What Are Watts..?

So much confusion exists regarding the output rating ofpower amps in relation to their efficiency , that is felt chat some notes on the subject will prove of value, question as to loudspeakers and value of power and sound transducing deevices, enclouasure of l.s. speakers, quater wave, sealed cabinets or open baffle, back port or eitherk, comments please,
paper cones or other,
nando.

 

I'm still waiting for a convincing explanation of how the Sugden A21SE gives only 5 watts more than the A21a but to me gives the impression of being 10 times more powerful. Just as well I don't really care for tech-talk.

 

quote from TANNOY,:
the function of a correctly designed amplifing system is to give natural reproduction of speech and music over a given area or throughout a certain building . there are other factors besides output watts.
nando

 

http://en.wikipedia.org/wiki/Watt

seems to sum it up quite well

 

Lets have a go at this one from my limited understanding, if I can! Firstly, which units do we use? We use decibels (db) to measure loudness/volume and changes in this or whatever. 1db is just about perceptible and most people find a 3db rise in sound or so a noticeable increase in volume. This however can vary from ear to ear! 10db is a doubling of volume. What do dbs sound like? When listening to live music an orchestral crecendo/climax reaches around 100-105db whereas a loud rock concert can easily reach 120/130db or more, everyday background noise is about 30-40db. Note that the scale is not linear but logarithmic - curve not straight line.

We measure power in watts (W). The relationship between amplifier power (in watts) and perceived volume is also logarithmic – it takes 10x the power to double the volume ie a 100W amp will be twice as loud as a 10W, 1000 2x as loud as a 100W amp and so on – all other things being equal.

Speaker sensitivity and efficiency next – this is a measure of how well the loudspeaker converts the watts (electrical power) from your amplifier into dbs (the sound you hear). Sensitivity is measured by giving the loudspeaker to be tested a test signal of 1 watt (or 2.83V) and measuring the output in decibels1 metre away. The next thing to affect perceived volume is listening distance from the speaker. This is governed by the inverse square law (remember your school physics!). If you have a light on in your garden at night as you walk away from it the decrease in illumination provided is not linear, again it’s logarithmic, the same applies to sound and speakers, when you move from 1m to 2m away from the speaker you need 6db more for the same volume, from 2m to 4m another 6db increase and so on.
Something else to think about is the load the speaker presents to the amplifier – this impedence is expressed in ohms, 4 or 8 being typical for hi-fi speakers (and is why valve amps sometimes have 4 or 8ohm taps on their transformer outputs). The lower impedence (4 ohms) needing more oomph for the same volume level (2.83 Volts into an 8 ohm load is 1 watt. 2.83 Volts into 4 ohms is 2 watts) – hence my Dynaudio kit at 4ohms needs a lot more current up ‘em than my Merlins do. My head hurts now so I’ll leave it there for the present.

 

To try to cover all aspects of speaker design in a quick post is well nigh impossible. As there are others on the forum with more knowledge than I have in this area I'll leave the more practical and complex explanations to them.
Here's a starter for 10: Speaker design, even before we get to cabinet construction, can be seen as juggling with 3 variables: cabinet size, low frequency bandwidth(bass!) and sensitivity (driver choice/crossover design). Simplistically this means that eg 1. if you want lots of bass then cabinet size will increase or efficiency go down, 2. you sacrifice bass bandwidth or/and efficiency for a tiny cabinet and so on - it depends how the pie is sliced.

 

the quality or "naturalness" of the reproduced sound is of far greater importance than mere volume, the " watts output" of an amplifier has no relation to this feature, . the frequency characteristics is usually the only other point quoted, a characstesistic that is stated to be linear from 50-10.000 cycles implies that anyfrequecy between these limits is equaly amplified.the amplitude characteristics is even more important..
nando.

 

furtherr more, an amplifier is said to have a linier amplitude characteristic if an increase in input ratio gives the same the same in output ratio.
nando.

 

Nando, you say "the quality or "naturalness" of the reproduced sound is of far greater importance than mere volume, the " watts output" of an amplifier has no relation to this feature" - that's a completely different ball game to the OP! I'll turn my mind to it!

 

MF seller in company marketing line discussion shocker..

 

quote

this , my dear friend is something that goes back to the late 60's on speaker technology as we worked in recording studios,merelly passing resarch we done, nothing to do or single out any manufacturer, funny you single out m.f.
nando.

 

volts X amps

 

3db uplift nessitates a doubling of power

 

i think that ,"sorry to bore you all " the efficiency of the loudspeaker affects the acoustic output, an efficient loudspeaker used with a small amp may give twice the volume of sound obtainable from an inefficiant loudspeaker?
nando

 

less power , more chance for better sound

 

thanks neil, shame this did go further but i did also threaded a prt two.
regards,