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frequency question...

Discussion in 'Amps and Cabs [BG]' started by bassplayajew, Sep 18, 2002.

  1. bassplayajew


    Mar 14, 2002
    Bethesda, MD
    So it is to my understanding that the frequency of the Low B is 30.8 hz, correct? My speaker cabinet has a frequency rating "105 dB SPL @ 1W1M (-3dB @ 40Hz and 15KHz)". My eyes only see the 40 hz part, but obviously the cabinet can reproduce lower frequencies because I can hear the low B through my cabinet. So what am I missing here? And can someone please explain to me what does "105 dB SPL @ 1W1M (-3dB @ 40Hz and 15KHz)" mean??

    thanks in advance
  2. dmaki


    Apr 29, 2000
    If your cab can't reproduce a low B, then what you are hearing is its overtones...
  3. 1W1M means an input power of 1 watt and the sound pressure is measured 1 meter (39.37") from the driver.

    There is a similar measurement of 2.83 volts at 1 meter. For 8 ohm loads, this is identical to 1 watt at 1 meter. For 4 ohm loads, it becomes misleading.

    Power = (Volts * Volts) / Resistance

    An 8-ohm example is:
    (2.83 * 2.83) / 8
    (8) / 8 = 1 watt

    A 4-ohm example is:
    (2.83 * 2.83) / 4
    (8) / 4 = 2 watts

    So, using 2.83 volts on a 4-ohm driver puts 2 watts into the driver and makes it louder because of the higher input power.

    Yawn... I know this is boring sh*t, but what it actually gives you is a reference of how much noise your cab will make compared to other cabs. Compare your cab at 105 SPL to an Acme B4 at 95 SPL, and yours will sound exactly twice as loud, using the same input power. A 10dB difference is heard as twice the apparent loudness, but it requires 10x the input power to achieve this. That is why going from a 350w amp to a 750w amp doesn't make much difference.

    Trade-Off Time: Loud cabs don't go down very low, and cabs that go down low (Acme) aren't very loud.

    The -3dB spec is that point where the cab response is reduced enough to where it is just noticeable to the listener. This is also where the cab manufacturers like to lie, because really loud cabs (105 SPL) are down a lot more than -3dB at 40 Hz. None of the manufacturers publish their measurement specs and methods, so they can lie and bullsh*t to their hearts' content.

    Response specs are quoted as "+/- (plus or minus) 3dB", which means the lower end at 40 Hz can be -6dB from the higher frequencies. This is a very noticeable variation in loudness. It is compounded by high frequencies being heard as louder than bass frequencies.

    The other bullsh*t part of the spec is "what frequency is the cab 105 SPL?". A Fostex tweeter is capable of 105 SPL, no problem. If the cab maker measures the SPL at 2,500 Hz he can claim 105 SPL no problem. That means squat for you as a bass player.

    Your ears are the best gauge for auditioning a cab. The specs get you into the ball park, but your ears will make the choice.

    High SPL = loud, not very low.
    Low SPL = real low, not very loud.

    Until they repeal a few laws of physics, this won't change.
  4. Captain Awesome

    Captain Awesome

    Apr 2, 2001
    In response to the question about the low B, the 30.8 Hz is the fundamental frequency of the low B. Even when working with cabs with flat response down there, the fundamental frequency still isn't a big part of what you hear unless you really boost it. Most of what you are hearing that lets you hear the note being played is harmonics. When a string is plucked it produces harmonics, lots of them, that are in a higher range then the actual frequency the string is tuned to. Your ears hear them as a note. This is why you can still hear the low bass notes on a recording played through a cheap boombox, which probably only goes down to about 100Hz at best.
  5. Munjibunga

    Munjibunga Retired Member

    May 6, 2000
    San Diego (when not at Groom Lake)
    Independent Contractor to Bass San Diego
    The cab can reproduce the 31 hz note, but its level will be probably 10 dB or more lower than the volume at, say, 40 hz.
  6. Get a 6542887 inch speaker, that should fix it
  7. bassplayajew


    Mar 14, 2002
    Bethesda, MD
    so would a speaker that goes down past 30 hz make the B string sound better? or just louder?
  8. geshel

    geshel Supporting Member

    Oct 2, 2001
    It depends. It might not sound "better" to you if you like it the way it is now. Does that make sense? All it will do is add more output at that 30.8Hz frequency - which to you might mean making it sound fuller. I think some people find notes sound "tighter" when the fundamentals aren't really there. It's very subjective though - don't take this to mean much.

    I love the sound of the low notes through my Acme, which covers the fundamental. Nothing quite like hearing that 30Hz. But, in a band situation with guitars and drums, the impact of this is pretty minor (unless you're pretty loud, relatively).

    Also, I've found that many people don't even notice frequencies that low, unless they're isolated.

    But I've also noticed how good the B sounds through my Tech 2x12, which I don't know the specs on but I'm sure rolls off quite a bit higher than that (small, ported cabinet with two 12s stuffed into it, probably rolls off at 50Hz if not higher). You can't hear the fundamental at all really, but it still sounds "good".

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