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Amp & Cab Compatible?

Discussion in 'Amps and Cabs [BG]' started by Kyyyle, Oct 25, 2018.


  1. Kyyyle

    Kyyyle

    Oct 25, 2018
    Hey everyone,

    I'm new to this, so please go easy on what may be a dumb question.

    Could I use a Hartke LH500 amp head (500 watts at 4 ohms) with a Hartke 4x10 Transporter cab (300 watts at 8 ohms). I'm still figuring out watts and ohms and amps and how it applies to speakers.

    Thanks!!!
     
  2. el murdoque

    el murdoque

    Mar 10, 2013
    Germany
    Yes, you can.

    In a Nutshell: When you have a solid state amplifier, the Ohms rating on the amplifier specifies the minimum load.
    You must not connect cabinets with a total load of less than that. The amp will do the rest.
    When you couple an 8 ohm cab with a 500W@4 ohm amp, you will get roughly 250-300W from the amp because it's not running at its limit.

    Add another 8 ohms cab later and the total load goes down to 4 ohms and you get full power.
    Add another 4 ohms cab later and the load drops to 2,67 ohms and you'll harm your amp.
     
    Eric DK and saabfender like this.
  3. Raf Seibert

    Raf Seibert

    Dec 16, 2013
    Texas
    Read the sticky. However, you should be fine. Just keep your ear peeled for sounds of distress from the speaker. Basically, you just don’t want to turn it up all the way.
     
    interp and Old Garage-Bander like this.
  4. The power (watts) rating for an amp is what the amp can produce given the load (speakers).
    Example: Amp is rated for 350 watts with an 8 Ohm load and 500 watts with a 4 Ohm load.
    Also the minimum Impedance (Ohms) rating of an amp means do not go below this number.
    Example: If your amp has a minimum rating of 8 Ohms, do not use a 4 Ohm cabinet or any combination of cabinets that equal less than 8 Ohms.

    There are a number of "types" or ways that power can be described, they are all in watts but you also need to pay attention to the wording that further describes the power. Peak, Music, Average, RMS are some of the most common. Be sure when making comparisons with amps and speakers that you are using the same type of power rating.

    For speakers, (or cabs) the power rating is how much power the speaker can handle.
    The impedance is how much of a load it will present to the amp.
    Speaker ratings may be determined at a certain frequency that does not include all of the bass spectrum.
    One may have to de-rate the speaker power rating for use with bass, even if it is a bass cab.

    This is the simple version. Definitely read the sticky as a starting point for your education in these technical details.

    Welcome aboard and if you still have questions after reading the sticky, please come back and ask.
    Like anything, it's not too bad once you start catching on. It just seems rather daunting when you try to take it all in at once.
    The more you learn now, the more you will be able to learn later.
     
  5. Jim Carr

    Jim Carr Dr. Jim Gold Supporting Member

    Jan 21, 2006
    Denton, TX or Kailua, HI
    fEARful Kool-Aid dispensing liberal academic card-carrying union member Musicians Local 72-147
    The above posts are all very helpful, but I feel I must add a caveat or two. Manufacturers frequently choose to rate their products in ways which make speakers or amplifiers look more capable than they actually are. There is no end to the silliness that ensues, but a good rule of thumb is that the weak link in most rigs is the speaker cabinet(s).

    In fact, in most cases, you can damage an average bass speaker with a ~300 watts @4 ohms amplifier by playing in the lowest register of the bass while boosting low frequencies and running the gain and volume at or near max.

    In addition, one may be tempted to think that a 600 watt amp is twice as loud as a 300 watt amp. This is not the case. To double apparent loudness, you need to multiply the power (watts) by 10. Thus, a 3000 watt amp is potentially twice as loud as a 300 watt amp. As you can see, with everything else being equal, the loudness difference between a 600 watt amp and an 800 watt amp is not that great.
     
    Last edited: Oct 25, 2018
  6. You got that right!

    This subject is complicated enough as it is for those who don't have some of the initial necessary background.
    It really gets -wack- when you have to sort through the marketing that is designed to take advantage of the technically inexperienced or uninformed.

    There are more uninformed opinions, myths, half truths, hype, fudging and outright lies in this area than you can shake a stick at.
    Be glad this isn't something sold used, on corner lots, by fast-talking people who wear cheap, plaid suits. (Though sometimes it feels like it.)
     
  7. two fingers

    two fingers Opinionated blowhard. But not mad about it. Gold Supporting Member

    Feb 7, 2005
    Eastern NC USA
    Welcome to TalkBass!!!!!

    Yep. You're good to go. As with any watts questions and amp/cab combinations, one you determine they are compatible from an ohms standpoint, use your ears.

    What that means is that the thermal power handling rating of a cab does NOT mean a 400W cab can take a 400W amp turned all the way up. So listen to your speakers. If they start to distort, back down in the volume.
     
    Old Garage-Bander likes this.
  8. Yup - no problem. Just don’t crank up the bass frequency and the volume. It’s a bass guitar amp, NOT a subwoofer. Once you understand that, you should be pretty safe.
     
  9. Great example except for a typo in the last load:

    - If you add another 4 ohm load in parallel to 4 ohm you get two Ohms, not 2.67 ohms.

    - If you add another *8 ohm* in load in parallel to a 4 ohm load you get 2.67 Ohms.
     
  10. el murdoque

    el murdoque

    Mar 10, 2013
    Germany
    Add to what?

    His cab is an 8 ohm one.
    If you add an 8 ohm cab, you get a total load of 4 ohms

    If you add a 4 ohm cab, you get a total load of 2,67 ohms.

    ...just as I wrote.
     
  11. Oh I misunderstood, you were saying an 8 ohm OR a 4 ohm, not sequential. They way you wrote it seemed like consecutive additions rather than two exclusive options.
     
    el murdoque likes this.
  12. el murdoque

    el murdoque

    Mar 10, 2013
    Germany
    Ah okay. I suppose one could read it like that - I just thought most people somehow naturally stop at two cabinets and refrain from adding another.
     
    HolmeBass likes this.
  13. groove pump

    groove pump

    Oct 24, 2006
    So NOT a dumb question. If you can't ask here, where can you ask, right?

    Keep in mind down the road that if you need to be "loud enough" for your specific situation, it's generally easier to get louder by adding more speaker so that you can push more air. You may easily get that in the form of an extra cab as long as your head can handle the minimum resistance (ohms).

    You have a substantial setup on your hands now, but most rigs have their limits. I've learned this the hard way in the past, so I thought it might be good food for though here. Even if you triple your power by let's say switching to a different head, your speakers are still the same speakers.

    I can also say that I've benefited from changing my cabs from just okay options into premium alternatives that are a good deal better at putting out sound - and can also handle higher wattages. With my better cabs - I use a pair of 2x10's - I can play at the same volumes without flirting with my speakers "farting out".

    Agree with our pals - your head and cab matchup looks good. If your cab is eventually straining for some reason, you'll probably (hopefully!!) hear it and be able to adjust without much trouble.
     
  14. I think you are right - *most* people understood it as you intended! I got confused, thanks for helping me sort it out.
     
    el murdoque likes this.

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