Speakers Blown

Discussion in 'Home Cinema Speakers' started by NeilH, Jan 9, 2008.

  1. NeilH

    NeilH
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    I have managed to kill the drive units and crossovers on my Sonus Faber Sonus Faber Grand Piano floorstanders and also a Sonus Faber Solo Centre.

    SF themselves are blaming the amp (an ageing but good Denon AV1SE). The bill to rectify the damage is £1000.

    What could have gone wrong within the amp to cause such catastrophic failure?

    Thanks in advance.
     
  2. Badger0-0

    Badger0-0
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    Bad luck mate
    Certainly does sound like the amp.
    Sounds like a really major fault.
    I wonder if mains voltage got into the output?
    Certainly sounds like it might have.

    Whatever, I'd be very loathe to plug any other speakers into it.
     
  3. NeilH

    NeilH
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    Agreed.

    The speakers are being repaired on Sunday and as part of the arrangement, they are checking the amp too.

    Whatever they say, I'm still going to be wary of plugging the newly repaired speakers into it.

    Might be time to start looking for a new one!!

    The dealer suggested that just too much volume could have blown them. What do you think?
     
  4. Badger0-0

    Badger0-0
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    I wouldn't have thought so myself.
    A tweeter/driver/crossover maybe, but all at once?
    No way, IMO.
     
  5. BlueWizard

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    NeilH said -

    "The dealer suggested that just too much volume could have blown them. What do you think?"

    Well, you know that last party you had last week, the one where the roof caved in and the windows blew out of the house, that could well be your first clue.

    Seriously though, how much volume did you apply to them? Personally, I think anytime you go over 60% turn on the Volume Control, whether high powered amp or low powered amp, you are pushing your luck. With the right combination of equipment, you might be able to go to 65% or rarely 70%, but I can guarantee you are getting substantial clipping at those levels, and if you sustain them, you are pretty much guaranteed to damage something.

    So, once again, exactly how loud were you playing them?

    If this happened at normal listening levels, then, absolutely, something went wrong. But if you were blowing the doors off the place, then what else did you expect?

    I've always said that it is the guy running the volume control that blows speaker not underpowered or overpowered amps. Though I have to admit, not knowing the detail of your situation, I can't lump you into that category.

    There are a few reasonable test they can try on the amp to confirm that some malfunction wasn't the problem; DC offset on the output, oscillation. But you also need to tell the people performing the tests exactly how you were using the equipment when the problem occurred. I've worked in tech support, and that is the first question I ask, though the answer is alway invariably, and most inaccurately, "I wasn't doing nothing".

    Steve/BlueWizard
     
  6. Helicon

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    I have mentioned many times on these forums that people are underestimating the level of amplification needed to properly drive, and get the best from these types of speakers. We're not talking WPC before anyone comes back with that old one. We're talking current capabilities and control, and having the sort of headroom needed to supply high end speakers when they demand it. Some of the speakers people are using with Onkyo 605 amps make me cringe, god knows whose advice they've followed, if any. These sorts of combinations will just end up in tears.

    These sort of amplifiers have silly amounts of power (not current), and will go stupidly loud for a long period of time (they have to, they wear a THX badge). But putting on current hungry speakers seriously affects how these amps perform and react to certain situations. Once things become unstable, anything can happen.

    Neil, i hope the reason for the fault is identified, as it could save problems in the future. Keep us posted.
     
  7. Badger0-0

    Badger0-0
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    I understand what you're saying but surely power and current go hand in hand?
    And the fact is it's the only spec the vast majority look at.
    Are you a proponent of buying amps with twice the required power?
    If so, I reckon that would easily cause more blowups.
    Too many people like to turn it up too much, is the problem, myself included.
    Although I am moving up the range power-wise.
    Hmm, now where can I find a Multichannel amp with 250W per channel? :D

    I guess, as is often said on here, people really ought to be looking at Watts in, as a better way of judging amps.
     
  8. Helicon

    Helicon
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    Usually yes, but with AV amps we're not talking about a product that's geared 100% for hi-fi use with hi-fi loudspeakers. AV amps use cheaper internal components to help keep their costs down. Everythings built to a budget. Notice how many AV amps state their current output in amps in their spec?

    Almost any AV amp now is rated at 100wpc, even at the £300/400 mark. So if it's possible to buy an AV amp that includes a radio, picture switching, surround sound processing, 2nd Zone facility, auto set up, room EQ, AND provide 100watts into each of their 7 channels, why can't you buy a 2 channel hi-fi amp providing 100wpc even at £200?! People are starting to learn that AV amps don't really provide the power they state on paper, especially the cheaper ones, and care should be used when partnering them with higher quality hi-fi speakers.

    The amount of real power some speakers need is usually well underestimated. I'm not saying you should have twice the power needed, just a bit more in reserve, and the knowledge to know when the speakers are starting to struggle.

    (note: I'm not saying in this case this has happened to Neil - there is the possibility the amp might've gone DC or something)
     
  9. Badger0-0

    Badger0-0
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    the knowledge to know when the speakers are starting to struggle.

    Strongly agree with this.
    But there lies a problem in itself. It does mean you have to know when it's too much. I first heard it on my Mordaunt Short setup. Fortunately, turning it up a bit too much brought on the rapid onset of what I can only describe as horrendous screeching and I quickly turned it down, no damage done.

    Your views on power ring true too.
    I'm currently throwing a genuine 140W at my 120W rated speakers.
    It seems a pretty good blend to me :smashin:

    Sorry OP, if the threads moving OT a bit :rolleyes:
     
  10. drashp

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    Hope I'm not talking down to anybody, but this wattage argument really masks what's going on - it's all about current - that's what drives a motor (speaker) and that current is pushed by the voltage across the unit. Keeping things *really* simple just to get a feel of what's happening:

    Some simple numbers using a perfect 8 Ohm load
    power (W) = V^2/R or I^2R so 100W equates to +/- 28V ish [V=sqrt(100*8)] also equates to 3.5A [I=sqrt(100/8)]

    This is a basic capability of the amp, think of it as +/- 28V power supply which only has to supply 4 Amps to live up to its rating. Now some good stereo amps can peak at 30A. That equates to 30*28=c.900 W. That's per channel - you aren't going to get many of those out of a 3000W mains socket! There is a physical limit to how much you can draw consistently (even given a massive bank of capacitors) and drawing a seventh rather than half is going to mean drawing less per channel. You could spec up the 7 ch amp but if it tried to draw all seven channels at once you'd have a fuse blow or a house fire. So you want louder you need more efficient speakers (higher sensitivity) not higher powered amps.

    Given that, a 100W x 7 amp with a 600W PSU isn't going to perform as well as if it had a 2 or 3 kW PSU. When the PSU runs out of current it starts acting in all kinds of bad ways which ultimately mean something gets damaged. Given the dynamic nature of speaker load that can happen anywhere on the volume dial given the wrong set of circumstances. Your ears would/should alert you to this hopefully before any damaged actually occurred.

    Essentially all I'm saying is that the wattage rating is no real indicator of the amps capability, or the speakers for that matter. Caution is required whatever, saying that electronics does go t*ts up and blow things without misuse.
     
  11. BlueWizard

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    drashp,

    Excellent points you've made. I will expand on that by saying that frequently power ratings for A/V Amps are given for one channel driven. Now, if you drove all channels, you would quickly run out of BOTH Voltage and current.

    As an example, I bough a small power supply transformer from Radio Shack, let's say for this illustration, it was rated as 24volts and 5 amp. What I discovered was that you could have 24 volt OR 5 amp, but not both.

    As the current demand goes up, the available voltage drops down, and that is true to greater or lesser degree on all power supplies. Now drawing current for 7 channels from a single power source, means less voltage and therefor less current available to each amp.


    Now some comments on power in general. When you change the perceived volume of your stereo by 3db, you have doubled the power. To put 3db in perspective, if you nudge your volume control up just enough to notice the change in volume, you have increase it by 3db. Sound wise 3db isn't much, but again, power wise, it represent a doubling of power.

    Now, as a point of illustration, lets say you are cruising along at a health 50 watts. Now you nudge up the volume just one small notch, BOOM, now you are cruising at 100 watts. One more tiny nudge upward of the volume control, and BOOM, you are cruising at 200 watts. Yet, the overall perceived volume has changed very little. It will be noticeably louder, but not substantially so. And there are your blow speaker. That one last nudge upward pushed it over the limit, and snap, crackle, pop, buzzzzzzzzzzzzz ...blown speakers.

    Do you see how see how easy that makes it to blow speakers? Just one tiny notch above the reasonable limit and you have overpowered both your amp and your speakers. That's why I say, it is always the guy running the volume control that damages equipment and not overpowered or underpowered amps. Again, rarely, and only in the most extreme cases have I ever gone over 60% to 65% turn of the volume control. That will fill any average room to painfully loud levels.

    On the other hand, outdoors or in a large hall, that same 60% is going to seem a little weak. If you are going to play a large venue like that, you need lots of speakers to push lots of air and tons of first rate high powered equipment behind it.

    Steve/bluewizard
     

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