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JasonH's avatar

What is the differance between 4 ohms 6 ohms & 8 ohms?

Asked by JasonH (107points) July 8th, 2008

looken @ a 18” subwoofer its at 8ohms but also there is one that is 4ohms whats the Differance? what is ohms? 4,6,8?

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14 Answers

PupnTaco's avatar

Can I be the first to say 6 is 2 more than 4 and 8 is 4 more than 4?

JasonH's avatar

aah cunfusing me doesnt help lol pupntaco.

JasonH's avatar

oh wait i got it now haha. smartass grr:)

sndfreQ's avatar

In audio electronics, the usage of Ohms refers to the amount of resistance that a circuit has to current; it is an inversely proportional ratio, that is, with a lower Ohms rating, a higher current flows through the circuit and load.

In the case of speakers, an 8 Ohm speaker can only “accept” a load current that is 1/2 as great as a 4 Ohm speaker; likewise, a 2 Ohm speaker can handle a current that is double that of a 4 Ohm rated speaker.

Ohm’s Law is the clearest illustration of this principle, and if you know two of the three terms (the Voltage used in a system, and the current), you can calculate the resistance (V=I/R, where Voltage is equal to Current divided by resistance in Ohms).

This is a common calculation in determining the load of a speaker or driver, in order to properly match the amplification being delivered from a power amp. If your amp is switchable, it will decrease its current when the resistance is increased. Usually smaller speakers can handle lesser currents, so they will have 8 or even 16 Ohms. Larger reinforcement speakers, subs, etc., can often handle 4 or even 2 Ohm loads, given proper amplification. More sophisticated “pro-level” power amps have this switch on the rear panel, where it will say something like “250 Watts (Voltage x Current) @ 4 Ohms, 500 Watts @ 2 Ohms.” Usually, amps and speakers use multiples of 2-that is, 2, 4, 8, 16. I have not seen systems with 6 Ohm ratings, though in electronics they do exist (not so much in audio applications).

sndfreQ's avatar

A layperson could understand the concept in the following analogy: If you had 50 gallons of water with which you could water your lawn, which would you choose-a soda straw or a garden hose? Both are capable of dispersing the water, but the garden hose allows for a greater water pressure (current) and greater/faster coverage (similar to Wattage). True the soda straw will get the job done, but given the “job” of a 50-gallon watering, is that the most appropriate choice?

Conversely, have you ever tried to water a delicate orchid plant (potted) with a full-force garden hose? How about a fire hose?!

JasonH's avatar

i know the smaller the hose the harder pressure, the bigger the hose the less pressure. so for say a speaker aka sub woofer at 4 ohms current wattage rating of that speaker something like 800 watts than id want a 1600 watt amp \? right?..

sndfreQ's avatar

The issue is you have to check the amp rating-if it’s 1600 watts at 2 Ohms, then it would be the equivalent of 800 watts at 4 Ohms; you also want a little bit of overhead, as in the power amp should have at least the equivalent wattage or higher (higher is always better from the power amp side); you never want to under-power a speaker-that will always lead to failure issues when the speaker driver is not “given” enough current for its load (that is the cause of drivers blowing out the majority of the time).

sndfreQ's avatar

The other issue is that watts are a measurement of volts times current; so if your voltage is a constant (for example between 110/120 volts is the US standard), then if you try to plug in the those units into an equation, you’ll always run into some sort of “maximum” for current based on the wattage. So let’s say (for easy math) that the wattage for an amp is 1200 watts, then if you take 120 Volts into account, the current is 1200 / 120 = 10 amps.

That said, 10 amps is a lot of current in most cases; a 1200 watt amp yields a current around 10 amps then in this case. If you had a 100-watt power amp, then given the constant voltage, it’s output is: 100 / 120 = 0.83 amps, or less than 1 amp.

From those two comparisons, you can see that the 1200-watt amp can produce >10-times greater current (“water pressure”) than a 100-watt amp does. So to say that a smaller hose can “spray” with harder pressure works in the world of “water”, but in electronics, it’s not so in most cases.

whatthefluther's avatar

@sndfreQ: excellent explanations both here and Andrew’s question. 6 Ohm’s is not too unusual…I’ve seen it Sony speakers and some lesser known brands. Perhaps you can help me with an issue. I don’t believe I’m getting the most out of my JBL 600W subwoofer and admittedly have not systematically attempted wiring alternatives and setting adjustments (mode setting, crossover frequency). I will PM you when I can dig out of mess I’m up to my eyeballs in (including removing 400 CDs {ouch} from one of my changers so I can send it in for service to fix a problem Sony appears to have built into these units {double ouch}).

sndfreQ's avatar

@wtf-is your sub powered or non-powered? If it is a powered unit (amp is inside the subwoofer box), then your problems are a lot simpler in terms of tuning the system.

If you can PM the model number to me I’ll look it up and get back to you. I’d have to take a look at the input types, plus the other settings and makeup of your system (receiver, other speakers in the system), in order to tell you the possible settings for crossover frequency. Engineers and acousticians alike take these into account with the dimensions of the room to determine the “sweet spot” for both placement and tuning frequencies for subs etc.

Yeah, send me those specs and I’d be glad to help you out :)

Kirbymar's avatar

I have a 1990 Jag and I need to replace two 4” 6 ohms speakers to handle the bass. I am replacing the other front and rear with paris of 4” 4 ohms speakers. What pair of 6 ohms 4” inch speakers would you advise and do you know a good place to buy them?

sndfreQ's avatar

@Kirbymar: welcome to Fluther! May I suggest you ask that question on the main site (from the home page as a new question). I think you’ll be casting the “net” to a wider audience and may get more responses and differing perspectives.

yan's avatar

how can I calculate what gauge of speaker wires I need for a 6ohms, 30wattRMS rear speaker that would be for example 30 feet (wire length) away ?

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