An Amplifier's ability to drive speakers

Oxfordian

Well-known member
Mar 20, 2021
868
744
2,770
I am hoping that someone can explain why it is not just watts per channel that need to be considered when thinking about an amplifiers capability to drive speakers. What are the factors that could / should be taken into account when assessing whether an amp is a suitable driving force for your speakers.

For example; I have some ATC SCM 7's which have a recommended amplifier requirement of 75 - 300w, my Hegel only has a miserly 60wpc but appears to drive the speakers just fine, at least for the volumes I listen too in my spare bedroom based listening room.

Reading through these threads it would seem that there is some flexibility if the Amp is particularly well put together and that maybe a class A amp could drive my little ATC's even though its wpc is well below what is recommended, how could that be? Equally others have mentioned that an class A/B amp with an output of less than the recommended number of top quality watts can be better than (dare I say it) an amp with lots of poor quality watts that meets the speakers manufacturers suggested amplification requirements.

Now I may have my wires crossed and be misunderstanding things but I was under the impression that 'Watts are Watts' but this is seemingly incorrect. At some point I am going to scratch the upgrade itch on my Amp, do I just need to factor in Watts Per Channel or are there other factors to consider and understand before I splash the cash.

Thanks.
 

Al ears

Well-known member
Watts are indeed
I am hoping that someone can explain why it is not just watts per channel that need to be considered when thinking about an amplifiers capability to drive speakers. What are the factors that could / should be taken into account when assessing whether an amp is a suitable driving force for your speakers.

For example; I have some ATC SCM 7's which have a recommended amplifier requirement of 75 - 300w, my Hegel only has a miserly 60wpc but appears to drive the speakers just fine, at least for the volumes I listen too in my spare bedroom based listening room.

Reading through these threads it would seem that there is some flexibility if the Amp is particularly well put together and that maybe a class A amp could drive my little ATC's even though its wpc is well below what is recommended, how could that be? Equally others have mentioned that an class A/B amp with an output of less than the recommended number of top quality watts can be better than (dare I say it) an amp with lots of poor quality watts that meets the speakers manufacturers suggested amplification requirements.

Now I may have my wires crossed and be misunderstanding things but I was under the impression that 'Watts are Watts' but this is seemingly incorrect. At some point I am going to scratch the upgrade itch on my Amp, do I just need to factor in Watts Per Channel or are there other factors to consider and understand before I splash the cash.

Thanks.
Watts are indeed watts.
It is more about delivery of current to your speakers.
Amps have to be able to deal with huge dips in impedence of some speakers.
Some amps can handle this well.
If wouldn't worry too much about said class of amp however Class A are better suited to really efficient speakers. Your ATCs do not fit this category.
 

nopiano

Well-known member
Now I may have my wires crossed and be misunderstanding things but I was under the impression that 'Watts are Watts' but this is seemingly incorrect. At some point I am going to scratch the upgrade itch on my Amp, do I just need to factor in Watts Per Channel or are there other factors to consider and understand before I splash the cash.
As Al said, watts are indeed watts. The current is what defines how an amplifier responds as impedance drops. (I’m sure we’ve had posts about how speaker impedance isn’t a fixed number, though that’s how it’s expressed for simplicity in speakers specs. Look at any Hi-Fi News or Stereophile review of loudspeakers in the lab report, and you’ll see a graph that goes up and down like a ride at Alton Towers!)

Confusingly for many, is that lower impedances are harder to drive. One might assume the opposite, in the way that a car full of passengers and luggage requires more power than when it’s just you driving. However, as speaker impedance drops, the current must increase to maintain the power. (Did you learn V= IR at school? Ohm’s Law. Voltage equals current times resistance.). The less desirable amplifier can’t increase the current enough (or not quickly enough) to sustain the power output, and sounds weak driving difficult speakers. Difficult here meaning low impedance ones.

Your ATCs are not very sensitive, so needs lots of watts for a given output. But they are quite a friendly impedance, not too low or bumpy. So they don’t demand very high current, but unsurprisingly ATC make powerful amps, their weediest being rated at 100wpc and delivering more on test.

At the lower volumes that you seem to value, then low noise and low distortion matter, and your Hegel is a nice clean sounding design.

An unusual example is my Pass Labs power amp, a class A transistor design. Rated at 25 watts into 8 ohms, but on test in Stereophile: “…the amplifier exceeded its specified power output at the clipping point, which we define as when the THD+noise equals 1%. At that THD+N percentage the XA25 delivered 80Wpc into 8 ohms (19dBW) and 130Wpc into 4 ohms (18.1dBW).” So in English it can handle big peaks, but sounds very pure at lower levels.

Apologies for the monologue. Someday maybe try to borrow a more powerful amp to try at home. You’ll soon know whether it makes the sort of difference that matters to you.
 
As per both above posts.

Some amps can't handle dips in speaker ohms, but yours doesn't fit into that category.

The perfect example was my A65+. When I used it with MA RS6s it could really struggle, depending on recording and with a low Millivolt cartridge. Those speakers could dip to 2 ohms.

By contrast, when I home demoed PMC DB1i it didn't struggle at all with the same recordings.
 
  • Like
Reactions: Oxfordian

Oxfordian

Well-known member
Mar 20, 2021
868
744
2,770
As Al said, watts are indeed watts. The current is what defines how an amplifier responds as impedance drops. (I’m sure we’ve had posts about how speaker impedance isn’t a fixed number, though that’s how it’s expressed for simplicity in speakers specs. Look at any Hi-Fi News or Stereophile review of loudspeakers in the lab report, and you’ll see a graph that goes up and down like a ride at Alton Towers!)

Confusingly for many, is that lower impedances are harder to drive. One might assume the opposite, in the way that a car full of passengers and luggage requires more power than when it’s just you driving. However, as speaker impedance drops, the current must increase to maintain the power. (Did you learn V= IR at school? Ohm’s Law. Voltage equals current times resistance.). The less desirable amplifier can’t increase the current enough (or not quickly enough) to sustain the power output, and sounds weak driving difficult speakers. Difficult here meaning low impedance ones.

Your ATCs are not very sensitive, so needs lots of watts for a given output. But they are quite a friendly impedance, not too low or bumpy. So they don’t demand very high current, but unsurprisingly ATC make powerful amps, their weediest being rated at 100wpc and delivering more on test.

At the lower volumes that you seem to value, then low noise and low distortion matter, and your Hegel is a nice clean sounding design.

An unusual example is my Pass Labs power amp, a class A transistor design. Rated at 25 watts into 8 ohms, but on test in Stereophile: “…the amplifier exceeded its specified power output at the clipping point, which we define as when the THD+noise equals 1%. At that THD+N percentage the XA25 delivered 80Wpc into 8 ohms (19dBW) and 130Wpc into 4 ohms (18.1dBW).” So in English it can handle big peaks, but sounds very pure at lower levels.

Apologies for the monologue. Someday maybe try to borrow a more powerful amp to try at home. You’ll soon know whether it makes the sort of difference that matters to you.
Thanks for this, it would seem that I have a steep learning curve to get my head round this issue.

My schooling was more languages and the arts rather than the sciences, (not that I was much good at school and just about managed to scrape a few passes in the basic necessities).

I am going to borrow a more powerful amp early next year, probably a H190 but it all depends on what the store has available for me to borrow, they believe that the H95 is ultimately going to be a blocker on future source upgrades, the speakers they are sure that they are spot on for my listening space, and I have to say it is hard to argue that.

I just want to understand how this whole process works, there is a fair bit to understand.
 
  • Like
Reactions: nopiano

Oxfordian

Well-known member
Mar 20, 2021
868
744
2,770
Some amps can't handle dips in speaker ohms, but yours doesn't fit into that category.
Why doesn’t my amp have a problem handling these dips?

I guess that it is going to be part of my learning curve but what does my H95 have that allows it to handle these dips.

I feel a bit daft that I don’t know the answer to this, but I just assumed that at 60wpc it was underpowered for the speakers and ultimately to get the best out of the 7’s I needed to upgrade, in many respects I should have kept the H120 I had on demo at the same time as the H95 but decided to save a few hundred quid and go with the H95.
 

WayneKerr

Well-known member
Jan 21, 2022
1,353
1,305
4,070
I don't profess to know much about the technical aspects of amps but after reading various forums and reviews I knew I wanted my next amplifier to be capable of doubling its power into half the impedance. In short I think this means plenty of juice available in reserve when needed. This would enable to me to put whatever I wanted on the end of the speaker cables without worrying about available juice to run them properly.

Being a Marantz fanboy I stuck with the brand. Specs state 100W into 8ohms, 200W into 4ohms. However, bench-testing has proved these figures to be conservative - actual 170/280 into 8/4ohms. Running "cheaper" speakers on the end of this sounds excellent to my ears.
 
Why doesn’t my amp have a problem handling these dips?

I guess that it is going to be part of my learning curve but what does my H95 have that allows it to handle these dips.

I feel a bit daft that I don’t know the answer to this, but I just assumed that at 60wpc it was underpowered for the speakers and ultimately to get the best out of the 7’s I needed to upgrade, in many respects I should have kept the H120 I had on demo at the same time as the H95 but decided to save a few hundred quid and go with the H95.
Others will give a technical answer, but my understanding is how pure the current supply is from the power amp section of your integrated.

Exactly the same with my Leema, that doesn't suffer from dips in ohms either.
 
  • Like
Reactions: Oxfordian

Stuart83

Well-known member
Jul 22, 2023
239
164
470
The longer post by nopiano is best digested it's correct but I've also known amps to lie.
I've had many over the yrs and watts is the best indicator of power but some qoute way over what is there.
 
  • Like
Reactions: WayneKerr

WayneKerr

Well-known member
Jan 21, 2022
1,353
1,305
4,070
Amps with plenty in reserve do seem to show outputs into 8, 4 and 2Ω. A 'perfect' amp will show a doubling, but from what I've seen there's usually some roll-off even with the beefiest of amps.
Agreed. Published specs for my amp is 100/200 into 8 and 4ohms. HiFi News lab test results were 170/280 - 8/4ohms continuous power, 200/360/610/370 - 8/4/2/1ohm dynamic power. Seems it almost holds it all together until it gets to 1ohm :) Think I'll stick with Marantz conservative figure as that's a definite :)
 
Last edited:
  • Like
Reactions: Oxfordian

Oxfordian

Well-known member
Mar 20, 2021
868
744
2,770
Others will give a technical answer, but my understanding is how pure the current supply is from the power amp section of your integrated.

Exactly the same with my Leema, that doesn't suffer from dips in ohms either.
The promotional blurb from Hegel states that the H95's 60wpc is more than sufficient to drive difficult speakers with ease.

Apparently this ability comes from Hegel's proprietary Sound Engine 2, which allows this 2x60w amp to get some real grip and control on speakers through its 'damping factor', I presume that it is this DF that is allowing the ATC's to be controlled by the H95 in the manner that you describe?

Data on what the H95 produces at 6, 4 and 2 ohm isn't revealed (at least I can't find it on Hegel's site) all that the bumf states is that the amp will go down to 2 ohm.

My listening is usually between 50 and 60 that is displayed by Hegel's volume control, I find that this is loud enough when in my small listening room and the door is shut.
 

WayneKerr

Well-known member
Jan 21, 2022
1,353
1,305
4,070
The promotional blurb from Hegel states that the H95's 60wpc is more than sufficient to drive difficult speakers with ease.

Apparently this ability comes from Hegel's proprietary Sound Engine 2, which allows this 2x60w amp to get some real grip and control on speakers through its 'damping factor', I presume that it is this DF that is allowing the ATC's to be controlled by the H95 in the manner that you describe?

Data on what the H95 produces at 6, 4 and 2 ohm isn't revealed (at least I can't find it on Hegel's site) all that the bumf states is that the amp will go down to 2 ohm.

My listening is usually between 50 and 60 that is displayed by Hegel's volume control, I find that this is loud enough when in my small listening room and the door is shut.
Here you go Oxfordian, HFN lab report: Hegel H95
 

WayneKerr

Well-known member
Jan 21, 2022
1,353
1,305
4,070
Same with mine. Still sounds the biz with RS6.

Oddly, though, it doesn't show details such as 6 or 4 ohms. Even though it's a relatively modest 80 watts into 8 ohms, it drives tricky speakers with ease, such as the Dalis and Totem Arros.
I've always tried to price-match components but if this hasn't been possible then putting cheaper speakers on the end of a beefy amp seems to work really well. There was someone on here who paired a £1.5K amp with £10K speakers... not something I would ever contemplate doing... what a waste!
 
  • Like
Reactions: Al ears

Al ears

Well-known member
I've always tried to price-match components but if this hasn't been possible then putting cheaper speakers on the end of a beefy amp seems to work really well. There was someone on here who paired a £1.5K amp with £10K speakers... not something I would ever contemplate doing... what a waste!
Whatever works for you I say....., Although it does seem a tad odd.
 
  • Like
Reactions: WayneKerr

WayneKerr

Well-known member
Jan 21, 2022
1,353
1,305
4,070
There's no spec sheet for my amp, the is for the MK3 which only states 8 ohms, whereas the Elements and Tucana does.

All quite strange.
I did look on HFN for Leema but found nothing current. Guess it's like WHF, if they're not sent a test sample then they can't test it. I do like the depth of the HFN reviews though (y)
 

TRENDING THREADS

Latest posts