John Buchanan

LOL - glad I saved AUS$14,000 by buying a demo 989 pair instead of the 2905s.

Holy shit! I've got 989s at home, but a double quad of Quads!!! How high are those ceilings?

CharlieX - whoa. Very nice combo there - listen first. Big $$$ to better

I kinda wanted to see if it was usable on a Sigma - the dimensions seem right TIA Duggeh - what's the weather like over there? 40C here yesterday - had a lovely day down by the marina chatting to a lovely woman most of the afternoon. All good.

WTF!!! I don't care about the re-capping - there may have been other reasons for that - but removing the wool from the Sigma Pros is just wrong headed. 2 obvious reasons - firstly reduced front to back isolation around the drivers will cause an even more severe deep bass roll-off than these phones already have. Secondly, the wool provides the equivalent of room type diffractive, reflective and absorptive surfaces. Remove it at your peril, my friends.

Duggeh, when you get that 4070 headband, could you please post pics of it?

Agreed - this is a real time saver.

Apart from colour differences and quality of cable differences, yes - the same.

I was very lucky. It is in absolutely new condition! Not cheap, but worth it. I've only ever seen one for sale before and it had seen far better days. Not this one - looks like it came straight out of the wrapper. Go for an SRM 717 - it's excellent also, and scales up well balanced......or......gulp......Spritzer's SRM-T2. You know you need to get that one LOL.

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Never heard the Sigma Pro, but Birgir's opinion of the other two is correct. IMHO, the Sigma/404 is the best as it has the best treble response, and a slightly smoother and deeper bottom end. I think Naotake Hayashi was a very smart man to have invented these phones. He really had a good lateral view, and came up with a different way of creating the illusion of listening to speakers in a room. He apparently liked the Sigma best, but at that time, there was nothing else in that line apart from the Sigma Pro. Now we have the Sigma/404 option.

No schematic, no manual, no box.

I'm not gonna pull any boards out - these are the best I can do in situ. There is a vertical daughter board and a horizontal mother board. The other side of the metal shield is the SRM-1 Mk2 board. Pictures by buchanan67 - Photobucket

The following is what I can understand of the theory behind the diffuse field equalisers Stax produced and an assessment of the sound of one of them. Diffuse Field Equalisation vs Free Field Equalisation. Headphone frequency response measurements, conducted with a microphone in front of the headphone driver, much as speaker measurements were conducted, observed that headphones with a measured flat frequency response did not sound as flat as they measured. Comparing the sound of a flat measured speaker with a flat measured headphone revealed extreme tonal differences that started off a whole lot of investigation into why they sounded different and how a headphone’s frequency response could be altered to make it sound like flat measured speakers. An experiment was set up as follows: 1. A loudspeaker playing a frequency sweep was recorded by a high quality, miniature microphone in one of two types of room – either an anechoic chamber or an approximation of an ordinary room (see later) – and the frequency response was charted. 2. The same microphone was inserted into a subject’s ear canal and the same speaker replayed frequency sweep was charted again. 3. It turned out there was quite a difference between the charted frequency response of the two recordings. 4. It was postulated that if the frequency response of the recording made by the microphone in the ear (see 2) could be altered by pre-equalization to ultimately match the shape of the frequency response of the recording of the same microphone when not in the ear (see 1), and further, that replay of that in-ear microphone recording could be made to sound the same as that of replay of the recording made by the same microphone in a room if that pre-equalisation was applied. 5. This gave rise to a target measured frequency response for a headphone to sound like a flat measured speaker i.e. if the headphone had a measured frequency response that looked like the target response, it should sound flat when reproducing a recording that had been mixed with speakers in front of the mixer, and sound as if one was listening to speakers in front of him/her, rather than via headphones. 6. The concept of pre-equalisation of headphones was thus born. Pre-equalisation could either be mechanical (i.e the driver frequency response was manufactured to behave that way e.g. the AKG 240DF – not so easy) or electrical (which should be cheaper, easier and field-adjustable), and meant that although the headphones now had a frequency response that had been altered to something that looked decidedly non-flat when measured, it reproduced the sounds coming from a sound source with the same frequency response at the ear canal as if recording and replay over headphones had not been introduced into the chain i.e. the headphone replay should now sound the same as sitting in the room and listening to the speakers. Two main theories of the correct pre-equalisation curve were forwarded. The first, called free-field equalization, suggested that the above experiment be conducted in an anechoic chamber (like a field, free of reflective, asbsorptive and refractory surfaces). So, to reiterate, a free field equalized headphone is designed to sound like the reproduction of speakers as if a listener is sitting in an anechoic chamber. Although an anechoic chamber is more reproducible as a standard, it was argued that nobody listens in an anechoic chamber (and indeed, most listeners find even speaking in an anechoic chamber uncomfortable) and a reasonable approximation of a standard listening area be used to conduct the above experiments. This was called diffuse field equalization. There are many things that alter sound between the release from the sound source and arrival at the ear canal. Reflections, diffraction and absorption from objects in the listening environment, reflection, diffraction and absorption by the head, hair and ears all contribute to alteration of sound before it reaches the ear canal. Diffuse field equalization, as mentioned before, is an attempt to make the replay of a recording on headphones sound like you are listening to the same recording through speakers in a non-anechoic room. Experiments were also done so that headphone users were asked to equalise various sharply limited frequency bands’ playback on headphones until they had matched the loudness of the same playback through speakers and with headphones removed. A good correlation was obtained between this method and the probe microphone recording method. The direction of sound (from the front in a reverberant field) with speakers is far removed from actually injecting the sound directly into the ear canal. Stax, pondering this problem, possibly because they couldn’t successfully mechanically create a diffuse field equalized headphone, and any electrical equalizer would have to be a custom unit, first decided to create a new headphone that coupled its own reproducible miniature room (complete with uneven diffractive, reflective and absorptive surfaces) called the Stax Sigma. It had headphone drivers that fired from anterior to posterior instead of laterally into the ear canals. The sound was bounced off irregular “wool” into the canals, creating a mechanical diffuse field room for each ear as well as having "speakers" that fired sound from the front, rather than straight into the canals. It was partially successful, but listeners either hate it or absolutely love it. Personally I love it, but they were inefficient headphones, they sounded quite rolled off at both ends of the frequency spectrum. They were also huge and very odd looking. Better drivers than the original Sigma drivers (which were the same as the then current Lambda) improve the frequency extremes, allowing the merit of the theory to finally shine through (e.g. the very rare Sigma/404 hybrid). Stax later decided (around 1988), instead, to bite the bullet and build custom equalisers to electrically equalize their latest headphone range to provide individual target diffuse field responses for each of its various then current headphones (the ED-5 for the SR5 normal bias headphone, the ED-1 and SRM-Monitor for the Lambda Professional high bias phone and the ED-Signature for the high bias Lambda Signature). The headphones could then be less bulky than the Sigma and more fashionable (see my avatar for what the Sigma looked like – it definitely had a style only a mother could love). Again, reactions to Stax engineers’ diffuse field equalized headphones literally polarized listeners into “hate it” or “love it” camps. I would guess that economically, this proved to be a dead end, and any research into diffuse field equalization has never been publicly mentioned again by Stax. As mentioned above, the three ED diffuse field equalisers were designed for three different Stax phones (the ED-5 for the SR-5, the ED-1/SRM Monitor for the Lambda Pro and the ED-Signature for the Lambda Signature). The ED-5, ED-1 and ED-Signature were placed between the source and the headphone driver and are connected by way of RCA cables. The ED-1 matched the construction and size of the SRM1 Mk2 and was finished, like those units, in either black or silver. The ED Signature matched the chocolate brown of SRM-T1/S/W. The SRM-Monitor incorporated an ED-1 and an SRM1Mk2 Professional into one large package and was finished in either black or silver, and had switchable RCA and XLR inputs. The ED-Signature would most likely also match the 404 and Lambda Nova Signature. The ED-1 equalisation (in my case, provided by a very rare SRM Monitor) sounds rather nice with the Lambda Nova Signature and surprisingly good on the Omega 2 Mk 1, despite being the wrong equalisation for the latter. The upper midrange/lower treble, in particular, sounds quite a bit flatter and the low end remains in good balance with the mid and high. As Bill Sommerweck said in his review of the ED-1 in the April 1989 issue of Stereophile, track 9 on Stax' own “Space Sound” CD changes from objectionable (without the equalizer switched in) to quite listenable with the equalisation switched in. In my opinion, there is no magical out of the head experience, except when listening to the aforementioned CD, or the Ultrasone binaural tracks (i.e. binaural recordings). These are seriously spooky. Try them with someone who is not used to listening to headphones and see what happens when you cue up track 1 or 2 of the former, or the fireworks track of the latter. Sabine whispering in your ear - Oh yes! Shower spraying on your shower cap - OMG! Now, here is where things start getting weird. I had a listen to the Sigma/404 and the SR-007 phones with the equaliser on and they both sound great - it may just be happenstance, but I've never heard "Kind Of Blue" sound so wonderful and with plenty of lower bass (which even the SRM-717 doesn't seem to match). This is strange, as the above frequency response for the ED-1 is flat in the bass, and should not be suited to the Sigma/404 or SR-007 anyway. Maybe it's a de-emphasised treble spike? I don't know, but whatever, this pre-equalisation is not just scientific theory and sounds really good. To me, the sound has gone from lots of good hi-fi parts and moved to an organic whole. To my ears, the Stax SRM Monitor is the single best piece of equipment I have ever purchased.

Thanx Duggeh.....

The Sigma/404s are definitely singing their siren song to you......listening to them now.

That is just not true.

LOL - I suspect that what you are looking at is the DAC portion of the Phillips LHH-2000. BIG dollar machine even now.

It's pretty cheap in Western Australia too! Beautiful dark red brown colour. I had some side panels made for the CD player from this wood - they look better than the original factory supplied option.

I was incorrect - the coloured wires, because they are so short, have to be connected to the back of an amplifier. The other terminals are for the speaker cables to connect to. Sorry about the senior moment. To repeat (correctly) for a normal amp with speaker cable screw down terminals, the coloured wires connect to the speaker terminals at the back of the amp, the screw terminals are used to attach the speaker wires. Sorry about that!

[url=http://earsp.web.fc2.com/kako-d/srd-5/np-srd5-3_jpg_view.htm]STAX

Presumably these are the plugs attached to the ends of the left and right speaker outputs from the SRD-5. They are of no use unless you want to connect those outputs to a speaker with the equivalent female terminals, and as these are nearly unheard of, I would suggest removing the connectors. The inputs (from the amplifier) should be bare screw down terminals also at the back of the unit from memory. You should run your amp output to the bare screw terminal inputs of the SRD-5 and the cabled outputs on the unit to the speakers + and - terminals. The speaker/headphone switch will then work correctly.

I would have a go at inserting microphones into the canals, but leave the microphones poking out of the canals with their diaphragms at the same position as the diaphragm of the replay headphone. It seems odd that most dummy heads have the microphones nestled into an ear canal, where the only correct replay for this recording will be with an in-ear-canal headphone, because if you are using an around ear headphone, the sound will be modified by the dummy head pinna on recording and your own pinna on replay. It would be interesting to try a dummy head with the microphones in several positions for different headphones. 1. buried in the ear canals for IEM replay 2. with the microphones poking out of the canal slightly for on ear phones 3. with the microphones as mentioned above for around pinna headphones 4. at the side of the head and facing forward for something like a Stax Sigma or an AKG K1000 (with the microphones placed at the centre of a prospective headphone transducer)

Windows XP has a fax program. http://support.microsoft.com/kb/306550

Duggeh, you're gonna love that ESL63 - my father has a pair and they are superb. I have the 989s and they are magic.