Techie question...

This sounds atrocious coming from a person who's purchased and owned hi-fis for over 30 years, but as most of you know I've never bothered about the specs. If it sounds great then I'll buy...

That aside, can someone explain, in layman's terms, what this means:

Output Power into 8 Ω

80 W RMS per channel

Output Power into 4 Ω

130 W RMS per channel

As my manual is up in the attic, I've copied this from Leema's site on the MKIII version.

Does it mean that if 4 ohm speakers are played thru the amp, the power section automatically changes to 130 watts?

Any help is appreciated.

Ta, PP.
 
Craig M. said:
You could find this information out for yourself very easily. Did you bother reading those links I provided you?

Maybe I can, but I don't understand technical jargon, hence why I mentioned "in layman's terms" on my initial post.

No, haven't looked at the link yet, been on important family errands since Monday evening.
 

Paul.

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Think of your speakers as big resistors. Lower resistance means higher output power. Thats probably a dramatic over simplification but you don't really need to know more.
 

Covenanter

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Mathematically:

P=IV where P is power, I is current and V is Voltage

and:

V=IR where R is resistance

So substituting for I

P=VV/R

So power is inversely proportional to resistance and as Paul says the lower the resistance the higher the power.

Of course it isn't as simple as that as speakers aren't pure resistors and nor are amplifiers pure linear current generators but it's close enough.

Chris
 

Ketan Bharadia

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Hello,

The amplifier's power output is directly related to the amount of current it delivers. A 4ohm speaker will demand more current than a 8ohm alternative, that's why the amplifier's power output figure goes up.
 
Ketan Bharadia said:
Hello,

The amplifier's power output is directly related to the amount of current it delivers. A 4ohm speaker will demand more current than a 8ohm alternative, that's why the amplifier's power output figure goes up.

So the amp automatically adjust to the ohms or does one need to flick a switch or have it tweaked to raise the wattage?
 

scene

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plastic penguin said:
Ketan Bharadia said:
Hello,

The amplifier's power output is directly related to the amount of current it delivers. A 4ohm speaker will demand more current than a 8ohm alternative, that's why the amplifier's power output figure goes up.

So the amp automatically adjust to the ohms or does one need to flick a switch or have it tweaked to raise the wattage?

Depends on the brand. Some have a 4/8 or 4/6/8 ohm switch on them.
 

Andrew Everard

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Think of the amp as a bucket with a small hole in it – big enough to allow water to to flow out, but small enough to impede the rate of flow (geddit?)

Make the size of the hole twice as big, and water flows out twice as fast, because the hole is only impeding the flow half as much as before.

It's not quite that simple: although some amps do double their power as impedance halves, in others it increases significantly, but doesn't double, because the power supplies in the amp aren't hefty enough to supply the extra juice (or water in the analogy above) required.

In the bucket analogy, imagine the bucket hanging on a garden tap, and the water flowing from the tap endeavouring to keep the bucket filled despite the leak. The tap is the amp's power supply section, and if there's insufficient water pressure behind it to allow you to turn the flow up to compensate for the bigger hole in the bucket, eventually the bucket will run dry.

By the way, and keeping with the 'in simple terms' caveat, clipping occurs when the amp isn't replenishing the power required by its output devices as fast as energy is flowing out of them to the speakers. The output devices thus clip off the extremes of the waveform, causing distortion able to damage speakers. Usually the tweeters go first, the thin wires in their voice-coils being especially susceptiable to either 'burning out' or simply melting together due to overheating.
 

hoopsontoast

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Paul. said:
http://www.gcaudio.com/resources/howtos/spkramp.html

Great Link :)

plastic penguin said:
This sounds atrocious coming from a person who's purchased and owned hi-fis for over 30 years, but as most of you know I've never bothered about the specs. If it sounds great then I'll buy...

That aside, can someone explain, in layman's terms, what this means:

Output Power into 8 Ω

80 W RMS per channel

Output Power into 4 Ω

130 W RMS per channel

As my manual is up in the attic, I've copied this from Leema's site on the MKIII version.

Does it mean that if 4 ohm speakers are played thru the amp, the power section automatically changes to 130 watts?

Any help is appreciated.

Ta, PP.

So ideally your amp would double the power as the impedance halfs. In theory, your amp would deliver 80w into 8Ω, 160w into 4Ω and 320w into 2Ω. The Amplifiers output is usually limited by the output transistors, power supply (size and capacity) and heatsinking on the output devices.

This is different on valve amps as they can have seperate windings on the output transformers for 16,8 or 4 Ohms. No idea how OTL valve amps work though.
 

hoopsontoast

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As an example, this Luxman amp does pretty well as a voltage source delivering 24dBw into 8, 4 and 2 Ohms

http://www.stereophile.com/content/luxman-b-1000f-monoblock-power-amplifier-measurements
 

Anatta

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An amplifier has the current reserves or it doesn't. Most loudspeakers impedace fluctuates with frequency and the lower it gets the more current it sucks from the amplifier.

Transistor amps try to be a constant voltage source, that is, to maintain the voltage constant irespective of the load (the impedance it sees) but in order to do that they must have a capable power supply.

1W into an 8 Ohm load means 2.83V and the speaker sucks 0.35A along; now for a 4 Ohm load in order to maintain those 2.83V the amp must deliver twice the current, 0.7A and you have 2W; cut again in half the impedance and for those 2.83V the amp must give 1.4A, 4W.

If an amplifier doesn't double its power as impedance is halfed it means it isn't a constant voltage source into varying loads and the limit is represented by the current capacity of the amp.

80W@8Ohm = 25.3V x 3.16A


130W@4Ohm = 22.8V x 5.7A

160W@4Ohm = 25.3V x 6.32A
 

drummerman

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Also one of the reasons that amplifiers used in active speakers can be specifically engineered to only have to cope optimally with the drivers used. They do not have to be able to drive the varying speakers and loads by separates.

There was an interesting conversation going on over at AVI forum some time ago about their quoted power figures. As always, they were rather evasive about those '250 watts' or thereabouts quoted. Measurements are not freely accessible as far as I know. - It doesnt really matter, what sounds good sounds good but I think it would be fair to say that the wattage stated has to be taken with a pinch of salt as, it has to be said, is probably the case with certain less forthcoming separates manufacturers (and certainly a lot of AV receiver/system companies) which use different yard sticks, usually what looks best on paper.

regards
 
Many thanks to Andrew, Scene, Paul. and others.

I generally don't have the technical knowledge of amps, CDPs, speakers etc. so that info is mightily informative.

The sole reason for asking is because I am seriously considering buying Totem Arros, and although they were great on a weekend home dem, never managed use them long enough, in any individual period, to gauge how long it would take for the Leema to become warm (to the touch).

Fully take on-board the simple explanations, but just to clarify, in a car analogy:

I could push a Austin Mini, with brakes off and gears in neutral, only using probably 50% of my body strength. Push a Transit van, for example, and my power and strength needs to increase to get the van moving to a similar speed. Would that be a fair assumption (or comparison)?

Once the decorating is done then I'll be looking at the Totems in earnest.
 

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