Why .5ohms and not 4ohms?

[Propimp 10+ year member]

Why do alot of amp companys make there amps to put out rated power at .5ohms or 1 ohm, Why not make the amp od rated power at 4 or 2? Wouldnt it be easier on the amp, electrical and such?

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[2000LaDe 10+ year member]

not really because it still takes a certain amount of amps and such to produce a certain amount of power.

 

[Propimp 10+ year member]

but wouldnt it be easier on the amp though to run @ 2 or 4 than .5 ohms

 

[dman4486 5,000+ posts]

but wouldnt it be easier on the amp though to run @ 2 or 4 than .5 ohms

.5ohm is just less resistance allowing the amp to put out more power....

 

[skadude016 5,000+ posts]

but wouldnt it be easier on the amp though to run @ 2 or 4 than .5 ohms

in theory yes. Most of the time the lower the ohm the less efficient it is

 

[Propimp 10+ year member]

I was just wondering, I have a older MTX 1501d and it puts out rated power at 2 ohms and Some subwwofer that I look at only sell it dual 2... so its eaither 1 or 4 ohms //content.invisioncic.com/y282845/emoticons/frown.gif.a3531fa0534503350665a1e957861287.gif and I was thinkg about this amp question.

 

[skadude016 5,000+ posts]

I was just wondering, I have a older MTX 1501d and it puts out rated power at 2 ohms and Some subwwofer that I look at only sell it dual 2... so its eaither 1 or 4 ohms //content.invisioncic.com/y282845/emoticons/frown.gif.a3531fa0534503350665a1e957861287.gif and I was thinkg about this amp question.

there is a way to mod that exact amp to run at a lower ohm load

 

[n2audio 5,000+ posts]

Don't quote me, because this comes with a lot of less than polished theory. Helotaxi or some other electrically educated contributor can probably clean it up, but...

Driving high impedances with high power requires a lot of voltage, of which a car has little of.

Driving low impedances with high power requires a lot of current, which a car has a lot of.

Compared to a home that has a lot of voltage w/o a lot of current 8 ohm is the std imp.

 

[koolwhipman 10+ year member]

Don't quote me, because this comes with a lot of less than polished theory. Helotaxi or some other electrically educated contributor can probably clean it up, but...
Driving high impedances with high power requires a lot of voltage, of which a car has little of.

Driving low impedances with high power requires a lot of current, which a car has a lot of.

Compared to a home that has a lot of voltage w/o a lot of current 8 ohm is the std imp.

I quoted you.

Cause that sounds logical.

 

[Propimp 10+ year member]

there is a way to mod that exact amp to run at a lower ohm load

I know, but im content with it now. and I still have 8 months of warrenty on it //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif

 

[Propimp 10+ year member]

and thanks N2 always a help

 

[helotaxi 5,000+ posts]

Yep, voltage vs. current. To get a high rail voltage out of an amp with a switching power supply you need big, high voltage caps which cost big money. More, higher current switching devices and a slightly beefier transformer or inductor can suffice for high current and cost considerably less.

Even still, very few amps are rated at 0.5 ohms. There is a limit to the amount of current that the power supply and outputs can handle. Ohm's law states that the voltage drop is proportional to the current and the resistance. And the voltage drop multipled by the current is the wattage lost as heat and is the basic inefficiency of the output stage. The amp will try to flow twice the current into half the impedance and the loss will be double resulting in a lower efficiency. The difference from 4 ohms to 1 ohm can be managed, but that final doubling of current is usually more than the output devices and power supply devices can handle. there just comes a point where you can only cram so many redundant output devices or power supply switching devices in a heatsink.

 

[helotaxi 5,000+ posts]

deleted, stupid network

 

[helotaxi 5,000+ posts]

x2

 

[thch 10+ year member]

i'd place it more on an economic side then an engineering side.

speakers in cars were designed for 4ohm. the 12V system without power supply pretty much limits you to reducing impedance to increase power. the inability or lack of interest in HUs capable of 2ohm loads (and the longer, thinner wire used for speakers) probably explain the reason there are so few 2ohm non-woofer speakers.

and for woofers, well, since the bridgeable amplifier became popular there really hasn't been a huge need for monoblocks. and quite often amplfiers were made to be used with speakers, or woofers, or even both.

from there you have the cycle of people building amplifiers for the market -- which uses 4ohm speakers. then competitions started playing ratings games that made lower impedances more practical. and then people wanted to bridge amplifiers to existing 4ohm speakers, so that gives a 2ohm nominal per channel. and speaker makers tend to build to the market. even manufacturer's of 6-8ohm car speakers will list them as 4 sometimes -- it sells.

this keeps woofer makers and amplifier makers largely trying to make speakers for a couple of mainstream markets, with a few oddballs here and there.