Electrostatz (In2uit, Mitchell and Johnson, Cyberdrive, Verisonix, Verisonic etc.) headphones

[spritzer]

Now here is something that has been out for a while but I've never really looked into.  Now these carry a wide variety of names and there is a plethora of models but they are all pretty much the same, hybrid units with an electret driver to cover the top end and a regular dynamic driver for the rest of the spectrum.  I decided it was time to look into this so I bought two units, the Mitchell and Johnson GL2 and some Cyberdrive unit for 30$ which looked the same as the GL2 minus the wood. 

The GL2 arrived first so some pics:

Here the baffle which shows how the drivers are setup

Small transformer and 10uf/50V NP cap are all there is to this and the electret driver is clearly angled. 

Now with that thick plastic sheet on the back of the driver... yeah it won't play nice but then again the housing design here is crap so that's probably why they did this.  Let's just call it extreme damping...

I played around with them for a bit and tried to upgrade the cap from the ChangX shit they had in there.  Minor improvements but these are pretty crappy headphones to begin with. 

Now a couple of days ago the Cyberdrive units arrived.  I forgot to take a picture of them before I stripped them down but they look like this:

https://www.ebay.com/itm/CYBERDRIVE-Noise-Cancelling-Over-Ear-Professional-Hi-Fi-Deep-Bass-Wired-with-for/223201026938?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m2749.l2649

Now from the outside, these are clearly made by the same OEM as the GL2 even though the finish may be a bit...crap on some of the pieces.  All of the chrome pieces look really cheap but they are identical to the same parts on the M&J set.  Now for the nitty gritty... 

Yup, same baffle piece....

Same everything really except the cap is a different brand but that is to be expected as the production could be spaced a bit apart.  Same PCB and the same transformer too... 

Yup... everything is the same so any claims that the M&J units are somehow better (as I've seen on HF) are just as baseless as most things over there.  I have little doubt the entire product line has the same stuff in there.  Since these are horrible headphones that I'm never going to use, let's do some digging:

It's hard to see but the angle on the electret driver is some good 30°compared to the baffle and it partially obscured by the dynamic unit.  I need to dig out the LCR meter to measure the drivers but I did some quick measurements on the transformer.  It is clearly some off the shelf unit and the primary measured as almost no DC resistance (0.1ohm) and the secondary was 3.3K so high ratio indeed. 

I am going to do some more experiments with these though so I'll update in the future. 

[lkong]

Is there a high pass/low pass between electrostatic and dynamic? Or they are wired in parallel.

 

[spritzer]

The cap is the only crossover component plus the natural response of the drivers.  The signal goes through the cap and into the transformer with the other end grounded. 

[catscratch]

DIY Audio Heaven tested a M&J headphone with this design including frequency response for each driver.

https://diyaudioheaven.wordpress.com/headphones/measurements/mitchell-johnson-jp1-dj/

There appears to be no crossover. The dynamic driver contributes most of the sound while the electret pretty much plays in the background. The FR is a mess. At least the cheapo version I can understand, but for hundreds of dollars?

Thanks for the teardown.

[spritzer]

The cap alone isn't a crossover but a highpass filter so yeah it doesn't do too much.  I did disconnect the cap and the HF was reduced but the electret doesn't do a whole lot. 

I did do some experiments yesterday and hooked up the drivers to a Stax amp.  It did work well so I threw up a quick baffle design so we'll see how they play on their own.