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Stupid newbie questions on heads and cabinets

Discussion in 'Amps and Cabs [BG]' started by snatch, Oct 29, 2000.

  1. snatch


    Sep 24, 2000
    First off, Im stupid. Second, what is a "head" and a "cabinet/cab"? what is a "ohms", what is a "watt" and what is the difference between a "head" and a "cab". I am pretty sure that you need a "head" to have a "cab". Thanks. Also, please dont make fun of me :)
  2. First off, you're a beginner.. none of us knew this right away so be quiet :p

    second.. the head is the amp thta powers the cabinet... the cabinet is just a thing that holds the speakers (unlike in combos where the speakers and the amp are together)... ohms.. I'm not going to get into that.. we'll have the super-techs getting into it and it'll make sense until they start giving you all the equations and stuff.. but the most common ohms you will see are 4 and 8.. then you have 8 ohm cabs.. you have a total of 4 ohms.. and 2 4 ohms.. 2 ohm total.. it's not good to have too little ohms if your amp can't handle it.. anyway.. I'll let everyone else give the better answers now! later and good luck!

  3. jazzbo


    Aug 25, 2000
    San Francisco, CA
    Jim Roberts has the definitions I like best:

    An amplification system has four main components: preamplifier, signal processor, power amplifier, and speaker cabinets. The preamplifier has an input jack, where you plug in your instrument cable. The preamp's main job is to prepare the signal coming from your bass to be amplified, primarily by boosting its voltage. Most preamps have a signal processor section, which may be as simple as bass and treble tone-control knobs. In most modern amps, this section includes an equalizer, and it may also have built-in effects units, such as a compressor and/or chorus.

    After the signal has been adjusted by the preamp and modified by the signal processor, it's passed along to the power amplifier. This is where it's increased to the boltage level required to be loud.

    The last step in the signal chain is the speaker babinet, where electrival energy is converted into mechanical energy by the speakers. To do this, the electrical signal is passed through a voice coil attached to aflexible cone; as this cone moves in and out, it produces sound waves in the air.

    Okay, so those are the components of an amplifier. The simplest type of amp is a combo amp, which has all the components in a single unit. They make great first amps, or practice amps. Another type is a stack or piggyback system consisting of a "head" (sometimes called a "brain") and one or more speaker cabinets. In this type of system, the preamp, signal processor, and power amp are all contained in the head enclosure. "Cabs" are just the cabinets that hold the speakers.

    Any electronic circuit has 3 properties of importance: voltage, current, and resistance. (Plus some more based on these three). Electric current consists of electrons moving along the wires. Voltage is the amount of energy carried by each electron. Current is the nubmer moving passed in each second. The total power of the circuit is given by:

    Power = voltage * current

    - thus, increasing either the voltage or the current will increase the power of your amplifier.

    Resistance is the tendency of a circuit to resist the flow of electrons (hence the name). The formula for resistance is:

    Resistance = voltage/current, or, current = voltage/resistance

    Thus, for a given voltage, a circuit of high resistance gives low current, and a circuit with low resistance gives high current.

    Voltage is measured in volts: you get 110 volts out of the wall (220 if you're in Europe). This is usually transformed by the amplifier to some other voltage, and there's not much you do to change it. However, you can alter the resistance of the circuit by changing the resistance of the speakers. Changing the resistance will change the current flow, and therefore the power of the circuit. resistance is measured in ohms: typical speakers and cabinets have 8, 4, or 2 ohms resistance. The current of a circuit can be deduced from these. Power is measured in watts.

    Thanks to Bassplayer magazine.

  4. Matthias


    May 30, 2000
    Vienna, Austria
    Thanks jazzbo!
    Short and precise!

    White Knight:
    That's a good one for the future FAQ section! ;)

  5. snatch


    Sep 24, 2000
    Ok, so.... I want to get a lower end "Head" and "Cabinet", maybe totaling $800 or less. Because I dont have a job, I am going to need to earn this money $10 at a time maybe. But me and my friends are going to start a band, and when we get gigs, Im going to need something that will reach. So another question, how do you know how loud your "Cab" will be?
    And, so you are saying that I need a 4 ohms "Head" and a 4 or 8 ohms "Cab", because the "Head" needs more wattage, so that Im SURE that it will be enough to power my "Cab" right?<p> By the way, I just got Primus's "Tales from the Punchbowl", you guys like Primus right?! YEA BABY!
  6. pkr2


    Apr 28, 2000
    coastal N.C.
    Snatch, there are no stupid questions, only stupid drummers and guitarists.:) :)

    It's a joke, Bruce. Don't even go there! :)

  7. jazzbo


    Aug 25, 2000
    San Francisco, CA
    Do you know what type of music you'll be playing, what types of gigs, how big of a venue and crowd, and what the instrumental lineup of the band will be? This will help give a better idea of what you might want to purchase.

    My best advice is to get more power than you'll need now. You can start with a combo amp. They're definitely within your price range, and can support certain gigs, but with a head/cab rig you're going to give yourself more room to grow, because if you're like me, inevitably, you'll find that you keep wanting more and more headroom.

    You don't necessarily need a 4 ohm cab. Most cabs will provide a rating at 4 and 8 ohms, and possibly 2. How loud your cab is will depend upon the type of speakers in the cabinet, the wattage, and the impedance. One thing I didn't mention earlier is that there are different variations of speakers in cabs. You can have a cabinet with 2 10" speakers, 4 10" speakers, 1 15" speaker, 1 18" speaker, or many other variations. A 210 cab, or a cabinet with 2 10" speakers, will sound different than a 118 cab, or cabinet with 1 18" speaker. They're used for different purposes.

    If you have a head that's rated at 300 watts into 4 ohms, and your cab is rated 8 ohms, you're getting less than the 300 watts, because of the higher impedance on the speakers. You'll probably be closer to 200 watts or less. If you had a 4 ohm head, a cab with 2 10" speakers that's rated at 8 ohms, you would need another 8 ohm cabinet to get the full 300 watts for that head.

    So, with a 4 ohm head, you would need one 4 ohm cab, or two 8 ohm cabs. This is when you get into bridging and all that, which I am still learning about.

    Does that help, or confuse further? :eek:

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