I think I mis-represented my statement - it had been a long day at work

Just because it can be measured, doesn't mean it can be heard.

If it can be heard, you had better be able to measure it.

That is all

 

Your questions show thought was put into them.

Unlike statements that are based on what joe blow said and are worthless. It’s why I hate the cap debate; people go by what others have said and make no effort at trying to understand why. You can try to explain but unless its 2+2=4 then it’s to complicate so it must not work lol.

I am by no means an audio expert but I think this is fairly straight forward.

We need a common starting ground.

Start with a definition "improve Transient response" what does it mean?
It means that the output follows the input. The input is the speaker terminals the output is the sound coming out of the speaker. So a change on the input needs to make the same change on the output in the same amount of time. Since it’s an amplifier we are talking about the input gets multiplied by an amplification factor and this is your output. What controls how quickly a speaker responds? Current, more current will make a speaker respond quicker. We all know V=IR correct? Since R is relatively a constant a drop in V will also cause a drop in I.

Now lets look at an alternator. Everyone knows DC transformers don’t exist correct? This is an important concept because it’s how an alternator works. The word "alternator" should be a big clue. An alternator produces an AC (Alternating Current) voltage similar to how an AC transformer works. I imagine its 3 phase with 3 poles separated by 30 degrees. What does it regulate? Voltage, based on current demands. Internally it produces significantly higher voltage then the 14.4V it puts out. This is run through a voltage regulator that regulates the voltage to 14.4 volts. We all know what an AC voltage looks like correct? It’s a sine wave.

Now how do we turn an AC voltage into a DC voltage? Well we can’t completely do it but we can come close. If you take the bottom half of the sine wave and fold it over you get a bunch of humps nnnnnnnnnnnnnnn. This is what a bridge rectifier does. Now notice there is a short amount of time that the alternator would be supplying 0 Volts!!!. Do we care about this? No not normally for the same reason you don’t see your light flicker in your house. They are blinking on and off faster then you can see. We have the added benefit of having a battery that will produce 12V so the voltage in the car will go from 14.4 to 10V(lowest battery voltage) not 0. It can drop lower but the current would need to be higher then what the battery can supply. For anyone that says a battery can not go below 10V they are wrong stick a large metal object between the two battery post the voltage will go to 0 very quickly.

One thing to keep in mind is when will the highest current demands be? If you still believe V=IR as the alternator voltage drops from 14.4 to 0 the devices it powers will begin to pull more current so they can maintain a constant voltage (if they have regulated power supplies). As the devices pull more current the voltage will begin to drop. This creates an unstable supply that varies with current; every electronic device in the car will see this change in voltage and possibly be forced to work harder to overcome it. You can visually see this occurring when you see your headlights blinking.

So why does a Capacitor reduce the amount of blinking?
The capacitors job is to fill in when the alternator drops its voltage. If you take the ESR of the cap multiply it by the current draw you get the "ripple voltage". The amount of voltage the supply will still vary by. The lower the ESR the lower the ripple. The larger the Capacitance the longer it can fill in the holes left by the alternator. Doesn't the cap just provide an additional load? Yes it does when the alternator begins supplying voltage again the cap represents a load. V/ESR = I which will vary over time. When the cap is at its lowest voltage is when the largest load will be placed on the alternator. As the cap reaches 14.4V the cap is no longer a load. You end up with a much more stable supply.

Now we get back to "improve transient response". If we look at our speaker again current determines how fast a speaker responds. Different amplifiers are designed differently. Some amplifiers already have a large capacitance bank built in. Some have tightly regulated supplies. This means that adding a large capacitor externally probably won’t improve transient response much on these amplifiers. It will improve transient response but not by a significant amount. It will however reduce ripple voltage and provide a more stable supply to the rest of the car. If we vary voltage to an amplifier we vary the output voltage that goes to the speaker. As before since V=IR and R is relatively constant any drop in V means a drop in I. Since we have a drop in I we loose some ability for the speaker to respond.

At some point you reach a point of diminishing returns. You can add lots of capacitance but if you’re consistently pulling more current then the overall system can provide then your voltage will drop anyway.

Please keep in mind this was dumbed down so you dont need an engineering degree to understand. This will fall off next week anyway and we will get the same questions again. Now hopfully some of you have a better understanding.




Modified by nsxxtreme at 4:20 PM 6/14/2006