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ohms questions?

EIwood

Standard Member
When buying an audio receiver is it better for the receiver to give out more ohms that the speakers? Say you have a 5.1 setup, all 4-6 ohms. Would it better to have a receiver give out 4-6 ohms, or should it be higher, like 6-8 ohms? Is there a limit to how many ohms you can put into the speakers?

Also what does the wattage mean, like if the speakers are 150w, should the receiver give the same amount out, more or less?
 

Phlog

Active Member
When buying an audio receiver is it better for the receiver to give out more ohms that the speakers? Say you have a 5.1 setup, all 4-6 ohms. Would it better to have a receiver give out 4-6 ohms, or should it be higher, like 6-8 ohms? Is there a limit to how many ohms you can put into the speakers?

Also what does the wattage mean, like if the speakers are 150w, should the receiver give the same amount out, more or less?

I think there's a slight misunderstanding here.

"Ohms" refers to impedance.

For the amplifier, it's giving a range of impedances that that the attached loudspeaker should be within.

For the speaker, it's giving the nominal impedance of the speaker.

The two should be matched.

"Wattage" refers to power. So in the case of a speaker, 150 watts refers to maximum power it can withstand.

It is actually better to have an amplifier rated above that of the speaker - especially if you play music loud.
 

BlueWizard

Distinguished Member
Ohm are a measure of resistance or impedance. In short they determine how much current will flow out of your amplifier.

However, most amps can tolerate a range of impedance from the speakers. Typically, and somewhat universally, most amps can tolerate a total load on one amp channel in the range of 4 ohms to 16 ohms. Some AV amps though, can only tolerate 6 ohms to 16 ohms. As long as your speaker ratings are within the normal range for the amp, you will be fine.

Power is Voltage times electrical Current.

Voltage is the presence of electrical potential. Keep in mind a battery has voltage even when it is not doing work.

Current is the actual flow of electricity.

Power is the work being done when a voltage is applied to a resistance and current flows.


Power = Volts X Current

So, if the amp applies a voltage to an 8 ohm speaker, current flow and work is done.

Think of it this way. Voltage is like a tank full of gasoline. The tank has gasoline even if the car is not running. Current is like the flow on gasoline through the gas lines to the engine. Power is like the gasoline being burned; this is where the work is actually done.

Amps have a power rating, but it is based on the available voltage and the amps ability to deliver current at that voltage. How much current flows is determined by the resistance or impedance of the load. Low resistance load equals high current, equals high power. High resistance load equals low current, equals low power.

Speakers have a power rating, but it is more an indication of the limits of the speaker. What limits the ability of the speaker to survive is how well it handles heat. Just like a car engine gets hot when it does work, so does a speaker. As long as the speaker can lose heat faster than heat is building up, the speaker works fine. But when heat exceeds the speakers ability to lose that heat, the speaker can be damaged.

There are many types of power ratings for speakers. Typically you will be given a working range, as in 25w to 100w. That specification is saying, we would prefer that you used at least 25w with our speaker, but also, do not recommend using more than a 100w amplifier.

You will sometimes see continuous and peak power ratings on speakers. As an example, 100w continuous and 200w peaks. That means the speaker should sustain 100w for a reasonable length of time. But, you could use it with a 200w amp as long as you never let it reach and hold 200w for any length of time. It can peak at 200w for extremely short periods of time.

So, functionally, the speaker's power rating is a guideline. It gives you an idea of the range of amp's power that these speaker will work with. But, it is a range, and a general idea, not an absolute. Remember this is about heat and how fast the speaker can get rid of it. If you drive the speaker loud and long, heat is building up fast, and dissipating slow. Sustain extremely loud playing, even if you are within the rated power range of the speaker, can cause damage. This usually happens when amps are played for a long time at well over 50% volume.

So, speaker power ratings are a guideline, not a guarantee. They give you an indication of the range of power amps that these speaker will work well with. It is not necessary to precisely match speaker power and amp power. 100 watt speaker will work fine on a 40 watt amp; and 40 watt speaker could work fine on a 100 watt amp, assume you are conservative and use some common sense.

Hope that helps.

Steve/bluewizard
 
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EIwood

Standard Member
thats fairly helpful, thanks. So just a few questions, for watts you say the speaker rating is a guideline for minimum and maximum watts? Some of my speakers lowest watts are 30, 40 and 20. What I'd like to know, is if I used a receiver with 40 watts minimum output, would the 30 and 20 suffer? If I got a receiver with an output as low as 20 however, would that cater to both the 30 and the 40?
 

BlueWizard

Distinguished Member
thats fairly helpful, thanks. So just a few questions, for watts you say the speaker rating is a guideline for minimum and maximum watts? Some of my speakers lowest watts are 30, 40 and 20. What I'd like to know, is if I used a receiver with 40 watts minimum output, would the 30 and 20 suffer? If I got a receiver with an output as low as 20 however, would that cater to both the 30 and the 40?

The power rating on a speaker, is like the speed limit on a highway. Technically, you can go any speed from ZERO up to the speed limit. With speakers you can go from very low watt up to the maximum rating of the speaker.

And just like when driving a car, you can go above the speed limit, if you are careful about it.

The minimum power rating is what the manufacturer feel is the minimum to get the best out the speaker. But they will work with less power. Keep in mind that when speakers are tested, they are driven with a mere ONE Watt to very loud sound levels approaching 90db. Ninety DB is about as loud as you could stand music in a normal sized room. So, yes they work even with only one watt. But, any speaker, regardless of ratings or specs is going to sound best when it it fed some serious power.

So, yes, when used with care and common sense, pretty much anything will work with anything else.

Steve/bluewizard
 

EIwood

Standard Member
so since my lowest watts is 20 and my highest is 150 I should get a receiver in that area or near enough. That is 50 higher than my third highest rating though, but you say the speakers wont get damaged so long as I don't put the speakers up really high?
 

Mark.Yudkin

Distinguished Member
since my lowest watts is 20
Not quite. Your "lowest watts" is 0, known as silence. That "20W" refers to the lowest maximum: your receiver should be able to emit a (continuous) maximum of at least 20W.
and my highest is 150
That means that the maximum before melt-down is 150W, where melt-down is meant literally - it's where the insulation in your speaker driver's coil will melt and your speaker will fail. If you try to draw more than 150W, sooner or later you'll need to pay for a repair.

In the end, the actual power you need is a function of the volume control - solely. Provided you don't try to make the amp and speakers go louder than they're designed to, you'll be OK. Conversely, attempting to achieve greater volumes will cause damage.

Given the specs for your speakers, a receiver roughly around 50W - 75W should work fine, but there's no need to worry if it's 40W or 150W.
 
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EIwood

Standard Member
yeah my current one is rated at 140w per channel, so its over the lowest few, but not by far. I'l try to find one more suitably rated.
 

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