Orchid XP v3 wrote:

> My phone typically needs charging once every 9 
> days or so. (Bearing in mind that I never make or receive any calls or 
> text messages.)

Actually, come to think of it... usually the meter shows "full charge" 
constantly, until you actually attempt to *use* the phone. Then the 
meter instantly drops right down to empty. ;-)

As I understand it, it's just very hard to measure how much charge is in 
a battery. If you're not drawing any current, the potential will stay up 
at maximum until the battery is *really* low. The battery's maximum 
current diminishes long before its maximum unloaded potential does...

-- 
http://blog.orphi.me.uk/

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>>> Interesting, how do they do that?
>>
>> You think *I* know?
> 
> It used to be that more efficient speakers in general had more unwanted 
> resonances and lumps in their frequency responses: IOW poorer fidelity.  
> I don't particularly know why but that's how it was.  Obviously the 
> designers would have overcome that if they could have, but some chose 
> low efficiency in return for better sound quality.  I don't know how 
> well they are doing now with that trade-off, it's been some years since 
> I last read any reviews.

That sounds about right.

>>> Hard to see how you could deliberately make the system less efficient 
>>> without just plonking a huge 50W resistor in series (which would 
>>> totally screw up the quality of the sound).
>>
>> And why would that be?
> 
> The answers lie in the way passive networks of electronic components 
> work and in speaker mechanics.
> 
> Firstly, the crossover network divides the signal from the amplifier to 
> the woofer and the tweeter drivers.  It must be tuned to the right 
> frequency and shape the frequency falloff curves and phase so that the 
> sound levels from both drivers are balanced without dips or humps or 
> comb-filtering at the crossover band where both drivers transmit part of 
> the signal.  It is also supposed to keep the signal phase true between 
> the two drivers over the frequency range so they operate in a unison 
> making the sound wavefront from both drivers combine and arrive at your 
> ear together.  That is fekking difficult to design, because...
> 
> Crossovers are passive networks of resistors, capacitors and inductors. 
> Networks behave much more complicatedly than isolated components because 
> everything interacts with everything else, not just its immediate 
> neighbours.  Speaker drivers are *also* R-L-C networks, so crossovers 
> must be designed with that driver's electrical properties being integral 
> to it.
> 
> In short, the whole thing is interbalanced, so if one resistor, 
> capacitor or inductor changes, everything goes out of whack -- crossover 
> frequency, frequency response, phase response, impedance response, 
> resonances and ringing -- and the speaker sounds like crap.
> 
> For predictability, a speaker and its crossover also rely on the 
> amplifier's output stage being very low impedance. Signal-wise, the 
> amplifier is near to a short-circuit, regardless of the voltage swings 
> it generates.  A speaker is a motor and when moving, it generates 
> back-EMF through its crossover.  It has mechanical inertia and wants to 
> overshoot.  It  also has natural resonances from driver suspension 
> springiness, cabinet air volume, acoustic transmission line length, 
> tuned acoustic port, etc.  That colouration is NOT part of the original 
> signal.  If the amplifier doesn't soak up that energy (absorb the 
> current), to damp the unwanted motion (overshoot and ringing) it will 
> reflect back into the network and colour the sound you hear.
> 
> So if you plonk a great big resistor in series with all that, the amp 
> can't damp unwanted speaker motion, the crossover detunes, the frequency 
> response goes lumpy, the sound goes muddy, and you think "bleccch!"  :-)

I'm sure that would be the case.

Now, what if that resistance was part of the design right from the 
beginning?

By the way... The documentation for my mum's amplifier claims that it 
contains special circuitry to cancel out the electric signals generated 
by the speakers themselves. (I have no idea whether this is special or 
whether it's something all modern amps do and they just wrote about it 
to make themselves sound cleaver...)

>>>> Hmm, I think my amplifier (nothing special) is rated at 60 W per 
>>>> channel. (IIRC, into 8 ohms at 1 kHz.)
> 
> For listening at home, the real reason for high-powered amps is not to 
> make louder noise, but for fidelity.

Hmm, isn't that what *I* said several posts ago? ;-)

>> (It's like all toasters 
>> have a special setting that transforms bread into charcole. We don't 
>> know why, but they all have it.)
> 
> <Ahem>  Just because you didn't figure it out, doesn't automatically 
> make the manufacturers into idiots.  The high setting on toasters is 
> needed to get even a _little_ colour into *crumpets*.  But, as you 
> apparently haven't toasted a crumpet before, they obviously don't exist 
> and every manufacturer out there is stupid for gratuitously making 
> toasters with a nuclear setting.
>  :-P

Wait... Surely to toast a crumpet you want a *lower* heat? (Since it's 
thicker and hence nearer to the heat source - and also you want to cook 
it slower so it cooks through completely.)

>> (I once tried connecting a line-level output to the phono input. Big 
>> mistake...)
> 
> Ow.  :-(

Sounded a bit like a metal guitar. Also made the sound come out on *all* 
input selections. o_O

-- 
http://blog.orphi.me.uk/

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Brian Elliott wrote:

> Firstly, the crossover network divides the signal from the amplifier to 
> the woofer and the tweeter drivers.  It must be tuned to the right 
> frequency and shape the frequency falloff curves and phase so that the 
> sound levels from both drivers are balanced without dips or humps or 
> comb-filtering at the crossover band where both drivers transmit part of 
> the signal.  It is also supposed to keep the signal phase true between 
> the two drivers over the frequency range so they operate in a unison 
> making the sound wavefront from both drivers combine and arrive at your 
> ear together.  That is fekking difficult to design, because...
> 
> Crossovers are passive networks of resistors, capacitors and inductors. 
> Networks behave much more complicatedly than isolated components because 
> everything interacts with everything else, not just its immediate 
> neighbours.  Speaker drivers are *also* R-L-C networks, so crossovers 
> must be designed with that driver's electrical properties being integral 
> to it.
> 
> In short, the whole thing is interbalanced, so if one resistor, 
> capacitor or inductor changes, everything goes out of whack -- crossover 
> frequency, frequency response, phase response, impedance response, 
> resonances and ringing -- and the speaker sounds like crap.
> 
> For predictability, a speaker and its crossover also rely on the 
> amplifier's output stage being very low impedance. Signal-wise, the 
> amplifier is near to a short-circuit, regardless of the voltage swings 
> it generates.  A speaker is a motor and when moving, it generates 
> back-EMF through its crossover.  It has mechanical inertia and wants to 
> overshoot.  It  also has natural resonances from driver suspension 
> springiness, cabinet air volume, acoustic transmission line length, 
> tuned acoustic port, etc.  That colouration is NOT part of the original 
> signal.  If the amplifier doesn't soak up that energy (absorb the 
> current), to damp the unwanted motion (overshoot and ringing) it will 
> reflect back into the network and colour the sound you hear.

I read about this kind of thing in a DSP book. Damn, IIR filters sound 
so complicated! Fascinating, but... I wouldn't want to design them for a 
living.

-- 
http://blog.orphi.me.uk/

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Orchid XP v3 wrote:
> The maximum load I saw was 40W (during the boot sequence - when
> everything turns on at once). In normal running it hovers somewhere
> below that.

Ah. Right now rendering two scenes (in a mind of testing) with max
brightness on the screen, ie. burning the CPU. I'm not consuming extreme
memory nor using wireless interfaces

groath ~ # cat /proc/acpi/battery/C1B5/state
present:                 yes
capacity state:          ok
charging state:          discharging
present rate:            2749 mA
remaining capacity:      3797 mAh
present voltage:         11671 mV

2749mA*11671mV=~32W.

> I didn't check specifically. My laptop has a very dim LCD with poor
> saturation and a horribly narrow viewing angle. No matter how you
> position your head, 50% of the display is always inverted...

For me the display was the most important part of the machine, I got
nearly what I wanted (I got 15" 1400x1050 matt display, I'd wanted 14").

> Should be noted: It's an *ancient* laptop!

Heh. I though more of an ancient (and broken) Linux distro.

> (Now *my* laptop seems to do all this in hardware, not software. Doesn't
> matter what software is running, the fan turns on and off now and then...)

Which is wise choice.

-- 
Eero "Aero" Ahonen
   http://www.zbxt.net
      aer### [at] removethiszbxtnetinvalid

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scott wrote:
> Well yeh that's kinda my point, the speaker system is designed to sound
> good.  Trying to minimise the efficiency (so that input voltage is
> higher) is not really on the list of things to do when designing a
> speaker system.
> 
> 

Yep, but practically creating a good sound leads to less efficient
speakers - afaik real Hi-Fi -speakers with over 90dB/W/m are rare stuff.

-- 
Eero "Aero" Ahonen
   http://www.zbxt.net
      aer### [at] removethiszbxtnetinvalid

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On Wed, 05 Sep 2007 07:57:09 +0200, scott wrote:

> Oh wow, that would annoy the hell out of me if I had to charge my phone
> every 24-48 hours...  Mine usually lasts about 5 days with a few texts
> and short calls per day.  I do make sure that bluetooth is turned off
> when I'm not actively using it though, maybe that makes a difference?

Probably, yes - I leave bluetooth turned on because I have a wireless 
headset for it - but I also can charge it off a USB port, so I frequently 
plug it in when I'm not using it.

But I also do a fair number of long phone calls for work on the days I 
work from home.

Jim

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> Well yeah, poor 3D, 1HD, 2x1,8GHz C2D, 15" TFT etc (the screen backlight
> is one big consumer for me, to be noted).

Yep, and expect the power consumed by the backlight to drop significantly in 
future as finally everyone switches from CCFL to LED backlights, LED 
efficiency continues to rise, and LCD technology improves (to let more light 
through).

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> Whatever it is, that is what you see. If it moves faster than 50 Hz you 
> either see it not moving at all or, viewed in the right direction, as a 
> semitransparent surface. If you can prove that you can see something 
> moving at, say 200 Hz, I have a couple of friends working on the retina 
> that would be most interested in such a physiological anomality. ;)

It's easy to see things moving above 200 Hz.

One method is to light the thing with a special light source (eg a pulse at 
190 Hz or something).  On high speed machinery they use this technique so 
that operators don't accidentally put their fingers into something moving at 
200 Hz....

Second is to quickly move your eye from side to side to try and "follow" the 
movement.  You eye can move at an incredible angular speed to follow 
objects, and in doing so will make the object you are tracking look less 
blurred while the surroundings get blurred.  Try flicking your eyes from 
left to right as you watch a wheel that is spinning too fast to see, as you 
do it some parts become clear.  If you do this while looking at the beam of 
a cheap projector (one that uses a rotating colour wheel) you will see the 
RGB primaries separated because they are hitting different parts of your 
retina (I assume this changes at 60 * 3 = 180 Hz).

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46dfae45@news.povray.org...
>> Well yeah, poor 3D, 1HD, 2x1,8GHz C2D, 15" TFT etc (the screen backlight
>> is one big consumer for me, to be noted).
>
> Yep, and expect the power consumed by the backlight to drop significantly 
> in future as finally everyone switches from CCFL to LED backlights, LED 
> efficiency continues to rise, and LCD technology improves (to let more 
> light through).
>
And what about e-paper?
http://en.wikipedia.org/wiki/Electronic_paper
No backlight, no need of light most of the time, viewable in plain sunlight.

Marc

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> And what about e-paper?
> http://en.wikipedia.org/wiki/Electronic_paper
> No backlight, no need of light most of the time, viewable in plain 
> sunlight.

Yep, already used in some supermarkets (eg the Edeka at Munich airport uses 
it) for price tags that consume little or zero power and are fully readable 
under normal lighting.

The main problems that need to be overcome though are switching time, 
resolution and contrast ratio.  At cold temperatures the switching time for 
black to white is counted in MINUTES not milliseconds, even at room 
temperature they take a couple of seconds to switch...

Totally reflective displays are already used (eg in Game Boy Advance I 
think) but for colour ones you only get ~33% of the reflectivity of a 
black/white display due to the colour filters.  Also in order to see it in 
dull conditions you need to add a frontlight (as opposed to a backlight) 
which further reduces the reflectivity, leading to lower contrast.

Rest assured there is huge research in this area, expect something like 
ePaper to one day become mainstream.  There are a lot of hurdles to get over 
first though...

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