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Proper Precautions Playing with Plenty of Power


KikkyMonk

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I bought a crown k2 (800 WPC @ 4 Ohms) for my 2 acme b-2s and dont want the cones to be sent into a low orbit.

 

How should I power up the system and how can I be sure that im not damaging the speakers? I want to know how to safely turn up the volume and how to know when I shouldn't turn it up no 'mo.

 

Also how should I have the gain structure set? High preamp output with lower amp output, or lower preamp output with higher amp output?

 

I want to protect my investment!

 

Dave

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I was taught to power up through the signal chain (front to back), (but that may have changed with recent equipment advances)...trying to avoid surges/peaks from loading up the next step in the chain.

As far as Gain Structure...that may depend on the tone you're looking for, and the bass you're working with. I used to use (decades ago) a Furman pre-amp/parametric and PAS Amp, and the only way I got great tone was to jack up the pre-amp signal...different strokes, maybe...check the manual - they may have specific instructions and schemes.

Jim

Confirmed RoscoeHead

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Power-amp always goes on last, no matter what the application. You should have your power amp set pretty high and adjust your volume with volume knobs, not the speaker's power output controls.

 

Are the Acme's 4 or 8 ohms? If they're 4 ohms a piece, the crown should still be able to handle the 2 ohm load (although I don't know this model's specs), the amp will need some serious cooling if it's delivering a lot of 2 ohm power for a long time.

...think funky thoughts... :freak:
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They are 4 ohms. The crown has 2 channels which should run at 4 ohms each with the 4 ohm speakers. I dont think that it will drop to 2 ohms because its a two channel amp. If it does than I've made a HUGE mistake.

 

Dave

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The speakers handle 350w (and Andy at acme says 500w is a good number) but my k2 outputs 800w. I know that this is alright to do so long as the volume isnt set too high.

 

But how do i know when the volume is being set too high? I dont wanna get my amp, crank it up, and blow a speaker.

 

Dave

 

Thanks for the advice so far. Powering the power amp up last is a good one!

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firstly, the K2 can handle the 2 ohm load, although there's really no reason to do that. i would be shocked if cooling ever became an issue: the chassis is made of 14 gauge aluminum with a thick, cast aluminum faceplate for excellent passive cooling. it can get rather warm to the touch when you work it hard, but that's ok, and the amp is fine with it, too. if you're still paranoid, mount it in a rack with some space above and below it. then set the rack on its side. because warm air rises, it actually draws a small amount of cool air over itself, and you have your very own convection cooler.

 

i think the best way to run it is to give the power amp as much volume from your preamp as possible, set the gain switches to 1.4V, and turn the Y-input switch to on. that puts the same signal on both channels (it doesn't matter which input jack you use). as far as volume, i don't think you understand how loud the K2 gets -- especially with two cabinets. i doubt you'll ever go much past halfway, although maybe two-thirds every so often. i wouldn't be worried if it were my rig (though i like 8 ohm cabinets, so i would have no reason to worry... :P ). the beauty of the K2 is that, no matter the cabinets, it's pretty much going to deliver a boatload of clean, tight bass that is very loud. you don't have to worry about putting cabinets together or what the ohm rating is.

 

the reality is that you'll probably never actually drive 800W out of your amp -- most preamps just aren't hot enough to give the amp that much signal, and even if they are, it will be for only very brief moments. everything in audio is measured and rated with sine waves (RMS, continuous, etc.), which is an order of magnitude more energetic than a bass guitar signal, which is all peaks.

 

the only other advice i'd offer is to watch the IOC LEDs (they're the amber ones between the clip LED and the signal LED). if they ever come on, try turning down a notch on the amps controls. you'll probably have already done that, though, because that kind of volume will make your ears ring after a few minutes.

 

good luck and enjoy. if you have any questions at all, of any nature, about the K2, private message me. we've really only scratched the surface...

 

robb.

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why do you prefer 8 ohm cabs?

 

Thanks for the nice write-up. So pretty much my ears should hurt before I am at any risk of blowing a speaker? I don't think I'll need that kinda volume as there are PAs but I figured with the amount of money I got that I should buy one really nice amp with enough power to do anything I want too and be mantainence free (the major reason with getting the K2 instead of the MA)

 

Anywho

Dave

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Originally posted by KikkyMonk:

I figured with the amount of money I got that I should buy one really nice amp with enough power to do anything I want too and be mantainence free

i agree with that theory; i think you made the right decision. play with your new toys. treat them with kid gloves at first, but i think you'll find your limits. as long as you don't turn everything all the way up, you should be ok (except for your ears).

 

as for 8 ohm cabinets, there are many reasons why i prefer them. i'll start with the amplifier. most people prefer 4 ohms, because they get more power out of the amp, which is fine. you'll always get more power from any given amplifer into 4 ohms than into 8 ohms.

 

it's more difficult to design an amplifier with high voltage and high current, so most bass heads and PA amps that are generally affordable just don't have enough high voltage to adequately power an 8 ohm load (high current is a must). when you have an amp that does both, though, as in the K2, you can reap the benefits.

 

primarily, an 8 ohm cabinet draws less current than a 4 ohm cabinet at the same power level, so it puts less stress on the amplifier (at 400W, 4 ohms draws 10A, 8 ohms draws about 7A). less current equals less heat equals happy amplifier. and while i'm on the subject, heat is the bane of good sounding loudspeakers, so if you can get the higher level of power without as much current, your speakers will not compress thermally as much. this gives you longer lasting power and cleaner, more dynamic sound.

 

secondarily, an 8 ohm cabinet will be tighter in the bass. damping factor is the ratio of the load to the amplifier's output impedance. so when an amp has a damping factor of, say, 3,000, as in the K2, what that means is that its output impedance is about 600 micro-ohms. 2ohms/600u-ohms = 3,000. 8ohms/600u-ohms = 13,000. so with an 8 ohm cabinet, you're going to get tighter bass and a more controlled, detailed sound.

 

the drawback is that you have to have a really high voltage amplifier to adequately power an 8 ohm load, and that costs more, so most folks can't or won't pay for it. 8 ohm cabinets put less stress on the amplifier and on themselves, and sound better in almost every way. those of us who have the luxury of a powerful amplifier (can i hear an amen, PJR?) may as well get 8 ohm cabinets and reap the benefits.

 

robb.

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Originally posted by robb.:

primarily, an 8 ohm cabinet draws less current than a 4 ohm cabinet at the same power level, so it puts less stress on the amplifier (at 400W, 4 ohms draws 10A, 8 ohms draws about 7A). less current equals less heat equals happy amplifier. and while i'm on the subject, heat is the bane of good sounding loudspeakers, so if you can get the higher level of power without as much current, your speakers will not compress thermally as much. this gives you longer lasting power and cleaner, more dynamic sound.

 

secondarily, an 8 ohm cabinet will be tighter in the bass. damping factor is the ratio of the load to the amplifier's output impedance. so when an amp has a damping factor of, say, 3,000, as in the K2, what that means is that its output impedance is about 600 micro-ohms. 2ohms/600u-ohms = 3,000. 8ohms/600u-ohms = 13,000. so with an 8 ohm cabinet, you're going to get tighter bass and a more controlled, detailed sound.

 

the drawback is that you have to have a really high voltage amplifier to adequately power an 8 ohm load, and that costs more, so most folks can't or won't pay for it. 8 ohm cabinets put less stress on the amplifier and on themselves, and sound better in almost every way. those of us who have the luxury of a powerful amplifier (can i hear an amen, PJR?) may as well get 8 ohm cabinets and reap the benefits.

 

robb.

Thanks for that explanation. Much appreciated. I knew the part about damping (although not the actually formula), but it was good to read the rest.

 

You da' man, robb.

 

Peace,

--sweets

spreadluv

 

Fanboy? Why, yes! Nordstrand Pickups and Guitars.

Messiaen knew how to parlay the funk.

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Thanks Robb!

 

I'm very impressed by your knowledge and your willingness to teach others! If you don't mind me asking what were your duties at crown? I realize you do not work there anymore so it is all the more impressive that your still hold a special regard for thier products. It speaks loads about crown.

 

Anywho thanks for the help!

 

I changed my order to 8 ohm cabs. I figure I have the power (500w @ 8 ohms) so why not go with less heat and better bass (that is what I play after all!) Also 500w is what Andy @ acme recommends so I will not live in fear of ruining my cabs with too much power. And last but not least I can run 4 b2s 2 on each channel. :D I don't think I'll ever need to though.

 

Dave

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Originally posted by KikkyMonk:

I changed my order to 8 ohm cabs. I figure I have the power (500w @ 8 ohms) so why not go with less heat and better bass (that is what I play after all!) Also 500w is what Andy @ acme recommends so I will not live in fear of ruining my cabs with too much power. And last but not least I can run 4 b2s 2 on each channel. :D I don't think I'll ever need to though.

 

Dave

Remember, you can run both cabs bridged mono. The K2 is 500W per channel into 8 ohms stereo, which is probably plenty of power. But it's 1600W bridged mono into 8 ohms if you wanted to use one cab and 2500W bridged mono into 4 ohms if you ran both 8-ohm cabs parallel -- that's over 1000W per cab! Plenty of headroom -- even for Acme cabs!

 

You may not need to run stereo at all.

spreadluv

 

Fanboy? Why, yes! Nordstrand Pickups and Guitars.

Messiaen knew how to parlay the funk.

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Originally posted by KikkyMonk:

If you don't mind me asking what were your duties at crown?

i was a design engineer. it was my first job out of school, so don't think i actually designed anything of what i'm talking about. i learned a lot about how a proper amplifier is designed and built, and a lot about how to be a professional design engineer, but i didn't get to design anything serious.

 

i'm trying to get my explanation chops up, because i've always played with the notion of teaching about audio and electronics. i like to teach.

 

cool. anything else that you ever need explaining, let me know. this is my life, my career, my hobby.

 

robb.

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I always wondered why 8 ohm cabs seemed to sound much tighter to me. Your explanation has helped me get rid of the idea that it was all in my head. I thought it might be psychosomatic. You know...just a perception thing.

 

My current band has a very loud stage volume. I'm using a single 400 watt, SWR, 8 ohm, 4x10 speaker cab, powered by a GK-1001RB, which is giving me a solid 350 watts RMS with the 8 ohm load. The sound is VERY tight indeed.

 

I run the GK with the power amp control maxed out, and control my volume by adjusting my pre-amp gain over a very small sweep from about the 11 o'clock to 1 o'clock position on the knob.

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Don't forget that heat is a nasty thing, especially with digital electronics. Even if the amp cab handle the heat it produces (as any decent amp should), don't expect other things in your rack to have similar abilities. Cooling spaces and an open back rack are crucial, especially with loud volumes and long sets.

 

And don't forget the cables! Get cables that are as large as are practical.

...think funky thoughts... :freak:
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Originally posted by matt C:

And don't forget the cables! Get cables that are as large as are practical.

Just to clarify, by "large" you mean thick (or lower gauge), not long, right? I've been under the impression that keeping cables as short as is feasible is the way to go.

 

Thanks.

spreadluv

 

Fanboy? Why, yes! Nordstrand Pickups and Guitars.

Messiaen knew how to parlay the funk.

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that is absolutely correct: keep them as short as practical, and as large in gauge or diameter as possible. and as long as i'm talking diameter, make sure it's not just insulation (a la Monster Cable), but actual copper that makes the cable fat.

 

i use ProCo FatMax speaker cable, because i got it for free, and because it's 8 gauge. that's sick.

 

think about it in terms damping factor -- whatever resistance the speaker cable is can be added to the output impedance of the amplifier, and down goes your damping factor. if your cable is 10 milliohms, for example, and your amps output impedance is 600 micro-ohms, your damping factor at 8 ohms goes from 8/600u = 13,000 to 8/10.6m = 755.

 

robb.

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I looked up the pro co fat max and noticed they only sold them in 25 or 50 foot lengths. I don't want a 25 foot speaker cable. At most I want 5 feet!

 

Is there anything to do about this? I have spent lots of money on a nice amp/pre/and cab... and dont wanna skimp on the speaker cable.

 

Dave

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Just about any place that does pro sound rental and repair will custom make a cable for you of any length, and do so with very high quality heavy gauge wire and pro quality connectors. You can save even more money by just buying the wire and connectors and making the cable yourself.

 

If you're gonna go with 1/4 connectors, go with Nutriks connectors, and wire with a gauge number 14 or smaller. The smaller the number, the heavier the gauge. My speaker cables are all made with Nutriks 1/4 connectors and 14 gauge wire. They sound fine and are completely trouble free.

 

As a matter of fact, all my instrument and studio routing cables have Nutrik connectors on both ends. I highly recommend them.

 

:thu:

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Try to go with Speakons or banana plugs if you can. As stated before, both of these are better for handling high power than 1/4" plugs. That Crown's got plenty of power.

 

In terms of finding out where you can get short, fat speaker cables, you can always try calling or e-mailing a bass-centric music store that does national business. The first two that come to mind are:

 

Bass Northwest

Bass Central

 

The other thing you can do is contact Andy at Acme, who made your speakers, and ask him for advice about where to score your "perfect" speaker cable.

 

Peace.

spreadluv

 

Fanboy? Why, yes! Nordstrand Pickups and Guitars.

Messiaen knew how to parlay the funk.

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the K2 only has banana outputs. you can, however, get a cable that is banana on the K2 side and speakon or banana on the acme side.

 

check out sweetwater. they have a six foot banana to speakon cable that also comes in three foot and ten foot lengths. it's also available banana to banana.

 

i like fat max specifically because the connections are sonically welded. a welded connection is better than solder or solderless (e.g. set screws, like on a speakon) connection, so you'll have less resistance and transfer more current to your speakers.

 

i'm sure there are other speaker cables like this out there. i used to live in kalamazoo, MI, where ProCo is, so i'm kind of partial to them. i also know their former national sales manager, so i got mine for free. :D

 

robb.

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Great links, robb. Those 8-gauge cables seem like they'd be pretty awesome.

 

Dave, you could also check Monster Cable speaker cables to see if they have anything of interest. Unfortunately, their webpage doesn't give specifics about gauge. Maybe I didn't look hard enough, though. They do offer the option of having different types of connectors at either end of the cable. My guess is, though, that those ProCo cables would do you right (and probably come in cheaper than Monsters).

 

Peace.

spreadluv

 

Fanboy? Why, yes! Nordstrand Pickups and Guitars.

Messiaen knew how to parlay the funk.

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