Output power of amplifiers

[RayLi]

On the markets, the output power on the spec sheet is quite confused. From 1x w to 16xx w, when I learned electronics, my lecturer told me that the power output in cinema is about 1xx w only. How come does a power amplifier for normal consumers deliver thousands watts? Too big power for the house of normal customers and too costly. In the past, FTC and EN standard govern to quote the RMS output power in spec sheet. Do those rules become invalid? Any new standards to replace the previous ones?

[suzyj]

It’s fairly straightforward. The mains power (240V at up to 10A, or 2400W max hereabouts) is fed through a transformer with around 85% efficiency, giving us say 2100W max, then rectified and filtered, then fed through a class A-B power amp with maybe 60% efficiency, giving us say 1200W max from an Australian plug. Finally they feed the power through a complex marketing bullish!t network, and put 4kW out to the speaker. Funny enough, the whole mess only weighs a couple of kilos, so it must be terribly clever.

[wiseoldtech]

It's apparently reared its ugly head again - the wattage misinformation statistics.
This has been growing since the beginnings of the Digital Age.
And yes, to do nothing more than confuse or dazzle the dumbed-down hoardes of newer consumers that don't have a clue what wattage really is.



To pick up a 15 pound amplifier in one hand, and its front panel clearly labeled with "2000 Watts" - is laughable.


Yes indeedy.... it's a bunch of BS for sure.

[Ian Finch]

That's largely the difference between hifi speaker sensitivity and PA speaker sensitivity in, for example, old school type cinemas, auditoriums and arrays for outdoor events. Tubes and transformers of any quality in former times were expensive and required regular parts replacement and maintenance - sensitive speakers were not particularly expensive so the choice was obvious then.

Some loudspeakers and arrays show a staggering 20dB SPL difference for the same size drivers but used in different applications. That translates to an enormous difference in power requirements and for tubes, several small amplifiers (with some out of service for maintenance) was the most economical way to provide the sound for movies and PA.

Modern cinemas are a different story. First they are smaller with fewer seats that in Dad's day but amplifier watts are now quite cheap. Sensitive, high linearity speakers that go loud are no longer cheap, so you can see where this is going - more power with more linearity and lower cost works better and cheaper for high SPL, high sound quality, extended bass and more dynamic sound.

Home theatre amplifiers are really a number, 5 or more, very efficient and cheap class D amplifiers. but the specifications of bona fide products are generally correct and an 8 channel home theatre system with big subwoofers, front, centre, rear and side speakers in a big den under your house can really chew up the power - maybe not a full 1kW continuously, but certainly approaching that with some dramatic, bass heavy sound effects.

I don't pretend to know much about FTC standards which in Australia are about fair trading and EN standards apply to European Economic Community technical standards - very broad areas of government, lots of talk and paperwork, perhaps more fit for a lounge or "everything else" forum discussion.

Yes, there is a load of nonsense ratings from nonsense sellers out there - you can pick the charlatans out, can't you? Hint: they don't originate from local sources, do they...

[bansuri]

100W sounds like 4x 6L6GC in those times, much more was not available at reasonable cost.

[duncan2]

RayLi--was your lecturer working for "Big Media " ( you know who )?


Movie theater Noise .....



This is a major issue in America and now the UK.


Its so bad now US audiologists are having to supply American kids with hearing aids ( no complaints from the hearing aid companies) --check out share prices .


Dr.John Bedolla -emergency room doctor-- Seaton Health care ( just one of many ) -quote " Human beings did not experience sound louder than 90-100 decibels for much of human history until the invention of gunpowder and machinery .
So for the vast majority of human existence our ears NEVER adapted to loud noises "---


He goes on-- Quote--"certain types of high spectacle movies , such as Transformers ,have decibel levels of 90db for almost the entire movie and have decibel levels of 120db for significant periods and some points getting to 130db .


Now 130db is a jet engine at about 10--TEN meters " end quote .


Why have US authorities not stopped this and yes I can quote many US citizens with ears bleeding at the end of the movie as well as REAL stats --if required ?


Because they get round the law by the old fashioned use of Compression techniques --very sly .


I have a wealth of data if anybody want to criticize this--mainly American as they have been doing it the longest so casualty figures are available --no Big Media shareholders please.


Real life- once the hairs at the end of your auditory nerve system die --they do NOT regenerate -has anybody seen somebody totally deaf with a hole drilled in their skull and a miniature amplifier connected direct to their brain ---I have.

[bansuri]

The noise made by just one set of bagpipes equals 122 decibels.

[duncan2]

Played out in the open NOT in an enclosed movie theater - did you search for that poor rebuttal because I am in Scotland ?


Not relevant but how about Italian opera singers can be well over 100db .

Turandot .

[OldDIY]

Sounds of nature. Singing birds, the sound of rain (water).
Thunder. Rustle of leaves. Steps behind.

[wg_ski]

It all has to do with the peak to average ratio of music. If you want to convince yourself,try a little experiment. Get ahold of an old-school iron horse amplifier rated at 100 watts per channel, 8 ohms. And a big PA speaker that can take abuse, a 28 volt (at least 100 VA) transformer, a 100 watt incandescent light bulb, and an oscilloscope. Connect the speaker to one channel, and the transformer and light bulb to the other, and play music from a mono source. Monitor both channels with an oscilloscope. Slowly turn the music up until you start to see clipping. Then take note of how bright (dim) the light bulb is, and how much peak voltage you see on the scope. Then turn the music UP until you see the light bulb at full brightness and tell me how distorted the music sounds - and how LOUD. The result is very enlightening (pun intended). Don’t do this with a home hi-fi speaker or you will be at least buying a tweeter, and perhaps a woofer and midrange.