Horniness

13 March 2012 — dan

A reader writes:

Why do horns make things louder?

I mean, I accept that they do, on gramophones and megaphones and PA speakers at the train station and brass instruments and so on, but what's actually going on there? Why does the sound of your voice get louder just because you're holding a conical thing in front of your mouth? Is it just making it more... directional?

Dennis

The great problem of audio production, and audio reproduction too, is coupling the sound-producing thing to the sound-transmitting medium, which is usually air.

Air is very light. Most things that make sound are, in comparison, very heavy. The moving parts of loudspeaker drivers, the strings of a violin or piano, the lips of a trumpet-player who's blowing a sort of highly controlled raspberry into the mouthpiece of the instrument; all very very heavy, compared with air. All not good at moving lots of air, which is what you want your sound-making thing to do. Wave a brick around in the air and you'll invest a lot more energy in accelerating and decelerating the brick than you manage to impart to the air.

One way of solving this problem is to make your speaker driver very light too. Electrostatic speakers use a big flat sheet of super-thin plastic as a driver; the sound-producing element in a plasma speaker is made out of ionised air (or other gases, if you're a big wuss who doesn't want ozone poisoning).

Horns are a simpler way of solving, or at least reducing, the coupling problem. When you put a heavy-compared-with-air vibrating object at the small end of a horn, the only air it can move is the air right in front of it at the small end. Moving this air is still pretty easy, but the restricted air's mechanical "impedance" is nonetheless quite a bit higher than it'd be if it were unconfined.

As sound pressure waves move down the horn, the gradually widening shape of the horn (for loudest results, an exponential curve) allows the small amount of higher-pressure air next to the driver to transfer its energy to a large amount of lower-pressure air. The end result is that more of the energy of the driver ends up as sound waves.

A sealed-box loudspeaker has an acoustic efficiency - the amount of the input electrical energy that comes out as sound energy - of about one per cent, at best. Horn speakers can manage thirty per cent without much trouble, and quite a bit more if you design them for loudness rather than fidelity. Take the horn off a phonograph and you'll have to put your ear right next to the diaphragm to hear much of anything, but with a big horn on it, a wind-up phonograph making sound by scraping a needle over a disc of shellac can legitimately be described as quite loud.

(Some phonographs let you remove the horn, or never had a horn in the first place, and allowed you to listen through one or more rubber tubes that went to a headset of some sort - essentially, primordial headphones. This allowed you to listen to your records in privacy, albeit with weird stethoscope-y sound colouration on top of the lousy fidelity of the phonograph system in the first place.)

Outside of Physics Experiment Land, acoustic horn design and implementation has many engineering tricks. For instance, modern horn loudspeakers usually have a horn throat that starts out much smaller than the diaphragm of the actual driver, which may be in its own actual rectangular speaker box stuck on the small end of the horn. There are also horn loudspeakers, like the legendary Klipschorn, that use various workarounds to fold something that acts somewhat like a horn into a speaker that can be mainly built out of flat wooden panels.

Also, the lowest bass frequency a horn can reproduce is determined by the size of the mouth of the horn; that's why public-address and hand-held megaphone speakers always sound tinny. Speakers like the Klipschorn have their horn mouth on the back of the enclosure, and are meant to be shoved into the corner of a room, so the walls behind them can provide a bit more effective horn size. Horn loudspeakers are also deliberately designed to be further away from an ideal horn shape than is strictly necessary, to balance the efficiency of the horn with the hard bass cut-off that a "pure" horn, with a mouth small enough to fit in a room, has at low frequencies.

The old phonograph horns have been reborn, too, as "amplifiers" for MP3 players and cellphones. The phone, MP3 player or ear-bud headphones plug into the small end of a horn, and suddenly the tsss-tsss-tsss of someone else listening to their iPod on the bus turns into actual music.

Some of these devices are very fancy and very expensive, but if you search eBay for "amplifiers" for MP3 players you'll find lots of cheerful-coloured horn doodads among the actual electrical amplifiers. The going rate for a combination iPhone stand and horn "amplifier" now seems to be about two bucks delivered.

Psycho Science is a regular feature here. Ask me your science questions, and I'll answer them. Probably.

And then commenters will, I hope, correct at least the most obvious flaws in my answer.

Posted in Music, Psycho Science, Science. 1 Comment »

An exciting new thing to worry about

5 March 2012 — dan

Australia, or at least Victoria, is getting "smart" electricity meters.

Unlike the old spinning-disc or slightly newer digital meters, smart meters can report power usage in real time, to the customer via a display inside the house and to the power company as well, without any requirement for legions of meter-readers. Smart meters can do various other tricks, too, like for instance changing the cost of electricity by time of day, to make it more expensive when there's high demand and deter some people from turning on the air conditioner and adding their own little electrical vote for a new coal-fired power station.

Heck, the smart meters may even be able to measure power factor, and theoretically create a need for those zillions of "power saver" gadgets. Which the power saver gadgets will not actually fill, of course, on account of how they usually don't do anything at all, but you can't have everything.

The Australian meters seem to report every thirty minutes, via radio.

So, naturally, people think they cause cancer.

But I'm getting ahead of myself.

I was delighted beyond human comprehension to discover a one-stop shop for Aussie smart-meter opposition, stopsmartmeters.com.au. Actually, I was first pointed to this page on "Holistic Help", but I only made it to the oddly popular claim that smart meters somehow kill nearby plants before I went somewhere else, lest I burst an important blood vessel.

Herewith, a response to Smart Meters in Victoria: Information and Concerns.

There are some valid complaints on that page. Apparently some smart meters have overcharged customers, for instance. And there've been some typical government-program deployment boondoggles - cost blowouts, the possible need to spend more money to change the radio frequency band the meters communicate on because of interference, and so on.

There are also privacy concerns about the every-30-minutes communication of household electricity use, and whose hands this information could get into. I'm having a hard time figuring out a way in which selling of this data to marketing firms could be a major problem, beyond just contributing its own particle to the mountain of privacy-damaging things in the modern world. But if the data isn't encrypted well enough, and meter IDs can be converted into addresses relatively easily (possibly even if you need a directional antenna to do it), then it might become possible for one burglar in a van to quickly figure out who, nearby, seems to have gone on holiday.

There are also concerns about coupling of the radio-frequency output of the smart-meter antennas to household wiring, possibly damaging appliances, though I don't think anybody's done a proper study to see whether the rate of appliance failure is actually any higher after the new meter's installed.

And then there are some real, but not necessarily valid, complaints. People object, for instance, to power being made more expensive at certain times of day, which they say is unfair, though I'm not sure exactly how. If it's unfair to charge more for peak-period electricity, then it's also unfair if you're only allowed to park your car in some particular location for half an hour during the day, but can legally occupy the same space all night.

There's a claim that consumers don't benefit from the new meters. OK, that's a reason to object, I suppose, but consumers don't benefit when, say, petrol becomes more expensive, either. This is an argument against silly PR from the electricity companies that tries to make you think the new meters will make your life better, especially since the stingy buggers don't even seem to be providing any indoor display units. But that's all this complaint is. Just because you want to keep paying low prices for something doesn't give you a right to do so, especially when that "something" is electricity which previously sold at an artificially low price because the cost of warming the damn planet wasn't factored in.

And then there are feeble complaints, like the possibility that the meters will not be installed safely.

And then, there's the bulk of the lengthy page, which is proudly devoted to ridiculous complaints.

To start with an easy one, the notion that coupling radio energy to household wiring could cause fires betrays a serious misunderstanding of the amount of energy the meter emits, and how well it could be received by household wiring. You could pump that one whole watt of high-frequency RF directly into your wall wiring, and I swear to you upon my beloved Necronomicon that no wires would get hot and start fires. If the only way in is the fraction of one per cent of the energy that the household wiring will manage to receive... well, it's good of Stop Smart Meters to so quickly make clear their opinion of mere "knowledge" and "logic".

And, of course, now we're off and racing with good old mobile-phones-cause-brain-cancer claptrap. The smart meters broadcast in the same 900MHz band as our GSM mobile phones here in Australia, so clearly they pose a similar risk, right?

The World Health Organisation say it's "possible" that mobile phones cause cancer. People who relay this information are generally less eager to make clear that the WHO has categorised this possible risk, from "long-term, heavy use" of mobile phones, as being in the same "Group 2B" class as traditional Asian pickled vegetables, and coffee.

The Stop Smart Meters page is at least aware of this, and points out that there are plenty of straight-up poisons on the Group 2B list too, like for instance lead. But then the author erroneously tries to claim that since lead is poisonous and phone radiation is now on the same possible-carcinogen list as lead, phone radiation should be treated as something similar in danger to lead.

This is, to be frank, stupid. Yes, lead is poisonous, but there's only feeble evidence that it's a carcinogen, which is why it's on the 2B list, and not for instance the 2A "probably carcinogenic" list, or the Group 1 "definitely carcinogenic" list. Phone radiation is self-evidently not a poison like lead. None of the IARC carcinogen lists are lists of poisons. Phone radiation is on the same list as lead because there's only feeble evidence that it's a carcinogen.

Stop Smart Meters go on to claim that "a significant proportion of Victorians refuse to use devices such as mobile phones or baby monitors because of sensitivities or concerns about future health implications". This not only uses a rather stretched definition of the word "significant", but also pretends that science is a democracy. Which it isn't. It doesn't matter how many people think baby monitors cause cancer, if they don't. Likewise, it doesn't matter how many Koreans think having an electric fan in your bedroom is very dangerous, if it isn't.

Trundling down the extra-big Stop Smart Meters page, there's a fine example of the kit-and-kaboodle routine of collecting supporting quotes from as many people as possible, without paying any attention to the reliability of the sources.

The American Academy of Environmental Medicine, for instance, claim that smart meters are dangerous, and that claim is mentioned on the Stop Smart Meters page. The AAEM also oppose fluoridation of drinking water (PDF), on the grounds that "fluoride is a known neurotoxin and carcinogen even at the levels added to the public water supplies". This is news to the World Health Organisation that Stop Smart Meters were so enthusiastic about a moment ago.

The AAEM also believe that "mercury in vaccinations constitutes a significant exposure" (PDF), even though the mercury-containing preservative thiomersal is no longer in almost any vaccines that anti-thiomersal campaigners insisted were causing terrible harm to children, and this change has caused no epidemiological effect at all. I refer you once again to the World Health Organisation.

Oh, and the AAEM are really keen (PDF) on that whole multiple chemical sensitivity thing. Which is one of those illnesses that doesn't seem to manifest when a sufferer is exposed to the alleged causative agent but doesn't know it, and does manifest when a sufferer thinks they're being exposed, but they aren't.

The World Health Organisation has little to say about MCS, except to point out that people who believe they have it seem rather like the people who think they're "electrosensitive".

Funny they should mention that. Because Stop Smart Meters believe, of course, that "electrosensitivity" is real. Which it is, in a sense; people who suffer from it really do suffer. There's just no good reason to suppose that this suffering actually has anything to do with "radiation", and numerous studies that show it does not.

Anything a smart meter broadcasts is, apparently, bad. Stop Smart Meters complain that mesh-networked meters broadcast more frequently than meters with long-range radios, because mesh networks need relays to get the feeble signal from each meter to the actual power-company receiver for the area, and the relays are built into the meters. But since this is all because the radios are more feeble, I fail to understand why Stop Smart Meters automatically assume that this is yet another thing to worry about.

People hold mobile phones to their heads, often for extended periods. So if a watt or two of nine hundred and something megahertz radio waves actually can hurt you, it's sensible to presume that heavy mobile phone users would develop these diseases, presumably in their head, and presumably preferentially on the side they habitually press their phone to.

People are not in the habit of leaning their head on their electricity meter all day. And even the mesh meters do not normally broadcast all day. I think the non-mesh meters broadcast for a total of about five minutes a day, but I don't have a strong enough source for that to bet anything on it.

Even if you're sitting in a chair on the other side of the wall from the meter, with its antenna a mere metre from your head, then you'll be exposed to way, way less RF energy per second than you would with an iPhone pressed to your head in a dodgy reception area, and the exposure may be for only minutes, or even seconds, per hour. Arguing that this is a major risk, even if heavy cellphone use is dangerous, is like saying that hypothermia is lethal, so you'd better never eat ice cream.

Stop Smart Meters also appear to think that RF from the meter getting into the home wiring will cause those terrible microwaves to radiate from all of your house wiring. Once again, this completely ignores the concept of "power", how much of it there is in the first place, how much of it can manage to get into the house wiring via a miserably inefficient "antenna", and how much it attenuates with distance from the wires.

I could go on with this, but life's too damn short. Yes, there are reasons to object to the new meters; the new system seems very likely to come with more electricity price hikes, for instance, and you may even be overcharged on top of that.

But the bulk of Stop Smart Meters' argument isn't about that.

Stop Smart Meters appear to be, like many other people, under the impression that anything called "radiation" must be bad. I would not be surprised if they also don't want any "chemicals" in their food. People like this should logically therefore be frozen into a zero-Kelvin lump and stored in a an earthed lead box containing a hard vacuum, but for some reason they seem to be fine with light bulbs and moonlight and the drinking of dihydrogen monoxide.

If you don't know what radiation is, and you don't know what chemicals are, and the inverse-square law might as well be the Collected Proceedings of the Vorlon Linguistic Society for all the sense you can make of it, then I implore you to seek education, and remind you that activist organisations of any kind are much more likely to be in the bullshit business than the education one.

If you don't fancy the idea of education, I suggest you live a life of happy-go-lucky ignorance, taking cues from a housecat, or a domestic dog, depending on your preferences.

Just please don't spend your time worrying about the terrible threat someone says is posed by technologies, cultural changes or particular types of other human whom you do not understand. Every minute you spend worrying about Islamists conquering the world, or commercial airliners spreading mysterious poisons, or electricity meters giving you cancer, does nothing but move you one minute closer to your actual death, and gains you nothing at all.

Posted in Electricity. 19 Comments »

"Sucrosa. It's a pill."

4 March 2012 — dan

A reader writes:

One of your recent posts got me thinking.

Everyone (or anyone who's ever had occasion to read any sort of scientific study), knows about the placebo effect. I'm curious as to whether the magnitude of said effect has ever been studied, in order to determine the extent to which placebo effect is an actual effect, or just the natural history of a disease (or whatever).

I'm thinking that a randomised, NON BLINDED study might be necessary.

Take a bunch of people with the same usually-harmless disease, say a simple cold, or something like Bell's palsy. Tell them that there's a trial of a new wonder drug to treat their condition, and would they enrol in said study. Tell some people that they are getting the 'drug', and tell the others they are getting placebo. Give everybody placebo.

If there's a significant difference between the two groups, then that would be an actual placebo effect (ie thinking you're going to get makes you get better), as opposed to things just getting better on their own.

Has something like this been done? Would there be any problem with it, other than the ethics of telling people they're in one study but actually studying something entirely different?

Ben

Yes, there have been some studies of this sort. Placebo hasn't achieved much.

It's popularly imagined that placebos can do all sorts of amazing things, just as adrenaline makes a tiny woman able to lift a crashed car off her baby, and acupuncture can be used for surgical anaesthesia.

None of these things are actually true.

The reason why the placebo-controlled trial is such a central tool of medical research is that placebos don't do much of anything. If placebo treatment really was effective for all sorts of things, then, one, doctors could save a lot of time and money by just giving patients placebos all the time, and, two, placebo response could be a confounding factor on the non-placebo side of placebo-controlled trials. There's nothing stopping someone from having a placebo response to a real treatment, on top of whatever the treatment itself does.

The reason why trials are placebo-controlled, rather, is so that they can be blinded properly - preventing at least the patients and preferably also the doctors from being able to tell whether they're administering the medicine or the placebo. Unblinded tests are terribly susceptible to all sorts of biases, and a number of practical problems as well, like for instance all of the subjects who discover they're not getting any medicine not bothering to turn up next week.

The placebo effect, insofar as actual empirical science has been able to quantify it, is a delusion. That's "delusion" in the technical psychological sense - a counterfactual belief. But if you're given a placebo as a treatment for pain, or anxiety, or depression, and it works, then you have a delusion that your illness is not as severe. Which, for all practical purposes, is the same as "real" medicine for conditions like this that're all about what you perceive and how you think, rather than empirically measurable phenomena.

This is not the case for most illnesses, though. If you're given a placebo treatment for diabetes, or cancer, or yellow fever, you may if you're particularly amenable to positive delusions sincerely and unshakably believe you're getting better. But you won't be. Just as some dangerously thin anorexic people can literally see a fat person when they look in the mirror, some people undergoing worthless treatment for, say, cancer, can literally feel the lump getting smaller. Until they die.

(The flip-side of this is the not-terribly-well-documented situation in which someone is given a "nocebo", something inert which they believe to be poison or black magic or what-have-you, and then develop real symptoms or even die. There's no very persuasive evidence that people who believe themselves poisoned or cursed in one way or another actually can "worry themselves to death", but it's uncontroversial that someone who sincerely believes themselves to be in a nonexistent deadly situation can worry themselves into a state requiring serious real medical treatment. Note that it doesn't count if the patient just has a fatal car accident while driving frantically to the hospital after, say, being bitten by a non-poisonous spider.)

To really tell how effective placebos are, you need to do a three-pronged study, with one group getting a treatment, one group getting a placebo, and a third group getting nothing at all, if you can persuade that last group to stick around. (Or you can do a two-pronged study with placebo and no-treatment, if you can get such a thing past your Ethics Committee.)

When people do this, testing placebo against nothing at all, there tends to be little difference, and no objectively measurable difference at all.

There are lots and lots of real individual clinical observations (as opposed to friend-of-a-friend stories) of placebos creating real physical changes in real diseases like irritable bowel syndrome, asthma, ulcers and quite a lot of other conditions. These changes are hard to pin down, though; they exhibit the same deadly weakness seen in claims of paranormal powers, in which the harder you look to see if the effect is real, the smaller it becomes.

Useful placebo effects are, at best, highly variable between patients. And, again, you can't really tell what's going on without running a pretty big study of one kind or another, testing placebo versus no treatment at all. This is ethically difficult, and probably not a great use of researchers' time, compared with trying to develop non-placebo treatments that work whether the patient believes in them or not.

I could continue to ramble on here, but I've really got nothing much more to say about placeboes than actual-medical-doctor Harriet Hall says in this excellent article.

(The title of this post is from this Onion article.)

Psycho Science is a regular feature here. Ask me your science questions, and I'll answer them. Probably.

And then commenters will, I hope, correct at least the most obvious flaws in my answer.

Posted in Psycho Science, Science. 3 Comments »

Sproing

2 March 2012 — dan

A reader writes:

If you take a spring - a metal one I suppose (I know nothing about springs other than they're fun to play with) - and hang it by one end, with no weights or anything attached to the other end, and just leave it hanging there, will it eventually (like really eventually) become completely straight? Or what will happen? Does it matter what kind of spring it is? Will it's own weight straighten it out, or is there something about its structure that would prevent that from happening? And the follow-up, if the answer is yes, is, let's say it's a Slinky; about how long would it take?

I wish I could say I had a beer riding on this, but the truth is I'm just geeky and thought you might know.

Michael

No, a hanging spiral spring won't straighten.

The key concepts here are elasticity and plasticity. The whole idea of a spring is that it's elastic - you can stretch and/or compress it, and when you let go, it returns to its original shape. If the force applied to an elastic object exceeds the limits of its elasticity then the object will be permanently deformed (or just break), but you'd need a pretty darn long, but skinny, spring for that to happen just from the spring's own weight.

Slinkies are an extreme case, here, because they're a quite unusual kind of spring, with peculiar dimensions compared with most spiral springs. Dangling a brand new Slinky may actually give it a slight permanent stretch, but it clearly doesn't stretch it very much, and you can leave it hanging as long as you like without getting any more stretch than happens in the first few minutes.

It's actually normal for a new spring to distort somewhat when put to use. This is called "taking a set", and has to be accounted for in the design of devices that use springs, from the huge ones in heavy vehicle suspensions to the incredibly delicate ones in mechanical wristwatches. It's unusual for a spring to take a set just from its own weight, though.

If you made a spring out of, say, tin/lead electronics solder, then it wouldn't need to be very long in order to straighten out under its own weight. It'd probably continue to straighten for some time, too - meaning hours, though, not years. Tin/lead alloy is of course a terrible material for springs, since it's highly plastic and hardly elastic at all.

Apropos of this, there's a really neat guide to making your own springs here. Home handypersons usually regard spring-making as a black art and just end up with a parts box full of springs cannibalised from other items, but you really can make them yourself without being a master metalworker.

(Oh, and I know I sound like a broken record, but J.E. Gordon's "The New Science of Strong Materials, or Why You Don't Fall through the Floor" and "Structures, Or Why Things Don't Fall Down" both have a lot to say about the springiness of actual springs and of many other objects, and about the foundational concepts of stress and strain.)

Psycho Science is a regular feature here. Ask me your science questions, and I'll answer them. Probably.

And then commenters will, I hope, correct at least the most obvious flaws in my answer.

Posted in Psycho Science, Science. 3 Comments »

This sensor for sure, Rocky!

28 February 2012 — dan

A reader writes:

Nokia 808

"Nokia announces 808 PureView ... 41-megapixel camera(!)"

HAHAHAHAHAHA, HAHA, HAHAHAHA, HAHAHAHAHAHAHAHA
HAHAHAHAHAHAHAHAHAHAHAHAHAHA

*choke* *gasp* *groan*

When I read that I immediately thought of your "enough already with the megapixels" page. I figured I'd send you the link so you can knock yourself out. :D

And now, back to frantic laughter...

Lucio

This thing may actually be less ridiculous than it looks.

The sensor in the Nokia 808 is much larger than normal phone-cam sensors - much larger, in fact, than the sensors in almost all point-and-shoot compact digital cameras (not counting expensive oddballs like the new PowerShot G1 X).

In the inscrutable jargon of camera sensor sizes, the 808's sensor is "1/1.2 inches". This means a diagonal size of around 13 to 14 millimetres.

The "APS-C"-sized sensors in mainstream DSLRs have a diagonal around the 27 to 28mm range, and thus four times the area of the 808 sensor. "Full frame" DSLR sensors are way bigger again, but they're also way more expensive.

For comparison, the (surprisingly good) "1/3.2 inch" sensor in the iPhone 4S has a diagonal of less than six millimetres. Consumer point-and-shoots these days usually seem to have 1/2.3" sensors, giving a diagonal of less than eight millimetres. (I haven't researched this in detail, but the eight Canon consumer compacts and five cheap Nikons I just checked out were all 1/2.3.)

Fancier point-and-shoots, like Canon's PowerShot G12 and Nikon's Coolpix p7100, have somewhat larger sensors; those two both have 1/1.7", giving diagonals in the neighbourhood of nine to ten millimetres.

(The abovementioned PowerShot G1 X has a "1.5 inch" sensor, which after compensation for endowment-overstating jargon is a 23-point-something millimetre diagonal. That's very nearly mass-market-DSLR size, but you'd bleeding want it to be for a street price of $US799. You can get an entry-level DSLR with two unexciting but functional zoom lenses for that price. If you want something more compact, you can even get a mirrorless camera - a Nikon 1 J1, say - and a couple of lenses, for $US799.)

So the 808's 13-to-14-millimetre sensor isn't impressive by interchangeable-lens-camera standards, but it's pretty darn huge compared with compact cameras, and huger still by phone-cam standards. But it apparently has the same immense photosite density as the tiny sensors. So it really does have about 41 million photosites.

The 808 sensor is meant, however, to operate by "pixel binning" lots of adjacent photosites together, creating an image with a more sane resolution (apparently as little as three megapixels), but of higher quality than the same image from a tiny sensor with that same resolution.

Pixel binning is not a cheat like interpolating a low-res sensor's output up to a higher resolution. Done properly, binning really can make lots of super-small, noisy photosites into a lower number of bigger, less noisy ones.

I hope the 808 sensor actually does work better than it would if it were the same size but with bigger photosites in the first place. It seems a long darn way to go just to get a big megapixel number to impress the rubes, but stranger things have happened.

(The hyper-resolution also apparently lets the 808 use the much-maligned "digital zoom", a.k.a. just cropping out the middle of the image, without hurting image quality. Though, of course, the more you "zoom", the less pixel-binning the sensor can do. On the plus side, it's much easier to make a super-high-quality lens if it doesn't have to have any proper, "optical" zoom, and the minuscule lenses that phone-cams have to use need all the help they can get.)

The principal shortcoming of the small super-high-res sensors in phonecams and compact digicams is low-light performance. And "low light" can mean just "daytime with a heavy overcast", not even normal indoor night-time lighting.

The best solution to this problem is to avoid it in the first place by not being so damn crazy about megapixels, but that seems to be a commercial impossibility, largely thanks to my favourite people.

The next-best solution is to use a lens that lets in more light. But large-aperture lenses are much more expensive to make than small-aperture ones, and also tend to be unmanageably physically large for slimline-camera purposes. Oh, and the larger the aperture, the smaller the depth of field, which is bad news for snapshot cameras that often end up focussed on the end of a subject's nose.

Another low-light option is to use slow shutter speeds, but that'll make everything blurry unless your camera's on a tripod and the thing you're photographing is not moving.

Or you can wind up the sensitivity, and turn the photo into a noise-storm.

Or, if your subject is close enough, you can use the on-camera flash, which will iron everybody's face out flat.

(Approximately one person in the history of the world has managed to become a famous photographer by using direct flash all the time. Here's his often-NSFW photo-diary site. Half the world's photographers hate him.)

Some of the better compact digicams have a flash hotshoe on top. Bouncing the light from an add-on flash off the ceiling is a standard way to take good indoor photographs. A compact camera plus an add-on flash isn't really compact any more, though. It might be possible to work some kind of hinged flash into a phone-cam, but nobody's managed that yet.

My suspicions about the Nokia 808's low-light performance were increased by Nokia's three gigantic sample images (32Mb Zip archive)...

Nokia 808 sample image

Nokia 808 sample image

Nokia 808 sample image

...all of which look pretty fantastic, as demo pics always do.

If you look closely, the blue sky is noticeably noisy, shadow detail is a little bit noisy and a little bit watercolour-ed out by noise reduction, and at 100% magnification none of the demo shots are what you'd call razor sharp, especially around the edges of the image.

But the full-sized versions of these pictures are 33.6 and 38.4 megapixels. If you scale them down to the ten-to-twenty-megapixel resolution of a current DSLR, it'd be hard to tell the difference between the 808 shots and DSLR ones.

But not one of the demo pics was taken in low light.

Nokia have, however, just added several more demo images on the 808 press-pictures page here. The new images include some lower-light shots. In every case, the lower the light, the lower the image resolution, as a result of that pixel-binning trick. But those lower-res images look good.

Nokia 808 sample image

I'm not sure what the light source is for this one - possibly a floodlight pointing upwards at the climber - but it's 33.6 megapixels, and looks pretty good, except for some watercolour-y noise reduction on the far rock wall. Presumably the light source is pretty strong.

Nokia 808 sample image

This seems to be an actual night-time shot, possibly taken with the on-camera flash but suspiciously nicely lit for that. It's a mere 5.3 megapixels, but not very noisy at all.

Nokia 808 sample image

This dusk shot is the same resolution but with a 4:3-aspect-ratio crop, taking it to only five megapixels. Noise is noticeable, but not obnoxious.

Nokia 808 sample image

Nokia 808 sample image

These two shots are both overcast daylight and are the low five-ish-megapixel size too. Their noise isn't a big deal either.

Nokia 808 sample image

And then there's this sunset picture, which sticks to the lower-light-equals-lower-resolution rule; it's back up at 33.6 megapixels, because it's exposed for the sunset, with everything else in silhouette.

Time, and independent review sites, will tell whether these pictures are representative of what the 808 can do. But it looks good, and plausible, so far.

Which is unusual, because odd sensor designs that're alleged to have great advantages do not have a good reputation.

Fuji's Super CCD did close to nothing in the first generation, and has developed to give modest, but oversold, increases in resolution and dynamic range.

Sony's "RGB+E" filter design didn't seem to do much of anything, and was used in two cameras and then quietly retired.

Foveon's X3 sensor genuinely does give colour resolution considerably higher than that from conventional Bayer-pattern sensors.

But, one, the human eye's colour resolution is lower than its brightness resolution (a fact that pretty much all lossy image and video formats, both analogue and digital, rely on), so higher colour resolution is something of a solution looking for a problem.

And, two, Foveon and Sigma (the only maker of consumer cameras that use the Foveon sensor, if you don't count the Polaroid x530, which was mysteriously recalled) insist on pretending that three colours times X megapixels per colour makes an X-megapixel Foveon sensor as good as am X-times-three-megapixel ordinary sensor. That claim has now been failing to pass the giggle test for ten years.

The Nokia 808 sensor, on the other hand, may actually have something to it. We've only got the manufacturer's handout pictures to go by so far, and any sufficiently advanced technology is indistinguishable from a rigged demo. But this actually could be a way out of the miserable march of the megapixels, without which we actually probably would have had, by now, cheap compact cameras that're good in low light.

Or it could turn out to just be more marketing mumbo-jumbo.

But I really hope it isn't.

Posted in Photography. 8 Comments »

Pretty, but smelly

24 February 2012 — dan

A reader writes:

Why is "cloudy ammonia" cloudy?

I've used household ammonia for decades now, for cleaning windows and floors and so on, and never really questioned why it has that swirling cloudy look. But the other day I realised that this stuff is just a solution of ammonia (NH3) in water, and I don't think there's any reason why that shouldn't be clear, like a solution of many other simple chemicals in water.

Where do the clouds come from?

Jennifer

Some readers may be confused at this point, because different parts of the world have different kinds of supermarket ammonia-water. I think cloudy ammonia is the standard kind in the Commonwealth, with the non-cloudy version being normal in the USA, but don't quote me on that.

For those who haven't seen the cloudy kind...

Cloudy ammonia

...here some is. It's really quite pretty; you can see a similar pearlescent swirling effect in various shampoos that're trying to persuade you they're not just detergent.

Jennifer's right, though: There's no reason why ammonia in water should look like this. Bubble ammonia into water and you get a solution of ammonium hydroxide, which is clear.

The reason why cloudy ammonia is cloudy is simple enough: The manufacturers put soap in it. I've also read that there can be some oil or other instead of, or in addition to, the soap. In any case, the additive makes the substance look interesting, and may also make it a better cleaner. Probably not a better window cleaner, though, since straight ammonia-plus-water will evaporate to nothing and not leave marks, while ammonia-plus-water-plus-soap can leave streaks.

The ammonia in the above picture had been sitting undisturbed for some time, so it wasn't actually very cloudy at first...

Bottom of ammonia bottle

...because a lot of its "clouds" had settled out. I took this photo first, then shook the bottle up and took the other one.

While we're on this pungent subject, I have recently accidentally created an ammonia-water generator.

We have, you see, four indoor cats. They use cat litter fast enough to make "flushable" litter a pretty quick ticket to a drain blockage, if you're dumb enough to actually flush it, which, at one point, I was.

Now, next to the phalanx of litter trays, there's a flip-top rubbish bin that I shovel the nasty stuff into for later, non-plumbing disposal.

Urine, left to sit, generates ammonia from the breakdown of urea.

(If your surname is "Fuller", then someone in your ancestry was probably rather familiar with this phenomenon.)

All that ammoniacal goodness is contained very effectively by the bin's fitted lid. It only comes out to say hello to my sinuses when I've got the bin open. It's less gross than you'd think, too; it doesn't really smell like wee and poo at all, because the wall of harsh ammonia-smell covers everything else.

When the litter stays there a bit longer than usual, it warms up a bit from its own slow decomposition. When the ambient temperature was about 20°C, I measured the temperature in the middle of the litter at around 26°C.

When this has happened and I open the bin, the ammonia-smell is really strong, and the underside of the lid is covered with droplets of quite clear, clean-looking liquid. Which is ammonium hydroxide; a solution of ammonia in water. It's probably got a high enough pH to be pretty much sterile, too; if I were more dedicated to perversity, I could bottle it and use it as a cleaner.

Oh, and while we're on the subject of well-aged urine, if you're unhinged enough to boil down aged urine, you can isolate phosphorus.

Or possibly not.

Psycho Science is a regular feature here. Ask me your science questions, and I'll answer them. Probably.

And then commenters will, I hope, correct at least the most obvious flaws in my answer.

Posted in Psycho Science, Science. 7 Comments »

Entrée: Two ice cubes. Main Course: Oxygen.

22 February 2012 — dan

A reader writes:

Is there such a thing as food with less than no calories?

You're supposed to be able to eat lettuce or celery or something, and the energy your body uses to digest it is more than you get out of it.

(Well, I don't really know if you're "supposed" to be able to or not, but I've certainly heard people say this.)

What about eating ice? Obviously you get no nutrition at all from that, but I've never seen a Get Thin By Eating Snow diet book, so I figure it's not practical.

Nat

There are foodstuffs that have very little "food energy". They're pretty much what you'd expect, and do include a lot of green vegetables.

But digestion is good at sucking energy out of food. Your body does better than break even, even when you're eating celery. It's not easy to gain weight eating nothing but undressed salads and vitamin supplements, but it's possible.

The eating-ice thing, in contrast, sounds like a great idea. But only if you make a particular mistake, having to do with the term "calorie".

There are 540 calories in a Big Mac. But the enthalpy of fusion of water is about 80 calories per gram. And then you need another calorie to heat one gram of water by 1°C; if your ice starts out a few degrees below zero and ends up at body temperature, that adds up. And the only place this energy can come from is your body's own reserves.

So you can more than offset the entire nutritional value of your hamburger by crunching up one lousy ice cube! Right?

Sorry, no. Because the "physics" calorie, the one being used on the melting-ice side of the equation, is one thousandth of the "dietary" calorie, on the food side of the equation.

(This is noticeable when the dietary calorie is clearly indicated, as "kcal", for instance. The modern metric alternative to the two kinds of calorie is the joule and kilojoule; fortunately, there's no colloquial tendency to call both of these units "joules".)

A hundred grams of celery is about 14 kcal. To offset only that much energy value, you'd need to eat more than a hundred grams of ice. A whole tray of ice cubes would probably do it; the ice-cube trays in my fridge hold about 160 grams.

So as few as 35 trays of ice cubes might compensate for a Big Mac!

Presuming, of course, that you actually can Freeze Yourself Thin at all.

The human body runs warm as a matter of course. If the ambient temperature is below body temperature, which it is for most humans most of the time, then the body's leaking heat all the time anyway, and eating cold stuff may change where the heat goes, more than it changes how much heat is lost.

This page at livestrong.com gives a ballpark figure of only one dietary calorie burned per ounce of ice eaten. 80 small calories of enthalpy of fusion per gram of ice, plus 40 small calories of heat to take the water from a bit below freezing to body temperature, times about 28 grams to the ounce, gives 3360 small calories or 3.36 dietary ones of raw heating power. If that only adds up to one extra dietary calorie burned, the tooth wear and ice-cream headaches don't seem like much of a trade-off. Especially since you don't actually get any ice-cream.

(If you really apply yourself to slimming via low temperatures, I would not put it past your body to decide that all this shivering indicates you're now living in a cold climate, so more incoming food should be directed towards creating a nice insulating layer of fat.)

Your natural basal metabolic rate is probably closer to 2000 kcal per day than it is to 1000. Adding a couple of dozen kilocalories to that by ice-eating may actually hurt more than doing an energy-equivalent amount of exercise.

(Exercise is not really a great way of burning calories. Run ten kilometres, burn 700 kcal. As a general rule, if you're not some sort of athlete or heavy manual labourer, exercise will make you fitter and stronger, but not thinner.)

Needless to say, Wikipedia has a page about negative-calorie food. And a funnier one about the "Negative Calorie Illusion".

Psycho Science is a regular feature here. Ask me your science questions, and I'll answer them. Probably.

And then commenters will, I hope, correct at least the most obvious flaws in my answer.

Posted in Psycho Science, Science. 11 Comments »

Fire from, or at least near, ice

20 February 2012 — dan

A reader writes:

Got a science question of sorts.

WTF is actually going on here?

Chris

The ice cube is not glowing. The induction coil is.

Induction heaters are interesting things. You make a coil out of a sturdy conductor - usually copper bar stock - and you put a whole lot of current through it at, usually, a pretty high AC frequency. The alternating current then induces current in any conductive object you put inside the coil, and the resistance of the object turns the current into heat, which heats the object. It's the same principle that heats up a wire, or an actual heating element, when you put current through it. The source of the current in an induction heater is just less obvious, and the electricity in the heated object isn't going round and round in a circuit; it's just jiggling eddy currents.

(Magnetic braking relies on induced eddy currents as well, and also heats up the object the eddy currents are being induced in.)

The induction coil was actually the first, and worst, kind of transformer. It was the worst because the purpose of a transformer is to turn one voltage of AC into another (or keep the same voltage but isolate two circuits). The more energy a transformer wastes as heat, the less useful it is. Modern transformers have laminated cores made from "electrical steel", specifically to minimise unproductive transformer-heating eddy currents.

A powerful enough induction heater can do all sorts of neat tricks, like heat-treating part of a piece of metal - all the way to glowing hot - so fast that the heat won't have managed to conduct through the metal to other parts of the object before the bit you're heating gets to the right temperature and can be quenched. You can also use an induction heater to melt metal in a crucible without a flame.

Or even to levitate a light enough metal, while it melts!

Induction cooktops work this way too. That's why they'll heat a metal pot, but not glass cookware. If it's conductive, they heat it; if it isn't, they don't.

[UPDATE: As commenters have pointed out, only ferromagnetic cookware actually works on an induction cooktop. I'll fix this properly when I have a moment.]

Ice is very slightly conductive (as I have proved to my own satisfaction), but can generally be considered an insulator, and won't be significantly warmed by an induction heater. So the induction coil in the ice-cube video is essentially being run "empty", and just rapidly heating itself up, and in due course glowing, in a simple resistive way. That ice cube will actually melt pretty quickly, because of radiant heat and air convection from the coil. But it'll last as long as you'd expect it to if it were sitting next to a similarly glowing plain resistive heating element.

(The glow probably isn't really as impressive as it looks, either, because digital cameras of all sorts are sensitive to infrared light. Most digital image sensors have an IR-blocking filter on them to minimise this effect, but the filters aren't completely effective, and so very hot things like this coil or the aftermath of certain pyrotechnic entertainments look hotter than they are. The human eye may see some glowing metal as orange, but most digital cameras will think it's white.)

Psycho Science is a regular feature here. Ask me your science questions, and I'll answer them. Probably.

And then commenters will, I hope, correct at least the most obvious flaws in my answer.

Posted in Electricity, Psycho Science, Science. 8 Comments »
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