Slight concern in my mind

  • Hi all. I bought a matrix amps nl12 cab to use with my powered kemper, it's rated at 60 watts. I went to their factory and tried a bunch of stuff, it was the best sounding option to my ears, and using it at home plugged into the speaker out from the amp, with the speaker modules off, is delivering some fabulous tones. I have played it pretty loud to break it in, and when I get 'carried' away, but as yet haven't had the chance to use it in conjunction with our drummer, but it certainly sounds loud enough. My slight concern is simply a few reports about the reports of speaker cabs being blown, and as this is intended to be my live rig, whether there is a risk for me, I would never anticipate turning the kemper up full, don't play the kind of venues that would warrant that at all, but even so, is there a risk, and if so, anyone any advice about a different way to use it?


    Welcome your thoughts chaps

  • Well, the power an amp outputs in its normal workflow is quite low. A 100-W amp, even loud, usually stays under 20 W (continuous output) But, spikes may happen, specially on clean sounds, and the temptation to raise the volume to compare with the drummer (or when you have the feeling you're not cutting the mix) crouches in the dark soul of any rock guitar player... ;)


    Having said this, 700 W (Kemper) against 60 (Matrix) is really a huge difference, and I'd never crank it up! You shall get used to not overcome a certain output level.
    Knowing the loudspeaker's minimum impedance it's possible to calculate how many dB would be safe to set the Profiler's output to. If I were you, I'd contact Matrix and ask them how is safe to set the Profiler's.


    :)

  • ...be sure to turn up the power amp boost a fair bit, which in the end is supposed to reduce spl-spikes in uncompressed sounds and... well, the celestion century vintage is only 150,-€ - you could drag one along as backup ;) exchange is easy. unfortunately it sounds like i know the problem... :S


    i'd love to have an option in the (powered) kpa to offer some limiter where you just dial in the eventual speaker wattage of your cab and be on the safe side... one century vintage might be "cheapishly" replaced, but how about 4 alnicos...? ;(

  • Ok, will have to check this out further to avoid a meltdown


    May seem like a daft question, but here goes, why put such a powerful amp in the unit without the ability to limit it's output other than by trial and error, surely it has the capacity to blow most cabs if the numbers are accurate?

  • Well, would you say the same if you bought a 100 W head? It would be your responsibility to couple it with a proper cab, wouldn't it? :)


    Having said this, +1 for a power limiter!


    PS: Note that, if a loudspeaker (or a combination) is tagged with a nominal power of say 100 W, you can safely use a power amp around 120-150 nominal power. A power amp outputs its nominal power only when the volume knob and all the tone controls are maxed out, and the power amp is fed with a very robust signal: a situation hardly matched in real life.

  • Thanks viabcroce for your usual honesty


    I get it now, am exploring trading up to their 2x12 which has a power rating of 120 watts so hopefully much safer territory


    It's just a pain I guess, this amazing unit is the centre of guitar playing life, it just seems that this extra function would prevent anyone with any cab from having to worry


    I love the nl12, it's frequency range is wider than a normal guitar cab, it's not frfr, but using it with the cab function off has allowed me to dial in my perfect sounds, it's just a tad frustrating, and worrying, that for those live occasions, I might suddenly descend into silence, which some might say was a blessing!

  • I bought the NL212 but had a word with them before committing as I had the same concerns. Apparently no need to worry, though admittedly there may be a difference with a single rather than double speaker.

  • I get it now, am exploring trading up to their 2x12 which has a power rating of 120 watts so hopefully much safer territory

    Yeah. I've seen that the 12" cone is tagged as 60 W continuous power, 120 W peak. So the 2x12" should be 240 W peak. You won't be able to crank the Profiler all the way up with it, but as you say it will be a much safer territory :)
    The danger practically remains tho, specially since the feeling of safety will possibly make your attention get loose. It all depends on how much volume you need.

  • I don't get beyond bar band with a drummer levels, I'd really hope that if I go up to 2x12 it should be capable of handling what I need


    Will experiment with the power amp boost in the next couple of days, now I understand that it's actually more of a form of compressor/limiter on high peaks


    Very grateful for everyone's advice


    As a completely random mention btw, got married on a hilltop in Umbria last year, adore your country


    Many thanks


  • Yeah. I've seen that the 12" cone is tagged as 60 W continuous power, 120 W peak. So the 2x12" should be 240 W peak. You won't be able to crank the Profiler all the way up with it, but as you say it will be a much safer territory :)
    The danger practically remains tho, specially since the feeling of safety will possibly make your attention get loose. It all depends on how much volume you need.

    Sadly, thats not quite right. The 16 ohm cone in the NL12 is indeed rated 60W "AES" .. which will handle 120W of music/programme so far so good.


    The NL212 has two of them .. so yes, it handles 120W AES, or 240W music/programme ...


    But ... the NL212 has an overall impedance of 8 Ohms, where as the NL12 has 16 ohms ... so while the maximum power of the Kemper is around 300W into 16 ohms ( about twice what the speaker can take) .. it is 600W into 8 ohms (again about twice what the speaker can take) so the situation is the same.


    Really it makes a lot more sense to think of the amplifier as a VOLTAGE source, not a power source. You can consider the speaker cone has a maximum voltage it will be safe with, so if you connect 1 of them or 2 of them across the amplifer terminals, the volatage applied will be the same.


    It would be great if the kemper had a "power level" control on the amplifer itself, allowing you to limit it to a certain level. They could even display it for both 8 and 16 ohms at the same time, which might help people understand that really you are setting the output voltage, not the output power.


    So, at the end of all that ... if you keep the maximum output around -6dB, you will be fine. this should deliver around 75W into 16 ohms (150W into 8 ohms) ... after that, it depends on your playing style etc, you culd push it as far as -3dB and still be safe if you are playing fairly dynamic clean tones. Probably best to stick to around -6dB if you play "heavier" stuff.

  • But ... the NL212 has an overall impedance of 8 Ohms, where as the NL12 has 16 ohms ... so while the maximum power of the Kemper is around 300W into 16 ohms ( about twice what the speaker can take) .. it is 600W into 8 ohms (again about twice what the speaker can take) so the situation is the same.


    Replacing one speaker with two gives you half as much power across each speaker - 600w through a 112 means 300w through each speaker in a 212. If the 212 is 8 ohms, that means it's wired in parallel, so the voltage hitting each speaker is the same but the current coming out of the amp is split between them. Thus, half the power.


    It's also worth noting that speakers don't typically have a voltage or current rating in their spec sheet, just power.


    It would be great if the kemper had a "power level" control on the amplifer itself, allowing you to limit it to a certain level. They could even display it for both 8 and 16 ohms at the same time, which might help people understand that really you are setting the output voltage, not the output power.


    This would be really neat to have - even just a couple of toggle buttons so the KPA knows if you're running to a FR speaker (and therefore wanting full power) versus guitar (and thus wanting to limit yourself).

  • Thanks for all the advice guys, I'm going to have to look at the db output level, I assume that's monitored on the front screen when you adjust the master output


    I have to say that if I'd known this issue could be this limiting, I'd have stayed with my first kemper and just bought a powered speaker, I thought it having the amp in was really neat and simple for live use, it's limitations really we're not clearly explained, not in words of one syllable for a dumb guitarist like me anyway


    Hey ho

  • This is the email from the really helpful people at matrix which basically re-confirms everything you have all said


    Seems to me this is a bit of an Achilles heel in the whole idea of the powered kemper, which wasn't, it doesn't feel like, clearly explained in it's presentation,and does slightly beg the question why when many of us are guitarists with cabs it wasn't configured so it could be safely used by us as well as those with high performance PAs


    bit fed up to be honest, although I still love it's sonic performance, wish I'd not gone near the powered deal


    Here's their quote


    "Hi Andrew,


    Hi Andrew, you mentioned you have an 8 Ohm NL12, if you want to swap the driver for a 16 Ohm one, thats not a problem. A 16 Ohm driver instead of an 8 ohm one will reduce the kempers power output by half, making things a little safer.


    You are welcome to upgrade to an NL212 if you wish, the NL212 has 2 x 16 ohm speakers wired across the amplifier terminals, so will handle twice the power of a single 16 ohm NL12 ... thats the good news.


    The bad news is of course that the Kemper will now see 8 ohms with the NL212, instead of 16 ohms with a single NL12, producing double the power, putting you back where you were, but now twice as loud :)


    Another way to look at it, the maximum position on the volume control will be the same for a single 16 ohm NL12 and the NL212, the difference will be that the NL212 will be producing twice the power.


    Remember the speaker is rated 60W AES (ie continuous) on music/programme material it will handle 120W, so an amplifier that delivers about 120W into 16 Ohms is about correct. The same setting will deliver 240W into 8 ohms, which is correct for the NL212, you may like to use a setting of around 100W / 200W peak to keep things a little safer.


    Let me re-state that again ... whether you are using a single 16 ohm NL12 (60W rated) or an 8 ohm NL212 (120W rated) the setting on the Kemper for maximum level will be the same. Assuming the Kemper is around 600W out ( I still cant find any mention of it in the site or manuals!!) and that is the 8 ohm figure, then the 16 ohm figure will be around 300W ... still too much, so if you set it at a level producing 100W into your 16 ohm NL12, when you plug the 8 ohm NL212 in, you will get 200W with the same setting. Thats the way amplifiers work, they are constant voltage, not constant power.


    I have no idea if the powered version of the Kemper has a "maximum power" or "power amp level" control, as I only have the non-powered one, but if there is some control, it would be an idea to not set it somewhere around 200W (peak) into 8 ohms (which will be the same setting as 100W peak into 16 ohms) this should drive both speakers nicely. Somewhere between -3 dB and -6dB of power amp attenuation would seem to be the correct figure.


    You are going to have the same trouble with ANY guitar cab out there ... nothing I know of will safely handle the Kempers full power of 600W into 8 ohms ... whatever cab you use, you are going to have to turn the power of the thing down from maximum to a lower level"


    .

  • They must advertise the powered Kemper differently in Europe versus the US. All the music supply chains in US (that I've seen) list the powered Kemper as 600W in all the advertising titles. In fact, that is why I decided against the powered version when I bought mine earlier this year. 600W was may more power than I would ever need and speakers to handle that much power were way out of my price range. Hope you find a solution that works for you.


    Tony

  • Well, I did not know there was an 1x12 16 ohm... It seems from the letter that Andrew owns the 8-ohm version tho.
    Yes, if you like the form factor you could just have your cone swapped for a 16-ohm one.


    IMO, the Profiler being "too powerful" is a false issue: if you keep the level low you'll sound as if it was less powerful, with the bonus of being able to drive more "powerful" loudspeakers in the future. You just can't crank it all the way up. Every 6 dB less in the maximum output level will cut the output voltage by half.
    Also remember that the maximum output is reached when (with the output LED unlit) the Master volume is cranked all the way up. That will be 600 (continuous) watts/8 ohm. Usually, output is much much less, and from there you can still lower the volume.
    When operating close to the loudspeaker's limit, one issue might be that the cone's impedance is by standard measured at 1 kHz. At other frequencies it might be lower.


    PS: You got married in Umbria? Gorgeous! :thumbsup: