[luvmusik]

Back-Electret curiousity. I have an entry-level standard-electret Stax SR-30 Professional (SRD-4 box + SR-30 Pro = SR-34 combo).
Bought new many years ago and wonder how it rates soundwise to these back-electrets & want to delve into back-electret info.
 
These are the 10 Back-Electret headphones have read about:
 
Toshiba HR-910
Aurex HR-910
 
Toshiba HR-810
Aurex HR-810
Rotel RH-930
Roland ? model # ?
Belcor BH-705
 
Signet TK33
Audio-Technia ATH-8
 
Audio-Technica ATH-7
 
Have grouped into what may be the same headphone badged/mfr'd by different brands. May only be 3 or 4 different headphones. Some cans in groupings may be nearly identical or may only differ in cosmetics & headbands.
 
Please correct if wrong.
 
Please add any other Back-Electrets known.
 
Other than cosmetics, what are the differences in these back-electret models listed, for sound & construction ?
 
Does the thickness of the diaphragms elements also vary ?
 
Which models have better bass ? Which ones allow more bass EQ to increase low frequencies levels ?
 
How would these compare to the electret Stax SR-30 Professional for sound and energizer box effect on sound ?
 
How would these compare to electret Stax SR-80 Professional (SRD-4 box also + SR-80 = SR-84 combo) Lambda Junior for sound  (Lambda JR) ?
 
Noted the 2 Stax electret models are not back-electret.
 
Interested in knowing any other Back-Electret headphones not listed. Thanks.

 

[luvmusik]

Anyone ?

 

[luvmusik]

Read thru almost every thread related to these models here on HeadFi (may have missed some info in the enormously hugh threads with hundreds of pages). It may appear the Signet and Audio-Technica models listed may not compare in sound to either Stax model listed, from other HeadFi threads read thru.
 
Still wondering about the other models...especially...
 
What is the difference between HR-910 and HR-810 models badged by both Toshiba and Aurex. Is the 910 just newer in the timeline, or did it have modifications pro or con ?

 

[luvmusik]

Anyone, at all, please ?

 

[ericj]

The staxen and technica / signet are not back-electrets. They are bi-polar electret films that work under the same principles as the stax electrostatic headphones. 
 
It is theorized that audio-technica manufactured all of the electret drivers used by stax and a-t. Signet of course was technica's prestige brand. If you look at the pictures of the drivers, the construction is nearly identical. Also, design concepts used in the stax frames are very similar to technica frames of the era and even in use today. 
 
Aurex was Toshiba's prestige brand at the time, and the rotels are rebadged aurexes. I'm unfamiliar with the roland and belcor. 
 
In the Stax / Technica design (and Sony uni-electrets) the electret is the diaphragm. Since by nature electret films have to be cast from certain polarized materials, this means that they are not as thin or pliant (or durable) as stretched polymer film. 
 
In a back-electret, the electret acts as a stator that attracts or repels a metalized film. (iirc) - this allows greater sensitivity and accuracy due to the lighter, more pliant diaphragm. 
 
contrary to popular belief, electrets do not "lose charge" over time except in the geological time scale. However, the A-T/Stax design has a tendency to build up a capacitance that cannot be drained, which saps their sensitivity over time. You can read all about that in Sony's Uni-Electret patent. 

 

[luvmusik]

This is great info - much appreciated, Thank You.
 
For the Toshiba/Aurex HR910/810 (or Rotel-Roland-Belcor badges) back-electrets - how do they sound compared to the electret Stax SR-80 Lambda Junior (SR-84 = SRD-4 + SR-80) and also electret Stax SR-30 Professional (SR-34 = SRD-4 + SR-30 Professional) ? (Either Professional or Standard versions to compare against).
 
Did any other manufacturers make a BACK-electret headphone other than Toshiba/Aurex (Rotel-Roland-Belcor) ?
 
Was there any difference between the HR-910 and HR-810...sonically or construction ?, Or, was the model number just changed in timeline depicting the newer made, same thing ? Not sure if 910 and 810 were sold at same time or 910 replaced 810 ?  It's been really hard finding info, but HeadFi'ers know & I need to learn.

 

[ericj]

Dunno, never heard a back-electret in person. I just know the history. 
 
I do not recall what the 810/910 difference was. I'd suggest searching this site more in depth. wualta may have known what it was, but he doesn't come around here anymore. he probably stated it in some thread about electrets or electrostatics, possibly even in the orthodynamic roundup thread 
 
Try the head-fi megathreads search tool at headfi.qix.it? 
 
I am unaware of any other back-electret headphones. In theory you could use a microphone production line to make a killer back-electret IEM, but to my knowledge nobody has made any back-electret non-microphone transducers since Toshiba stopped. 

 

[luvmusik]

OK, Thanks, appreciate the help. The info helped me narrow to only further interest in 910/810, their isomer rebadgers or any other back-electrets we may not yet know of.
 
Wow, wualta has also written very informative posts, have read very many, some related to this. I'll continue to search, the megathread search tool is something new to me and will check it out. I still have more to read in the various vintage, electrostatic and electret threads - some have hundreds & thousands of posts.
 
I wish wualta was still around - he or faust3d would probably have the last set of answers - thought I saw wualta post not too long ago on another site, but maybe it was longer back. Maybe with luck they both may see this thread & offer info as well.
 
Cool mention of microphones, as some companies, such as Sony later issued back-electret mics after their original electret condenser line, stating technological advances. Mics, speakers, headphones and cartridges have some common physics, even if some are inverse related.
 
Will keep digging, now it's down to Toshiba & Aurex/(Rotel-Roland-Belcor) 810 & 910/(930-?#?-705) vs Stax SR80/SR30, with any other back-electret mfrs .

 

[luvmusik]

Wow, that megathread search tool works well - really nice, Thanks !
 
New information found is that there was also a Toshiba (and maybe other badges-Aurex, Rotel, Roland, Belcor) HR- 811, so now it gets more interesting as to what the 810-811-910 differences were ? Don't you wish we had a Toshiba brochure !
 
Having read that some of these may have had thinner bass than the Stax SR-30 (and then so SR-80 assumed, either standard or professional also), or possibly similar bass, not sure how to interpret. Some said thin bass was due to small transformers used in Toshiba HR-811 model specifically (again not sure of 910 & 810), but the Stax energfizer box SRD-4 used much larger transformers.  Wondering, too, if construction of the earcups in any of the rebadgers was a little different, more bass may have been reinforced as a longshot.
 
Reading again thru wualta's posts in very short Toshiba thread seems to infer the Stax SR-30 Professional may have better bass than the Toshiba HR-910, but he equally ranks them for different sonic reasons in a very brief rating. I think the impression is Toshiba's bass may roll off quicker, but that is my inference from reading. Maybe that bass also withstands a good amount of EQ to compensate. He went on to say, although he ranked these two models as a tie - it was for very different sounding reasons (unspecified between these two models). So, we know at least one headfi'er has heard these comparatively - wish we could get his detailed impressions on sound.
 
Looks like a site in Japan had files displayed in 2007 on the Toshiba models, but the site is down now !!! Roadblock there.
 
Wonder if spritzer has heard any of these models listed in this thread compared to the 2 Stax models listed.
 
It's getting interesting.

 

[ericj]

Oh, you forgot Stax SR-40, which is the oldest of the stax electrets. 
 
There are two versions of the SR-30 and SR-80, sometimes referred to as "pro". They have gold lettering on the plastic. Said to be more sensitive i think? 
 
To make things more confusing, in europe the later SR-30 is called an SR-60. I think. I'm confused, after all. 
 
At any rate, the SR-30 versions are generally regarded to be the best sounding. And it's theorized that the only difference between the SR-30 and SR-80 drivers, within their own series, is the size of the fiber cookie on the back. 
 
The SR-80 gives up the bass in favor of "soundstage". People who call it "Lambda Jr." are trying to sell one, or suppressing buyer's remorse. There's no comparison, despite the similar-looking frames. 

 

[luvmusik]

Good mention of SR-40 (started 1975).
 
My Stax are SR-30 Professional, and I have a Stax SR-80 standard (non-professional) on it's way here so should have a good reference soon.
 
I've read that the Professional with thinner micron measurement sounded better in the SR-30 than the standard, but for some reason the SR-80 standard sounded better for that model than the professional to add to the confusion. Also read the Pro versions can withstand much bass EQ, and one of the series is capable of more volume overall, but forget which series - may know that answer soon on listening comparison.
 
You're right on with all the info I'm also seeing. SR-60 was possibly the European badged SR-30 which I guess hit Europe to sell before USA. Makes sense about SR-80's soundstaging due to maybe the Lambda appearance of earcups - soon I'll report after hearing.
 
Another part of confusion - is some printed material puts the bass low frequency response the exact same for the SR-30 and SR-80 models. I have saved my Stax brochure that came with my newly bought SR30 Pro's back in 1989-early 1990's and brochure in my Stax box that came with it (also seen on googled images) lists response as  - SR-84 as 20 to 25 KHz and SR-34 as 25 to 25 KHz, a 5 Hz difference. The system nomenclature (84 vs 80, 34 vs 30) wouldn't change the response, as both cans use the same SRD-4 energizer box as a constant factor. The few other specs given are identical for both models. Descriptively - Stax brochure says  about the SR-34 cans (system)- "similar electret transducing element as the SR-84", and not much else in comparison; likewise the brochure in comparison about the SR-84 says little vs the SR-34  - most points are shared, other than..."an unique open back enclosure virtually eleiminates cavity resonances...", thus alluding to that soundstaging attribute possibly. Funny, my brochure printed in 1984 is for "standard" models, packed in my factory "Professional" box - they probably did not update the printed material...my later manufactured "professional" was made starting 1989. I think both models used a high polymer film diaprhagm - brochure describes it for SR-84. Back of brochure is coded, but looks like dated 1984 brochure (84-5-10K) ?
 
I think the SR-80 has slightly angled asymmetrical earfoam on cups of varying foam thickness conformity to match ears better, but could be wrong - the SR-30 are uniform earfoams. Will know when my 80's get here.
 
There was also another much different creature the electret Stax SR50 model, with the closed-back, rounded bulbous shaped cups...very cool for collectors, but reports say it doesn't sound as good as these others.
 
A quik timeline on the electret Stax, if we haven't already confused everyone in all, is
SR40 - 1975
SR60 - 1975
SR50 - 1979
SR30 - 1982
SR80 - 1982 Lambda Junior
SR30Pro - 1989
SR80 Pro - 1989 Lambda Junior
 
SRD-4 energizer box - 1975...this box with headphones completes system as termed SR34, SR84, SR34 Professional, SR84 Professional, for those model 30 and 80 cans.

 

[ericj]

My SR-80 arrived with pads that were quite dead - the vinyl was very hard. I disassembled them in hopes of duplicating them but this never really happened, in part because i just don't think the potential is really there. In part because i'd really need a glove weight leather to do a good job. 
 
The foam inside them was wholly uniform. only about 2mm thick also, and very low density. 

 

[luvmusik]

Update - brochure also describes the SR-80 and SR-30 both as having the same 4 micron thick high polymer film diaphragm on the last page. So, thickness of that in both models is the same, and this thickness does correspond to the more efficient Professional series. So, the correct brochure came in the box - it just does not say "Pro or Professional" anywhere on brochure. The photos of all the cans are at an angle not showing the lettering either. The non-Professional series had the thicker microns measurement. Funny, I always thought I had the older brochure, but microns printed corresponds to the Pro series headphones and labelled box.

 

[luvmusik]

  My SR-80 arrived with pads that were quite dead - the vinyl was very hard. I disassembled them in hopes of duplicating them but this never really happened, in part because i just don't think the potential is really there. In part because i'd really need a glove weight leather to do a good job.
 
The foam inside them was wholly uniform. only about 2mm thick also, and very low density.

Yeah, I am mistaken about the SR80 earfoam, you're certainly right - just took a look at a foto of ones coming to me and they are uniform - I must be thinking about some other model/brand that did that "shaping" of the thickness in foam. Not sure what condition my pads will be in - I think acceptable - only had foto of 1 pad, headband looks a little flattened on bottom foam at one point.
 
I am anxious to test...it's not a total perfect A-B, as the SR30 Professional series was bought new and never abused (sound great) vs the SR80 Standard series (non-Pro) bought used and am told were taken care of properly. It will be a fun run-off.
 
With the Toshiba/Aurex (Rotel-Belcor-Roland) 910, 810, 811, 930, 705 etc, vs the Stax SR 80, 30 - either Pro or standard series, it may be a close run-off. We may be splitting hairs in comparison, but maybe there are some standout sonic differences. They may all tilt to mid-centric, but maybe vary in bottom parmeters, top roll-off, airiness, bandwidth detail, volume, smoothness, imaging & present or lack of soundstage. Speculation is tuff without hearing them, but it is a good showdown among similar models. I'm curious.

 

[luvmusik]

While electrets is discussed, maybe related or not - question - was the Kenwood KH 82 electret model made by another mfr ? I can hardly find any info about it. One fellow posted about it on Head-Fi, but I think the foto was them in a box -sorta looked like Audio-Technica from a distance. Know anything about those ? Maybe really bass-shy, or who made them - Kenwood or sourced ?