If you listen to your music loud, a cap will never hurt. Even at low volumes you will get improved sound, but it is not necessary. Upgrading your charging system is definitely not necessary unless you have a car from the 60's pushin a 40 amp alternator like I used to.
It isn't the cap shortening the life of the alt but the systems demands itself. I agree, an eletrical upgrade is a must but even then you may not get rid of the disco affect. I have a 300A alt, 1200cca battery and dual runs of 1/0ga everywhere and I was still getting flashing. It takes a split second for the voltage regulator to kick in the alt so the voltage would fall from 15.1V to the batteries voltage. I call it the bounce effect. GlassWolf posted a nice article on this in another post. I added a 3Farad stinger super cap and the voltage is rock solid. Honestly in my opinion, a cap should be able to prolong the life of the alt by providing a "cushion" from the full ripple effect of the voltage relieving some of the strain. The big killer is that the alt at high drain will not get a break and will heat up and eventually fail. Polo...
No voodoo here... it i provable fact- you will get a more linear response even at lower volume levels due to the fact that car amplifiers contain limited capacitance in their own power supplies. At low volumes, the small amount of reserves are handled by the teeny tiny capacitors in the power supply section of the amplifier resulting in low bass output at lower volume levels. At higher volumes the amp is designed to take its reserve power from your charging system, which causes the infamous light dimming we have all encountered at one time or another. Run a spectrum analyzer before and after adding a capacitor at different volume levels- the proof is in the numbers and the ears.
I agree with you chad, that is when I buy amps I do not buy from the first batch, I do a search for internal pics and look for key parts like large @ss torroid transformers, Large filter/supply caps and quality fets. It would mean more linearity with a more inferior amp (on a lower level) because the lack of quality, especially the internal caps. A more well built amp may not suffer such a fate at lower levels but can/will draw a higher current at higher levels because of the better quality components. A cap either way will not hurt your charging system, it can't. People hurt there charging systems by asking too much from them, period. I think people who are taking a chance by using there stock charging system should at least put a battery monitor on there dash to keep an eye on the voltage. JMHO.. Polo..
I love this forum- Lots of very well argued points from knowledgeable people- I still learn a lot by reading these posts.
I specialize in doing "budget" systems for myself and friends in my infrequent spare time, so if I get a little myopic in my viewpoint of the construction of mobile amplifiers vs. 120 volt, I apologize. Most of the amps I get are used on EBay to save money, and I stay away from the really high end stuff like Zapco and US Amps in favor of the Fosgate and Kicker kind of stuff. Little doubt that the majority of mobile amplifiers are constructed to rely more heavily on the charging systems than their own on board capacitance as opposed to higher end home amplifiers that sport massive power supplies if even rated at 60 watts RMS. Installing a capacitor can result in improved sound quality, not only by increasing the reserve supply but also through filtering out any intereference that may exist in the system. If the rule of thumb is 1 farad for every 500 watts of amplifier output, it would only make more sense to give the amplifier the power supply to handle its own rated output. Thanks for the posts.
chad - the fact is if you can hear a .1 or .2v fluctuation in voltage to your amp's power terminals you have hearing that's one in a million - or better, and I'd bet you what's in my savings account right now that you wouldn't hear a thing in a blind test.
Plus that .1 or .2v would be .1 or .2 less at the peaks, and .1 or .2 more at the dips. RMS values running maybe .1 lower overall. That simply is not audible no matter how much you want it to be.
Your math is pretty close- the difference between a 13.8v input and a 13.6v input on a 4 ohm load is about .16 watts RMS, but consider that we are talking about lower volume levels. Most humans can hear a difference in sound levels of +/- 3dB, and that .16 watt makes at least that difference in the bass frequencies at lower volume levels. Play a 60 or 80hz test tone with and without a cap and see the difference on a sound level meter. You might not hear it because of the time between listening from with cap installed and without cap installed, but givien two identical systems with and without a cap in place, it can be audible.
Chad, part of the big difference there is that home amps rely on a typical 15 to 30A circuit with 120VAC.. that's substantially more to play with than a mobile amp that takes 12VDC @ usually a peak of about 50A to play with in a typical car sustained, then convert that to a high voltage AC output. More is lost to the re-conversions and heat, along with the initially limited power supplied. There are some big differences to consider even between say, a good McIntosh car amp, and a Krell home amplifier.
That aside, the problem with capacitors as a crutch for a lacking power supply simply boils down to this: Capacitor voltage parallels circut voltage, so if the voltage rails sag in the circuit, the capacitor isn't going to be able to do anything to help that, even momentarily. This is why it's always better to stabilize voltage rails with a larger alternator, and batteries, and use the capacitors as filtering, and not a substitute for an adequate charging system.
PS, on the power issue.. remember most car amplifiers these days use a regulated PWM power supply so even if the voltage does fluctuate, so will the power supply duty cycle to compensate, thus the output of the amplifier isn't going to alter between say 11 and 15 VDC input.
Also, a decibel is defined as the smallest change in volume a human can detect.. so 3dB would be 3 audible changes typically.. +3dB would be equivalent to adding a second identical speaker or double the power to the one speaker. double the audible volume would be +6 to +10dB difference, or a difference of ten times the power to one speaker.
Typically unless you at least double the power of an amplifier you won't hear a big difference in output as mentioned though.. Going from 40 to 50WPC on door speakers for example, is hardly noticeable. Going from 50 to 75 or 100WPC will be a significant enough change to warrant the expence in most cases.