2 broken 12" speakers in the same day with powerhead¡¡¡¡¡¡¡¡gggggggggggCAUTION

    Hm.


    FWIW I'm currently using a Weber Vintage 12F 100W RMS 16 ohm speaker in a 1X12 cab with my Powerhead (although hope to move to a Beyma 12GA50 soon).


    The reference manual spec says 300W for 16 ohm load and 600W for 8 ohm. No mention of type (AES, RMS, peak, or otherwise), so not certain exactly what the power is, however since it is half the value with twice the impedance, suspect it may be RMS (look at the definition of RMS power and you'll see what I mean, for same peak voltage twice the resistance yields half the power). ANYWAY I am really paranoid about blowing the speaker, so I don't use any power boost at all, keep the monitor output level below -2 or -3dB, and keep the front panel level less than about 5/8 and I haven't had any issues with the speaker, and it seems to have plenty of power. Ran it for three 1 hr sets the other night and no issues with the speaker. The little 1X12 (with a closed back, no less) was clearly heard above my quite-loud band (my FOH connection had some problems, so was running on cab itself plus a K10 monitor for myself driven from the main out). And that is with a 16 ohm speaker.


    Not sure if it may have contributed, but - was the cab sim on? I do have my cab sims off. I noticed that the sound is sort of thicker and louder in some rigs with the cab sim on and currently don't use them with my 1X12. However, if you had them on, perhaps some of the transients may have been enhanced and over time overheated the coil. Just throwing out an idea.

    I'm fairly certain I understand what it means... are you saying that, by increasing the boost level, you decrease the volume?


    From the Basic Manual, page 27:


    "Power Amp Booster
    As mentioned, the power amp is connected to the Monitor Output, which provides enough headroom to
    support even loud attacks and transients of clean guitars. However, this comfortable headroom will naturally
    lower the signal volume for the power amp, so you might not achieve the desired loudness. Turning
    up the Power Amp Booster will increase the loudness by up to 12dB.     Although this will shrink the headroom,
    this is no bad thing, as this happens in tube amps as well. Very loud signals and transients will then
    be compressed by a nice, organic-sounding soft-clipping circuit."


    I understand this to mean that, as the Power Boost level is increased, the continuous power delivered to the speaker increases and the headroom (the remaining available volume before clipping) decreases. When the amp hits the ceiling, it soft clips, as it states. As pointed out in the manual, it is the same as in tube amps, you can turn it up but as you do so you lose clean headroom. A tradeoff, as usual. Increasing the Power Boost level increases the continuous power delivered to the speaker. Hence my concern at cranking it up.


    The Power Boost level is nominally set to allow maximum clean headroom (0 dB, as I recall) and if you turn up the Power Boost level the loudness increases, at the expense of clean headroom. I have verified this personally wth my Powerhead. It says it can provide up to 12 dB of loudness, going by power increases by 3 dB for every doubling of loudness, that works out to 8 times as loud. I know I turned it up to 6 dB and it was considerably louder, I didn't measure it with my level meter but it certainly could have been 4X as loud.

    Quote from ucnick

    I'm fairly certain I understand what it means... are you saying that, by increasing the boost level, you decrease the volume?


    No, what I try to say is: If you increase the booster, you can reduce the level to achieve the same volume like before. You don't just add Boost to get even more volume out of your speaker. You use it to get the same volume with less power peaks from hard attacks and transients (less headroom).

    TBH, I'm not sure I'm following either... At a given pressure level, the loudspeaker sees the same current (both peak and RMS) regardless themix between volume and booster. The manual quote just says that, if you use the booster, you earn volume but loose headroom.


    Am I missing something? :huh:

    Yes, I think you're missing something. :)
    If you record an uncompressed audio signal with lots of dynamics ... and you take care that the peaks stay just below clipping, then the overall perceived volume is much less than with a compressed signal recorded just below clipping. So with both signals you have the same max level, but one of them is much louder. That's what is used for pretty much ALL commercially produced pop music. They reduce the dynamics using compression.


    The above said can easily be translated to the Power Amp Booster. You can increase the loudness of your Power Amp Output while still making sure that you don't increase the peaks at the same time. Add some Power Amp Boost and roll back the overall Output level. You'll loose some headroom (dynamics) but you increase the perceived volume within the limitations of your "weak" speaker. It's like "keep the peaks below 100W but at the same time increase the lower volume parts of your playing".


    I don't know how to explain better in english. Sorry if I can't make it clearer than that.

    Quote from Ingolf

    No, not the speakers (we don't want speaker distortion!!) but the poweramp gets driven into saturation more easily because there is less headroom in a 50 W tube amp than in a 100 W.



    With the poweramp of the powerhead/powerrack being as neutral as possible we don't want it to distort EVER (contrary to a tube poweramp). You're right about the amazing clean headroom the 600W poweramp in the powerhead provides.



    Thank you, Ingolf, for such a clear explanation. That all makes perfect sense now.

    so basically it's the output limiter someone got bashed for asking for here recently, because one would loose all that great dynamics of the profiler...? :P
    another question: it only concerns the poweramp, right? monitor out, main out, etc. are not affected?

    Today in a music store we played a Kemper Powerhead the entire day into a JVM 2x12 ( one Heritage and one Celestion) with the Poweramp Booster set halfway, 6dB... the volume was so loud that I now have toothache. :D
    No problem with the speakers, and the same setup will be gigged 3 times this weekend.


    I can't even describe the tone, it was simply unbelievable, only using factory Profiles.
    The stock 'Kemper AC30' Profile sounded so incredible (yes, through the wrong speakers :D ) that a guy standing listening who gigs a real AC30 conceded he couldn't get that kind of tone using his real amp.

    I have a question regarding the JVM212 and in general: How would you mic such a cab with two different speakers live? How can I make sure that the mixed sound of both speakers is captured? Or in other words: What's the best position for the mic?

    I could have farted and it would have sounded good! (Brian Johnson)

    Quote from lightbox

    Yes, I think you're missing something. :)
    If you record an uncompressed audio signal with lots of dynamics ... and you take care that the peaks stay just below clipping, then the overall perceived volume is much less than with a compressed signal recorded just below clipping. So with both signals you have the same max level, but one of them is much louder. That's what is used for pretty much ALL commercially produced pop music. They reduce the dynamics using compression.


    The above said can easily be translated to the Power Amp Booster. You can increase the loudness of your Power Amp Output while still making sure that you don't increase the peaks at the same time. Add some Power Amp Boost and roll back the overall Output level. You'll loose some headroom (dynamics) but you increase the perceived volume within the limitations of your "weak" speaker. It's like "keep the peaks below 100W but at the same time increase the lower volume parts of your playing".


    I don't know how to explain better in english. Sorry if I can't make it clearer than that.

    That reads most clearly. The impulse-peak destroys the speaker. If you lower the possible dynamic-range in the output-stage (by increasing power-amp-boost), you achieve a higher output level. So you can reduce the output-level via the volume-knob on the front and simultaneously get less peak-overdrive.

    The information about the Power Amp Boost is not correct, unfortunately. This might be inspired by the wording in our manual that are a bit misleading:


    Turning up the Power Amp Booster will increase the loudness by up to 12 dB. Although this will shrink the head- room, this is no bad thing, as this happens in tube amps as well.


    I will change the words to:


    Turning up the Power Amp Booster will increase the volume loudness by up to 12 dB, in addition to the other volume controls in the signal flow, such as Monitor Volume or Rig Volume. Although this will bring the signal closer to the headroom ceiling, this is no bad thing, as this happens in tube amps as well.


    That means, the Power Amp Boost is just a simple volume control. It does not shift the headroom towards to a lower wattage or earlier soft clipping.

    Ups - yes, that's the oposite what most uers expect - if Power Amp Boost is used the speaker is even more in danger to be damaged!

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    I really can not believe it !
    I played for months now with my Kemper power rack and use the power boost at +_10db.
    With one or two speakers at 8 ohm ( celestion v30s ).
    It is loud but not any louder than a half way turned up Engl sovereign or a Bogner 100 watt Ecstacy with the same speakers.
    So should the speakers get damaged ?
    Never had a blowed up a celestion, not with the Kemper at full volume and not with any other amp.