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blown speaker...

Discussion in 'Amps and Cabs [BG]' started by raised_fist, Nov 29, 2003.


  1. raised_fist

    raised_fist Guest

    Dec 16, 2002
    Okay, I was using a harke 350w head, into a Peavey black widow 1x15 cab. The other day I blew my Peavey, using the 350 watt head. The cab is supposed to be a 400watt cab? So why did it blow? Where is this extra 50 watts of power coming from in order to blow it up?

    400W + 350W = KABOOM
     
  2. Lockout

    Lockout

    Dec 24, 2002
    Illinois
    Feeding too much power into speakers isn't the only way to blow them. In fact, it's probably one of the less common ways.

    I think clipping is most likely to blame for your blown speaker. Were you pushing the Hartke near its limits?
     
  3. raised_fist

    raised_fist Guest

    Dec 16, 2002
    ummm...
    well...... sort of :bawl:

    dammit, I just thought that if the speaker can take up to 400, and the amp can only put out 350, then I would be in the clear for sure!
     
  4. raised_fist

    raised_fist Guest

    Dec 16, 2002
    okay well can someone please explain speaker clipping in greater detail for me please? So I don't go and do this again:)
     
  5. ahaha i laugh at you but pitty you at the same time. poor bugger u are.

    shayne
     
  6. clipping ****s up speakers, thats the best explenation you can get for the time it take to read.
     
  7. wneff

    wneff Supporting Member

    May 27, 2003
    Woburn, MA
    There are two ways to kill a speaker:

    1) Pure power overload
    2) Slamming the voice coil into the magnet.

    These are two different issues. The pure power overload happens rarely for most good speaker and amp combination. I believe (and I may be wron there) that for all pracical cases if you have the Hartke and a speaker with more than 200 W specified power handling you'll not gonna burn it up with brute force.

    For bass player slamming the voice coil into the magnet is much more common. This is because I wanted to get too much bass out of my speakers (killed two so far for this reason).
    I did not have this happen since I added a 2x10" on top of my 15".

    I blew up a single 15" Electro Voice and a singe 12" Euphonic Audio. From this experience I would say that for my style and volume I need either 15" + 2x10" or 15" + 12" or 2x12" or 12" + 2x10", all top of the line speakers.

    The power amp clipping is a subject where different people have differnt opinions.

    My opinion: When an amp clips its not working like intended, and damage of the speaker is much more likely when you use a small clipped amp and if you use a large unclipped amp. however, if you slam you voice coil into the magnet with the small amp the larger one would have done the same.


    350 W should be plenty, if you add a 2x10" or (if you like the sound of the 15" add another 15") I would imagine that you are save.

    Wolfram
     
  8. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    The amp puts out 350 watts at the onset of THD (Total Harmonic Distortion). But it the amp is clipping, it puts out more than that. At 100% pure THD, it can put out up to 2.5 times the rated power, though in practice 100% THD would sound so badly distorted you couldn't play that way. Mild THD is often herd to hear, especially with the rest of the band to compete with.

    Most speakers can handle brief spurts of clipped signal. But frequent clipping is a pretty good way to blow a speaker.

    Try this - grab the blown speaker, spread your fingers evenly around the cone, and press the speaker inwards. Does it move freely? Are there any scraping or rubbing sounds?
     
  9. Underpowered amps...I sometimes think these manufacturers make them specifically to keep some of us buying replacement products (like blown speakers)!
    Now, I'm not an electrical engineer but I do a little fiddling around and occaisionally fix gear for people. My experience has shown me that the culprit in most cases of blown speakers (let's just say, they don't work) is from underpowered amps exhausting their menial headroom...throwing out crap signal and frying the voice coils.
    Without going into great detail...if you want to avoid the frying...use an amplifier rated at DOUBLE the rated wattage of the cabinet. That's optimal...if you can't afford or whatever the reason may be...be sure you've got one that'll at LEAST be a couple of hundred watts over the cabs rating. Believe me, unless you're a complete idiot or just too high to notice; you'll know when you're putting too much juice into it and you'll back off...and hopefully add more speakers if you need more volume. Remember your ohmage and that adding more speakers means that you may put yourself back in that 'underpowered' situation again. And once you play with the power I'm talking about (even at low volumes), you'll never go back to buying gear that's designed (in my opinion) to cause you to dig deeper into your wallet in the long run!
     
  10. wneff

    wneff Supporting Member

    May 27, 2003
    Woburn, MA

    I think there is a big confusion out there what amps and speakers do:

    A 100 W amp for example puts out anything from 0 W (typical) to maybe 200 W or so.
    How much it puts out depends on what you do: If you don't play a tone it does not put out anyting, if you plug real hard it puts out maybe 200 W. The most you can get out and still get a CLEAR TONE is 100W, thats why they call it a 100 W amp.
    The speaker now has to deal with this power it gets from this amp. It does the following things with it:
    a) Convert to heat
    b) Move membrane and air
    c) Store energy in various places and push it back into the amp at a later time.

    Only a small fracion of the power is used to produce sound. Most of it is heat.

    Now lets look at a typical signal from your bass. Its very loud right when you plug and falls off really quickly. For the amp that means: Lots of power at first, a lot less most of the time. If you average it out you may get that the actual speaker would typically get only 50 W for any normal bass playing - no thermal problem.

    But now the player switches on the octave pedal and now produces really deep tones.
    Now the membrane makes huge movements, and if you hit some resonance you bang the coil against the magnet. (Compare this to a swing set: It does not take a lot of effort to get the swing going rally high if you push at the right frequency. Same for is true for a speaker). You still blow your speaker becasue of exessive movement.
    If you add a second speaker, every speaker makes about half the movement and you have more chance to not kill your speaker with this mode (thats why they build 4x10" cabs).

    Knowing this, underpowered amp is a relative term.
    First, manufactureres don't build underpowered amps. They build amps that can put out a certain amount of watts. And if you are playing in a setting that is appropriate for that amp you're fine.
    An example would be my 100W Gallien Krueger for a church or in any acoustic setting.
    When I add my Euphonic Audio to that, I have a 300W speaker on a 100 W amp. Is the amp underpowered? No, because I won't need the full power, I never reach the limit, so even though I have a 100 W amp and 300W speaker everything is fine.

    Now lets take this to Midnight Jones for rehearsal (www.midnightjones.com). I crank the amp, but the limiter in the amp keeps it from clipping -> still no problem, but it sounds compressed.

    For my full power need I follow the following rules:
    a) Bring much more power than you need
    b) Bring speakers that can handle the power

    For high volumes I am playing for 12 years a 400W amp with 700W of speakers with no problems.

    Therefore I disagree with the statement above that you need an amp that I twice as much power than the speaker. I think the best way to go is to buy twice as much power as you NEED (so you don't clip), and buy cabinets which are rated around the same wattage or more. (This is difficult because the power you need depends on the speakers, and you don't really know until you play out.My feeling is: 350W should be enough with good speakers, and the more the better. If you need to be louder get differnt speakers - with higher dB/watt, not neccesarily more power, but here again: More is better).
    Adding more speakers will not put you into the underpowered range, for the following reasons:

    a) Adding speakers increases speaker sensitivity (output per watt) for the stack compared to a single cab because of added speaker surface (up to 3 dB for same speaker)
    b) If you run one 8 Ohm right now on a 4 Ohm amp you'll not use the full power of the amp. Adding a second cab will bring it to 4 Ohm. Careful: If you go below the rated impedance of the amp you may damage it or decrease power drastically.
    c) You split the load each speaker has to carry in half.

    When I blew my speakers I didn't notice the distortions because everything was so loud on stage that I barely heard myself. So, you can't go by that. Also, if you hit it with the right frequency you can blow about any speaker with any amp by cone over excursion. Unless you know you have enough power and good speakers that can handle it you're not safe. Well, I blew two speakers in 18 years, I think I can deal with that.
     
  11. Also keep in mind that wattage ratings on speaker decrease with age and abuse. Old drivers just die sometimes. The cone or spider can rot or the coil can build up all kinds of funk on it from years of use which will hang it or cause it to build up heat faster. That said, a 350 watt amp driven over the edge would have NO problem putting out a VERY dirty 400+ watts (700 at TOTAL clip).
     
  12. Chasarms

    Chasarms Casual Observer

    May 24, 2001
    Bettendorf, IA USA
    Clipping a power amp is probably the most common way of frying speakers. Although over excursion isn't the healthiest thing for them either, it is harder to do than you think.

    Speakers are transducers. They convert electrical signal into mechanical motion. Unfortunately they aren't 100 percent efficient. So, in the process a great deal of heat is generated.

    Fortunately, the mechanical motion of the speaker moves air and thus aids in dissipating heat. More signal means more heat, but it also means more motion thus better heat dissipation.

    Under normal conditions, the two take care of each other. But when an amp begins to clip, the input voltage of signal continues to rise as the clipping grows progressively worse, but because the waves are clipped, the mechanical motion of the speaker doesn't progress with it.

    A point is reached where the heat can not dissipate quickly enough. Eventually the voice coils get hot enough to fuse or simply melt in two pieces. This creates a short in the voice coil and thus a dead speaker.

    Of course a speaker rated 500W RMS would likely handle all of the heat of a 50 or maybe even 100W amp clipped well into audible distortion. But, in the case of the original poster, the differences may not have be audible.

    I don't mind the double the rated power theory, but it is probably overkill. The trick is to not clip the amps. The nice thing about the amp being overrated for the speaker is that audible distortion, when heard, is almost certainly coming from the speaker itself and is easily remedied by simply trimming back some point in the gain stage.