.

    When you get down to very low notes, like the low B on a 5-string, most, if not all, speaker systems have a falling response down there, meaning they can't play those very low frequencies as loud as the rest (low B has a fundamental frequency around 31hz), so you're hearing a greater amount of harmonics (62hz, 124hz, 248hz, etc.) in comparison to the fundamemtal. This is why some speakers can seem to lose "depth", or change tone, or "fart out" (distort) on very low notes. They're struggling to put out frequencies they're really not capable of, like somebody trying to lift 200 pounds when they can really only lift 100.

    The equalizer (tone knobs) on your bass amp are like little volume knobs for different parts of the frequency range, making some harmonics louder or quieter than others, thus changing tone.
     
  15. will33

    will33

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    Good description.

    FWIW, when mixing my own band (PA system/live sound), my default starting point is to filter off about an octave on either end, meaning below 40-45hz and above 12khz or so).

    Basically the bottom stuff is indestinct rumble/noise and the high stuff is hiss. The important stuff is in between.
     
  16. Downunderwonder

    Downunderwonder

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    Such a concentration of real deal info here!

    Might as well point out a sensitivity gap of 10dB requires 10x the power to equalise.

    And human perception of frequencies being lacking at the low end means the measured loudness needs to be much higher for bass than a chart would tell you. It follows that we bassists need to shove about lots more air than guitars, big cabs, lots of speakers, stronger speakers, and pushing manufacturers to tell bigger and bigger lies about power handling specs.
     
  17. will33

    will33

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    Good points as well.

    OP, search the "Fletcher-Munson curves"....again, named after a couplescientists named Fletcher and Munson.

    Basically, our ears are calibrated to hear middle range frequencies much better than the very low and very high. This is where the human voice is. Instruments like the bass require more power, and more speakers pumping more air, to be percieved at an equal loudness to instruments who's native voice is already in the midrange. It's the reason it takes a couple/few hundred watts and good performance speakers to appear the same loudness as a guitar player using 15 or 20 watts and 1 or 2 speakers. Same reason a snare drum sounds loud by itself without using a microphone. Same reason a flute (high pitched instrument) gets easily lost when playing with amplified instruments.

    The extreme of this curve evens out a little more the higher in volume you go. At quiet volumes it is very obvious, at very loud volumes, less so, but the disparity still exists.


    It's one reason why when bass players say they're having trouble hearing themselves on stage, people say "turn up the mids". That sound, while not sounding very pleasant on its own sometimes, "sits in the mix" better and make it easier for us to hear ourselves.

    It also usually sits better with the audience. Really fat, bassy tones up close to the amp can turn to indestinct mud out in the audience. Likewis, tones that are too midangey or "harsh" can sound well balanced out in the audience.
     
  18. michaelandrew

    michaelandrew The bass player is always right. Supporting Member

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    Sorry to nit-pick on your otherwise good example, but in this case it's sort of important. The harmonic series for the 55 Hz fundamental would be:

    55 hz (A)
    2 x 55 = 110 (A)
    3 x 55 = 165 (E)
    4 x 55 = 220 (A)
    5 x 55 = 275 (C#)
    6 x 55 = 330 (E)
    7 x 55 = 385 (somewhere between F# and G)
    8 x 55 = 440 (A)

    So 220 Hz (A) is the 4th harmonic and 440 (also an A) is the 8th. The note names are for the closest "equal temperament" (another long story entirely:)) tuning note. The 7th harmonic is notoriously out-of-tune - all kinds of theories and opinions about that too.

    I hope I didn't make any mistakes; I don't type with my thumbs and have no bacon grease for an excuse.;)
     
  19. Mr. Foxen

    Mr. Foxen

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    Good to bear in mind that if the high frequency is 15-20k, cab has a tweeter, and cabs with woofers and tweeters often have a gap of an octave or two between them, especially off axis, and that is pretty important. Its also kind of ugly giving part of that 'I hate the sound of tweeters' thing, when you actually might like it fine without the gap, because they don't show up as a separate sound without the gap. Although if you use distortion, might still hate it.
     
  20. will33

    will33

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    Righto.

    I started to type that, but then left it out for reasons of simplicity. AFAIK, Jessica is still a teen, or maybe 20. More knowledge is always better of course, but I didn't want to make things more complicated than they needed to be to get a basic grasp of the thing.

    You're absolutely right, all multiples of 55 are involved in there.


    My apologies to Miss Jessica if I seemed to be "dumbing things down". Was just trying to describe it in a way for it to be easy to grasp. For all I know, she's a genius and just playing us like a big, giant fiddle. :)
     
  21. will33

    will33

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    When I started learning about all this stuff, one big hurdle to overcome was distinguishing between frequency, pitch, and tone/timbre.

    They're all related but they're not all the same.
     

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