Ohms question

    The Profiler Model referred to in this thread is ...
    ☑️ Profiler Head/Rack

    Hello everyone,

    I have a fairly unique question based on the gear I own. I did search, and know that I can use 4, 8, or 16 ohms with the Power Head.

    My question is, I have a Hughes and Kettner 4x12 cab (CC 412 A25).

    The cab has an option for Stereo (8ohms) or Mono (4ohms). If I were to select Stereo on the cab (there's a switch for stereo/mono), but Mono on the profiler, would I be using the 8ohms on my cab? and would I be losing anything from the Kemper?

    I feel like I know it'll work, but I also know that I'm uneducated in this area, so there might be something I'm missing.

    Thank you!

    You can use either with the kemper as it only has a mono power output and can accept 4, 8 or 16 ohms without issue.
    If the cab switch is set to mono, you will feed all 4 speakers in mono.

    If the cab switch is set to stereo you will only be feeding 2 speakers still in mono and the other 2 speakers will be silent.
    The ohms wont matter to kemper aside from a change in volume and punch really. 4ohm mono will be more immediate and louder whereas 16ohm mono will be a little more laidback as it reduces the kemper ouput.
    In order to feed stereo to the cab you need to hook up 2 amps, one to each input and if they are tube amps you'd need to use the 8ohm tap on each.

    The power amp probably has something to prevent overheating, but turn it up far enough and it’ll melt most any guitar speaker.

    Your ears will bleed before that. Or you’ll pass out from the pain. Or both. :)

    Ohms (resistance) relate directly to available power:

    4 ohms - 600

    8 ohms - 300

    16 ohms - 150

    Each time you double speaker resistance, wattage is cut in half. There’s no safety concern with any of these choices. 150 watts is ridiculously loud.

    This. 16ohms is probably your best bet as I believe that HK cab is rated at 100 watts. Keep in mind that the overload protection circuit in the kemper is to protect the kemper, not the cabinet.

    Quote from dfdfan

    This. 16ohms is probably your best bet as I believe that HK cab is rated at 100 watts. Keep in mind that the overload protection circuit in the kemper is to protect the kemper, not the cabinet.

    Is there any sign that I’m damaging my speaker?

    Our rehearsal space is small and I’m competing with loud drums and a Marshall JVM half stack. I feel like I’m cranking the Kemper up, I could feel my pant legs moving from the air coming off the speaker when I had it at a proper volume.

    It really doesn’t matter.

    Case in point - the powered Head and Rack come with a 600 watt (at 4ohms) amplifier. No guitar speaker is rated for that. Even at 8ohms, it’s 300w.

    The Kone speaker is 200 max at 4ohms.

    V30s are 60w. Greenbacks 25. All survive just fine plugged into 50/100w Marshalls etc.

    If you turn the amp all the way up, yeah….you’ll roach the speaker. But you’ll be so far past the pain threshold you’ll have done it on purpose.

    Practically speaking, the wattage of the amplifier doesn’t matter.

    Strictly from en engineering view:

    A speaker will have a wattage value. That value should include time. So a speaker rated for say 30w should be able to handle that forever. Or you will have angry customers returning dead speakers.

    It also takes time for heat to build up depending on the mass of the speaker coil etc. So playing at 35 watts for s hort time may not heat things up enough to do damage.

    There is also a time value on what is being played. Heavy bass beats will have high wattage usage only for short bursts. Metal guitar will be full wattage all the time. And the closer the sound gets to being a square wave the more power is being dissipated on the speaker.

    There are also physical movement limitations. The speaker cone can only move so far before it gets damaged, etc.


    All that said I have no useful help for how much to overdrive a speaker. Just trying to drop hints on what may cause it to fail eventually.

    Quote from JesseLuciani

    Is there any sign that I’m damaging my speaker?

    Our rehearsal space is small and I’m competing with loud drums and a Marshall JVM half stack. I feel like I’m cranking the Kemper up, I could feel my pant legs moving from the air coming off the speaker when I had it at a proper volume.

    Bad smell, bad sound and literal smoke in the air. I put a 25 watter in a 65 watt solid state peavey bandit once, cranked it to max just to see what would happen. It worked great for almost 10 minutes until the magnet assembly had a bitchy little meltdown. Smoke and fire. Good times.