[leeperry]

I guess this guy didn't get the memo: http://thereifixedit.com/2010/05/17/epic-kludge-photo-working-lunch-doin039-it-right/

 

[Don Quichotte]

 
Quote:

Yup, there's more than one reason I sold my Stax...

To be honest, this is something I don't quite understand. Let me quote a bit from here:
 
Quote:

Electric fields are created by differences in voltage: the higher the voltage, the stronger will be the resultant field. Magnetic fields are created when electric current flows: the greater the current, the stronger the magnetic field. An electric field will exist even when there is no current flowing. If current does flow, the strength of the magnetic field will vary with power consumption but the electric field strength will be constant.

So power consumption of the headphones would be a good indicator, which led me to some calculation.
 
Now, in electrostatic phones the DC (bias) voltage is high, resulting in a comparatively strong electric field, but that is static so I kinda doubt it could produce any notable harmful effects. The AC voltage at 100dB is 100V with a peak headphones impedance of 133 kohms at 10 kHz for my Stax SR-303 (I don't know the impedance at lower frequencies, but let's assume it's 10 times lower, so 13.3 kohms). I know that the rated impedance at 10 kHz is the peak impedance from Stax themselves. The approximate current would be 100V / 13,300 ohms, so about 7.5mA, while the power would be 0.75W. Now, at a 75dB average listening level this would translate into ~ 2mW power consumption of the headphone.
 
The above calculation is an approximation mainly because of the assumed 13.3 kohms average impedance and I have no background in electronics, so please feel free to correct me.  An an indirect confirmation: my Stax SRM-313 amp is class A and gets warm to the touch, so most of its 29W power consumption translates into heat and only a small part becomes music (at maximum volume, that is 350VAC rms). My usual listening level is midway between 9 and 10 o'clock on the volume knob, so much less power is carried by the musical signal.
 
Now here is what I don't understand. It makes sense to me that the magnetic field (and the current) should actually be lower on the electrostatics than on the dynamics because of their greater efficiency - that is, SPL for a given power consumption (by the headphone). A good part of the electric energy that arrives at a dynamic driver becomes heat that is dissipated by the coil and only some of it is translated into sound, while the heat losses of an electrostatic are much lower, I guess. However, my AKG K501's rated sensitivity is 94 dB / mW, or ~ 4mW at 100 dB which is much much lower power that the Stax 303 phones' above calculated 750mW at 100dB (even if the average impedance of the Stax phones is 100kohms, the resulting 100mW would still be much higher that the AKG's 4mW for a 100dB output). Basically, the Stax' power consumption appears to be in the same ballpark as the K1000s', and this definitely seems wrong.
 
Something's fishy. What am I missing?

 

[haloxt]

Electrostatic headphones have the possibility of outputting huge amounts of electromagnetic radiation due to being high voltage. I have an ionizer air purifier that shoots emf many feet away lol. Guessing won't work because there's many variables, distance to head generally being the first to consider. If you want to know the actual number, the only way is to get some AC field meter, or one that measures AC and DC separately.

 

[udauda]

Some time ago I transferred some of Richter Di's interviews to Hydrogenaudio.org to discuss this matter:
http://www.hydrogenaudio.org/forums/index.php?showtopic=73327
 
Well we figured Dr.Königs, the founder of Ultrasone, is definitely a man of self-cross-referencing when it comes down to EMF issues on headphones. It could simply be due to the lack of the amount of studies in the field, or maybe he's truly BSing the whole thing..

 

[haloxt]

Or maybe he just likes to reference himself.

 

[momomo6789]

so i read this so i went and found my meter it is reads .6 for ultrasone pro900s and 3 for stax o2 100 + for cellphone ^_^

 

[haloxt]

milliGauss right? Very cool the stax has such low emission, the mean average for all headphones is ~10mG.

 

[Don Quichotte]

Well, I suppose my post was too long. Let me summarize:
1. there's high bias (DC) voltage in electrostatics, but I think that generates only a steady electrical field, without the magnetic component, unless I misunderstood the concept of bias voltage in electrostatics, as (I think) there's no current flowing at those 580V. Sorry if I'm saying something stupid

. It is my understanding that a steady field is much less of a problem compared to a variable field and that the higher the frequency of the latter, the greater the risks involved. Am I totally off here?
2. there's a certain amount of current running through the AC (signal) circuitry, resulting in both the electrical and the magnetic components of the field, but neither the voltage (say 10 V as order of magnitude) nor the current are so great after all. What puzzles me is the unlikely conclusion I get from my calculation - underlined in my previous post.
 
You may be right and electrostatics might output lots of emf, but I can only rely on these numbers as I cannot afford paying a few hundred dollars on a measuring device, at the moment and in the foreseeable future at least.

 

[haloxt]

Emf produced by drivers is wasted energy and hard to predict, it depends on the driver. momomo6789 measured one stax, and it's not anywhere close to the 20mG+ put out by many household appliances.

 

[momomo6789]

re-1 = 35mg at the front plate
 
ipod + protector = 2.2mg
 
the wall sockets in my house are all 1-2 mg
 
lcd screen 4mg
 
digital camara 1mg
 
router 2mg ?
 
this is fun
 
wish i had amp to test other headphones

 

[leeperry]

yes, but if you check what Beyer told me we're only interested on the EMF at the ear! and all serious "systems"(as Beyer call them) carry a big metal grill between the driver and your ear.
 
OTOH, chinese "Superlux" cheapos don't: http://i157.photobucket.com/albums/t69/pinkfloyd2007_bucket/DSCF1469.jpg
 
but Sony/Denon, they all do:
 
http://s953.photobucket.com/albums/ae15/Wilashort/Headphones%20y%20Mods/Headphone%20Drivers/DenonAH-D2000DriverFront.jpg
 
http://i7.photobucket.com/albums/y285/heildriver/YamahaHP1Drivers.jpg

 

[Don Quichotte]

I see. Thanks, haloxt, for keeping answering me.
 
Momomo6789, would you be so kind to disclose how much you measured on the Stax phones? Did you measure approximately at the ear position, i.e. on the inside of the pads? What Stax model was it?
 
My 303's do have a metal grill between driver and the ear, shouldn't it screen the emf as well?
 
Thanks!

 

[momomo6789]

o2 mk1 . meters like a little brick so i just put the meter in the middle

 

[Don Quichotte]

...and the result was...?
 
Edit: sorry, just found the answer above.

 

[Lazarus Short]

Quote:

Quote:

I'm afraid this needs more explanations.

 
1.  I wasn't using them much anymore
 
2.  I had gotten nervous about the electrical fields near my brain
 
3.  I needed the money
 
4.  Why does it matter?