Philips EM6721 BALANCED Electret, anyone knows them?

There's a Philips EM6721 BALANCED Electret for sale at a Dutch tradingforum.
I can't find any information about them. Who can enlighten me?

just picked them along with original box - they are 800 Ohms and truly power-hungry. I'll post more later on

Just made some photos:

I have to measure my amp output, because on the box stays, that the input voltage can be as high as 5V!
 
I can say for now, that they lacks lower end - but it can be amping issue. on the other hand - they do got nice soundstage and instruments separation.

photo of the driver: its 70 (!) mm big!!

 
Such a nice driver MUST have some potential: I've made some experiments, these are my conclusions:
 
1. Adding damping only changes virtually NOTHING.
2. Sealing the back of the headphones improves bass impact greatly (used paper tape).
3. To have a decent amount of bass - bass boost on the amp is needed.
4. They need really powerful amp do play.

800 Ohms? That's quite high.

Got them not long ago.
Yes, they are really need good amp - Xonar Essense can drive them more or less only on last level of amping. They have lack of bass cause open construction, but have very light and clear mids and highs, good soundstage. Building quality is good, they are comfortable. Really interesting headphones.
 
JeckyllAndHyde, thanks for photo of drivers. 70mm - they are really big and beautiful. 

A new mod for these .
Seeing as how this is the only real thread on this particular set, Here's a mod I just did up and am quite happy with so far. It's tightened up the sound and added a bit more bass.
Really easy to mod these just watch out for stiff wires off the transformers leading to the stator. The cups just drop off after you rotate them to face outwards then pull out the headband posts.
 
Here's the pics:

It may be good to refer back to the previous post that shows the unmodded spots I'm talking about.
 
I was really concerned about damping directly on the back of the driver as the stator is right out in the open and exposed so if anything used for damping that was directly touching it built up a charge at all, well we all know that's a no-go there. So because no-go on direct damping I had to opt for the air damping, which meant sealing up every single spot as much as possible other than where the venting on the bottom half of the cups is.( and restricting it there.)
 
Sure I may lose a bit of soundstage but the acousti seems to help add a bit if used properly and half the cups would still be open but harder to push air. So this mod is a compromise between raising bass up, cleaning up resonances inside the shell, and keeping the soundstage as much as possible.
There's really nothing else I could do with this mod other than swapping out the felt I placed over the vents and trying another material. It's done to the max of what it can be without losing S.S.>
 
 
SO:
All around the bottom half I used a bit of thick felt insole to cover the venting ( see thickness in picture ), which was basically some semi-transparent nonwoven black material you could almost see through.The material sat directly between the brace that held the outer metal mesh in and the outer mesh, so I had to go over top of it. I secured the felt in place using thin strips of doubletack tape on the plastic brace crossmembers. Around this you can see where I had to use putty to seal up the spots where the mesh was clear right out to the back.( used an led flashlight from behind to check for holes )
Not much point in having all those there if you're trying to restrict airflow with that black fabric, but then again the build on these is very leaky anyhow. Not anymore.
Also seen surrounding the small transformer is some Acousti brand 3 layer acoustic foam to deal with the wierd spaces and edges around the transformer area, preventing any stray reflections and absorbing at the same time.
 
On to next picture:
 

If you look at the first picture you can see there are a number of small notches around the perimeter of the back cup edge ( the side with transformers ) and when the cups are normally assembled these act as venting also. In order to leave those as ventings but restrict them I made some strips of Acousti foam and where the vents were I carefully stripped away the adhesive layer just in that spot to still allow for sound passthrough, albeit restricted. This strip was mounted just a hair higher than the top ridge to also act as a seal when the cups were pressed back together, the mounting surfaces had a very slight gap which this seems to have helped seal off as much as possible( not %100 perfect but heck ), while providing extra resonance damping in the cup interiors at the same time.
When remounted the driver sits at an angle . The two screw posts in the picture are at the bottom of the cups and the driver bottom is raised inside the final assembly by the same as the height of those posts; top screw post is almost flush.
 
picture above shows where i had to use the Silver Conductive epoxy (a tiny bit of red heatshrink right by it )
 
All done, once these have been reassembled you'd be hard pressed to notice anything cosmetically from the outside. They do have a bit more weight than stock but not much. Also added a very tiny bit of silicone grease where the headband hinges enter, and no more squeaks.
 
 
 
Do sound really solid-tight with some raised bass over what I recall stock. Generally a better cleaner sound overall which I will chock up to that foam. Soundstage seems relatively intact BUT I will have to try to find another stock pair just to compare Anyone got one they'll part with cheaply?
 
I'll check back in on sound after listening some more.

I can't leave it alone if it's not quite close to a WOW experience, ( and no I don't game...) so here's mod #2/3.
 
Simply damping the back vents wasn't cutting it so :
THIS

The outer white ring still has adhesive layer on it, you can see how I stuck it to the table and carefully sliced it off leaving an acoustically transparent area in the middle ( the big black area ) junk on the table still is the adhesive layer. Getting pro at removing it without leaving much of the foam behind.
 I initially was worried about the foam possibly causing static issues if it were to touch the exposed rear stator of the drivers, but I'll show this seems unfounded in a bit. Worrying about that made me first try this ( next picture ) with a few insulated computer wires mounted to stop the middle of the foam from hitting the live stator ( as much as possible ) It did however make small rattling noises so out it came after trials. The white ring is a second layer of doubletack to hold them in place.

Guess where this goes after the wires are removed and the tape backing is taken off.
I made a slit for the stator lead wire and used a bit of electrical tape just in case where the wire will directly hit it. Probably not needed. Sealed on the top and bottom of this slit after it was installed to keep the foam as continuous as possible for damping.
 
Here it is installed and pulled tightly around the outer ridge to keep it taught and off the driver back, even if it is only a matter of maybe 3 millimetres off:

Direct side to side trials on mono and stereo made me remove the dense felt over the venting to keep soundstage/openness.  I have even MORE soundstage than stock with this.
These are generally rather harsh in stock form, not something to listen to at any sort of loud volumes, but I have these maxed as far as I want to safely listen for about an hour now, with NO EQ. If you know these or the other Philips 6325/6326 ( and that other one ) electret cans from firsthand experience that's quite something. No loss of detail, actually slightly better, and minus the knives in the ears..or the feeling of being hit in the face with a purse, as someone just described them in a PM to me. Slightly more bass, and just simply top notch so far.
 
On second thought these are absolutely atrocious so don't even bother. Worst thing I have EVAR heard ( and that's worse than EVER! ) SO just pass them by and forget you ever read this I'll collect all of them just to save you the trouble of hurting yourselves and ruining your hearing to make this place safer for all.....Report any of them for sale to me so I can dispose of them properly.
 

Oh, and the worst thing of all? They're not real electrostats. No!  Electrets, pah!  Made from old rubber bands peeled off golf balls recovered from water hazards, and recycled alligator hide. Operate on the toilet-plunger principle. They're like SEW totally fraudulent. My speaker wires are like way more musical. All by themselves. 'Cause they've got, like, moon-rock voodoo autocatalytic cryogenetic silverplatinum wires plated with some secret element that's invisible that you or NASA haven't even HEARD of, so there. So musical they don't even need an amp to make music, plus they purify the air. I know, right?
 
Better than yours, so don't even try to double-blind me, bro. Nyaa.

Wow that's a downer Wualta,here I was feeling all good about things and blammo, you remind me of their inadequacies... but I have to sort of admit that it's true if you say so like everyone else in here... And electrets will fade to crap after their charge wears out , don't turn them up too loud at all EVAR: it's TRUE I read it in here somewhere! Everyone knows it's true but they really hide it well  Gimme a break, actually they'll break themselves haha., sort of like the giant rhinocerous/ elephant/ t-rex lasergun battle in the room nobody wants to acknowledge, that's even more worstester. ( yeah T-REX SPACE LASERS to the ears believe it! ) After all this work.  They made my ears bleed all over anyhow. ***when you wear them outside it attracts every mosquito within 3 square miles due to the electrical charge! Combine that with the bleeding ears and lemme tell ya : recipe for disaster.
 
 

Hello. i'm from Serbia. I also  bought that philips electret headphones. i got actually problems with their soundstage. They are in good shape.but their sound quality on standard amplifier like ONKYO ,which i have, is not satisfaying.also i got sennheiser hd600 and other hi fi headphones ,and they all sound very good with this amp. but philips are on 800 ohms and lame ,so to speak. So, i need help. How to built a proper amp or preamp, and which amp is good for my cd-player to get the full sound picture from these headphones? thanks  in advance. 

Are you driving the Philips from the speaker terminals or the headphone jack?

i am driving headphones from jack input. this amp is reciver from 90's. it's very good for sennheiser on 24-32 -60 or 100 ohms. but i,m not satisfied with this philips electret phones.they have vey nice soundstage,but lack of power.

HELLO. I,VE  got those philips phones. they are very good . but ,they are on 800 ohms and they needed some more amplifying . do you have any sugestions what amp is good for that headphones?