[keysersoze123]

Hiya,

For example, a particular amplifier specifies its power output as

Maximum Power Output 140wRMS into 8ohms (0.5% THD)
250wRMS into 4 ohms (0.5% THD)

So the watts differ depending on the ohms.. Please explain what this means, in laymans terms..

Tried google, but just got long winded confusing explanations!

How should "ohms" be relevant to me when looking at different amps, how are they significant and why do I need to consider them?

Cheers, and sorry for my lack of basic knowledge!

[IncredibleMrFox]

basically think of ohms as the resistance (impedance) of a speaker so it is relevant to know what ohms rating the amp is in order to match it with speakers or vica versa.
like you said yourself there is a lot of complicated stuff that you dont really need to know.
if you match wrong speakers with wrong amp (mixing 4 ohms and 8ohms) there will be excessive heat build up possibly wrecking your speakers or amp.
hope this helps. and also that what is say is right :S

[Gaspode_TWD]

A loadspeaker attached to your amplifier will have a rated level of resitance. This is measured in Ohms. A lower resistance will try to draw more current. In theory half the resistance (from 8 down to 4 ohms) should double the watts avaiable. The amp manufacturer will normally recommend the level of resistance it is designed to work with.

Thats the simple answer. However, when playing music, 'speakers rarely offer a static resistance across the frequecy range nor over time. One of the elements that helps some amplifiers sound better is their ability to cope with these changes.

Edit: beat me to it MrFox

[keysersoze123]

Originally Posted by IncredibleMrFox

if you match wrong speakers with wrong amp (mixing 4 ohms and 8ohms) there will be excessive heat build up possibly wrecking your speakers or amp.
hope this helps. and also that what is say is right :S

Hey thanks both you guys for clearing that up.

I was sort of under the impression that most amps will work with most speakers... So is that incorrect?

An 8 ohm speaker should always be matched with an 8 ohm amp?

Does this mean that in practice a lot of amps and speakers are incompatible?

Or in general, will most amps work fine with most speakers? (Is there perhaps a standard 'ohm' rating of, e.g. 4 ohms, that 99% of speakers and amps use? Thus making them all compatible..?)

It would kinda suck if I found speakers I liked and only 20% of amps were compatible, but maybe that's just how it works.

Thanks

Edit: Example - Monitor Audio GS60 speakers which I am interested in are rated at 6 ohms. I just pulled up specs on a random Arcam amp, A38, and it was rated at 8 ohms in 2 channel mode, or 4 ohms in single channel... So would this amp be no good with the GS60s?

[Gaspode_TWD]

Most speaker are in the 6-8 ohm range and most amps are rated for 8 ohm speakers. Most amps rated for 8 ohms will cope with 6 ohms.

Also important is how efficient they are. 90dB/w is pretty efficient and will mean 90dB for 1 watt at 1 metre. You can approximate that an 87dB/w speaker will need 10 times the watts to go get the same sound (subject to frequency response, room interaction, level of detail in the sound, etc., etc...).

[keysersoze123]

Originally Posted by Gaspode_TWD

Most speaker are in the 6-8 ohm range and most amps are rated for 8 ohm speakers. Most amps rated for 8 ohms will cope with 6 ohms.

Also important is how efficient they are. 90dB/w is pretty efficient and will mean 90dB for 1 watt at 1 metre. You can approximate that an 87dB/w speaker will need 10 times the watts to go get the same sound (subject to frequency response, room interaction, level of detail in the sound, etc., etc...).

Hey thanks Gaspode, I really do appreciate all the advice you guys give me. I'm always the one asking questions, and there are people like you willing to help me out, educate me and explain stuff to me - you truly are good people! Very much appreciated indeed.

Thanks

[keysersoze123]

Indeed I started another thread posing this exact question, but I'm interested in the Monitor Audio GS60 speakers for a variety of reasons. I don't know if you have any experience with the GS60s, but I'd really like to know some amps that would go nicely with them, amps that would be worth a demo with the GS60s.

If anyone has any suggestions, cheers!

[Gaspode_TWD]

I don't know the speakers specifically but I have listened to a few of the MA products. They are efficient, fast and have a potential to go towards ... sort of .. hard/aggressive. Difficult to describe, but it can get wearing.

I'd suggest something with a smooth-ish sound. You shouldn't need a lot of watts but good control and good current delivery. Mind you, lots of good amps tend to end up with lots of watts as a by-product of the way they are engineered. I'm not good with current products as I've got out of buying new boxes.

The other issue is the type of music you listen to and what you like to hear in that music. Are vocals your main interest or is it pionos? Heavy rock of folk melodies? If you're spending that sort of money you should be able to sort getting some home to try.

[keysersoze123]

Originally Posted by Gaspode_TWD

I don't know the speakers specifically but I have listened to a few of the MA products. They are efficient, fast and have a potential to go towards ... sort of .. hard/aggressive. Difficult to describe, but it can get wearing.

I'd suggest something with a smooth-ish sound. You shouldn't need a lot of watts but good control and good current delivery. Mind you, lots of good amps tend to end up with lots of watts as a by-product of the way they are engineered. I'm not good with current products as I've got out of buying new boxes.

The other issue is the type of music you listen to and what you like to hear in that music. Are vocals your main interest or is it pionos? Heavy rock of folk melodies? If you're spending that sort of money you should be able to sort getting some home to try.

Yeah home demos would definitely be ideal... I like reggae, acoustic, light rock/punk, harder rock too, psychedelic, electronic, drum n bass, but of pop!, dance.. love Jazz!!!.. classical is not a big part of my listening, but i do like it increasingly... but yeah good vocals would definitely be good...

So quite a varied type of music really! Not very helpful perhaps!

When I demo I will do so with a wide variety of music, hopefully I find a system that excels (to varying degrees) with most kinds of music...

I definitely like a punchy bass line at times, but also the involving and warm, slightly foggy bass when needed... hence g60s over the lesser g20s... more bass all round apparently

I'm not very good at 'genres' - a lot of my music I wouldn't really know how to put it into a genre.

I do like some modern instrumental music too, generally of the 'happy' kind lol, but not necessarily the "fast" kind... don't get me wrong, a bit of melacholy can be good too...

Something that can play Aphex Twin - Windowlicker, in all its glory, would be good

Also love all the classics, Dylan, the Doors, The Stones, bit of The Beatles, defo some Nick Drake - these would make up a large amount of my listening

I like a lot of different music, basically!

[keysersoze123]

Originally Posted by Gaspode_TWD

I'd suggest something with a smooth-ish sound.

When you say something with a smoothish sound, do you mean instead of the monitor audio speakers? Or I think you mean a smoothish amp to go with the Monitor Audios, right?

[BlueWizard]

I think the basic question has been covered, but I will try it from a different perspective.

Ohm's Law -

P = V² / R ( Power = Voltage Squared divided by Resistance)

P = Power
V = Voltage
R = Resistance

Amps are really Voltage devices, they feed Voltage to a speaker, and as a result the speaker consumes power. The ability of the amp to maintain a give voltage is based on its ability to deliver the current being demanded by the speaker. The lower the resistance, the higher the current.

So, if we feed 10 volts to an 8 ohm speaker, what is the result?

P = V² / R = 10² / 8 = 100 / 8 =12.5 watts

Now, what happens when we feed the same 10 volts to 4 ohms?

P = 10² / 4 = 100 /4 = 25 watts

Half the impedance, doubles the power. But nothing is really happening here. The amp has the same 10 volt limit in either case, so there is really nothing gained from the consumption of that extra power. Your amp is simply forced to deliver more current to keep the speaker working right. More current means more heat, and heat is never good for anything electronic.

Occasionally, you will see amps rated at a specific power at 6 ohms or 4 ohms. They will claim that this reflects more realistic operating conditions, but that is bunk, all they are doing is inflating the apparent power.

Remember Amp are voltage devices, the limit of available voltage is the limit of the amp. If you demand too much current, then the voltage falls, so again despite it seeming that limited current is the problem, it is really limited voltage.

That is why all amps should have a basic RMS or FTC or continuous power rated at 8 OHMS. That shows the amp under its most demanding circumstances with a common standard load. Now, once you have the Continuous power, you can use that as a foundation to evaluate power at 6 ohms, 4 ohms, and others. It also serves as the base to lend perspective to Dynamic, DIN, and other power ratings.

Continuous power is rated with a continuous sinewave tone. That is very demanding on an amp. Dynamic power is likely tested with white or pink noise, which sounds like the hissing static between radio stations. This is less demanding but more reflects a range of frequencies and a range of voltages, meaning the test signal is dynamic just as real music is.

Dynamic power rating will alway be higher that Continuous power ratings. But, to someone who understands, and when used in combination with continuous power, Dynamic power can give you a sense of how the amp will work under normal listening conditions.

Next is the THD (Total Harmonic Distortion), or just generally, the distortion figure. Trashy cheap amps can have distortion ratings as high as 10%. Good amps, will typically have distortion ratings at a minute fraction of a percent, such as 0.01% distortion. Generally, in decent HiFi amps, I would say anything up to 0.1% is OK. Anything more than that, and you are moving into the realm of cheaper amps; not necessarily bad, just lower cost. Though under all circumstances for HiFi or AV amps, the distortion should be 0.99% THD or less.

So, contrary to the common belief, there is no such thing as an 8 ohm amp, there are only amps whose power is rated at the accepted standard 8 ohms.

A majority of amps out there are capable of supporting a combined per channel loads in the range of 4 ohms to 16 ohms. By this I mean, you can add as many speakers as you want to a given amp channel, as long as the total of the speakers on that amp channel is within the range of 4 ohms to 16 ohms.

As an example, if you put two 8 ohms speakers on an amp channel, the total is 4 ohms, and that works for most amps. However, if you put two 6 ohms speakers on an amp channel, the total is 3 ohms, and that is too low for most amps.

There are a few AV amps, that would prefer it if you didn't go below 6 ohms per channel. Which in turn means you can never have more than one speaker per channel.

There are also a few consumer HiFi amps that will allow you to stray slightly below 4 ohms. PA amps can sometime tolerate loads as low as 1 or 2 ohms, though the distortion figures tend to be much higher.

That is probably a little more technical and long winded than you were looking for, but it is, none the less, important that you understand this information, to understand and evaluate amps.


In short, there is no such thing as an 8 ohm amp, only amps who have their power rated at the accepted standard 8 ohm load.

Most amps will tolerate a per channel load in the range of 4 ohms to 16 ohms.

Steve/bluewizard

[keysersoze123]

Originally Posted by BlueWizard

I think the basic question has been covered, but I will try it from a different perspective.

Ohm's Law -

P = V² / R ( Power = Voltage Squared divided by Resistance)

P = Power
V = Voltage
R = Resistance

Amps are really Voltage devices, they feed Voltage to a speaker, and as a result the speaker consumes power. The ability of the amp to maintain a give voltage is based on its ability to deliver the current being demanded by the speaker. The lower the resistance, the higher the current.

So, if we feed 10 volts to an 8 ohm speaker, what is the result?

P = V² / R = 10² / 8 = 100 / 8 =12.5 watts

Now, what happens when we feed the same 10 volts to 4 ohms?

P = 10² / 4 = 100 /4 = 25 watts

Half the impedance, doubles the power. But nothing is really happening here. The amp has the same 10 volt limit in either case, so there is really nothing gained from the consumption of that extra power. Your amp is simply forced to deliver more current to keep the speaker working right. More current means more heat, and heat is never good for anything electronic.

Occasionally, you will see amps rated at a specific power at 6 ohms or 4 ohms. They will claim that this reflects more realistic operating conditions, but that is bunk, all they are doing is inflating the apparent power.

Remember Amp are voltage devices, the limit of available voltage is the limit of the amp. If you demand too much current, then the voltage falls, so again despite it seeming that limited current is the problem, it is really limited voltage.

That is why all amps should have a basic RMS or FTC or continuous power rated at 8 OHMS. That shows the amp under its most demanding circumstances with a common standard load. Now, once you have the Continuous power, you can use that as a foundation to evaluate power at 6 ohms, 4 ohms, and others. It also serves as the base to lend perspective to Dynamic, DIN, and other power ratings.

Continuous power is rated with a continuous sinewave tone. That is very demanding on an amp. Dynamic power is likely tested with white or pink noise, which sounds like the hissing static between radio stations. This is less demanding but more reflects a range of frequencies and a range of voltages, meaning the test signal is dynamic just as real music is.

Dynamic power rating will alway be higher that Continuous power ratings. But, to someone who understands, and when used in combination with continuous power, Dynamic power can give you a sense of how the amp will work under normal listening conditions.

Next is the THD (Total Harmonic Distortion), or just generally, the distortion figure. Trashy cheap amps can have distortion ratings as high as 10%. Good amps, will typically have distortion ratings at a minute fraction of a percent, such as 0.01% distortion. Generally, in decent HiFi amps, I would say anything up to 0.1% is OK. Anything more than that, and you are moving into the realm of cheaper amps; not necessarily bad, just lower cost. Though under all circumstances for HiFi or AV amps, the distortion should be 0.99% THD or less.

So, contrary to the common belief, there is no such thing as an 8 ohm amp, there are only amps whose power is rated at the accepted standard 8 ohms.

A majority of amps out there are capable of supporting a combined per channel loads in the range of 4 ohms to 16 ohms. By this I mean, you can add as many speakers as you want to a given amp channel, as long as the total of the speakers on that amp channel is within the range of 4 ohms to 16 ohms.

As an example, if you put two 8 ohms speakers on an amp channel, the total is 4 ohms, and that works for most amps. However, if you put two 6 ohms speakers on an amp channel, the total is 3 ohms, and that is too low for most amps.

There are a few AV amps, that would prefer it if you didn't go below 6 ohms per channel. Which in turn means you can never have more than one speaker per channel.

There are also a few consumer HiFi amps that will allow you to stray slightly below 4 ohms. PA amps can sometime tolerate loads as low as 1 or 2 ohms, though the distortion figures tend to be much higher.

That is probably a little more technical and long winded than you were looking for, but it is, none the less, important that you understand this information, to understand and evaluate amps.


In short, there is no such thing as an 8 ohm amp, only amps who have their power rated at the accepted standard 8 ohm load.

Most amps will tolerate a per channel load in the range of 4 ohms to 16 ohms.

Steve/bluewizard

Thanks Steve,

Some very useful info in there, and really appreciate the time you took. I will have to re-read it to fully take in everything you said there.

When you said "However, if you put two 6 ohms speakers on an amp channel, the total is 3 ohms, and that is too low for most amps."

The speakers I am interested in are Monitor Audio GS60, and they are rated at "Nominal Impedance: 6 Ohms".

Based on your statement above, am I right in thinking this is not a problem, because they would be fed into two amp channels, in a stereo amplifier, rather than a single channel, so the total would remain 6 ohms, and I would have no problems?

Are speakers rated at 6 ohms unusual? At a (relatively) high end, £2k+ pair of speakers, would you generally expect 8 ohms?

[IncredibleMrFox]

thanks for that reply bluewizard. certainly expanded my knowledge about it

[BlueWizard]

When you said "However, if you put two 6 ohms speakers on an amp channel, the total is 3 ohms, and that is too low for most amps."

The speakers I am interested in are Monitor Audio GS60, and they are rated at "Nominal Impedance: 6 Ohms".

Based on your statement above, am I right in thinking this is not a problem,...


Yes, this is confusing because I keep referring to 'per amp channel', and I think people are not quite sure what I mean by that, as if, rather than the obvious, there is some subtle secret meaning to it. No, not subtle or secret, just the obvious.

A stereo amp is a 2-channel amp, one amp channel for the left and one amp channel for the right, you typically put one speaker on each channel; one speaker on the left channel and one speaker on the right channel. All well and good, but what happens if you want to add another set of speakers, so you have TWO speakers on each side?

Well, the combination of those two speakers on one side has to be in the range of 4 ohms to 16 ohms. Two 8 ohm speaker on each side equals 4 ohms per channel; two 6 ohm speakers on each side equals 3 ohms. FOUR ohms = good; THREE ohms = bad.

Now AV amps have 5 or 7 built-in amps, or 5 or 7 amp channels. Typically you will put one speaker on each channel, one left, one right, one center, one left rear, one right rear. So, we are good.

But what if you decide you want to put two speakers in front, two left front and two right front? Once again, the total impedance of those two speakers that are on the same channel, say the right front, has to be in the range of 4 ohms to 16 ohms.

How many speaker are on the whole amps is irrelevant. If you have a 5 channel amp with 5 speakers total, that is still just 1 speaker on each amp channel. Just one 6 ohm or 8 ohm speaker per channel.

So, in your case, you need to ask yourself, does the 6 ohm impedance of the Monitor Audio speaker fall within the range of 4 ohms to 16 ohms, and of course it does. So, as you guessed, you are safe.

The point I'm making is that you need to look at the amp channels in isolation. The total of all the speakers on one channel has to be 4 ohms to 16 ohms.

Speakers in parallel, the most common way speakers are connected, divide.

So -

- an 8 ohm and an 8 ohms in parallel equals 4 ohms. (8/2 = 4)
- an 8 ohm and a 6 ohms in parallel equals 3.5 ohms. ((8x6)/(8+6) = 3.5)
- a 6 ohms and a 6 ohm in parallel equals 3.0 ohms. (6/2 = 3)

For speakers that are the same -

Rt = R1/n ... where the total resistance is the ohm value of one speaker divided by the number of speakers. As you can see in the 8ohm+8ohm and 6ohms+6ohms examples above.

For two speakers that are different -

Rt = (R1 x R2) / (R1 + R2) ... the total is the value of the first speaker times the value of the second speaker, and that is divided by the value of the first speaker plus the value of the second speaker. See the 8 ohm with 6 ohms example above.

I know this seems complicated, but once you think about it for a while, it will all make sense. Just remember that we are looking at each amplifier channel in isolation.


Steve/bluewizard

[IncredibleMrFox]

i had no idea it was this complicated :S steve do you do this for your living or is it just a hobby? cos you are a legend!!

[BlueWizard]

Originally Posted by IncredibleMrFox

i had no idea it was this complicated :S steve do you do this for your living or is it just a hobby? cos you are a legend!!

I'm just a guy with too much time on his hands.

Steve/bluewizard

[keysersoze123]

Yeah, totally agree with IncredibleMrFox, you have enlightened me Steve...

Many thanks indeed! High praise!

So, I'm safe.. excellent

Now, anybody got any suggestions for amps that will sing gloriously with the GS60s? I like the aesthetics of the GS60s (shallow, I know) but I heard the baby brothers, the Monitor Audio RX8 and was seriously impressed. And on the net, I have only heard really good things about the GS60s.

I'm sure in my search for amps I'll find some good 'uns when I'm demoing, and I'm in no rush, but obviously if I had the perfect system tomorrow I'd be a happy bunny!

But if anyone's already got some good musical suggestions for me to go demo, it could be very helpful, cos dealers will probs just wanna sell me the most expensive stuff!

The source is probs gonna be a Linn Majik DS or Logitech Transporter, I like using my laptop to choose my music. May add a turntable at some stage too, gyrodec or something... But intially it's gonna be a good quality digital streamer...

[Gaspode_TWD]

Originally Posted by keysersoze123

When you say something with a smoothish sound, do you mean instead of the monitor audio speakers? Or I think you mean a smoothish amp to go with the Monitor Audios, right?

Right. A suggestion I'd offer is to try a few second hand amps. If you buy sensibly you'll be able to sell on at minimal cost to you and in the process learn what sort of sound you're seeking from the amp. The known brands (Rega, Naim, Audiolab, etc.) usually hold their value. You may want to consider (or to rule out) valve amps. They need more care than solidstate stuff and appear to offer little power. However, once you've listened to one you'll realise that power specs. don't really have a lot of meaning.

Oh! Just thought. If you can cope with big boxes the Usher Reference R1.5 is a box I have listened to and liked. You'd need a pre-amp though.

[keysersoze123]

Originally Posted by Gaspode_TWD

Right. A suggestion I'd offer is to try a few second hand amps. If you buy sensibly you'll be able to sell on at minimal cost to you and in the process learn what sort of sound you're seeking from the amp. The known brands (Rega, Naim, Audiolab, etc.) usually hold their value. You may want to consider (or to rule out) valve amps. They need more care than solidstate stuff and appear to offer little power. However, once you've listened to one you'll realise that power specs. don't really have a lot of meaning.

Oh! Just thought. If you can cope with big boxes the Usher Reference R1.5 is a box I have listened to and liked. You'd need a pre-amp though.

Thanks mate - very sensible suggestion, as it seems that the local dealers around my home in Edinburgh don't really do "home demos" unless you're spending mega mega bucks. (I think I am spending a massive amount, but the sort of gear I'm looking at wouldn't even be classed anywhere near "high end" by segments of the Hi Fi industry, although compared to your average punter, the gear I'm looking at is very high end indeed).

Cheers matey

[BlueWizard]

I think before we recommend amps, we need a budget, and also some sense of what you are looking for? By that I mean, are you looking for a good basic consumer amp, or are you looking for something more in the premium class of audio amps. Keep in ming that premium amps are not going to be cheap, and while good quality, you are not going to get as much power for a given amount of money.

But again, we can't even start without first a budget, then some sense of what you are looking for beyond simply wanting an amp. 'An amp' is far to general for us to work with.

Steve/bluewizard