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Orthodynamic Roundup

post #1 of 23556
Thread Starter 

P1010478a.jpg


In the fall of 2004 I declared my commitment to study the development, if any, of Yamaha's old line of Orthodynamic headphones, which used a driver type known generically as isodynamic, small-O orthodynamic, planar-magnetic, or magnetostatic. Why?  1) they'd been virtually extinct for 20 years, and   2) despite their age (they were made from 1975 to about 1990), they can still, at their best, give even an electrostatic a run for its money, and the simplicity of the drive principle makes it easy to tinker with them until they are at their best. This, plus the fact that examples can be had fairly easily on eBay for as little as $35 (and sometimes much less) makes them something of a bargain [UPDATE: No surprise, this situation couldn't last once the secret was out, but online-auction prices at least seem to have stabilized]. I believe that a good example of this type of headphone, given a little DIY TLC, can stand sonic comparison to today's popular enthusiast, even audiophile, moving-coil dynamics.

 

Yes, "orthos" partake of some the best of both the dynamic and electrostatic worlds. They won't be everyone's cup of darjeeling, but they have unique virtues that should put them on headphone enthusiasts' shopping lists and in manufacturer's catalogs. But until very recently (see the note below), they haven't been, and I wanted to know why.

Even though during the late '70s and into the '80s a buyer in the US could choose from examples of isodynamic 'phones sold by Audio-Technica, Radio Shack, Pacific Stereo, Lafayette, Bang & Olufsen and Burwen, I picked Yamaha's Orthodynamics to study because Yamaha stayed with the idea of marketing this type of headphone to the mainstream longer than anyone else, long enough to produce three distinct lines before the death of what we might call the isodynamic dream in the late '80s. Fostex is the exception, the company having kept the type in production from 1975 to the present, but Fostex is primarily in the business of supplying the professional and semi-pro audio markets, and, outside of the odd OEM here and there, its products rarely pop up in the mainstream, especially since its current production is not "audiophile" quality-- by design-- until extensive modifications are done.

What I propose here is simply to describe the pros and cons of living with examples of Yamaha's three Orthodynamic strains, since I now have an example of each. Under roof now are, in chrono order, models HP-1, YH-1, YH-100 and YHD-1. These were the most expensive models of their respective lines. You will have counted four examples, though I mentioned three distinct strains. To explain:

An unexpected discovery was that the highly-regarded founding model, the HP-1, and the later, much lower-priced YH-1 are very nearly identical; they look the same both inside and out and sound very similar. It's as if Yamaha were having another pass at the market with the same models at a much lower price point. Ergo, only 3 distinct lines, though there were four different model lineups.

The YH-100 and its predecessor, the frighteningly rare/expensive YH-1000, were flagship or statement models and not really part of a line as such; rather they represented a summation of everything Yamaha had learned up to that point, including how to hit the maximum on the cost/benefit curve, as you'll see.

If a budding Orthodynamicist wants to get his feet wet, he should start with an inexpensive and relatively common model like the YH-1, which should still go for about $60 on a good day, depending on the whim of the market and whether the item comes in its original box, et cetera. There are other possibilities as well, including a Fostex model or two.

 

Next I'll go into detail on the individual models, taking them in chronological order, and try to explain why these old dinophones still merit close attention.

 

So welcome to our little corner of the madness and our chronic fixation on a headphone type that with the exception noted went out of production more than 20 years ago. Our operating motto is whatever works.



NOTE TO ORTHOPHILES, 2011: You'll notice this thread is now very long. It threatened to die young, but then came back to life, and has been thriving ever since thanks to a group of dedicated Ortho enthusiasts worldwide whose tenacity and ambition and ninja procurement skills continue to amaze me. It's become a group (not to say cult) global effort. We've tackled many practical problems of headphone design over the last seven years, mostly because we had to learn how headphones work as a system, with their cups, pads, vents and baffles, in order to get the sound we wanted, the sound we knew was built into the vintage ortho phones from the beginning but never realized in the marketplace. Long threads means finding what you want to know can seem impossible, but put down that guitar of discouragement and fret not-- one of the thread's stalwart friends, Ludovico Magnocavallo, made for us a dedicated SEARCH ENGINE, which I commend to you. Or use Google by adding the term <site:head-fi.org "orthodynamic roundup">  to  your search terms in a URL field to restrict your search to this thread. 

The good news is that "orthos" are now back in the marketplace from two small companies, one in the US, the other in China, and with that, can orthos from the major brands be far behind? Hope is in the air.


Edited by wualta - 2/12/12 at 6:56pm
post #2 of 23556
Interesting. My old Yamaha receiver has a piece of plastic stuck in the headphone outputs that says "RESERVED FOR YAMAHA ORTHODYNAMIC HEADPHONES." I didn't realize that was actually something beyond just their seventies marketing, I'm curious to hear more.
post #3 of 23556
Sounds interesting.
If the technology was so good as to compete with even electrostatics in some fields, as you say, then why are they not still in production?
(Also, could you please post pics with it, too )
post #4 of 23556
Here's are a couple of pics of another planar headphone, the Wharfdale
isodynamic, circa 1975.

http://www5.head-fi.org/forums/attac...tachmentid=333

As can be seen, the headband and earmuff padding has degraded badly over the years.
I used to regularly listen to these phones up until about 1987.

This is a picture of the transducer opened up to show the diaphragm/planar
coil:


http://www5.head-fi.org/forums/attac...tachmentid=334


Even in this battle weary guise the phones still sound pretty nice.



setmenu
post #5 of 23556
I had a pair of Hp-1's for many years and loved them, I used and abused them until they developed a very minor buzz at low frequency's so I gave them to a friend.
Recently I decided to get back into headphones and after auditioning many different models I realised what a huge mistake I made.
What I remember most is that they had a fairly flat responce, did everything effortlessly, and sounded very natural. back then I didn't know that it was common for headphones to play one type of music better than another, allthough my tastes were more limited then.
PwM
post #6 of 23556
Thread Starter 

I'm startled, pleasantly, that we have so many replies already; I'd originally aimed this thread at the very small minority of headphone users who'd owned Yamaha Orthodynamics and wondered what the other models were like.
 

Quote:
Originally Posted by Frank M
If the technology was so good as to compete with even electrostatics in some fields, as you say, then why are they not still in production?

Fostex still makes isodynamic 'phones for the pro audio market-- as far as I know they're the only true believers left, and the only company to attempt isodynamic headphones using modern magnetic materials. But they've turned their backs on the audiophile market. Not that they didn't try-- they came up with a stat-killer back in 1978, the T50. It was marketed poorly and failed.

 

Sounds like an opportunity, doesn't it.

Your question raises another question that takes us back to the late '70s in the US home-audio market: Would most people have chosen electrostatic headphones if they could have afforded them? Not that many people recognized electrostatic 'phones as anything but screechy, lacking in bass and outrageously expensive. Far from the near-ideal status they enjoy today. So telling someone that the Yamahas were poor-man's electrostats would have gone over with a dull thud.

Besides, the Yamahas didn't sound 'statlike: they had much more bass, much less treble, and thus presented a sound that most people were used to and therefore would like. This may be the reason, over which I agonize again and again in this thread, why Yamaha didn't apply ten cents' worth of mechanical damping to their Orthodynamic drivers, but I'm getting ahead of my story.
 

Quote:
Originally Posted by SaturnNyne
I didn't realize that was actually something beyond just their seventies marketing, I'm curious to hear more.

I remember seeing those outputs on '70s Yamaha receivers and wondered if they'd actually optimized the outputs for the impedance and efficiency of the Orthodynamics. Not that they really had to: like Magneplanar speakers, the Yamas present an essentially resistive load to the amp. That is, this type of headphone is the easiest kind of load, nearly pure resistance, able to be driven properly by any amp with enough power, and unaffected by the varying stray inductance and capacitance of exotic cables and boutique amps.

So while there was no need to "optimize" the headphone outs on those Yamaha receivers, and there was some marketing involved, I like to think Yamaha was proud of their Orthodynamics back then (they seem to have forgotten about them today-- see below) and made sure that the headphone outs were more than just afterthoughts.
 

Quote:
Originally Posted by Setmenu
Here's another planar headphone, the Wharfedale isodynamic, circa 1975.
 
Wharfedale Isodynamic.jpg

Thanks for bringing up an important point about the isodynamic type. You don't need superstrong magnets and you don't need exotic materials and you don't [always] need great precision in manufacture-- the drive principle inherently takes care of many of the rigidity and resonance problems that dog moving-coil designs. Note: the Wharfedale turns out to have been the first isodynamic headphone in the world to reach market, in 1972. At £20, it was also one of the most affordable. After earpad restoration it still sounds great today. UK readers should rush out and save languishing examples of this valiant veteran and brilliant example of British engineering.

 



FOOL DISCLOSURE

Two words about the equipment I'm using: Old and nothing special. I have a couple of surprisingly good/cheap old receivers (the Realistic STA-2200 and the Kyocera R-851) with MOSFET amps, a couple of Sony and Yamaha VFET amps (well, I guess that's a little special), a bunch of late-'70s to mid '80s preamps from Hafler, Nikko, Sanyo, Yamaha and Sherwood, a collection of Hitachi's, Sanyo's and Sherwood's MOSFET power amps from the same period, and a couple of basic Chu Moy (aka CMoy) portable amps. The All of these are available (when they are available) at reasonable prices through online auction sites.

However, much of this old (say "vintage") gear is not typical of what young-type persons are using today, so taking Newform Research's recommendation of the Panasonic digital-amp receivers to heart, I obtained not one but several of them, finding them both readily available and affordable online. This has changed my characterization of a few individual headphones' frequency responses but hasn't fundamentally altered my evaluation of their capabilities. Being able to feed the Panasonic's amp digitally cuts down on a few variables and makes testing easier and more repeatable and thus reliable.

Also lying about are a couple of copies of one of the Yamahas' direct competitors, the Audio-Technica-built Realistic Pro 30 isodynamic. In the interest of full fool disclosure, I also own a Sennheiser HD 600, an AKG K501, a Stax Lambda Signature (1-micron diaphragm) and a Stax Lambda Nova Basic (2 microns) with an SRM-1 Mk 2 Pro amp; a Grado SR-80 with flats/HD414 pads; Sony EX71 earbuds, and several Koss KTX Pros. Oh yes, there's also a motley collection of old electret-electrostatic 'phones: the Sony ECR-500 (5 microns), a Stax SR-30 Pro (4 microns), and a Signet TK33 (2 microns).
Past 'phones include the watershed Sennheiser HD 414 (ca. 1973), the HD 424 (ca.'76) and the bizarre HD 44. There were also the Stax SR-X Mk2, Beyer ET1000 and Superex PEP-79 electrostatics and my first isodynamic, the oddball 1978 Audio-Technica ATH-1, aka the Gram Cracker (sic). It was this 'phone, with its so-right-yet-somehow-wrong sound, that made me rip it apart in frustration and stuff fibrous material into it.



FORM FACTOR

Here are the original HP-1 and the follow-on YH-1, both top of their respective lines. Can you tell them apart?



That's the HP-1 on the left.

This was more or less the form taken by the most expensive of each generation of Orthodynamics until the YHD series of the mid/late '80s. Inside each earcup is a sandwich of two perforated ferrite disc magnets about 2 inches in diameter with a nontensioned corrugated or pleated diaphragm between them carrying a printed aluminum spiral voice coil (see below). This assembly is called the driver. Here's a closeup of the driver from a YH-1. The roughly machined surface of the ferrite magnet is exaggerated a little in this photo. You can see some of the turns of the shiny aluminum spiral voice coil through the holes.



A good closeup of the later YH-100-style driver, which is essentially the same but with metal plates covering the outer faces of the magnets: http://home.hccnet.nl/joop.nijenhuis...1/RHP1P005.jpg


SO WHAT'S THE BIG IDEA?

The bright idea proffered by the isodynamic headphone (a Yamaha Orthodynamic is a type of isodynamic) is the happy combining of the simplicity and power of the magnetic drive used in moving-coil dynamic 'phones with the light, filmy, driven-over-its-entire-surface diaphragm of an electrostatic.

So imagine taking a coil of superfine aluminum wire and hammering it flat until it forms a thin, floppy spiral. Press this onto a circle of 2" wide clear packing tape, slap it between two perforated magnetic discs which are trying to repel one another, and you'll have the basic idea. Refine the idea by using photo-etching; make the packing tape Mylar, then pleat the diaphragm to give it compliance axially (in the direction of motion) and stiffness laterally (so that it tends to move as a disc). This combination, in the Yamaha driver, looks something like this:


PEERLESS PMB 100 DIAPHRAGM.................................................. ...........................................YAMAHA HP-50 DIAPHRAGM

The above left photo is a diaphragm from a Peerless PMB 100, kindly supplied to us on Head-Fi by member torrid ear (in real life MB Quart's Willi Presutti), showing the corrugations Yamaha used for their drivers' diaphragms up to the YHD series. HF member dBel84's closeup of a diaphragm taken from a well-used HP-50 shows how delicate it is and how much punishment it took out in the real world. The diaphragm is held in a frame but the corrugation removes the need for that frame to hold the diaphragm in tension. The corrugated diaphragm is thicker than a tensioned one, but it's self-supporting and supplies its own restoring force.

Note that the center voicecoil electrode, and thus the center of the diaphragm, is clamped inside the magnet structure, so the driver acts as a vibrating ring, very much like the driver in the Sennheiser HD 800.

By using magnetic drive we eliminate the need to generate high signal and bias voltages as well as the amplifier problems that arise when we try to drive a headphone that's basically a small capacitor, which is what an electrostatic driver is. In fact, an isodynamic driver is less reactive (that is, less like an inductor or capacitor) than a normal dynamic driver. Amplifiers simply love 'em.

A typical dynamic headphone driver's diaphragm must be mechanically rigid because it's driven only in a ring around the base of its central dome by a small, hopefully lightweight, coil. The undriven part of the dome has the thankless job of trying to follow the driven part as it vibrates 15,000 times a second. Rigidity, all other things being equal, requires extra material, which means extra mass. That extra mass should also keep the diaphragm of a dynamic driver from rippling, rocking, ringing, et cetera, but as the SPL climbs, increasingly it does not. Still, getting a heavy diaphragm moving isn't a tough engineering problem; if we want something heavy to accelerate rapidly, we hit it with a strong force. We hit it with a strong signal and use a powerful magnet. The tougher problem is getting that diaphragm to stop moving.

But-- if a diaphragm didn't have to be rigid, it could be made very thin and lightweight, easy both to accelerate and to stop. In an isodynamic driver, the uniformity and the simultaneity of the driving force makes the diaphragm effectively rigid, since the same force is being applied at each point over its surface (thus the term isodynamic)-- in theory, at least, and to a good approximation in real life. The penalties of high mass and the accompanying problems of stored energy and delayed release of that energy are thus reduced.

Having arrived at this point conceptually and having noted the success of isodynamic speaker designs like Jim Winey's Magneplanars, in 1976 Yamaha announced the HP-1. Its cardinal virtue was smoothness-- it may not have been flat, but cranking in a mild smiley on the graphic EQ gave a sound that, if it fell short of electrostatic clarity was at least reminiscent. Smoothness of response lends a 'phone clarity and the ability to listen "into" the music. It delays the onset of listener fatigue. It also indicates that nearly everything has pretty much been done right electromechanically. An astonishing (to me) number of HP-1s were sold for the then-princely sum of $200 (a 1976 Stax SR-X Mk3 cost about $300). There must have been a reason. Owners have repeatedly used the word "natural" to describe their sound.

Note: owners who bought their HP-1s in 1977 and later report a lower price, about $95.

By the way, Yamaha Japan has put a nice but brief look back at the HP-1 on its domestic website: HP-1 | DESIGN | ƒ„ƒ}ƒnŠ”Ž®‰ïŽÐ . If someone would like to translate the good parts for us, I'd be obliged. ..Aside from this, the usually helpful Yamaha site mentions nothing about their Orthodynamic headphones, almost as if the whole enterprise were an awful family secret too painful to remember. Because of this...


SPECS for the some Orthodynamics have been tough to come by, but the HP-1's look like this:

Magnet size: 55mm diameter. This remains true for the top-of-the-line Orthodynamics (except for the YH-1000) until the YHD series. Effective diameter (ie, the diameter over which the diaphragm is actually able to deliver sound through the holes in the magnets) is about 48mm. The less expensive HP-2 and HP-3 achieved their cost savings in part by using 46mm diameter drivers.

Impedance: 150 ohms. This is a function of both the length and thickness of the spiral aluminum track (its DC resistance) and its inductance (nearly negligible).

Diaphragm thickness: 12 microns of polyester, with the aluminum voice coil plated (or glued) 9mm thick on top of that. This compares to the Stax SR-40 electret electrostatics' 6 microns and the first Stax Lambda's 2 microns. So right away we know the diaphragm's not going to be as light as an electrostatic's, since it has to carry its own weight plus the weight of the voice coil. Right away we can also see a design problem coming: Just as with an electrostatic, there's no shock absorber function supplied by the driving elements as there is in a moving-coil driver, where the voice coil and the magnet work against one another to damp excessive motion of the diaphragm (primarily overshoot due to inertia). In an electrostat, you make the diaphragm light enough and big enough so the air load it sees can damp resonances that lurk in any diaphragm, whether under tension or not. The Orthodynamic diaphragm is far too massive and small in area for the air load to have an appreciable effect, so if nothing is done, the generic isodynamic driver will be characterized by one very broad but very audible resonance the location of which depends on diaphragm tension (in the case of electrostats and the YHD Orthodynamics, described later) or compliance, and mass. Therein lies a tale.

Sensitivity (efficiency): 94 dB/mW (102 dB/V). Fairly low, about 10dB below current dynamic models. This figure is printed on the US market HP-1 box. A German language brochure cites it as 96 dB/mW. We discovered an HP-1 variant (comes in a black, not silver, box) with "keeper" plates on the magnets that the box calls anisotropic, and a 96 dB/mW sensitivity, but still called HP-1. Looks just like a YH-100 driver, but isn't the same. Different versions for different markets? Could be. We've called this one the HP-1 Anisotropic.

Rated input: 3W. Pretty high. A good sign, given the low sensitivity.

Max input: 10W. Impressive. You could take this thing out of the headphone and use it for a tweeter, as Fostex did.



COST, COMFORT, AND THE DEVIL IN THE DETAILS

Variations in the thickness or width of the voice coil's spiral aluminum track would jeopardize that high power handling; a tiny nick somewhere in the track would turn the voice coil into a big expensive fuse. It's possible that a high initial reject rate of diaphragms as they fought to make the aluminum deposit perfectly uniform in thickness and width was a major part of the high cost of the HP-1, and that the lower cost of later models was made possible by Yamaha finally getting good yields of consistently-etched tracks.

The Mario Bellini headset design, revolutionary for its day, really was as comfortable as it looked, which explains why so many headsets have used a similar arch-and-strap design in the decades since. The magnets could have been twice as big and heavy (one can only imagine the bass output) and the phones would still have felt good. It's difficult today to imagine how much more comfortable the HP-1 was than the massive, head-clamping competition. There are, however, a couple of small mechanical problems: (1) the ball-joint earcup pivot connects to the headband via a small-diameter plastic strut. If the 'phones are dropped and this strut breaks, the 'phones are done for. (2) that ball joint pivots in a small, loosefitting metal socket inside the earcup and makes loud, annoying clicking and clunking sounds as the 'phones are settled on the listener's head. The sounds are carried through the entire structure; it's a sensation not unlike flicking a plastic ruler held clenched in the teeth. Not a problem if the listener holds still, but disconcerting, especially at first.

After some time spent listening to the HP-1, some owners began to notice a slight hollow, "plasticky" sort of quality to the sound, most noticeable during playback of the typical LPs of the time. Phonograph playback in the '70s wasn't the Platonic ideal of pristine sound reproduction many today would have you believe. Clean records, clean by today's standards, were hardly a given. So there was plenty of what's called impulse noise, ultra-brief needle-like (pun intended) spikes of sound, sometimes so frequent and continuous it was called "crackle". This was simply accepted BITD (back in the day)-- when you played an LP, the stylus would encounter little pockmarks and bits of gravel in the groove and play them. Result: tic! tic-tic! TIC!

Ideal waveform, as it turns out, for testing a headphone.

On the HP-1, LP impulse noises that used to be tic! were now coming out as thokkhh!. It was so unexpected that it was hard to know what to blame.

Some attributed it to the closed back of the earcups (when tapped, they sound hollow, though they're really not) or the "sound" of the plastic diaphragm. While the character of the 'phone, its smoothness and naturalness, dominated, at the same time there was definitely something not quite right about the sound. Eventually this good/bad quality drove some owners to put aside their Orthodynamics and look elsewhere for good headphone sound.


CAUSES, POSSIBLE CURES

What caused this? Let's look inside. For acoustic treatment, the interior of the HP-1's earcup contains only a thin, lightweight acoustically-transparent opencell foam pad just behind the driver, and although there are felt pads which cover the vents and fill the space around the edge of the driver, sound comes out of the back of the driver, passes right through the [useless?] little foam pad and smacks right into a smooth, reflective concave plastic wall. Yes, the cup is vented, but the vents are located around the cup's circumference (as you can see in the photo above) rather than directly behind the driver. What were they thinking? a labyrinth effect to delay the bass from the backwave? Perhaps. But what about treble reflections inside the cup? And could this be the source of the problem?

My working hypothesis throughout this series of posts is that while the reflective earcup certainly isn't helping anything except possibly to shore up a sagging treble, Yamaha's diaphragm is simply too massive for its oscillations to be damped by the acoustic resistance supplied by the little foam pad-- imagine a heavy jumper on a trampoline "damped" by nothing but a big fluffy layer of meringue on the trampoline's underside. This is why in other threads I've advocated applying discs of dense felt to the back of the driver. As the diaphragm tries to push air through the felt, it meets resistance that damps out overzealous (ie, due to resonance) motion, just like a shock absorber in a car. This, it turns out, makes all the difference.


When applied to the back of the driver in an Orthodynamic headphone, a damping pad's primary effect is to drastically flatten the response curve, depressing the broad lower-midrange resonance hump and effectively bringing up the formerly weak bottom and top ends. It also has the salutary effect of greatly tightening up the bass, making the HP-1s behave as they were presumably meant to 30+ years ago, maybe better. Bass becomes percussive, tactile, almost speakerlike. A damping pad also soaks up some of the treble backwave, keeping it from ricocheting around the cup.

It also makes the 'phones even less efficient.

You'll notice that most high-quality dynamic drivers also use either damping pads or tiny pinholes in their frames or baskets to perform the same shock-absorber function. For example, you can see the holes method used on the back of the Koss KTX and KSC drivers. You can easily see a white damping pad under the mesh grilles of Sennheiser's HD-600 and -650. A black strip of porous material is visible on the back of Grado's drivers.

Why didn't Yamaha do the same for the HP-1? Would that have raised the price to $200.10?


ONE MAN'S RESULTS

The first Head-Fi member to try damping his Orthodynamic 'phone based on the above recommendations, back in Feb '05, was Bias. His comments (from this thread) are reproduced here in their entirety:

"I modded my old Yamaha HP-1's earlier tonight as per Wualta's recommendations. The result is exactly what Wualta predicted: the addition of extra damping materials in the transducer housing (in this case a piece of round felt directly behind the driver across it's entire diameter) flattens the freq response by smoothing a low frequency resonance hump. This results in better perceived high frequencies and a better differentiation of lower bass extension from, say, the mid-bass area. Sonic characteristics (the amazingly smooth, non-fatiguing presentation, etc) remain intact. I never fully perceived the so-called 'orthodynamic thunk' so it's hard to say whether or not this has been lessened... but thanks for the tip Wualta. I must say, as a recording engineer, I've listened to many different types of headphones and monitor speakers. These Yamaha's now remind me very msuc of the vaunted Yamaha NS-1000's whose freq response was amazingly flat and accurate. I can now do final mixing and mastering on these headphones with this improvement. But who wants to do that...i'd rather just listen to great music all night long with these incredible cans. Team Ortho-fantastic!"

Bias' results encouraged me to begin this thread.


Edited by wualta - 1/28/11 at 4:00pm
post #7 of 23556
are they driven like normal dynamics?
post #8 of 23556
Quote:
Originally Posted by 1967cutlass
are they driven like normal dynamics?
Yes they they are, but they are not as efficient as many moving coil designs so they usually require a reasonably healthy dose power to get the best out of them.[and an amp with a low output impedance, no 120 Ohm source R here]


Quote:
Originally Posted by wualta
Setmenu: Thanks for bringing up an important point about the isodynamic type. You don't need superstrong magnets and you don't need exotic materials and you don't need great precision in manufacture-- the drive principle inherently takes care of many of the problems that dog moving-coil phones. Were the Wharfedales considered expensive when they were new?
I would not entirely agree with your interpretation here.
Planar transducer types suffer from, rather than do not need strong field strengths, due to the large flux gap the coil has to sit in to allow for the diaphragm movement.
My own phones use incredibly strong neodymium magnets to try to compensate
for the poor magnetic circuit efficiency.
Generally the vintage planar phones talked about here use poor strength
ferrite magnets, the Wharfdales especially, as they use ferrite 'flexi' magnets.
This low field strength probably accounts for some of the less than ideal bass control/ performance that these designs can provide.
As for manufacturing precision,critical areas require as much precision as
any other transducer, such as precise alignment of moving parts.

All transducer designs have their pros and cons, it would seem the moving coil
won the war of popular acceptance as the most of the output of the worlds
transducer manufactures is geared up to producing these designs.
New developments or advancement in alternatives seems to be a fairly rare backwater.
Modern moving coil based headphones are extremely good these days.

But, like yourself I have a certain love of the planar/ribbon driver concept,
there is a sort of purity in the directness if the design that greatly appeals
to me.
The purest concept of hanging impossibly thin conductive ribbons in a magnetic field just seems to be made for the 'perfect headphone' .
I have tried using the above simple aluminum ribbon but driving it successfully
requires combating the very low driving impedance etc .
I have yet to explore this to any great degree , instead going the etched coil route along the lines of the commercial phones mentioned here.




Setmenu

Team Planar
post #9 of 23556
Thread Starter 
Quote:
Originally Posted by setmenu
I would not entirely agree with your interpretation here.
Planar transducer types suffer from, rather than do not need strong field strengths, due to the large flux gap the coil has to sit in to allow for the diaphragm movement.

I don't mean to imply that the strongest possible magnetic field isn't desirable, but your Wharfedales work pleasantly well with what sounds like glorified refrigerator magnets. A designer can always decrease the gap the diaphragm sits in to crank up the field strength and maybe increase the tension on the diaphragm to add restoring force so the diaphragm doesn't hit the magnets. Bass suffers, but the result is a quick and dirty (and lightweight) headphone that has many of the sonic virtues of a strong-magnet design-- as long as mechanical damping is present, which is what I'm trying to demonstrate with the Yamas. Power handling and efficiency suffer with weak magnets too, of course. You always want the strongest magnets you can get.

EDIT: Here's a scan from a Yamaha brochure describing the HP-1A (which I still have not seen or heard) and HP-2. Notice the square holes in the magnet drawings. Notice also that the Yamablurb calls the foam behind the driver "damping material" and boasts of "excellent bass damping"-- well, it should have been:


Edited by wualta - 1/28/11 at 4:00pm
post #10 of 23556
Quote:
Originally Posted by wualta
Wualta replies:
I don't mean to imply that the strongest possible magnetic field isn't desirable, but your Wharfedales work pleasantly well with what sounds like glorified refrigerator magnets. A designer can always decrease the gap the diaphragm sits in to crank up the field strength and maybe increase the tension on the diaphragm to add restoring force so the diaphragm doesn't hit the magnets. Bass suffers, but the result is a quick and dirty (and lightweight) headphone that has many of the sonic virtues of a strong-magnet design-- as long as mechanical damping supplements the weak electromagnetic damping, which is what I'm trying to demonstrate with the Yamas. Power handling and efficiency suffer with weak magnets too, of course. You always want the strongest magnets you can get.
Hehe, you are not wrong when you describe the Wharfdale magnets as glorified fridge magnets!

Decreasing the flux gap is not an easy answer if you want to increase filed strength.
Adding tension to the diaphragm can play havoc with resonance if you
use it as a method to control excursion.[well it certainly does with my ribbon
type designs]
Though with modern neodymium magnets it is possible to achieve pretty strong fields even in large gaps. [relatively speaking]


Setmenu
post #11 of 23556
IMO a strong magnetic field can't compensate for a weak mechanical damping, since it has no damping effect at all with planar transducers: Keep in mind that there's virtually no back-EMF induced bass resonance in the impedance-response curve, and that would be the only area where some electrical damping could happen and actually happens in moving-coil driven dynamic transducers.

I agree that the closed back of the HP-1 was a serious design flaw and responsible for its mediocre sound. You can't combine an extremely sound-permeable thin mylar diaphragm with a barely dampened closed back. But even with an open back (which probably would have required a redesign of the membrane or a different tuning) there's still a fundamental weakness of the iso-/orthodynamic principle: The sound waves have to pass through the magnet system: the cause for serious colorations in the form of crippled transients due to abrupt changes of acoustic impedance as well as the introduction of near-field reflections and artificial acceleration of air molecules with their sonic consequences. BTW, that's what they have in common with electrostats, but in a worse form thanks to the lesser sound permeability and the hinted «wave guides» (due to the thickness of the holed magnet plate).

I had a weakness for planar transducers in general and headphones in particular -- from a technical perspective --, but I never really liked their sound, be it Wharfedale, Yamahas, Peerless... The latter, sort of Jecklin Float clone, was the one I liked best sonically (despite lacking low bass), but still not enough to keep it much longer than the others.

post #12 of 23556
Quote:
Originally Posted by JaZZ
IMO a strong magnetic field can't compensate for a weak mechanical damping, since it has no damping effect at all with planar transducers: Keep in mind that there's virtually no back-EMF induced bass resonance in the impedance-response curve, and that would be the only area where some electrical damping could happen and actually happens in moving-coil driven dynamic transducers.

I agree that the closed back of the HP-1 was a serious design flaw and responsible for its mediocre sound. You can't combine an extremely sound-permeable thin mylar diaphragm with a barely dampened closed back. But even with an open back (which probably would have required a redesign of the membrane or a different tuning) there's still a fundamental weakness of the iso-/orthodynamic principle: The sound waves have to pass through the magnet system: the cause for serious colorations in the form of crippled transients due to abrupt changes of acoustic impedance as well as the introduction of near-field reflections and artificial acceleration of air molecules with their sonic consequences. BTW, that's what they have in common with electrostats, but in a worse form thanks to the lesser sound permeability and the hinted «wave guides» (due to the thickness of the holed magnet plate).

I had a weakness for planar transducers in general and headphones in particular -- from a technical perspective --, but I never really liked their sound, be it Wharfedale, Yamahas, Peerless... The latter, sort of Jecklin Float clone, was the one I liked best sonically (despite lacking low bass), but still not enough to keep it much longer than the others.


Those perforated magnets covering the membranes always bothered me hence the open ribbon design.
Did you try the wharfdales minus that black perforated grill in front of the
transducer?
Removing it certainly opened the sound up.
As for the Yams my I have the HP2 and it sounds OK[ ish] but not really my
bag either.

Setmenu
post #13 of 23556
Quote:
Originally Posted by setmenu
Did you try the wharfdales minus that black perforated grill in front of the transducer? Removing it certainly opened the sound up.
No, I didn't go this far at that time -- it was more than 30 years ago...

post #14 of 23556
Thread Starter 
Quote:
Originally Posted by JazZ
IMO a strong magnetic field can't compensate for a weak mechanical damping, since it has no damping effect at all with planar transducers: Keep in mind that there's virtually no back-EMF induced bass resonance in the impedance-response curve, and that would be the only area where some electrical damping could happen and actually happens in moving-coil driven dynamic transducers.

JazZ is absolutely right; I gladly stand corrected on this. Despite looking at a planar, I was still thinking moving-coil. My clue was that the Fostex T50RP uses NdFeB magnets but still has a damper pad over the back of the diaphragm. I've corrected all of my earlier posts.

Bottom line: an isodynamic headphone driver of the type we're surveying always needs some form of mechanical damping. Weak magnets, strong magnets-- the sound quality doesn't change, just the efficiency and power handling.


We agree that the design of the Yamas is almost laughably primitive. Except for the fancy headband and the pleated diaphragm, this is about the simplest form an isodynamic can take (although the Wharfedale is in a class by itself; my hat is off), and with NdFeB magnets the "stators", for example, could be much more open. If we had to use ferrites today, we'd at least chamfer the holes to keep turbulence down-- and I'd love to know if that would make an audible difference. In any case, the magnets don't stifle the treble. We have too many people who've done too many mods where the high treble extension and level matched the brightest electrostats for that to be true. What's so much fun and so surprising about the Yamas is to hear how good they can sound despite being so primitive.

I'm certain the stingy little holes (more like short tunnels) in Yamaha's magnets do affect the sound for the worse. Still, with proper mechanical damping, I don't hear anything I would call a "crippling" of transients, but perhaps that's just my ancient ears. In fact, the transient response seems excellent, and as always, even if the theory looks good, the real test is: is the effect audible?

An elucidation (by someone-- anyone?) of the mechanism of alleged transient "crippling" caused by small magnet holes would be interesting to read. Partial reflection of the wavefront at entry and exit points of the sharp-edged, straight-sided holes, perhaps?

We don't agree that the closed back in and of itself was responsible for the flaws in the unmodified HP-1's sound. You can make a Yamaha sound very much like an old Fostex T50, which has an open back, and the differences are primarily some roughness and brightness in the treble and a collapsed soundstage on the part of the Yamas-- that "closed-in" feeling some owners report. It's possible that Yamaha chose the vented but closed back (which also appears on the B&O U70 and the Realistic Pro30) to boost the sagging high end of their underdamped drivers-- rank cheating, to my mind.

The audibility of flaws in any headphone rises with purchase price and expectations, as it should. It's good to remember that we're dealing here with 'phones that can be had for about the price of a Grado SR-60 and respond well to tinkering. We're talking cheap fun. Having said this, I happen to believe that despite the low outlay of cash, there are virtues that arise from driving a diaphragm isodynamically, however it's done, that are unique-- so far-- but that no driving principle is necessarily going to produce a 'phone that's the be-all and end-all. Hearing what a simple isodynamic can do can whet consumer demand for something even more advanced in today's market. Choice is good.

Anyway, next up are the YH-1 and YH-100. Thanks very much for all the comments, corrections and suggestions. Keep 'em coming..


Edited by wualta - 1/28/11 at 4:00pm
post #15 of 23556
Anway, technical discussions aside, how would you compare the sound to a set of Grados? I don't normally have upgraditis, but I do have a penchant for unconventional designs. And they don't sound like they're horribly expensive either, which makes them all the more enticing.
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