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Please help me understand Hz...

Discussion in 'Amps and Cabs [BG]' started by DLM, Oct 22, 2004.


  1. DLM

    DLM

    May 25, 2004
    California
    If I have a bass cab that's rated down to 40hz, andI have a 5-string bass that has a fundamental low-B string of 31hz, are there frequencies of the B string (that are below 40hz)that won't be heard? In the same way, if my pre-amp has variable eq adjustments below 40hz, are these being wasted?
     
  2. BruceWane

    BruceWane

    Oct 31, 2002
    Houston, TX
    The notes below the cabs rolloff point will still be heard, but they will probably be somewhat quieter than those that are above the rolloff point.

    When a cabinet is said to "go down to 40Hz", that doesn't mean it puts out nothing below that, it means that it's response starts to roll off somewhat sharply at that point. A cab that is rated as "40Hz to 15Khz" will play all the frequencies between 40Hz and 15Khz at roughly the same level, while frequencies outside that range will be less loud. This particular example might be -10db at 31Hz.

    Also, a lot of what you hear coming out of your bass is not actually the fundamental, but harmonics above the fundamental pitch. In other words, when you play an open B, there is some 31Hz signal in there, but there's also a lot of 62Hz, 124Hz, and so on. That's how you end up with low notes that still sound "bright". How bright or dark your bass sounds overall is affected by both the resonant character of the bass itself AND the frequency response of the amp and speaker cabinet.

    So overall, those notes below the rolloff point of the cab will probably have less "beef" to them, but may still be very usable. Frequency response specs can give you somewhat of an idea about how a cab is going to sound, but really you just have to give it a try and let your ears be the judge.
     
  3. Yeah. This is a controversal topic on the DIY cabinet thread. The above response reflects the general consensus. Your 31hz low B will come through depending on the roll off of the cabinet. Ported cabinets roll off steep but those sealed and horns seem to play more linear.

    I think the scale lenght of the strings has something to do with it, which is why a 4 string upright low E sounds "deeper" than most electric's low B (except mine).
     
  4. DLM

    DLM

    May 25, 2004
    California
    BruceWane, that was a great, informative response. Thanks a lot!

    What I'm taking away from it (and correct me if I'm wrong) is that when I get my new 5-string bass with a low B, I shouldn't necessarily be concerned with the 40hz ratings on the cab because I will hear a range of usable frequences (below and above the 31hz signal from the low B) through that cab. Moreover, I can still get real low frequencies, but the volume of those will be softer because they lie outside the 40hz range of the cabinet. And finally, ultimately my ears should be the judge.

    One last question: if I want to boost a low frequency, say 31 hz, below the cab's 40hz "floor," can I simply compensate for the roll-off by increasing the gain on my amp at the 31hz mark, thereby increasing the volume of this frequency to be more in line with the ones within the cab's ratings?
     
  5. DLM

    DLM

    May 25, 2004
    California

    Thanks for chiming in!
     
  6. Well your amp needs major balls. Otherwise, you might be sacrificing precious headroom trying to play that 31hz low B, which, if you're are like me, use sparingly.

    Low volume/recoridng situations are another story, since you have all the power and speaker you need.