Doubting My Own Knowledge!!!

[Mullardman]

F'book Ad for a Technics amp. Some chap claims at 150wpc or worrever, it's no good for his KEFs because they 'need' 200 Watts.
Spent more time than it's worth trying to explain speaker power handling/amp output/sensitivity etc.. blah.. but he insists that his speakers don't go loud enough without millions of Watts ...
I gave up... but I'm now doubting myself..
Help!!

 

[Peter Stockwell]

Hahaha, just remember what Nelson Pass said “It’s the first what that counts”. I spent years with c. 10 wpc Class D amps (Amptastic, Temple audio bantam)

No need for more, especially if you klipsch or similar.

 

[Mike Hanson]

Some speakers need a bit more juice to wake up, but KEFs aren't bad in that regard, and 200W is a lot of power.

The fellow is misinformed, or is just trying to sound knowledgeable. He probably doesn't even realize it: Dunning–Kruger effect

 

[booja30]

Dunning–Kruger effect

That link should automatically get posted in any cable/router/foo thread that goes over 10 pages.

 

[Peter Stockwell]

Dunning–Kruger effect

I worked with/for a raft a people with that syndrome!

 

[Chops54]

F'book Ad for a Technics amp. Some chap claims at 150wpc or worrever, it's no good for his KEFs because they 'need' 200 Watts.
Spent more time than it's worth trying to explain speaker power handling/amp output/sensitivity etc.. blah.. but he insists that his speakers don't go loud enough without millions of Watts ...
I gave up... but I'm now doubting myself..
Help!!

I don’t know why you bother to get involved in such discussions Col. Maybe you knew it wouldn’t be worth the effort but you still had to have a go

 

[RJohan]

Some people seem to think watts is a measure of sound quality. As long as the amp don't go into clipping, what ever power is enough.

 

[pocketkitchen]

All other things being equal 10x power is needed for doubling volume. A 50w uplift wouldn’t make too much difference at all in terms of how loud his system plays.

 

[James]

That chappie is confusing max power of his loudspeakers with necessary power.

 

[jimification]

In fairness to the bloke, most entry level hifi misinformation like this is probably largely the fault of marketing departments, who like to reduce everything to advantageous numbers they can print somewhere on the box on the: "Well it's one louder, innit?" basis.

 

[John Phillips]

F'book Ad for a Technics amp. Some chap claims at 150wpc or worrever, it's no good for his KEFs because they 'need' 200 Watts.
Spent more time than it's worth trying to explain speaker power handling/amp output/sensitivity etc.. blah.. but he insists that his speakers don't go loud enough without millions of Watts ...
I gave up... but I'm now doubting myself..
Help!!

Over-broadly, a power rating for a 'speaker is for the maximum power it can take. It is not a rating for how much power you need to reproduce your preferred music at your preferred volume. An approximation for the latter can be calculated but that does not involve knowing the 'speaker's maximum power rating. Don't doubt yourself.

 

[Mullardman]

Thanks for all replies.
Yes of course, -'never argue with an idiot' is a sound maxim but I assure you I only do so if it is either entertaining, or has the possibility of a breakthrough.
After explaining that most music even at high domestic levels is likely to only represent a few Watts of amp power, and that typical KEF sensitivity figures point to high levels with few watts and even sticking my neck out to speculate that an established, competent Co. such as KEF would be unlikely to sell a box with some horrific dips in the impedance curve, I was accused of producing an 'argumentative' reply.
'Argumentative'?....Moi?
At that point I repeated that he didn't understand this stuff.. despite advice from numerous posters and I gave up.

 

[Mike Reed]

Watts is one thing, but I've always understood that current capability in the amp and impedance characteristics and sensitivity of the speaker is as important. I've seen the tweeter damage caused by under-powered amps though. Awfully glad I don't do WhatsAp and the like, as I hardly have time to keep up with pfm nowadays ! No Smartphone here; strictly analogue in a digital way.

 

[awkwardbydesign]

Some speakers need a bit more juice to wake up, but KEFs aren't bad in that regard, and 200W is a lot of power. The fellow is misinformed, or is just trying to sound knowledgeable. He probably doesn't even realize it: Dunning–Kruger effect

Initial study included judging which jokes are funny! I stopped reading right there. I think I did rather well.

 

[amazement]

Isn't current or the ability of the amp to provide decent current more important than watts?

 

[Mullardman]

When I was still doing Youth Work, one of a pair of Sony speakers which were I think a donated item, caught fire, on the end of some sort of stack system.
Fortunately, the thing was mounted high on a bare wall and did no harm.
However, I wrote to Sony, pointing out the obvious danger of such an event especially considering the propensity for many domestic users to stick one speaker next to the curtains and the other behind the couch.
They sent a rep out, who took away the burned out box and presented us with a nice pair of Sony 'mid-fi' speakers.

 

[John Phillips]

Isn't current or the ability of the amp to provide decent current more important than watts?

What matters first is the ability of a power amplifier to put the right voltage across the loudspeaker terminals. A conventional loudspeaker is designed to convert voltage into sound pressure in accordance with its sensitivity. If sensitivity is quoted in "dBSPL per Watt" then the modern standard is that this means watts based 8 Ohms nominal impedance, so "per Watt" really means "for 2.83 Volts".

Current delivery and power delivery are actually by-products of putting the right voltage across the loudspeaker's impedance. Sufficient current and power capability are both necessary to deliver the right voltage. If either is insufficient the right voltage will not be delivered and there will be distortion.

 

[Cesare]

Isn't current or the ability of the amp to provide decent current more important than watts?

Kind of, it depends really.

The amplifier has voltage rails which limit the maximum voltage it can swing, but also a maximum current it can deliver, which might be limited by the output devices, or the capacitance of the amplifier. The limit of the amplifiers power is reached when either of these limits is exceeded.

If you make an amplifier, there is little point having massive voltage swing potential if you can't deliver current, or massive current delivery potential if the voltage output is limited. So, some sort of balanced design is typical, and that must be made based on an expected impedance load of the speakers, as this changes the current required for a given voltage.

Amplifiers in the 70s were expecting to see 16 or 8 ohm speaker loads, so the voltage to current delivery was designed with this in mind. The 80s trend for lower speaker impedance (6 or even 4 ohm) would mean the current delivery requirement assumptions in those amplifier designs was wrong. However, if you are never near the limit of current or voltage, you won't see any particular difference.

There have always been speaker designs which are grim to drive (e.g. ESL57s) and amplifiers which are massively over engineered in the current delivery department (e.g. Krell) but whether this will help you will rather depend on what you are doing with these things.

But I do agree, running out of current supply is probably the most likely failure mode when looking at an amplifier rather than running out of voltage rails since it's expensive to add current supply, and easy to add voltage support. I don't think i've ever got near an amplifier clipping in my years with domestic hifi, even with 20w amps.

 

[John Phillips]

Kind of, it depends really.
...
But I do agree, running out of current supply is probably the most likely failure mode when looking at an amplifier rather than running out of voltage rails since it's expensive to add current supply, and easy to add voltage support. I don't think i've ever got near an amplifier clipping in my years with domestic hifi, even with 20w amps.

Yes. For solid-state running out of current delivery capability is the more likely limit rather than running out of power/voltage.

However, I once listened to an acquaintance's home-built 4W SET amplifier sounding horrible (to me - he thought it was great). A test confirmed it was running out of voltage into 'speakers that were just not suitably sensitive, and soft clipping on peaks. I do agree this is a rather less common situation.

 

[Darth Vader]

Yes. For solid-state running out of current delivery capability is the more likely limit rather than running out of power/voltage.

However, I once listened to an acquaintance's home-built 4W SET amplifier sounding horrible (to me - he thought it was great). A test confirmed it was running out of voltage into 'speakers that were just not suitably sensitive, and soft clipping on peaks. I do agree this is a rather less common situation.

Some loudspeakers have low impedance dips and a cruel phase angle that makes current delivery a lot harder. If this happens at frequencies where the ear is at its most sensitive then the distortion will be heard. Less so at the low frequencies where the ear is at its least sensitive and the notes are felt as well as heard. Thats why in some circumstances a much more powerful amp is required than would at first blush seem like over kill to get the most out of such speakers. Well that my experience.

DV