[leeperry]

Hey guys, apparently some orthos come with polarity reversed:http://wiki.faust3d.com/wiki/images/2/24/U70review79.jpg

wired in reverse phase

 
http://www.innerfidelity.com/content/more-diy-orthos-and-two-akg-k-340

 Headphone has polarity reversed

 
http://www.innerfidelity.com/content/diy-orthodynamic-headphones-dbel84-page-2

Drivers are out of polarity

 
The funny thing is that 38mm SFI's and T50RP drivers come with clear +/- signs but some T10's are know to be properly wired and others not huh? I'd swear that wiring them properly improves SQ ^^
 
Anyway, I see that one of my T20's is wrongly wired but has a color spot on the (supposedly) - tab: http://img530.imageshack.us/img530/7687/t20rp003xe7.jpg
 
Usually Fostex indeed seem to put color spots on the ground: http://cdn.head-fi.org/9/94/94da1c85_20111211_223521.jpeg
 
The other funny thing is that round Fostex diaphragms can be reversed so who's to say that diaphragms have been sandwiched to match the +/- signs on the baffle ><
 
Long story short, is it possible to check for driver polarity using a DMM?

 

[Mython]

  Hey guys, apparently some orthos come with polarity reversed:http://wiki.faust3d.com/wiki/images/2/24/U70review79.jpg

wired in reverse phase

 
http://www.innerfidelity.com/content/more-diy-orthos-and-two-akg-k-340

 Headphone has polarity reversed

 
http://www.innerfidelity.com/content/diy-orthodynamic-headphones-dbel84-page-2

Drivers are out of polarity

 
The funny thing is that 38mm SFI's and T50RP drivers come with clear +/- signs but some T10's are know to be properly wired and others not huh? I'd swear that wiring them properly improves SQ ^^
 
Anyway, I see that one of my T20's is wrongly wired but has a color spot on the (supposedly) - tab: http://img530.imageshack.us/img530/7687/t20rp003xe7.jpg
 
Usually Fostex indeed seem to put color spots on the ground: http://cdn.head-fi.org/9/94/94da1c85_20111211_223521.jpeg
 
The other funny thing is that round Fostex diaphragms can be reversed so who's to say that diaphragms have been sandwiched to match the +/- signs on the baffle ><
 
Long story short, is it possible to check for driver polarity using a DMM?

 
 
In a stereo 1-way transducer system, it's reasonably easy to tell if drivers are wired incorrectly, just by listening to them.
 
As the article states, erratic bass response can be an obvious clue.
 
If both drivers are wired incorrectly, (i.e. both have reversed polarity), then bass peaks will sometimes sound obviously lacking in authority.
 
If one of the drivers is wired incorrectly (and thus out of phase with the other driver), then there will tend to be a rather diffuse presentation of the music, with a 'spacey' sound, which can be relaxing in the sense that the sound is not so much 'inside your head', but will rapidly become tiresome because it'll also sound a bit echoey with poor image placement and, again, a bass response which is erratic and lacking in authority (even more so than in the event that both drivers are wired incorrectly).
 
 
 
There is an old trick with full-size loudspeaker woofers, where one can simply connect the driver leads to an AA or PP3 battery (very briefly!), but I have never liked to risk it, and would certainly not risk it with a more-fragile headphone driver, regardless of transducer type.

 

[leeperry]

well yeah, when both drivers are wired incorrectly it's not all that easy to tell IME....but I'll give you that SQ improves once they are IME, anyway the owner of innerfidelity seems able to tell but does it take an oscilloscope to ensure that phase isn't reversed?

 

[Mython]

  well yeah, when both drivers are wired incorrectly it's not all that easy to tell IME....but I'll give you that SQ improves once they are IME, anyway the owner of innerfidelity seems able to tell but does it take an oscilloscope to ensure that phase isn't reversed?

 
 
 
Whilst it would be possible to place DMM probes across the terminals of the drivers, whilst running, I don't think this would provide any conclusive answer about what the drivers themselves are doing - it'd merely relate to the polarity of the incoming signal, from the cable, which, to further complicate matters, is, of course, an alternating current, anyway.
 
As for placing DMM probes across the driver terminals without them running, I don't see how one could attain a measurement, other than one of resistance, which isn't (AFAIK) relevant in any way.
 
 
I suppose an oscilloscope is a reliable way of telling, and I will admit that if you don't have a rapid way of simultaneously switching the polarity of both channels, it will be harder to distinguish if both drivers are simultaneously wired out of polarity, using the subjective listening approach, I earlier described.
 
If you are genuinely concerned about your headphone drivers, and do not have the necessary gear, I'm sure an audio engineer with an oscilloscope would be happy to do a quick test for you, without charging you too painful a fee.
 
Let me/us know what you find out!

 

[Mython]

I'm just giving this some more thought, and it occurs to me that if you have a microphone, you could play a 2-channel signal that you absolutely know to have correct phase, from an audio app like Adobe Audition, Audacity, etc. (where you can visibly see the waveform).  In fact, you could just strip one channel from a stereo track, and then duplicate it into a dual mono format (I mean delete the left channel, and then copy the right channel into the empty left channel, so you have 2-channels, containing the exact same data). But stagger the data so that even though it is technically a 2-channel track, there is only music data being played, solo, from the RH channel, and then, subsequently, solo, from the LH channel.
 
This signal would be fed to your headphones, and a recording taken for each earpiece in turn.
 
Something like this (I've been lazy and just shown you 2 mono tracks, for a rapid screengrab, but you get the general idea):
 

 
(if you did it with 2 mono tracks, then you'd need to ensure your mic didn't pick-up the sound emanating from the unwanted driver not intended to be recorded at the time). Or yet another way would be to just have a 1-channel track where you use the editor software to first play it to right-channel-only, and then to left-channel-only using the relevant slider controls in your software.
 
 
 
You could then look at each of the ad-hoc recordings you had made of the driver outputs of your headphones, in your audio editor, and see if the bass peaks match the phase of the original recording, and indeed, if the LH and RH of your ad-hoc recordings match each other.
 
It's not perfect, but it might get you the information you need.