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electrical info herein often wrong


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sparkinark 
Member - Posts: 1
Member spacespace
Joined: July 11, 2009
Location: Arkansas, United States
Posted: July 11, 2009 at 7:46 AM / IP Logged  

First let me say this is a very, very helpful site in almost every respect and is why I almost cannot live without Internet access anymore. 

My comments are from an EE with many years of experience in almost all areas of electrical engineering, and I've worked in areas from far-infrared FLIR systems for the HARM missile and on the synthetic aperture radar system on the (F22?  This was back in 1992 so the fact that the jet is still not in full production is rather amazing to me) to antenna design, home audio design including crossovers and power amps, home-wiring problems (the very low chip voltages and high heat of the new SMT boards is killing everything due to inadequate circuit layouts and shared neutrals).

Anyway, not a condemnation, but when I saw you mention 3rd order crossovers I knew something was wrong.  There is a huge compendium of IEEE papers from the '20s to near present day and 3rd order crossovers have pretty much been laid to rest and nails put in the coffin.

Also, wattage does not determine minimum wire size, nor does current actually;  one has to look as well at the heat factors of the insulation as well as what type of load is being draw (e.g. cranking your car is not the same as running a 10000 watt kill-your-ears stereo system.  Also, a zoebel is used mainly for two reasons:  one is to change the (seen) imput impedance and dampen an otherwise unstable system (I run into this when very good and highly inductive or capacative wiring is used with amps that have ratings like 100 watts [into a dummy 8 ohm non-reactive load) while the rating at 6 ohm loads, usually not mentioned, is like 120 watts).  In other words, they are probably more like 20 watt nominal into a reactive load and are designked to just play loud with a very low slew rate.

The other use, a home-cookbook fix, is to allay the inherent Z rise of a midrange speaker or (sometimes) a tweeter or to try to knock down from infinity the resonant point when it's within the working parameters of the system.

Be careful what  you say if you have to over-simplify it:  EMF is *NOT* in any instance a simple application of Ohms law.  It's a phenomenom, like heat or gravity, and is part of the energy-matter spectrum.

As Thomas Hobbes once said:  When you marry an ideal, reality moves in as the harshest of relatives.  I'm constantly surprised myself by how, say, a simple corner-loaded waveguide resonator can make a usb wifi "n" dongle outperform a 10 element yagi.

sparkinark / ShawnHarveyt

sparkinark / Shawn Harvey -- EE
KarTuneMan 
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Platinum spaceThis member has made a donation to the12volt.com. Click here for more info.spaceThis member consistently provides reliable informationspace
Joined: December 14, 2004
Location: Isle Of Man
Posted: July 14, 2009 at 9:41 PM / IP Logged  
Sometimes when I read things..... I don't feel so smart..... THIS is one of those times!electrical info herein often wrong -- posted image.
i am an idiot 
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Platinum spaceThis member consistently provides reliable informationspace
Joined: September 21, 2006
Location: Louisiana, United States
Posted: July 14, 2009 at 10:09 PM / IP Logged  
t&t tech 
Platinum - Posts: 2,608
Platinum spacespace
Joined: October 05, 2008
Location: Trinidad and Tobago
Posted: July 18, 2009 at 5:38 PM / IP Logged  

KarTuneMan wrote:
Sometimes when I read things..... I don't feel so smart..... THIS is one of those times!electrical info herein often wrong -- posted image.

if you can feel that way mr KTM, imagine how i must have felt,lol, electrical info herein often wrong -- posted image.

commit your way to jehovah and he will act in your behalf. psalms 37:5
KPierson 
Platinum - Posts: 3,527
Platinum spaceThis member consistently provides reliable informationspace
Joined: April 14, 2005
Location: Ohio, United States
Posted: July 18, 2009 at 8:28 PM / IP Logged  

Considering cross over design of any magnitude is extremly limited on this site I would say your title is wrong.

Most of the electrical info on this site IS ACCURATE.  There may be some misleading information here and there, but for the most part, the12volt is an extremely reliable source for 12vdc electrical info.

Kevin Pierson
howie ll 
Pot Metal - Posts: 16,466
Pot Metal spacespace
Joined: January 09, 2007
Location: United Kingdom
Posted: July 19, 2009 at 1:00 PM / IP Logged  
Oh how glad am I I so rarely do audio these days, all I remember is that speaker impedance can change. I might also add that I thought the title misleading. I'm used to working on vehicles this side of the pond with info from the US, it's amazing how many differences there are, so like most good people here, I believe nothing I'm told and check everything. That's what I thought our poster was refering to.
tommy... 
Gold - Posts: 1,901
Gold spacespace
Joined: December 10, 2004
Location: United States
Posted: July 19, 2009 at 6:27 PM / IP Logged  
Ive never been so confused...Title and contents...?? Anyway as Little John said...WWWWHHHHHAAAATTTTTTT....
M.E.C.P & First-Class
Go slow and drink lots of water...Procrastinators' Unite...Tomorrow!
tommy... 
Gold - Posts: 1,901
Gold spacespace
Joined: December 10, 2004
Location: United States
Posted: July 19, 2009 at 6:30 PM / IP Logged  
Maybe add some links to wrong info...To help out the next EE...?
M.E.C.P & First-Class
Go slow and drink lots of water...Procrastinators' Unite...Tomorrow!
lspker 
Silver - Posts: 503
Silver spacespace
Joined: November 23, 2003
Location: Canada
Posted: July 19, 2009 at 8:58 PM / IP Logged  
Euro fighter flying, F22 electrical nightmare.  Mig built like tractor works great.  May be overengeering not so good.   Some info presented here is based on "accepted" standards (short cuts) that work.  Not very thing needs to be calculated to fifty decimal places to work and go over buget.
howie ll 
Pot Metal - Posts: 16,466
Pot Metal spacespace
Joined: January 09, 2007
Location: United Kingdom
Posted: July 20, 2009 at 2:59 AM / IP Logged  
Ispkr you are so right.  Frankly for most audio work,  basic wiring knowledge, ohms law, inductive interferance, are all you basically need. Sorry,  not to question certain people here who I admire for their specialised knowledge which I always find most interesting. There is a recession on right now and in my neck of the woods, super quality aftermarket work has long vanished, it's the £100 + labour amp, sub and box market. Re the F22 reference, nowt wrong, its kill ratio is the right circumstances is probably 300 Su 30 to one. It's the bloody software, too complicated, US won't release it, special ref to F35, UK is joint 1st. tier builder, Israelis won't take it with US hardware or software, they'd rather develop their own and this is what's happenning with cars, change a lightbulb on the latest Mercedes?  Yeah right
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