Is a bridged amp necessary?

Question

My daughter got a small system installed in her car. The amp over-heated and cut off before leaving the parking lot. We were now being told we needed a capacitor. She has a 10" off brand sub, 4 kicker side/door speakers and a 300 watt 2 channel amp. After purchasing the capacitor they said she needs a distribution block as well. During a conversation with the installer he mentioned that he bridged the amp because it was only 2 channels. My question is.. is bridging the amp necessary with the amp overheating..couldn't it just be wired normally? and will this capacitor keep the amp from overheating? I feel like he doesn't know what he is doing and we're getting ripped financially. The small town we live in gives us limited options, I don't want to question him and sound like an idiot, so I really need simple advise since I don't really have a clue about this stuff. Thank you

Answer 1

(1) You DO NOT need a capacitor. Ever! Don't waste your money. It cannot prevent an amplifier from overheating. It is also of extremely limited use for other reasons.



(2) Bridging means two channels are tied together to make one single channel. The power is equal to the power of each channel added together. The impedance will be twice the impedance of a single channel. Therefore, if your "350 watt" two channel amplifier putts out 175 watts RMS per channel at 2 ohms, in bridged mode it will put out 350 watts RMS at 4 ohms. The main reason to bridge the channels is usually because a sub needs more power than a single channel can provide.



(3) A common reason for an amplifier quickly overheating and cutting out (going into protection mode) is that the attached speaker or speakers are lower in impedance than the amp is rated for. So, if that subwoofer is 1 or 2 ohms, and the bridged impedance of the amp is 4 ohms, the amp will overheat. Without a thermal protection circuit it would literally burn up the circuitry.



(4) Either you completely misunderstood what the installer was trying to explain, or that person doesn't know what they are doing. My guess is the installer is either not really knowledgeable OR he's trying to earn a few extra bucks.



(5) It would be a lot better if you told us exactly the brand and model numbers of the amplifier, the subwoofer and the door speakers so I can verify if the problem is an impedance mismatch or something else. Also mention whether the Kicker door speakers are being run off the amplifier, or directly off the Radio / CD player. You cannot adequately run 4 speakers and a sub off most 2-channel amplifiers.



(6) A distribution block isn't expensive but it has nothing to do with an amp overheating. A distribution block is most often used in a 2 amp setup so that only one long power cable needs to be run from the battery. I'm guessing he's using it to add the capacitor to the system which is completely unnecessary. No capacitor needed so no distribution block needed. It's that simple. You installer is barking up the wrong tree there.

Answer 2

I'm not sure you understand what "bridging" an amplifier means. When you bridge a 2-channel amplifier, you're combining the two channels into a single channel with more power. If you have a 2-channel amplifier with a single subwoofer, usually bridging the amplifier is the best option. The other option is just to connect the sub to one channel, leaving the other disconnected. The result is that the subwoofer gets about 25-50% of the power output it would get in the bridged configuration.



There are some limitations on how you can use an amplifier in bridged mode. Typically, a bridged 2-channel amplifier can only be used with a 4-ohm or higher subwoofer. If you use a lower impedance subwoofer with a bridged amp of this type, then it's very likely to overheat or trigger a protective circuit. So the first thing you need to figure out is whether you have a 4-ohm subwoofer. If it's a standard single voice coil sub, it's probably 4-ohm, and should work properly with the amplifier. If it's a dual voice coil sub, however, it might be wired in a way that presents too low a load impedance to the amplifier.



The amplifier might also overheat or go into protect if the subwoofer is damaged or mis-wired. Undersized wiring or a poor ground connection will sometimes cause overheat issues, but this is less common--usually an overheating or protect circuit problem is caused by the subwoofer or subwoofer wiring.



Adding a capacitor definitely won't fix the problem.



Can you edit your question with the brand and model number of the subwoofer, and the amplifier? That will help me figure out whether the two components are well matched, and whether it's likely that the subwoofer is too low impedance for the bridged amplifier.

Answer 3

In order to have a load on both channels and you have only one speaker, you must bridge the amp to run that one speaker. A capacitor will not solve your problem. A distribution block could help run with more than one battery, but that's the solution to not having enough current to run the amp efficiently. Perhaps the off brand woofer has impedance lower than the stability of the amp. That's your homework to look at what you got. Too low impedance will cause the amp to overheat from drawing too much current. It sounds like the shop sold you incompatible components, or wired them in wrong. Good stuff won't work when put together wrong.

Answer 4

Thank you everyone for all your input.. I sounded so smart when I talked to the installer (thank you!! SERIOUSLY). Sorry I wasn't able to give the brand names or model numbers to help ya'll give more detailed answers (my daughter works her butt off and wasn't home to get that info. but I can say the installer did have the 4 kicker door speakers on 1 channel and the sub on the other channel. The man we purchased the system from thought the installer would only use the amp for the sub, wiring the 4 door speakers directly to the radio. The installer admitted to his error and has wired ALL the speakers to 1 channel now and the amp is no longer over-heating. However they did go ahead and install the Boss 3.5 capacitor... stating that she now will be able to play her stereo while the engine is off. Honestly I think they didn't want to refund my money on the capacitor and I just wanted to get out of there and end this headache. If anymore issues come up I will make the long drive to Dallas and have it fixed right from an actual car/stereo business.

Answer 5

1. you never NEED a capacitor... if your system has the right cabling and fuses it will be fine

2. the overheating amp means your speakers are pulling more than the amp can supply (thus heating up)

3. your entire problem could be solved by getting a better amp (more watts rms looks like 400-500watts rms min) and an inline fuse of 40 amps or so (or dual 20 amp fuse)

Answer 6

Capacitors are useless in car audio. Don't ever buy it and don't even look at it.