over/underpowering speakers...very confused...

Discussion in 'Location Recording' started by tr3eman9, Apr 22, 2009.

  1. tr3eman9

    tr3eman9 Guest

    Hi all,

    My speakers are damaged, and I want to know why. Here's the situation:

    -Berhigner (sp) EP2500 amp (rated "2x1200 W @ 2 ohms, 2400 W @ 4 ohms mono bridged)

    -2 Harbinger Dual 15" speakers, each 600 W, 4 ohms

    -Usually we also hook up several 150 W monitors. Not sure on impedence

    I believe we usually use the amp in 'parallel mode' and plug one of the Harbingers into one channel, then daisy-chain it to the other one. The monitors are daisy_chained to the other channel.

    Usually, we only need the 'volume knob' at about 30% for the main (harbinger) channel and aout 15% for the monitor channel. This is on the amp, I mean. These low %s are due to the smaller venues we are accostumed to playing in. The PA is usally playing the vocals, keys(direct in), bass (direct in), and mics micing small guitar amps. Drums usually are left unmiced.

    I'm not sure of the exact nature of the damage, unfortunately. But I know that one of the Harbinger's 15" woofers was damaged, first the top one, then the bottom one. The harbingers have built-in crossovers.

    My drummer, who stores the equipment, claims that he was told (by some repair guy) that the damage was the result of underpowering the speakers and that we need another power amp. But I'm not even sure if we are underpowering the speakers, or if that can damage the speakers at all! Online info on this subject is extremely confusing and contradictory.

    If someone could explain a) how to even understand all these rating numbers (I'm not even sure how much power my speakers are getting, impedence confuses the hell out of me) b) what is damaging my speakers c) what to do about it.

    Thank you!!!
     
  2. Cucco

    Cucco Distinguished Member

    Here's the short answer.

    NEVER DAISY CHAIN YOUR SPEAKERS.

    Your amp is designed to power speakers at a certain resistance. By running either serial or parallel, you change that resistance and thus the load on the amp. The amp itself is probably part of the problem as B*** amps are known for having horribly off the wall specs.

    Basically, if you're not using 70V transformers though, you should never hook up more than one speaker to a channel of an amp.

    Cheers-
    J
     
  3. tr3eman9

    tr3eman9 Guest

    Resistors in series follow the pattern Rtotal = R1 + R2 + R3... so don't two 4-ohm speakers in series = 1 8 ohm speaker? The amp is rated at several different impedences, according to the manual.

    How do you suggest I align the two main speakers? 1 per channel?
     
  4. Cucco

    Cucco Distinguished Member

    In a perfect world, yes, the resistance of one in a series added to the other will simply equal the sum. The problems are:

    1 - the load on the amplifier itself isn't a constant. Speaers present differing loads at differing frequencies and phases.
    2 - If you have a speaker with an 8 ohm rating, that means that the minimum average resistances is roughly 8 ohms. I've seen some speakers that run up to nearly 10 times that at certain frequencies at odd phase angles. Compound that by doubling it (or worse, adding two differing types of loads at two differing phase angles) and you're looking for trouble.

    Your best bet is to get 2 separate stereo amps (ditch the B*** line and go with the more capable Crowns. They have an inexpensive series that blows the doors off of B*** amps) and run a split our separate outputs from your mixer. (Floor wedges are often fed by aux sends).

    There is information on this site by a poster by the name of "Anxious" regarding under and over powering speakers. Anxious is a VERY knowledgable speaker designer and builder and has his name on several very high-end speakers. His name is Ken Kantor and he is one of the pair of brains behind NHT speakers as well as a few newer lines as well. Do a search on this poster and you'll find your answer regarding under/overpowering your speakers.

    Here's another short answer -
    Distortion blows speakers (sligtly over simplified). If you're pushing your amp too loudly and it's over powering your speakers, you will indeed blow them.

    If your amp is reaching its clipping point and distorting, it can damage your speakers.

    The common way to blow up speakers is to operate them (or the amp) beyond the capabilities at which they're designed. Your best bet is to invest in a quality pair of speakers and a quality amp that have similar power specifications and resistance specifications and use them together.

    Personally, when I see B**** amp and "daisy-chained" in the same sentence with "blown" I don't have to look for any more of a reason.

    Cheers and best of luck.

    J.
     
  5. IIRs

    IIRs Well-Known Member

    A few more points to add to the excellent advice in this thread:

    You say you are 'daisy-chaining' your boxes together... I assume that means you plug the link out on one box into the input of the next as they were designed, rather than some custom wiring job of your own? If you are using them as intended, then 'daisy chaining' boxes means you are running them in parallel. So, your total impedance for your mains = 1 / ( 1/4 + 1/4 ) = 2 ohms.

    I would personally be reluctant to run any amp at 2 ohms, as they run hotter with more distortion, and are much more likely to fail. This applies even to professional makes such as Crown; I shudder to think how a Behringer would react.

    And this is without considering the unspecified number of monitors of an unknown impedance... lets assume these are 8 ohm boxes and you have 3 of them: total impedance = 1 / ( 1/8 + 1/8 + 1/8 ) = 2.66 ohms

    It is not generally considered good practise to load channels differently on the same amp (I assume a dual mono-block design is too much to hope for in a Behringer?)

    Another observation: you say you were running the amp with the volumes turned down quite a bit... as Cucco rightly points out "Distortion blows speakers". However, the distortion doesn't have to come from the amplifier to cause damage: a DJ can kill a speaker by redlining his mixer all night, even if the amps have plenty of headroom.

    So I would suggest that you turn the amplifiers back up, and lower the input gains on your mixer instead. This should ensure adequte headroom throughout the signal chain.

    And I would second Cucco's suggestion to buy a Crown amp, and would recommend one of these. These are excellent amplifiers which have the added bonus of built-in DSP so you could set a limiter to help protect your drivers, and could potentially go active in future without needing to buy a cross-over.

    You might get away with running just the monitors from the Behringer for now, if you don't have a budget for two amps...
     
  6. rockstardave

    rockstardave Active Member

    oh my god!!

    open the amp and let it run at full power! just turn down the mixer. the amp should NEVER be used as a "volume control"! amps should almost always be run wide open.

    although, the funniest thing was this:

    figured out a solution with just the first word!
     
  7. dvdhawk

    dvdhawk Well-Known Member

    You have been given A+ advice so far.

    There are some things I think you need to crystal clear on. If by "daisy-chaining" you mean plugging the speaker cable coming from the amp into jack A of speaker #1, and then another cable from jack B of speaker #1 to jack A of speaker #2 (and so on, into an undetermind number of cabinets of undetermined impedance) - you need to be clear that this is not putting the resistances in series. As IIRs explained, that would be parallel impedances and the formula he put in his post is all you need to calculate how your impedance might be just a fraction away from a dead short (zero ohms). Your two Harbingers cabinets at 4-ohms each would result in a 2-ohm load. It's also worthing noting that the impedance listed on your speaker is the "nominal" impedance. In reality the actual impedance might be significantly lower. Which can be a problem when you start hooking them up in parallel. We keep getting closer and closer to zero ohms.

    When the speaker impedance gets dangerously low the amp will usually overheat and go into thermal protection mode and shutdown. So in this scenario, the only mystery in my mind is how the cheap amp held together - without going up in flames - long enough to kill the speakers.

    I'm a firm believer that everyone who takes live sound seriously should own a multi-meter and know how to use it. If you have speakers of unknown impedance, test them. If you're unsure how to calculate ohm's law, the meter will help. If you've got a bad cable the continuity checker will help you find it and fix it. String the chain of speakers together as you normally do and test the total impedance load at the amp end. It's true there are known issues in metering impedance accurately, but at least you'll be in the ballpark.

    Also as a precaution I'd test the amp before I plugged any more speakers into it. If you have a meter or know someone who does, you might also want to use the volt-meter function and check the amp to make sure it's outputs haven't gone into a DC state. High levels of DC will destroy speakers as fast as you can plug them in. That will get expensive FAST. DC pushes the voicecoil out (sometimes across the room) and never lets it vibrate normally. Sometimes when an amp meltsdown it takes the speakers with it, so a quick test of the amplifier's outputs might prevent the untimely death of more speakers. Most modern designs have safeguards against it, but again with a bargain-basement amp who knows?

    Check the crossover too. The Achilles heel of a cheap speaker might be the cheap built-in passive crossover. An ohm meter will be able to confirm if the speakers are fried or if the crossover has crossed-over (to the afterlife).

    As far as the under-powering over-powering issue - It is always going to be better to be at or above the speakers' rated wattage. (this means real watts, not some BS 2-ohm hocus pocus) Getting double the watts out of an amp by cutting the impedance in half to 2-ohms is 100% smoke and mirrors - not real useable watts. Good speakers will often have three power ratings Continuous / Program / Peak, I would try to have the amp be at least in the neighborhood of the Continuous rating of the speaker.

    If given a choice between A) running a 200-watt amp into a 100-watt speaker OR B) running a 100-watt amp into a 200-watt speaker - I'll take option A everytime.

    And while we're on the subject - there are a lot of places manufacturers can fudge the wattage specs of an amp. There is a world of difference between how the top-notch amp companies [Crown, Crest, QSC, Carver to name a few of the best] rate their amps and the methods used by the cheap amp manufacturers [ a much longer list, including the one you have-sorry]. The same is true of speaker manufacturers, peak watts on paper is easy. Real world useable continuous power is what counts.

    Good luck!
     
  8. BobRogers

    BobRogers Well-Known Member

    This is very common advice, but I don't agree with it. I admit that if a system is correctly sized for a venue this is what you end up doing, but if you have an overpowered system you should turn the power amps down. If you fail to do this, you defeat the entire point of creating a good gain structure. Turing the power amp to full volume ignores the fact that the audience's ears are part of the signal chain. If the amp is full out the noise floor is at maximum possible volume and you are getting the minimum signal to noise ratio that the system can deliver rather than the maximum. Ideally, the amp should be set so that you are getting the maximum necessary SPL at the maximum comfort setting on the mix. I practice most people leave some extra volume in case they want to make everyone's ears bleed just a little. As I say, if the system is correctly sized that means the amps are turned up all the way. (In fact, that's probably a definition of "correctly sized.")
     
  9. Codemonkey

    Codemonkey Well-Known Member

    "I'm a firm believer that everyone who takes live sound seriously should own a multi-meter and know how to use it."

    My apologies, dvdhawk. I might know how to use one but hell if I own one. Or a SPL meter. I dunno how to solder.
    Hell, I could just be a bad example to everyone and scare them into buying quality amps instead of (point 2...)

    "If given a choice between A) running a 200-watt amp into a 100-watt speaker OR B) running a 100-watt amp into a 200-watt speaker"

    What about 90W amps into 300W (peak)/150W (continuous) speakers? :p
    (I already changed that amp to our older powered mixer which spits out about 300).
     
  10. tr3eman9

    tr3eman9 Guest

     
  11. TheJackAttack

    TheJackAttack Distinguished Member

    Don't be stubborn. Forget about 2400 watts. Even if you wish to believe the published specs are accurate it isn't really a 2400 watt amp. 4 ohms in bridged mono mode is how you would get there with a single speaker and that isn't your application. That means one (1) line gozinta the amp input and one (1) single 4 ohm speaker gozouta. Do not try to run at 2 ohms. Really.

    If you run in parallel mode at the amp itself-1 channel to FOH and 1 channel to MON-you have about 650-750 watts per channel at 4 ohms. That means either one 4 ohm speaker per channel or two 8 ohm speakers daisy chained (parallel again remember) per channel. Three 8 ohm monitors on one channel is too many. Three 4 ohm speakers is ludicrous without a k.

    Even if you can't or won't dump the Behringer gear, you really need one amp for FOH and one for your MON. You still need to test your current amp and speakers with the multi meter like advised so you know what is still good and what isn't.
     
  12. TheJackAttack

    TheJackAttack Distinguished Member

    Alternately you could invest in some in ear monitors and do away with the monitor speakers all together.
     
  13. dvdhawk

    dvdhawk Well-Known Member

    To each his own. Frankly I'm surprised, you seem like a guy who likes to take things apart and see what makes them tick.

    You are free to do as you please, all I can tell you is this - over 30+ years I have saved thousands and thousands of dollars in cable and equipment repairs that I would have had to pay someone else to do. Think of the new gear you can buy with the money you save over the long haul.


    Bless you for volunteering your time to run sound at church.

    If you ever get to where it's your investment, your profession, or serious hobby you would do well to reconsider.

    Wise words from some slacker in another post:

    Over the course of a long and interesting career in this business that relatively small £20 investment will save you hundreds or thousands. A multi-meter of your own wouldn't cost much more and the ability to troubleshoot and solve a problem in 2 minutes vs, 4 hours is priceless. I keep a meter at church, I keep a meter in my truck, and 2 more meters in my toolbox.

    But then again the qualifier was, "everyone who takes live sound seriously" - if you're content being the best soundman at your particular Congregational Church of Scotland, go ahead and put your feet up, you have arrived. You seem to have a great grasp of things in your comfortable environment. Problems are inevitable even in a fixed installation. And if you leave the nest and start doing field work, expect the unexpected. Good luck finding a new cable at 11pm on a Saturday night. If you strive to be better prepared and better equipped, these are tools you will have to master to get from point A to point B. Anyone trying to navigate to point B without some skill with these two simple tools had better have deep pockets.
     
  14. tr3eman9

    tr3eman9 Guest

    Therefore, it sounds like if I do away with the monitors altogether (I have a solution monitor-wise I know will work anyway that has nothing to do with any of this), then I can put the amp in parallel mode and put one 4-ohm 600-watt Harbinger out of eahc channel, and eahc speaker should be getting about 650-750 watts. That would seem to be enough power since I've never had to drive the speakers to anywhere near their capacity in any of our applications - so I won't have the problem of clipping the amp.

    But, despite the previous sentence, I will still make sure to turn each channel of the amp up to almost its full volume and leave the individual input gains/volume faders on the mixer nice and low. That way I won't get any clipping, the speakers will get adequate power, the amp will be pushing an adequate resistance...everything should be hunkey-dorey right? Any foreseeable problems?

    Of course, if I find an extra $1000 on the street I'll buy one of those Crown amps and use the B. amp for monitors.

    One mroe question - can someone explain if I should really use stereo mode or parallel mode here? The only difference that i know of is that the manual claims stereo mode = each output channel has its own corresponding input, while parallel mode routes one input signal to the two different output channels. But, I don't know how this works out electronically, and with regards to impedence, power, etc. therefore I don't know which mode is more appropriate here.

    By the way:

    The amp is supposedly rated for quote: "2x1200 Watts @ 2 ohms" which sounds to me like you could put two 600 watt speakers at 4 ohms each, daisy-chained in parallel, on one channel, and end up with the correct power (1200 watts for 2 ohms). But, then again, I really don't know $*^t and if there's one thing I;ve learned here its that manufacturers' ratings really aren't that trustworthy. Why, I don't know - it doesn't seem to their advantage to advise people to use their gear in a way that is bound to cause damage...whatever...

    Thanks all. More advice is still appreciated because even though I think I know what to do, I'm still just a hair fuzzy on why I need to do it...
     
  15. TheJackAttack

    TheJackAttack Distinguished Member

    2 ohms makes things go boom.

    I'm a Marine. I know all about making things go boom. When it absolutely positively has to be destroyed overnight....
     
  16. tr3eman9

    tr3eman9 Guest

    I'll keep that in mind...
     
  17. TheJackAttack

    TheJackAttack Distinguished Member

  18. BobRogers

    BobRogers Well-Known Member

    "Any" 2 Ohm rating is based on a 2 Ohm test load at a particular frequency - not a real speaker playing real music. In the real world its best to stay away from 2 ohm speaker loads.

    As far as the stereo/parallel - are you running your mixer in mono or stereo? If mono you have one output from the mixer so use parallel. (This feeds the same signal to the two separate channels.) If stereo...you can figure the rest.
     
  19. IIRs

    IIRs Well-Known Member

    Different manufacturers will have different business models.

    Companies like Crown or QSC trade on a reputation for quality and reliability, so it pays them to be conservative (or at least accurate) with their specs. And their customers will be professionals that are harder to BS.

    Behringer simply aims to be the cheapest, so inflating the specs makes them look like more of a bargain to unsuspecting amateurs.
     
  20. tr3eman9

    tr3eman9 Guest


    I think, usually, we have it in stereo mode, but the left and right signals are exactly the same (we don't pan any instruments), so I could do parallel just as easily.

    I just want to know if there's any other, more technical, electronic difference between the two modes, and if there is, which mode would help my situation more.

    Also (not to derail this thread but I'm just curious) why would you pan things in a live mix? It seems to me all this would accomplish is different parts of the audience hearing differenct mixes...and this doesn't seem like a good idea...
     

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