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Dell & VLC Debate regarding speaker damage

Okay, I’ve seen a bunch of shenanigans going on lately about the Dell vs VLC debate. Dell’s argument is that VLC allows users to damage components by using the components in ways they were not designed to be used. VLC’s argument is that because they are using official APIs this has to be Dell’s fault for poorly engineering a circuit and that Dell is overdriving the speakers anyways.

I’m going to present the information and facts as objective as possible.

 

First, let’s start with the basics of sound. Anything you hear is comprised of sound-waves. Pressure differences in the air that are received by your ear drum and then interpreted. Most of us know that speakers are electromechanical devices  (they take electricity and turn it into a mechanical motion). Let’s have a look at a sound wave.

Screen Shot 2014-02-12 at 7.59.45 AM

 

This is a typical sound wave captured from VLC at 100% volume. It’s smooth and is a sine wave. How do we know it’s a sine wave? It’s shape as shown here follows the mathematical function sin(x). You can see it looks almost like the waves in an ocean. Now let’s look at the anatomy of a sine wave.

679px-Sine_wave_amplitude

 

We want to concentrate here on the crest, trough, and amplitude as those are specific to our need here. Amplitude is the strength of the wave (this is important). The crest and trough are the highest and lowest points of the waveform, respectively.

Let’s jump to how sound is reproduced. A computer is digital (it has only 2 states, 0s and 1s). Sound however is analog (it has an infinite number of states). To reproduce digital sound to an analog signal we need a digital to analog converter. The digital to analog converter is fed a digital signal from the computer and in turn reproduces the analog sound. So in theory, the waveform you see above would be reproduced to that almost exact specification. The signal coming directly out of a digital to analog converter is too weak to drive a speaker so it must be amplified. The amplifier takes the analog signal coming in from the digital to analog converter and amplifies it. It uses the signal to generate an electrically amplified signal that is strong enough to drive a speaker.

A typical sine wave will cause a digital to analog converter to produce an A/C current. The same way the A/C current in your house is a sine wave operating at either 50hz or 60hz.

The amplified electrical signal travels through the voice coil of the speaker (copper wire wrappings) that sit inside the center of a magnet. The changing in electrical current going through the voice coil causes the speaker to move.  This drives the speaker back and forward.

Real quick side note: When dealing with a speaker or amplifier’s wattage, that is the wattage the speaker or amplifier can use or produce (respectively) before distortion sets in. This varies from manufacturer to manufacturer. Distortion is the disfiguring of a sine wave signal.

Voice coils are designed for A/C current. Now what happens when we start manipulating signals to extremes? Well, this is exactly what VLC does with it’s ability to output a signal at 200%. It manipulates a signal to it’s extreme. Here’s an example of the waveform above, captured from VLC at 200% volume.

Screen Shot 2014-02-12 at 8.01.19 AM

 

Whoa, that’s a massive difference. If you notice, the top and bottom of the wave forms are now flat. Remember how I was saying amplitude would be important? In this image we can see that VLC has gone to maximum amplitude for fairly sustained time. This is where the signals can become dangerous to a speaker or even amplifier. Maintaining maximum amplitude at maximum volume means your amplifier is outputting at 100% of it’s electrical power.

Remember how I said a typical sine wave will cause a digital to analog converter to produce A/C current? With this (now square) waveform, your converter is now producing DC current at those maximum amplitudes. DC current is dangerous to voice coils. They are designed for very short operation at maximum amplitude. I’m talking maybe 5% load cycle (meaning only 5% of the time). If you notice in this second wave, we are producing maximum amplitude for over 80% of the time. This is an 80% load cycle.

It’s this significantly increased load cycle that will destroy a speaker or the solid state amplifier (solid state amplifiers produce heat too, and when they are producing too much, they will get damaged). Ever ridden in car with blown out speakers?

This applies to all speaker components across all ranges of production value (cheapest to most expensive). This is why most editing and mixing software has clip indicators. Loudspeaker hardware also has clip indicators and protection circuits. Too much clipping? The amplifier will reduce or cut off output for a percentage of time to keep from damaging the speaker. (This is typically only present in more expensive gear.)

What if the amplifier is only 5W and the speaker is 10W? I can’t blow it out then can I?

This is incorrect. The same principles apply, just between the solid state amplifier output and the speaker. Under driving a speaker and causing the solid state amplifier to remain at maximum amplitude will still damage the speaker. (Remember the Wattage rating is *before* distortion sets in. Distortion is the disfiguring of a sine wave.)

Shouldn’t Dell put a self-protection circuit in?

Dell could do this. However, all it’ll do is counter-act the entire reason people use 200% volume and people will just complain. You can’t eat your cake and have it too.

So what’s the solution?

VLC should remove the option of 200% volume. There’s no reason for it to be present. If you want to increase volume of quiet movies look at Automatic Gain Control. Most OSes already have the option. It’s safe for your audio components.

  • They have removed that ability. For quite a while now. My (not completely updated) version caps at 125%. Also, however, users should understand how that all works and how to appropriately raise and lower volume.

    miles

    February 12, 2014

  • I can still increase my version on Mac OS X (latest) to 200%. That’s how I captured the data I needed for this post.

    segfault

    February 12, 2014

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