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This topic comprises 4 pages: 1 2 3 4
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Author
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Topic: Paranormal Activity blowing out Center Speakers
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David Buckley
Jedi Master Film Handler
Posts: 525
From: Oxford, N. Canterbury, New Zealand
Registered: Aug 2004
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posted 01-09-2014 07:29 PM
There are two ways to damage a loudspeaker driver.
The first is through thermal overload. This is as simple as it sounds; pump too much power into the speaker, it gets too hot, and the overheating causes failure. This is fairly easy to protect against, and for decades HF drivers have had light bulbs in series with them so as the power goes up the bulb acts as a crude limiter. It does this because as the filament of the lamp heats up its resistance increases, and thus reduces the power being fed to the driver. Push hard enough the lamp may even blow.
Thermal effects take time, as there is always more or less thermal inertia, so a short period of overload is not usually disastrous, but a moderate overload for a long time can be a killer.
The second damage mechanism is excessive displacement. Push the mechanics of the speaker too hard, and the suspension mechanisms cannot return the drive components back to their resting position, and the driver is knacked. This damage occurs instantly, push too hard once and its all over. It all happens far too fast for a simple thermal limiter, and it can happen without apparent excess power. Putting too low a frequency into a driver is a good way to damage it mechanically.
In terms of limiting generally; modern audio is now processed by DSPs, which do their magic by means of software, and software is free. Thus the cost to put limiting into a DSP crossover is zero, so any decent DSP crossover should have limiting on board. Of course, to be useful, it needs to be set up correctly, and setting up a limiter correctly is far harder than most people think.
This is why active speakers with onboard amplifier, DSP including crossover and protection from quality manufacturers is such a sensible idea. The safe operating envelope of the drivers is determined with destructive testing during R&D, and that knowledge is embedded into the onboard DSP, making such speaker almost indestructible no matter what you do to it. It also is perfectly set up out of the box.
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Steve Guttag
We forgot the crackers Gromit!!!
Posts: 12814
From: Annapolis, MD
Registered: Dec 1999
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posted 01-11-2014 09:31 AM
Square waves are an interesting thing...especially when digitized...they don't digitize well.
My suspicion, though I have not tested it, is yes, it would though it would depend on the system. You are essentially presenting a clipped signal to a speaker. The higher the mass (woofers) the harder a time it is going to have moving very fast...coming to a dead stop, then moving in the opposite direction. So I would think woofers would have a harder time, particularly those with very low f3s. They would tend to bottom-out easier.
The other issue with square waves is heat most drivers use the motion of the driver to cool itself...with a square wave, particularly lower frequencies, one is holding the driver in opposite extremes for a large period of time.
So to answer your question, with an educated guess, the higher the frequency of the square wave, the greater the chance that the properly speced speakers/amps will survive...note...again passive crossovers are more likely to send harmful power/frequencies into the higher sections of the speaker system.
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