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Thread: Cap or not to cap

  1. #1
    Constant Bitrate
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    Cap or not to cap

    I and a advanced/novice when it comes to stereo stuff...I know enough to do the job and if I don't I know how to find out. I am installing my second amp...here is my question. I see tons of arguments one way and the other. What is the beef with capacitors? I have never used one but my new amp is going to be running to the speakers at 1 ohm and I am getting support saying I should others saying they are crap...so why are cap's crap? I feel like I am in a Dr. Seuss book

    Should I would I use a cap?
    Could I should I not use a cap?

  2. #2
    Maximum Bitrate RAWPWR's Avatar
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    I found a bit of info that might help from ......http://www.audiogroupforum.com


    V = IxR. Where: V = Voltage I = Current. R = Resistance

    With a power amplifier, resistance varies with the volume and frequency of the music. As the resistance fluxuates the amp draws more current and expects the voltage to remain the same. It is the regulator on your alternator's job to make sure the voltage stays the same by dishing out more current when it is needed. If the regulator cannot react fast enough to the change in resistance, the voltage will drop.

    This means, each time there is a bass thump, the voltage will drop slightly until the regulator catches up. You will recognize this at night by seeing your lights flicker. The regulator is fast acting, but not as fast as a double bass drum.

    A capacitor tricks the alternator's regulator into thinking there is less resistance while the amp is in a low-output state by storing electrons and creating a faux current. When the amp changes to a high-output state, the capacitor is quickly drained and begins to charge again when the amp switches back to a low-output state. This happens very quickly...such as between bass drum kicks in a fast rock song.

    The result is a smoother current draw from your alternator which prolongs the life of the regulator. There is also an audible difference in music because the voltage will not fluxuate as much and your amps will get the current they want...when they want it.

    However, many new amps use regulated power supplies to combat this fluxuation in voltage. This means whether your alternator runs at 15 volts or 11 volts, the amp will operate the same. Essentially, they don't take advantage of the extra voltage when it is there. For this reason, a regulated amp will have higher SQ while an unregulated amp will have higher output while the car is running (14v) vs. while the car is not running (12.5v).

    Still, a regulated amp will cause a fluxuation in current even if it unaffected by the drop in voltage meaning a capacitor can still help your electrical system.
    Last edited by RAWPWR; 07-15-2013 at 03:55 PM.
    ephect likes this.

  3. #3
    Low Bitrate ephect's Avatar
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    i had always wondered, but never enough to research. Thankyou RAWPWR!

  4. #4
    Raw Wave
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    Actually, I dispute all the above (sorry RAWPWR).
    There is no resistance change nor regulator trickery nor unused "extra" voltage.

    In brief, a cap is merely a store of energy.
    So is a battery.
    But if your amp is a long way from the battery and you have a burp that causes a big voltage drop between the battery and amp, a cap near the amp will supply some energy.
    However a (2nd) battery near the amp will do the same, and since a battery is at least thousands of Farads, why buy a 1F etc cap when a 12V 1.2AH battery holds far more energy?
    One reason is to protect adjacent AGM battery(s), but only applies to amps that are typically above 3kW output (RMS of course!). There are also other reasons though they rarely apply to audio set ups.

    And interesting read is Richard Clark. Richard and David Navone pioneered car audio implementations and introduced "stiffening" capacitors.
    In the years since, Richard saw the fallacy of caps and now debunks them. (But too late, bad info often outlives the truth.)

    And if you are after (peak) SPL, most I know of advise against caps.

  5. #5
    Maximum Bitrate rray's Avatar
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    I have a 1F cap, and a Stinger SV35 battery, on the amp side of my starting battery isolator solenoid. I could not find closure to the debate so figured, what's an extra $100 just in case. So far I have not had any negative impact.

  6. #6
    Raw Wave
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    Alas many do not like spending $100 for no gain, else inferior gain.
    As I see it, $100 is an extra battery which can be used for emergency cranking etc. But I'd probably find better uses for my "spare" $100.

  7. #7
    Constant Bitrate FockMasterDan's Avatar
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    I am not personally a proponent of caps most of the time and don't use one myself, but they don't hurt anything to have. The worst case scenario is you waste some cash.

    The debate can rage on forever, but I always say upgrade everything else first. Battery, cabling, and alternator and if after all that you have dimming of your headlights then try a cap or extra battery.
    Computer is in the car, but in a very "raw" install right now.

    Worklog - here

  8. #8
    Raw Wave
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    Trust me, the debate is closed.

    Maybe I can paraphrase - except as I mentioned: eg, a cap to protect an AGM (at the expense of peak SPL) or where batteries are not practical etc; and some limited applications - a battery beats a cap hands down. IE - why spend on a cap when a cheaper battery will do better?

    If you already have a cap then IMO you may as well use it assuming it doesn't add extra path resistance and on-selling is not worthwhile.
    But to buy a cap or add a cap for low power amps (under 2k-3kW) irrespective of battery type is pointless.

    As FockMasterDan and most knowledgeable people will say - upgrade everything else first. As a general rule that means the big-3 or big-4; upgrading the alternator (before adding batteries depending on why the extra voltage or current is required); adding additional batteries if required (eg, near the amp for burps; via isolators, etc).
    And if adding caps to un-dim headlights, place those in the light's supply (usually before the relay or switch), but again, a battery will do better.


    AFAIAConcerned, apart from the exceptions I outlined in this thread and elsewhere, until someone starts defining burp/sag durations etc OR provides sample CRO waveforms of amp voltage sags (and comparing a 1.2AH battery etc interchanged with a 1-40F cap etc), there is no debate.
    All these pro-cap experts and manufacturers and yet no supporting CRO etc proof? Doesn't that seem strange?

    I can understand why many are confused or convinced. But why not add a ferric or gold battery base or tray to improve ripple smoothing and add battery capacitance? Gold-plated trays are available for $100 upwards. So too are gold amp housings.

  9. #9
    Constant Bitrate FockMasterDan's Avatar
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    I actually have a cap that I got second hand from someone I know years ago and it's still sitting on a shelf. I could easily install it, but why?

    I will say that space and ease of install could be potential reasons to use a cap over a battery. It's pretty easy to shove a cap somewhere in the trunk for someone that isn't up to fitting a battery in somewhere. I'm on the other end of the spectrum though, I just turned my whole trunk into an electronics bay that includes my primary battery for the car.
    Computer is in the car, but in a very "raw" install right now.

    Worklog - here

  10. #10
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    With low quality unregulated amplifiers Caps can make a difference. Caps have never been considered the correct way to do things. They are considered a band-aide and in today's high quality, high output regulated amplifiers they are almost totally worthless if the system is setup right. Some competition systems in the past incorporated CAPS more as an insurance than a need.

    Capacitors discharge much quicker than a battery can but they generally don't hold as much capacity as a battery. If you have a high powered system the proper way to do this is to have a battery as close to the amplifier bank as possible with as big a wire as practical to the amplifiers. In some competition systems you will see a solid bar used instead of wire for the majority of the power feed but a high purity copper wire with many strands is much easier to work with.

    If your power wire is under sized you can get a severe voltage drop at the amplifier during some deep bass notes. A capacitor can be used to diagnose an undersized wire but should not be used instead of a proper sized wire. If your system works well with the capacitor and sucks without it then your wire is undersized and potentially your battery is either old, or under sized as well. The PROPER fix for this then is to increase the size of wire used to feed the power from the battery to the amplifiers and make sure all ground paths have been upgraded as well. (Battery to block and block to body or whatever method your vehicle uses to ground from the battery to your amplifiers. If you run a wire directly to your battery then that wire needs to be the same size as the positive wire.) No such thing as too big a wire.

    A capacitor can also be used to get rid of system noise but again this is not the right solution. The right solution is the proper sized wire and proper routing. Sometimes a bad component can also cause noise.

    Main reason why this doesn't work with high quality amplifiers is they already have large capacitors incorporated into the power supplies and having an external capacitor is a total waste.

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