More Safety

come on baby and rescue me ... - The Supremes
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Caliber 4 rockets, red flares and orange smoke. And a “rescue me”.

It feels awkward to spend more than 500€ on stuff you’ll probably (and hopefully) never use. After some thinking I did bite the bullet. The old flares and rockets were more than ten years past their due date. Since I (officially) have no radio and electrickery likes to fail just when you need it most, some pyrotechniques might come in handy.

The little yellow/grey fellow is a fine example of modern electronics. Mostly sailing alone, going overboard is considered a death sentence. Your boat probably is on auto pilot and will go on until the battery is dead, the wind changes significantly or it hits something. So there you are, alone in the ocean. Many single-handers used to not wear life vests so it would be over fast if they go overboard. But nowadays you just call a cab. The little fella has batteries which last until 2025, a gps receiver to calculate your position and a satphone (or modem) to text your position to a maritime rescue coordination centre (MRCC). Since registration in germany is kind of complicated and the device must be bound to a ship (even though it’s a personal locator beacon (PLB)) I registered it in the UK. So in case I go overboard in germany, I press a button, the little thingy texts my position to falmouth, cornwall mrcc and then somebody rings up the folks at bremen mrcc who then ring up the nearest SAR unit and/or coordinates the search with other vessels in the area. Amazing!

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Tied to the innards of my life vest/floatation device

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… and its gone 🙂

more knowledge on bass / speakers

Friends pointed out to me that they don’t understand my writings about building/optimizing speakers and don’t even know what to google for. Sorry, guys, I was just writing down what I was doing and not thinking about that.

The Variables (Fs, fb, ….) are so called Thiele-Small Parameters, named after two aussie guys doing research on the matter. Wikipedia provides links to sites explaining the stuff in both german and english.

Don’t let the math scare you away, you don’t need it. To build a woofer you just have to look up these values and put them in some online calculator which is spewing out build dimensions. Just make sure to get a second opinion on the results, be it through research, online forums or just asking folks…

more bass #3

“Yeah Science, Bitch”  -- Jesse Pinkman

I did some research. The concept of tuning a vented box very low is called EBS (Extended Bass Shelf). This site explains it pretty good, the basic idea is getting more bass on low frequencies. You basically take an enclosure 160-180% the size of a “maximum flat” setup and then tune it close to Fs (Free Air Resonance of the speaker). As I already found out the previous owner did tune the enclosure to about that frequency. But how about enclosure size? The manual suggests “maximum flat” enclosures from 64 to 92 litres, suggesting an EBS setup between 102 and 165 litres. The enclosure has around 80 litres not accounting for the speaker and the vents. Well, I guess I found a problem here.

I tried some more online calculators and plenty of them tune close to Fs without even mentioning it. So it’s more than understandable to end up with this setup. But as always, you gotta trust your senses: If it sounds shitty there has to be a reason… Ah, and trust the engineers. If you deviate far from their suggested path you better know what you are doing…

So to wrap this up and continue other important work I’ll go the humble approach. I’ll measure the actual resonance frequency of the enclosure and tune it to something between 36-39Hz for the suggested “maximum flat” response.

Measuring shouldn’t be to difficult, the impedance of the speaker drops at the resonance frequency, so the current spikes ( I = U/R ). So just rig an ampere meter to the speaker, a frequency generator to the amplifier and play with the frequency knob until you reach maximum current. Well, my ampere meter doesn’t like low frequencies at all making it impossible to get a reading. Using a shunt (resistor in series) and measuring voltage I pinpointed the resonance frequency at 35,7Hz. That’s way lower than the expected 43Hz. Good news: That’s the lower end of my target frequency. Bad news: I’ve got to redo the math…

Some site suggests if the distance of the ports to any wall is less than their diameter the tuning gets lower. That’s definitely the case here…  The increase of Volume by damping depends strongly on the material, ranging from 0-20%. If I run the numbers with an estimated volume of 115 litres everything checks out and the estimated resonance frequency with the long vents would be around 24Hz. I guess I have to measure that as well 🙁 Hmmm, 27Hz, not too bad for an estimate…

Hmm, maybe I should give the 31Hz a shot. 18,5 cm for the vents… Let’s say 20 for good measure… After some try and error 21cm turn out to lead to 30.something Hz. Good enough. Yeah, there is more ooompfff on low frequencies, you don’t hear some but feel it in your guts. I had to adjust the woofer level back to +6db on the amp. But it seems to be a trade-off with quality. Most of the time there’s not enough bass and then suddenly it’s killing you when the frequency drops low enough. For example with “Clint Eastwood / Gorilaz”, some low rumbling for the whole song and then the break with a couple of low beats is just plain awful. Somebody suggested that EBS setups often have cancellation issues on the two octaves above the resonance frequency (so 30-120Hz). Yeah, that might be the issue here.

To cut a long story short: EBS doesn’t work out with this enclosure, even if you do it right. I guess that’s 2:0 for the engineers… Disclaimer: I’m working low volume settings (neighbours…) and the placement of the sub is bad. Maybe it’s getting better with optimal placement and if you crank up the amplifier. Maybe not. At least now the sound setup at my desk is ok. Time to actually do some work…

more bass #2

The new subwoofer has bass, I’ll give it that. But sounds like a trumpeting elephant somehow. Well, it’s probably not the speaker itself. The broken crossover / connection panel is already removed. Hmm, let’s have a look at the mods of the previous owner.

He reduced the volume by adding an enclosure for the connection panel, added some foam isolation and adjusted the length of the vents. Alright, the enclosure lowers the volume (obviously), the insulation increases the (virtual) volume of the enclosure (not so obvious). Measuring inside the box is difficult, I’d estimate the volume about 70 litres so with the insulation it’s probably somewhere between 70 and 80 litres. The original vents have 75mm diameter and are 120mm long. The previous owner extended them to 350mm / 360mm using pipes from the hardware store and claims to have calculated everything with some software.

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The vents should be the same length. They are extremely close to the rear wall of the box but I couldn’t find proof that this is an issue. Let’s start with the obvious: Some designer made this enclosure and even if it’s a cheapo they probably put some thought in it. The vents adjust the resonance frequency of the box. Changing them by a factor of three means either the engineer who build it was way off or the one doing the modification. I used an online calculator to run the numbers. With the extensions the resonance frequency (fb) of the enclosure is around 29Hz, without approx. 43Hz. The manual of the speaker comes with 12 suggested enclosure dimensions ranging from 36 to 50Hz fb. The interwebs suggest it makes some sense to go for a “bass shelf” by tuning fb to Fs (30,83Hz) or even lower. One formula I found suggests 31Hz being ideal for this setup.

The manufacturer of the speaker and the manufacturer of the enclosure obviously don’t think so. I removed the extensions and the setup is quite close to the “Standard Tight Bass” box design of the speaker manufacturer. Afterwards I had to reduce the amp setting from +7 to +3 (probably db) and it sounds pretty tight.

I guess I’ll rig up a setup to actually measure the resonance frequency to check my estimates and tune the box to “optimal sound quality / flat response”.

Adventures on ebay / more bass

My Desktop Stereo isn’t quite performing as I want it to. The JBL Control One are awesome but have no bass. Bi Amping with a leftover subwoofer from my station wagon didn’t really do the trick, a 25cm speaker is ok for a confined space like a car but sucks in bigger rooms as for example my office. Ebay provided some auctions with interesting items and I got lucky: A Hifonics OLM 1615 38cm Monster with a vamped up enclosure of a much cheaper omnitronics speaker.

0,33L beer bottle for size comparison..

0,33L beer bottle for size comparison..

DIY at it’s best, so it went cheap. 76€ for something that’s worth a couple of hundreds is more than alright. Then something weird happened:

Seller: I would like to cancel the deal because I dropped the speaker and there’s some rattling noise inside / something broke even though there’s no visual damage. I’m willing to pay some compensation for your troubles.

Me: Well, I can totally understand if you’re not satisfied with the price but it’s not my problem if you don’t keep track of your auctions. These speakers are designed to take quite a beating so it seems highly unlikely you broke it by dropping it. Are you really sure it’s broken?

Seller: Yeah, it’s broken. I’d send you 50€ if you cancel the transaction.

Me: Maybe I can repair the speaker. How about we take the 50€ off the price, so I pay you 26€. If I can’t fix it I still got the enclosure and you got rid of the broken speaker…

Seller: No thanks, I’d rather bring it to my dealership to get it fixed and then sell it on ebay again.

Me (to myself): Gotcha!

Me (to seller): Sorry to say but you raised my suspicions. By german law we have got a contract so you dropped my speaker and not yours. You owe me compensation for the difference between the 70€ and the normal street value of the item. In addition I’ll contact ebay’s customer support and they’ll probably ban you.

Seller: Alright, I’ll get the speaker fixed and then send it to you but it will take some time.

Seller (next day): It’s fixed, a large paperclip somehow got stuck inside. It’s on it’s way.

So yeah, there are quite some dickheads on ebay. The speaker arrived in the meantime, it’s got some minor scratches and the crossover is fried. The capacitor blew and the circuit board got cracks. Luckily I’m using active crossovers anyway, so I realized that while removing it. So I already fixed one problem. The sound is still not where I want it but the vents of the enclosure are loose and possibly to close to the back of the enclosure. I guess I’ll do the math on it as well, just in case the previous owner fucked it up.

 

Being Sick / Linux Audio Stuff

"He is dead, Jim" -- Leonard McCoy

(posted a week or so after writing…)

I thought this might have been the first winter (ever?) without getting sick. Didn’t work out 🙁 Whatever… After even netflix became boring I had to something else.

My stereo hasn’t been the same since I moved home. Today I finally looked into the issue. Some peak performance testing before moving to Hannover fried one tweeter completely and hurt the other one badly. The automatic eq / analyzer of the amp covered this failure up somehow (being a four way system the mid speaker range is overlapping with the tweeters). Since I use the amp mostly for surround sound, the other speakers helped covering it up as well. But after I bought some JBL Control One for my Desk it became quite obvious that some frequencies are missing. I still had some tweeters from the stereo of the 190 series ( a car…) catching dust so I went for a quick fix. It turned out they are too noisy but I got them more or less under control thanks to the equalizer.

Linux provides some great tools for audio testing and they are for free. So I cobbled together an audio analyzer using the mic which came with the amplifier for setting up surround sound. The following are all frequency diagrams, x-axis is frequency, y-axis is output volume. The actual numbers don’t matter, what we are looking for is a more or less straight line indicating that the pink noise is reproduced by the speakers “as is”.

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From left to right: original tweeter, audio system, gradient

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The Speaker with the completely fried tweeter. Note the drop!

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Quick fix: The audio system tweeters are a little bit small for the Infinity Reference 61 Mk II Chassis

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Audio System tweeters removed from the old Merc. Not too bad at all but a little bit too much. Probably because they are build for a two way system there’s too much overlap on a four way.

 

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Fancy Gradient Tweeters from ebay, used. I don’t like the peak around 8k.

Up to now the audio system + duct tape did a superior performance than fancy (and well fitting) Gradient Tweeters. Since both speakers have different volume levels on high frequencies (which you can’t see on the diagrams) there’s still something wrong. More investigation has to be done I guess. To be continued…

Counterintelligence TV Streaming

Alright, streaming TV Series legally in Germany sucks for different reasons: You have to wait ages and they are mostly dubbed. I already tried watchever.de who thankfully got the orginal voice available on most programs but it still sucked. Maxdome.de failed me as well. So where to go next? Some friend suggested netflix (from the US) which apparently is not available in Germany. Hmm, I guess I read about it on the interwebs. Some research turned out netflix produces about 30% of the internet traffic in the united states, that’s No. 1 for sure and about three times youtube. Sometimes I really believe we’re living under a rock over here… I think my research into TV Streaming should include the leading product I’ve barely heard of. Also the US offers other great sites with “geoprotection” as hulu.com, cbs.com, … and last but not least the annoying “this content is not suitable for your country” stuff on youtube is unknown over there as well.

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Wherever Psy got his clicks from, it’s not Germany. Video unavailable because the GEMA (german copyright annoyance) has not granted (as in sold) the suitable rights to youtube (rough translation).

Gathering a Greencard and moving over to the States seems a little bit over the top for just watching some telly. But what does it actually need to be “inside” the USA? I mean, we are speaking about the interwebs where national borders are blurry at best. So a US-based Server with a reasonably fast Internet Connection which is acting like some kind of proxy seems sufficient. There are services like hidemyass.com who offer this for about 7-12USD / month depending on the length of your subscription. A root server costs in the US is about five USD / month payable by credit card. Hmm. Netflix also accepts my (german) credit card. Hmmmmm. All available sources suggest that this is legal as well. Hmmmmmmmm!

One thing which is bothering me as well as others is the fact that the US is spying & recording data on everybody. Being german that reminds me constantly of the STASI (eastern German intelligence) and of course of the Nazis. Not so much about spying but about having data and using it. Say what? Well, to pull off the holocaust they needed to identify Jews. So the Gestapo (Nazi intelligence) started to pull all data already available in different registers which turned out to be quite extensive on stuff which must not bother a government like religion for example. To cut a long story short: I don’t like governments to have more data as they need to fulfil their job. So the NSA kind of pisses me off. The options from here are quite limited, all I can do is to encrypt my communication. And if I do that the NSA stores any traffic they encounter indefinitely (if you don’t believe it check out Jacob Appelbaum’s talk on 30C3 and/or the documents thankfully provided by E.Snowden.). Well. If that’s not an opportunity to kill two birds with one stone: Watching HD Television though an encrypted VPN while spamming NSA Harddrives at 3GB/hour.

I wonder if this activity would trigger Quantum-whatever attacks on my networks. Hmmm. Memo to self: install suitable honeypot. I’m a security researcher after all and there may be a third bird being interested in some stones…

Ah, and dear NSA: If you happen to cut me off from US television somehow I might get tempted to get two servers with unlimited traffic and do some research on VPN performance and possible usage caps for servers with “unlimited” traffic. 🙂

(most likely reaction of the NSA I can imagine) Dear Andi: The NSA datacenter at Bluffdale (one of our approx. 40 centers in the states) is believed to have a capacity somewhere in the range of exabytes up to single digit zettabytes (it’s so secret we don’t know for ourselves). Even if you produce 1TB of traffic per day it would take between 1 Million days to 1 Billion days to fill up the harddrives. Or in other words: With just ordinary TV consumption (say 100GB/month) it’ll be at least 10 Million months to fill our storage (if traffic scales as well as HDD Space). So as long as there are not millions of people using VPN we don’t really care…

Hmm, netflix alone has about 40 Million subscribers, 10 Million of which are not stateside. Please folks, encrypt your traffic. Just for a couple of months…

Adventure XBOX 360

Already owning a kinect for hacking purposes and wanting to play GTAV let me to the adventure of getting a XBOX 360. Buying it in sweden, registering it online in the UK and finally moving it to germany is not exactly a common case. After an account migration (which disturbingly is a “new” feature) to germany my xbox menu was a funny mixture between english and german, language- as contentwise. The only real problem was that it advertised only british apps (yeah, bbc and netflix) which wouldn’t work due to my german IP. And I couldn’t install any german apps due to the marketplace still thinking I’m in the UK. In short: Almost all Apps rendered useless and I was unable to use my watchever account.

Even magic support codes like “clean the cache for three times” and uninstall updates by pressing “LB RB X LB RB X” while highlighting the harddisk did nothing but making me remember some windows vodoo from back in the days and streetfighter special moves…

After an hour with the microsoft support chat they delegated my problem to the technical support because something with my account migration went wrong. Quite an educated guess, actually that was my best guess BEFORE I contacted the support. The adventure continues in approximatly three business days…

I hate you, smartphone! Recap…

I decided to get rid of smartphones. I bought a cheap phone (Nokia 100) and a Tablet (Asus Transformer) instead and thought I would carry the Tablet if I need Internet and stick to the phone otherwise. Then a good friend needed a phone fast so I traded the N100 for pizza and some beer (yeah, it really is THAT cheap).

Yesterday the screen of my HTC Desire cracked. Again. While driving my car. I put it under the armrest in the middle between the seats and when I arrived it was lying in front of the back seat with the screen cracked… Maybe it was my unusual reckless driving, I tried to figure out the top speed of the pornstyler. This was a failure as well, too much traffic and too many idiots on the autobahn. At least it runs 190km/h (GPS measured) and it was still accelerating. And the breaks are fine as well…

Anyways, a realized that a 10″ tablet with a keyboard is not just looking like a subnotebook, it in fact is one. So I don’t just carry it in my jacket… I wanted to get a replacement for the HTC fast so I did two things which I normally don’t: I synched my whole phone with google and I went to “media markt” to buy a (Google/LG) Nexus 4 Tablet Smartphone.

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The HTC Desire is not a small phone but it looks just silly beside the Nexus

While synching the phone was quite unspectacular besides the bad feeling giving my data to google the shop visit was. The price at the “media markt” online shop was 349€ if you pick it up in one of their stores. Since I didn’t want to give my personal data to “media markt” as well I just went to the shop. 395€ for the phone. Well… I asked an employee if I really had to order online to get a normal price. He was quite helpful, had a look at the website, adjusted the price in his software and that’s it. So if you just walk in and buy the thing they just rip you off big time. Interesting. I thought about buying some HDMI Adaptors (20€ each) and some Crimp Connectors for the car stereo (6€ each). But since these items are sold on the internet for maybe 2€ / 10 Cent I changed my mind quickly. So Dear Idiots: Please stop buying overpriced crap at “media markt”! Just imagine a world free of ridiculous “media markt” stores and silly “media markt” advertising… You can do it! Well, alright. You probably can’t because you’re stupid… My bad…