Robbo1802

Hi arnaud, purrin Well I have already stated my views on distortion and its measurement, although mostly regarding the phones rather than the amplifier. I believe IMD testing is necessary. I would be surprised if Stax got it that wrong but then I was so very surprised when Revox got it wrong. The multitone test that Linkwitz is so fond of might be interesting even when applied to an amplifier. Of course, the dummy load for testing is just a capacitor. The difference between a simple capacitor and the phones is quite small. If people were really concerned and wanted to use the phones themselves as loads, turning off the bias voltage would prevent damage to the phones. 'T'll be interesting. Regards, Bob

Hello arnaud Hmmm,well I can't comment on modern Stax, my Lambdas ( as well as my SRXMk3 pros) came from the old Stax. In the Lambda case 5 of us got together and did a bulk deal OS. We had to wait and wait. All the phones were different most subtly but one pair was to our minds quite different but still resonably balanced. At the time we bought the Lambdas, it was said by people (who seemed to know) that the major problems Stax was having was low yield and the difficulty of matching the drivers well enough for a stereo pair. Not long after this the old Stax ceased to exist. I don't know but I suspect that part of the high price may still be tied to this problem - specifically diaphragms. I note that there seems to be a similar issue with at least some of the planar magnetic types. I have 4 sets of original 70s era ESS AMTs (yes they survived, like some other parts of my gear they were on loan) and even when the same type of diaphagm was used, they varied slightly which is amazing to my mind considering the principle of operation and construction. Tyll, Speaking of AMTs, after this electrostatic testing is done you will have covered about every type of transducer short of AMTs. I know the field is rather thin ... ahhh 1... but have you thought of trying to get a pair? Testing floats might be a bit of a challenge especially when it comes to interpretation but.... arnaud Ohhh, I didn't know you did that sort of work (he says, figuratively inching away from the keyboard - hows the medication working out - sorry couldn't resist). Regards, Bob

Hi Nevod, I initially missed your post Different side to side diaphragm loading (or damping) should not create asymmetrical diaphragm movement and thus 2nd order harmonic distortion. The diaphragm 'sees' the load on both sides as the total load, and will respond to the total load ( again from both sides) independent of the direction of travel. Now if the behaviour of the damping material was asymmetrical, that is, there was more resistance to the air moving in one direction than the other, then it would produce asymmetrical movement of the diaphragm and thus even order harmonic distortion. Yes the LCD-2s do seem to show the best measured performance, certainly the distortion plots are very good with an outstanding CSD. Indeed the CSD shows far less stored energy in the midrange than any others I have seen shown here, the bass is astonishing, okay there are a few small ridges but.... The slope on the square waves is mostly a function of the now airtight the ear cup is, the flat part of a square wave is after all DC - consider a square wave of 1hz, the air will leak out. When you say dip are you referring to the absolute 'phase' of the headphones, that is, a positive voltage spike creates a positive pressure spike? I will not get into the debate over absolute 'phase' except to ask: are you sure that Tyll's test rig has correct absolute 'phase' and doesn't invert the signal, perhaps it is LCD-2s that are inverted? Regards, Bob Hmmm, The ESP-950s do seem to have ports in the stators rather than the usual holes, they appear to be asymmetrical with one end curved and one straight end, possibly..... nah, I just don't believe it, the fluid velocity could not be high enough for asymmetrical turbulence.

Hi Arnaud, I don't really know what to say. The power of modern software - astonishing! This is an edge clamped uniformly tensioned membrane,isn't it? In the last animation what are we looking at,displacement/velocity? I am rather confused by the large modal variation (what are we going to call the peaks and hollows?) at the edge of the diaphragm, intuitively the least likely spot for such variations. Quite frankly, at 3.7khz I would have expected a much lower mode (annular too),much more heavily damped - there goes my insight, fluttering away like that diaphragm. Still in all, very impressive, Bob BTW If you find some data on the compliance of real Mylar, remember that the bias voltage creates a negative compliance thus reducing the net compliance of the membrane.

Hi Tyll, Yes I note the pre-ring is also in the 007 tests but none of the others I downloaded from your site seemed to have it (that I can see in the smaller plots). Pre-ring implies a time machine or prescient headphones. I'll stick with the time machine (digital delay lines) so it is most likely an artifact of your measurement rig, It looks suspiciously like the pre-ring of a high order, low pass, Finite_Impulse_Response Filter. Have you changed anything lately? Perhaps a filter setting or windowing function?? I will have to think about some of this. My initial thoughts: The square wave and impulse responses are really testing the same thing when it comes to the early part of the waveform. The speed of attack, ringing etc is always a balancing act where damping sometimes has all the subtlety of a lump-hammer. The quest for lower and lower moving masses is all about reducing the stored energy and making it easier to damp out ringing without loss of attack. The compensation ( I assume you mean the free field etc) probably will not greatly affect what you see in the square waves. I am surprised by how different the impulse responses are between the two Staxs without huge differences in CSDs. The ears are surprising good at detecting some things,but it is a learned skill and it needs a reference point - what do these instruments really sound like? My own testing way back with the pianos and speakers involved listening to the piano for at least half an hour before auditioning the speakers - there were no recorders involved,the guy was a pianist and had a sound insulated studio complete with concert grand and another sound insulated room that was his music room (where the speakers were auditioned). When auditioning the speakers, the sound path was piano>mic>preamp>lineamp>power amp>speaker. Regards, Bob A rough estimate of the ring places the transition frequency of the filter at about 32Khz, have you done an electrical loopback test of the impulse test?. A second look at the CSDs for the Staxs does correlate with the impulse response, the problem with the CSDs is the linear frequency scale, so much of the important information is compressed on the left side that it always skews my perceptions.

Hi arnaud, A quick note. The main reference "Loudspeaker and Headphone Design" 3rd ed by John Borwick is currently in an active torrent and is also up on usenet in alt.binaries.e-book.technical Regards, Bob

Hi arnaud, Some references, The Streng papers and a copy of the Baxandall ES chapters out of Borwick (1st Edition by the looks) http://quadesl.nl/en/tech-corner.html The site is very interesting, but then I did have some ESL57s so I am probably more interested than most. A Download of a late JAES paper on electrostatics http://lahorde.is.fr...USTICS_HIFI.PDF A search for documents on the one thing site,shows some the original Wireless World papers http://www.google.co...=utf-8&oe=utf-8 Linkwitz site on distortion in woofers http://www.linkwitzl...m/frontiers.htm I found this page on Linkwitz looking for a reference on multitone testing of loudspeakers. But Linkwitz's work has always appealed to me A site with a lot of papers on distortion in loudspeakers http://www.klippel.d...ure/papers.html Although concerned with conventional speakers, the general discussion is still quite useful. Linkwitz's use of a 5 tone multitone test, is not a standard method but I find it quite illustrative of how even relatively simple signals get very complex very quickly as the non-linearities create harmonics and sidebands. Perhaps Tyll could took at this as it is well within the capabilities of his test rig. (Ooops, Tyll, I am sorry for referring to you in the third person.) Most of the dynamic phones show the classic rising distortion in bass caused by the increase in deflection and thus non-linearity. How would they compare to say the ES and magnetic planar headphones under this test. The assessment would be necessarilly subjective, along the lines of messy/verymessy/clean etc. As to the high order modes, I will stop using the term 'breakup' although I cannot think of another descriptive term that applies. I did remember the Bessel functions but Green's always stuck in my head because I had so much trouble with it, I would not even attempt it now. In any case, he uses Green's function in the "Sound Radiation from a Vibrating Membrane" paper - my memory is not so bad after all. In the papers, he demonstrates mathematically that almost all the cancellation occurs within a Z axis of .25 of the radius of the diaphragm, so say within 15mm of a ES headphone. Ahhh, linear systems, I remember the Quote of Stanislaw Ulam : "Using a term like nonlinear science is like referring to the bulk of zoology as the study of non-elephant animals.” >>>))) See ya, Bob

Hi all, Thanks for the welcome. Hopefully I will not make a fool of myself here or upset too many people. I don't normally use forums anymore - too much lost time on Usenet and Fidonet before it. Now to the first point, I unequivocally revoke all mention of the term Doppler distortion as I was not really thinking when I added that bit, fortunately no has one called me on it yet. Hi Tyll, I followed your link, a most impressive set of tests. I can appreciate the work involved in both the testing and writing of reviews. I understand your desire to keep the testing confined to the most useful measurements. Nevertheless, the ex-engineer in me (yep, you picked it) can't help but wish for you to test every possible parameter while all those phones are available. >>;-)> I downloaded the manual for your test equipment and did a quick scan, did you get the IMD option with it? I also noticed that the gear has a multitone test which also has some interesting possibilities. Being an ex-engineer I NEVER read the manual but just start playing with the knobs. Reading the manual for your gear makes my head hurt. Using the impedance measuring test is not that difficult but it does require a small modification to the ES amplifier to allow the measurement of the output voltage and current across a small series resistor in the output leads as well as a switch to turn off the diaphragm supply. I did a crude version of this to assess the impulse response of DIY ES phones I made 20 odd years ago - these were initially based on the Pollock design but started to diverge after a while. Ahhh, the plans - like most plans, they were never fully realised. Hi Spritzer, They were the MX-1s. I have started to look at some of the photos you posted of your disassembled phones. I was especially intrigued by the photos of the "super rare SR-Omega driver ", do you have a closeup of the stator mesh? Is there a site that fully explores the design and construction of the various Stax headphone variations? It has been a while since I looked at ES speakers and headphones, there is just so much more stuff available on the internet than even a few years ago. Hi Arnaud, The blocked impedance is a little more complex (inductances and resistances) but you are essentially correct. This technique of assessing loudspeaker performance is very established and I am sure you could find a good account of it on the internet. Nevertheless I will see if I can find a good reference about it. The technique is especially good with ES speakers given their very high reciprocity. The testing of the ES cells in free space is most useful for determining the sources of various resonances (as well as other problems) and assessing the results of various damping strategies. This information is useful in the design phase and of course is also useful for developing modifications. As to the IMD part, this got a little confused in my original post. I will thus refer to harmonic distortion (THD) and IMD with all non-harmonic distortion (this includes pure IMD, as well a form of FM distortion caused by the movement of the diaphragm that creates sidebands - this distortion occurs in even perfectly linear transducers, and some low order AM distortions) lumped under the name IMD . If there is any non-linearity in the system, it will produce both harmonic and intermodular distortion, there is no escaping it - the question is: how does this distortion affect the sound? More on this later. Unfortunately the diaphragms do not display the pure planar behaviour that we intuitively believe should occur. Streng proved it mathematically using Green's function (Memory?) and then validated the proof with measurements on a test speaker - I must really find a copy of his 4 papers. From memory the modal breakup was somewhat different to the rigid piston model and was entirely of the annular ring form, I vagely remember that the annular nodes actually swept across the diaphragm as the excitation frequency changed. The breakup resulted in localised 'movement of air’ parallel to the diaphragm from the 'in phase' part of the diaphragm to the 'out of phase' part of the diaphragm. One of the outcomes of the work was that a relatively small amount of damping material, close to the diaphragm, 'disrupted the air flow' and damped out the modal breakup - this may have consequences for people who like to remove damping in their ES headphones or who build ES speakers without damping. Now, if the diaphragm does breakup, the deflection will increase, the inherant non-linearity will increase, the distortion will increase, thus my reference to using IMD (and the not mentioned - THD) to indicate possible membrane resonance. Here is a possible avenue to explore, if a CSD shows a problem resonance and a distortion plot shows a peak in distorion at the same frequency, does this indicate that there is a high probability that the resonance is from the diaphragm rather than elsewhere in the headphone - just a thought, could be wrong. As to the loss of all that old gear, I am sad that some rare equipment is now even more rare, but there is a silver lining, my collection of broken (very expensive) phono cartridges is now gone. Every time I saw the box they were in I just got angry - that box was the reason I celebrated the introduction of the CD. I suppose the reason it doesn't drive me mad is that I don't really (not in my heart) believe that it is actually gone. I will start looking for those papers in different places. I do have a lot of PDF books on HiFi and acoustics but not the ones I want. One of Streng's papers looked at charge distributions on the diaphragms, if memory serves, this paper also had a sting in the tail - must find Streng! Hi Purrin, I had a look at your distortion plots of the ESP950s. They are most interesting. First, a look at the harmonic distortion measurements. Fortunately you show the spectral distribution of the distortion rather than just the THD. I find it interesting that the second harmonic distortion is higher than the third. The theory of push-pull ES consistently shows that the even harmonics should be very low, much lower than the third (actually, theoretically zero). There is a caveat, this cancellation of the even harmonics requires a high diaphragm resistance (the usual quoted value is 10exp9 per square or above, preferably 10exp11 per square). So either there is a problem with the testing <sorry>, Koss has got the diaphragm resistance wrong, or there is some other factor in play that I don't understand. Tyll, Would it be possible for you to produce the plots for the different harmonic orders, at least for one channel and level? Similarly, I believe the IMD is higher than it should be although I have no theory or data to back this up. I wonder if there are some IMD results for other ESs out there Now, as to the importance of IMD to the sound. IMD has always been my favourite boogyman. I believe the fundamental problems I had in finding good phono cartridges was their poor IMD performance. <rant mode on> The cartridges I liked the most were always the fringe ones, okay I did like the occasional moving coil but I lived in a sub-tropical climate and all those cartridge manufacturers lived in cold climates, bloody suspensions packed it in on every one except the Ortofon (which I disliked intensely) within a year. <rant mode off>. I believe that the lack of clarity I hear in so much HiFi gear is caused by the hash imparted on the signal from IMD, there is plenty of it in recordings as well. I have proved this to myself many times by comparing live music to music played back via several rather expensive speakers. A live grand piano is just so sparse compared to the sound of the same one played back through most speakers - the speakers just add so much hash. I was in a position to test this many times (friends with large houses, grand pianos, Schoeps microphones, etc), although I only tested speakers, not headphones. Best result (for lack of hash) was Quad ESL57s but they had their own problems especially with midrange colouration and a soft top end. Horns were also good at low hash but again coloured, we could never get Maggies to sound right - must have been doing something wrong. Oops, another long rambling post – things aren’t getting better. Regards to all, Bob BTW Just saw the Stax measurements – wow – much to think about

Hi, A total newb here but not to electrostatic drivers. I am a bit curious as to what you are trying to achieve with these measurements. Is this an attempt to correlate possible audible effects to measured effects, i.e. resonances to colouration? Alternatively are you trying to relate the design of the headphones to their measured performance? You guys are going to quite a lot of effort to get together a large collection of ES phones but have you worked out exactly what tests you are going to perform and how you are going to do it? This is not criticism, I am genuinely curious and quite excited by the prospect. Since this is all about electrostatics (as an addendum to the standard CSD etc tests), have you considered going back to basics and use the methods employed by Peter Walker etal when assessing their speaker designs? One of these would be to exploit the reciprocity of the electrostatic transducer and use it both as speaker and microphone. This is fairly easily done by measuring the blocked impedance (electrical) (with signals of choice eg. sweeps, MLS, impulse),measuring the unblocked impedance (electrical), subtracting the two to give an almost exact representation of the acoustic power being radiated by the diaphragm. This power will change depending on the acoustic impedance applied to the diaphragm by the real world and will show up resonances in the stators, casing, stator hole impedances, reflections from the stators, diaphragm primary resonances (but not many modal resonances - more later), even reflections from the room boundaries. For the uninitiated, the blocked impedance is simply the impedance of the system when the diaphragm is blocked from moving, in the case of electrostatics this is easily achieved by turning off the diaphragm bias voltage. One of the problems with this method is that it gives best results (from a designers point of view) when the transducer is radiating into an empty room - well at least one member of this forum seems to like pulling his expensive ES headphones apart. >;-) Other tests worth considering are the distortion tests, especially a swept Intermodular distortion test (IMD is sometimes referred to in loudspeakers as Doppler distortion). This test can often reveal unexpected diaphragm behaviour like the modal patterns shown by Streng in his papers (something often ignored by ES designers or their marketing departments - I notice that Wiki still implies but does not state the fallacy of pure planar behaviour). This is very important in ESs as unlike most other drivers an ES has its radiating surface inside the motor ( Ok, there are others such as AMTs and planar magnetic, in the former modal breakup would be very different if it occurs at all and I haven't much studied the later). So, in ES speakers, modal anomalies can significantly affect the 'motor behaviour' regarding distortion and overall available output levels even if they are not clearly audible (many modes have little net output as the positive nodes and negative nodes tend to cancel each other out [see Olsen, Berenak etc] and may not show up very prominently on CSD plots). Unfortunately, I am not in a position to help. I am currently traveling around Australia in the a motorhome (year 7) and have none of my library on ESs with me. Indeed, I have had to revert to dynamic headphones as I didn't deem the ESs sufficiently robust or their amplifier practical with our limited (off the grid) power resources. I should have brought them with me as a disaster last year has seen them and a great deal of other HiFi gear (which I had in storage) completely destroyed - some of it was practically irreplaceable - older, collectible stuff - often impressive to look at, some of it quite beautiful, and the odd bit here and there occasionally even sounded good. There are copies of PDF copies of Borwick 3rd ed floating around on the internet so Peter Baxandall's work on ES is available but this seems to have changed considerably from what I remember of the 2nd ed. I have not been able to source the Walker, Streng, etal papers off the internet. The Streng ones originally published in the Philips Technical Review are most interesting as they led to an experimental segmented ES loudspeaker that was shaped (from memory) as an isosceles triangle. I was tempted to post this in the CSD tread on HF but this one is specific to electrostatics so I thought it more appropriate. Regards, Bob BTW Sorry about the rambling post but my english skills as well as abstract mathematics skills have abanded me these days. My first electrostatic - Micro Seiki (Stax in disguise), bought new circa 1975. From memory( 25+ years), mine seem to be different to the one sometimes shown on the internet. The diaphrapms (which eventually failed) were not tensioned until the cell was assembled. There was a ridge on the stator molding which pressed against the diaphragm locating it centrally in the gap while at the same time tensioning it, when dissassembled the diaphragms were quite loose. I haven't seem this technique mentioned elsewhere although it may have been something to do with the diaphragm material which did not appear to be mylar - it seemed more elastic. From memory, the bias voltages were also quite different from what you would expect, maybe someone can shed some light on this. Ohh yes, the Micro Seikis sounded quite good as long as you were a bass atheist, even then I has hooked on ESs (and Heil AMTs).