Random musings on hifi components from 20+ years of upgraditis

dannnielll

Hi Gibbsy.. the following is an attempt of demystification...
A car battery output is at 12v. The little PP3 battery pack in the fire alarm is 9v. Sticking two of these together can produce 18V . .. obviously bigger than 12V.
A car battery can easily put 10 Amps into a car headlight and therefore a power level of 12V *10 A of 120 Watts of power..and do this for a number of hours.
Our two PP3s ,produce 18V but cannot drive more than 100mA even into a short circuit. ..so connecting a car headlamp would not even make it glow red.
We say the car battery has an internal resistance of maybe 1/20 ohm and our PP3 of probably 100 ohms.
When a voltage is applied to a circuit containing a resistance ,a current will flow and power will be consumed ,both in the resistance  and also in any internal resistance inside the voltage source.  The power in the resistance is  P = V*I .the voltage difference across the resistance times the current flowing in the resistance  . However because current depends on the voltage, there are a few math relationships we can swop around ...
power is also V^2/R  or power is I^2 *R
. Unfortunately the headphone manufacturers keep rearranging the deckchairs,and quote power which is a useless measure. Since they have already decided on the size of resistance in their  phones, what they should say is ..This phone needs X volts to generate Y dBs ,and never exceed Z volts ,

gibbsy

@dannnielll Thanks for the explaination, brought it down to my level of intelligence.

Derek S-H

@dannnielll - thank you very much for your detailed reply, which I must confess I didn't understand entirely!

I think the upshot was that headphone manufacturers quote watts when it's more useful to quote volts, as you have?

Anyway, thank you for taking the time to reply and you have just saved me hundreds of pounds, though it would've been nice to own a piece of equipment called Schiit!

And I shall forgive you whenever you criticise Vinyl, whether in the past, the present and undoubtedly the future!

dave48

Thanks for flagging headphone amps - I think I completely forgot them.  I had a Musical Fidelity X-Cans which looked cool but I couldn’t hear any difference to the headphone output on my old integrated amp (which was nothing special).  Now use a fiio rechargeable amp which is pretty good (I’ve only got Sennheiser 600HD so nothing exotic to drive).  Headphone outputs on Audiolab M-DAC and Hegel HD25 are both pretty good.

dave48

Also forgot phono amps.  Had a Musical Fidelity X-LP or something - like most of the other Musical Fidelity X products - I really wanted to like them as they looked so cool, but they all sounded tame and uninvolving.  Upgraded to a Lehmann Audio Black Cube SE.  I’m really happy with that - but it was only after spending quite some time with my hifi dealer tweaking the settings that it really came to life.  It needed some experimentation - the setting that was theoretically right just didn’t sound as good.  Now sounds even better with the Lyngdorf (this for me is THE revelation of the Lyngdorf).  So happy with the Lehmann and v. unlikely to ever change it whilst it is still working.

dannnielll

.. Leaving aside the Vinyl slur..which we will both ignore.!!!!. ..  ,The  low internal resistance in the amplifier is kind of important. Look at it this way. The amplifier squirts out a voltage to the headphone and the diaphragm starts to move. It was a cymbal clash and very short lived ,so the amplifier stops giving out voltage very quickly. However the diaphragm is still moving. Now. Things actually reverse. The head phone is a magnet with a coil of wire attached to a moving diaphragm, and it, instantly becomes a generator driving current BACK into the amplifier. If the internal resistance of the amplifier is low compared to the resistance of the coil, the kinetic energy of the diaphragm is instantly absorbed and it stops . Otherwise the diaphragm would continue moving and slurring the acoustics a little. Now with 50 ohm  internal and 300 ohms in the Senns, you have a Damping ratio of 6:1 ..which is good.  But in my case with the Sony and Cyrus the Damping ratio is 48:1 which is better.
Again you might well prefer a lower Damping Factor..many people do... One of the reasons why many people like  Valve amplifiers is that they have a lower Damping Factor ..

oldcootstereo

For those who never took any electrical/electronics training, a very basic parallel to water delivery:
Voltage is analogous to pressure
Current is analogous to flow
Resistance is analogous to friction
Power (wattage) is SOMEWHAT analogous to volume (gallons/liters), in that the amount of pressure vs friction will determine the amount of water flow/unit time.  

Tube (valve) amps are sufficiently different from semiconductor amps that it is comparing apples and pomegranates... both are fruit but neither is a direct substitute for the other.  

Ah, back-Electromotive Force, (aka counter-EMF) is where the real "fun" in coil/magnet mechanisms interacting with electronics begins.  Far too long and controversial a topic to be fully addressed here, or anywhere outside an engineering course, but one I'm sure any competent amp/speaker designer/manufacturer is well aware of.  

Here's a good explanation, no sense reinventing the wheel... scroll down to reply #3 by Aether Audio.  There are other instructive comments of his further down the thread too.  This is from 2005, but as far as I know the Laws of Physics haven't changed much since then.
                                                                                                                                                                                                        Back EMF ... what is it?                                                                                                        Back EMF ... what is it?                                                                                                                                                                                                        www.audiocircle.com

gibbsy

Ah, but. Does electrickery lose power as it goes up hill. Water does. Roughly one bar per storey. Got to give the branchman enough power to fight the fire.

It's a good analogy for a dim wit like me. Remember peeps, water and electrickery does not mix.