2 ohm vs 4 ohm

[scampo77]

i have seen in car amps that the wattage rating is based on ohm loading. when i started learning about car audio i just look for ways to get the ohm loading as low as possible and it wasent until this point that i started asking why am i doing this?

i can see how it would be easier to sell an amplifier that states 1000 watts stamped on the side vs 500 watt. but this doesnt really clarify what ohm loading the amp is recommended for normal use.

what is actually happening inside the amp 2 ohm vs 4 ohm load? do the transistors act differently when more resistance is introduced?

it doesnt help that there are people all over youtube boasting .25 ohm load on their car that can bend the trunk inside out.

it makes sense that if by halving the ohms you double available output of the amp then why not just keep halving it till you get the most power? i obviously realize this is a fast ticket to shorting the amp out but my question is still valid.

is there any difference in sound quality? efficiency? life span of the amp?

is there subs out there that come with insanly low ohms on a single coil? with the express intent of drawing a lot of current?

[wwenze]

There is always a maximum amount of current that can be drawn before something explodes.

[Glowbug]

it makes sense that if by halving the ohms you double available output of the amp then why not just keep halving it till you get the most power? i obviously realize this is a fast ticket to shorting the amp out but my question is still valid.

As you get lower, the amp becomes horribly inefficient. The lowest I've seen in person was the Incriminator Audio 20.1, stable into a quarter-ohm load (a real 1/4-ohm after impedance rise, not a nominal value)...it was a current hog like none other, though. This is why amp manufacturers won't offer warranty coverage below 1 ohm, generally - for a typical "street beater", it results in too many blown amps with people who don't know what they're doing.

[l7runner]

The low ohm loads became popular through SPL competitions. They were in classes based on the amp's power ratings at 4ohms. Therefore people would wire their amps down as low as possible to 1/4 and 1/8 ohm loads to get the most available power when burping. Obviously this results in more power and a higher score. Some amps handle in better than others, many Korean amps (IA, Sundown, Atomic, RD,some DD) work at the ohm loads, while others cannot take it. Therefore they became popular choices in the SPL scene. They also produce coil/custom make coils, that are DVC 0.5/0.25, quad 0.5/1.0 etc.

However this is not adequate for daily driving situation. Those low loads were used for short periods of time often on sine waves. They would have trouble playing music, and staying cool for everyday listening. The extra current draw and lack of efficiency at the lower loads would also drain your vehical's charging system if not adequately beefed up. I believe the amp's THD also greatly rises as impeadence is dropped. Not a problem in competitions but an issue for daily.

Therefore it is not very practical to try these low loads for most situations. I have run an amp at 0.5 ohms for some time with no ill effects (amp rated down to 1 ohm). But it draws more current. In most cases the wattage gains found by dropping impeadence may not be all that audable anyway, and it just puts more stress on the amp.

[shawnk]

it makes sense that if by halving the ohms you double available output of the amp then why not just keep halving it till you get the most power? i obviously realize this is a fast ticket to shorting the amp out but my question is still valid.

i obviously realize this is a fast ticket to shorting the amp out

You have already answered your own question

An amplifier is designed with certain goals in mind. Operating at a certain impedance is one of these goals. All of the components within the circuitry each have their own current limitations. Loading down an amplifier below it's rated limits will cause components to fail. Many times a protective fuse will not blow before some components will if the amp is abused.

is there any difference in sound quality? efficiency? life span of the amp?

(simplified answeres)
Typically sound quality goes down as impedance drops..
Efficiency depends on the amplifiers design..
Expect the life span of the amplifier to drop significantly if it is operating below recommended limits.
Keep in mind that as the load on the amplifier is lowered, current draw increases. More current draw=more heat. More heat=shorter life.

is there subs out there that come with insanly low ohms on a single coil? with the express intent of drawing a lot of current?

Yes. I've seen some drivers with .3ohm coils. Typically designed for the SPL arena, and used with amplifiers designed to run very low impedances and/or very short time frames

[multisync]

as you guessed power output P = Esqared/R E is the voltage the amp puts out and R is the resistance of the amplifier . From the formula if R is halved then power should go up by 2. Providing that the amplifier can deliver the SAME voltage to a lower load. Example. Voltage is 20 volts, for an 8 ohm load power = (20*20/8) = 400/8 = 50 watts, for 4 ohms 400/4= 100, for 2 ohms 400/2= 200 watts. etc. Not all amplifiers can drive 1 ohm or lower loads, and what is the loss in the connectors and the hook up wire for the speakers. At very low loads wire losses, power supply losses(battery), connectors, wire length all become important factors. These losses are also inside the amplifier as well. Have you ever used an electric kettle and ran it to boiling then unplug the power cord? Was it warm? Power loss in the cord. You can put all the speakers you want to in parallel to increase the power output of the amplifier, can the amplifier actually deliver power to a very low load and how much is getting to the speaker it self? It doesn't take much to flex a trunk. push on a car panel, how hard was it to bend. If you look at the speaker builders threads all the DIY guys are forever trying to find ways to reduce panel flexing and vibration and not trying to flex the panels as much as possible.

[Glowbug]

They were in classes based on the amp's power ratings at 4ohms. Therefore people would wire their amps down as low as possible to 1/4 and 1/8 ohm loads to get the most available power when burping.

Ah, USACi..."1 watt" amps that happen to do 3kW @ 1

[scampo77]

what is actually happening inside the amp that causes more power to be output?

i have an understanding of ohms law but it seems there would be a finite amount of power in the amp. rail voltage remains the same doesn't it?

[brandes.cm]

Nothing happens in the amp to produce more output power. You are changing the load that the amp sees. If you replace your 100 watt light bulb with a 250 watt bulb did you change anything in the lamp socket? No, you changed the resistance the socket sees.

The rail voltage will dip when the load impedence is dropped.

Infinite power, no, you can only get out what you put in. That is saying your amp is 100% efficient and it is not.

[tsmith1315]

1) Power out = power in minus friction

2) Power out = Voltage out * Voltage out / impedance

3) Voltage out = RCA Voltage in * amplifier voltage gain

A car amp is nothing more than a voltage multiplier. If the amp produces a gain of 20x, then a 1 volt input (RCA) signal produces a 20 volt output (speaker) signal.

Look back at #2 above:

The 20 volt output signal into 4 ohms will be

20*20/4 = 100W

into 2 ohms will be

20*20/2 = 200W

into 1 ohm will be

20*20/1 = 400W

This happens because for a given voltage output, as the load impedance drops, more current will be drawn. Hence, the power output is higher.

The higher output current must be delivered through the amplifier, which if it isn't designed to handle that, will smoke.