Stax Earspeakers Overview

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Stax Sigma, Stereo Magazine October 1980
Stax Sigma, Stereo Magazine October 1980


Image:Stax logo.jpg Earspeakers General Information

Timeline of the company

1938 - Stax Ltd. was founded

1960 - First electrostatic earspeaker made

1995 - Stax is out of business

1996 - Stax is reformed by a few Stax Ltd. engineers as new STAX company.

Old Company: Stax Industries Ltd.,Tokyo Japan (1938-1996)

New Company: Stax Limited, Saitama Japan (1996-Present)

Interesting Facts About Various Stax Earspeakers

SR-1: The world's first electrostatic headphone debuted at a Tokyo show in 1959 and was put into production in 1960. There were a number of different versions as the SR-1 evolved over its 8 year life span. Amongst the changes were a move from a 150VDC bias to 200VDC (which Stax used until 1977), and a new earpad design.

Stax Panoramic-sound Earspeakers: It was during the years when Stax Industries, Ltd. was run by the the president/owner Naotake Hayashi and later along with his son Takeshi Hayashi that Stax developed their Panoramic and Semi-panoramic Earspeakers.

With SR-Σ (Sigma) Stax attempted to recreate a natural, realistic sound field in a headphone format. After four years of development the huge Stax SR-Sigma series was released in 1977. SR-Sigma's design positioned an oval driver at about an 80-degree angle to the ear. This created an illusion of a sound field located in front of the head, not on the sides. The very large driver, larger than the ear, allowed the outer ear to guide the sound into the inner ear, thus removing the in-the-head effect.

Stax Semi-Panoramic-sound Earspeakers: SR-Sigma was followed by the SR-Λ (Lambda) series in 1979. The SR-Lambda series was based on SR-Sigma research and utilized the same driver in a less bulky frame. The use of angled pads and slanted housing was an approximation of the tricks of driver positioning used in the SR-Sigma's design.

During the 1980s Stax developed the Professional Series, originally developed for Daimler Benz, the German car manufacturer. SR-Lambda Pro was the first headphone to utilize a driver with a wider 0.5 mm electrode gap and 580V bias voltage.

By the end of 1995 Stax Industries, Ltd. along with its American subsidiary, Stax Kogyo, ceased business operations due to a disagreement between owners of the firm and its employees. However, around 1996 some engineers from the old company formed a new company, Stax Limited, in Saitama, Japan. The design of the Lambda frame was very successfully updated (e.g., the headband's arch was widened) and continues to be used to this day with only minor modifications by the new Stax.

Sigma Series, Panoramic-sound Earspeakers (1977-1994)

Name: SR-Sigma (-, Pro)

Transducer shape: Elliptical/Oval

Electrode type: Perforated metal plate

Diaphragm thickness (micron): High polymer film 2 (230 V), 1 (Pro)

Electrode gap: 0.3 mm (230 V), 0.5 mm (580 V)

Bias Voltage: 230 V, 580 V (Pro)

Frequency Response: 30-35 kHz, 25-38 kHz (Pro)

Signal cord: 6-pin OFC, 5-pin PC-OCC (Pro)

Lambda Series, Semi-panoramic-sound Earspeakers (1979-Present)

Name: SR-Lambda (-,Pro,Signature), Lambda Nova (Basic,Classic,Signature), Numerical Series (SR-202,SR-303,SR-404)

Transducer shape: Elliptical/Oval

Electrode type: Perforated metal plate

Diaphragm thickness (micron): High polymer film, 2 (230 V), 1.5 (Pro), 1 (Sig), 1.5 (Nova Series), 1.35 (Numerical Series)

Electrode gap: 0.3 mm (230 V), 0.5 mm (580 V)

Bias Voltage: 230 V, 580 V (Pro/Signature/Nova/Numerical Series)

Frequency Response: 8-35 kHz, 7-38 kHz (Pro), 7-41 kHz (Sig/Nova/Numerical Series)

Signal cord: 6-pin OFC (230 V), 5-pin OFC/PC-OCC/Wide PC-OCC (580 V)

Notes: The Nova-series and later have an improved stator design

Gamma Series Earspeakers (1985-1989)

Name: SR-Gamma, SR-Gamma Pro, SR-Alpha, SR-Apha PRO Excellent

Transducer shape: Round

Electrode type: Perforated copper plate

Diaphragm thickness (micron): High polymer film, 2 (230 V), 1.5 (Pro)

Electrode gap: 0.3 mm (230 V), 0.5 mm (580 V)

Bias Voltage: 230 V, 580 V (SR-Gamma Pro, SR-Apha PRO Excellent)

Frequency Response: 15Hz - 30KHz ?

Signal cord: 6-pin OFC (230 V), 5-pin OFC/PC-OCC (580 V)

Notes: Gamma and Alpha series share drivers with the earlier SR-5, SR-X and SR-5N

Omega Limited Series (1993-1994)

Name: Stax SR-Omega

Transducer shape: Circular

Electrode Type: Gold-plated copper mesh

Diaphragm thickness: High polymer film, 1.5 micron

Electrode gap: 0.5 mm

Bias Voltage: 580 V

Frequency Response: 6-41 kHz

Signal cord: Wide format high quality LC PC-OCC, 5-pin

Notes: Stax developed the Omega-series as a direct competitor to Sennheiser's Orpheus Series. Limited Edition. 300+ sets have been reported being produced (more likely around 350+). 50% larger diaphragms than Lambda Series, electrode mesh structure instead of flat perforated metal plates

SR-007 Series (1998-Present)

Name: SR-007 (Omega II)

Transducer shape: Circular

Electrode Type: Gold-plated perforated printed circuit board material

Diaphragm thickness: High polymer film, 1.35 micron

Electrode gap: 0.5 mm

Bias Voltage: 580 V

Frequency Response: 6-41 kHz

Signal cord: Wide format high quality LC PC-OCC, 5-pin

Notes: Fewer (and smaller) holes than Lambda Series

Detailed information about various Stax Earspeakers can be found by clicking on the links in the chart below

Stax Electrostatic and Electret Earspeakers Models

1960's 1970's 1980's 1990's 2000's











SR-40 Electret





SR-Λ Signature



SR-α PRO Excellent

SR-30 Electret

SR-50 Electret

SR-80 Lambda Junior Electret

SR-Λ Nova Signature

SR-Λ Nova Classic

SR-Λ Nova Basic

SR-Λ Spirit




S-001 MkII








Stax and non-Stax Amplifiers & Energizers for Electrostatic Earspeakers

Stax Amps with Pro bias socket

(5 pin socket)

Stax Amps with Normal bias socket

(6 pin socket)

Stax Energizers

6 or 5 pin sockets

Non-Stax Amps

(with Stax connector)

Non-Stax Energizers

6 or 5 pin sockets










SRM-001 (mini connector)

SRM-001 MK-2 (mini connector)











SRM-1/MK-2 Pro

Stax SRM Monitor












Stax SRM Monitor









SRD-7 Pro












Singlepower ES-1

Singlepower ES-2

HeadAmp KGSS


HeadAmp Aristaeus

HeadAmp Blue Hawaii

HeadAmp Blue Hawaii SE

Rudistor Egmont Signature

Rudistor Egmont

RSA A-10 Thunderbolt

McAlister Audio EA-6

McAlister Audio EA-4

McAlister Audio EA-1

Woo Audio GES

Woo Audio WES

Masters BA-215TM

Illusion ESC-1001

Woo Audio WEE

Brochures, Marketing Materials and Photos of Drivers


Stax 1970's Brochure

Stereophile 1971/1972, Stax SR-3 and Koss ESP9 reviews

Audioscan 1983 - with Stax Info and Stax SR-Sigma, Stereo Magazine October 1980

Stax 50th Anniversary - 1988 Brochure

Stax Lambda Nova Signature Manual, Stax Lambda Signature Brochure

Stax SR-Sigma Brochures, Stax Lineup Brochures

Photos of Drivers

Hifi Choice Article

STAX - It's a family affair

The Hi-Fi Choice in Japan series continues with Dan Houston and photographer Chris Richardson boarding the bullet train and heading for the home of the electrostatic "earspeaker".

The story of Stax is also the story of modern electrostatics - the firm's founder even named it by shortening the word electrostatics. Today Stax is nearly 40 years old and is famous throughout both the audio and recording worlds for its electrostatic headphones. But it also makes floor standing electrostatic loudspeakers, gigantic amplifiers on castors, the Quattro CD player, and a new digital to analogue converter which uses valves in the output stage - the DAC Talent.

Stax is run by a family; the 84 year old founder and chairman Naotake Hayashi, his wife Toyoko, and their son, the company president Takeshi Hayashi.

The current factory was built 20 years ago and has been added to over the years - the end result being a collection of prefabricated units which looks as though someone has just plonked them down on the plot. The factory employs 35 people, mainly assembling components which are supplied by a range of (often local ) firms. A main corridor on the ground floor leads to the spartan offices, a carpeted listening and reception room; workshops full of test equipment and, at the end, an anechoic chamber hung with rolls of acoustically absorbent material. Plain duckboards across bare earth lead off to speaker assembly units, while back in the main building the first and second floors house dust-free rooms for the assembly of headphones.

Heading for the toy room If the words tawdry, run down or functional spring to mind then one must take heed of Wordsworth's aphorism: 'plain living; high thinking'. And posters around the walls, of musicians like Chick Corea (wearing his SR Sigmas the wrong way round!), confirm the standing of the company. The one room which is far from plain is Naotake Hayashi's office - or toy room as his son refers to it.

At 84 Naotake still puts in a full day's work, striving to develop electrostatic principles ever further. During our visit he was testing his latest invention - a six feet high horn-loaded electrostatic loudspeaker. The new unit was playing with a dedicated transformerless vacuum tube amplifier; the tube being connected directly to the diaphragm. The speaker folds like a screen, with the wide baffles acting as a straight horn to the diaphragm, and will be finished by the autumn. Although the type we listened to was made of wood, eventually the hinged baffles will be made from Coran, a heavy, inert plastic material manufactured by Du Pont.

”We first thought of this 25 years ago,” Takeshi told me, ”but it was too big and cumbersome and used a round, wooden horn. The new material is expensive but very inert and there is less vibration. The horns can fold so users can adjust the sound. We're thinking of making a smaller one but the problem of a smaller diaphragm is that it would give more coloration and less frequency extension.” Even with the prototype it was possible to hear how the system worked with the horn amplifying the sound of the driver without making it too directional or harsh.

The company was founded in 1952, its first product being a cartridge using electrostatic theory to convert vibrations into electronic signals. In the toy room, papers and case files surround the walls, along with examples of the company's products over the years. Books on music therapy confirm Naotake's long held belief that music is essential to good health: ”soft but clear sound is important,” he told us. A small tool box contains a saw (for fine tuning the horns perhaps) while several industry awards collect dust on the shelves and indescribable boxes with their electronic innards spilling out reflect a hands-on approach to design.

Takeshi takes up the story: ”After the second world war my father worked in Shanghai as a recording engineer with the Chinese Recording Company. He was always interested in systems which would deliver the best sound quality and he started researching electrostatic theory.

”Electrostatics were invented by a German in 1880, but the materials for the diaphragm were never good enough for quality sound reproduction. Chemical technology had improved during the war and there were better plastics available - even though we now believe purity of sound is better with just the bare metal. Our first products were the Monaural Radio Frequency Condenser Phono Cartridge and an integrated tonearm designed especially for use with the cartridge.

”In 1956 we were still only a cartridge manufacturer and my father patented a design of cartridge with a rotating stylus. Because you rotated the stylus every time you played a record we could use a softer sapphire tip. Another feature of the stylus was its extremely light tracking weight - about a gram - which gave better tracking performance at a time when other styli were tracking at between 10 and 20 grams.

Stax first came to prominence with its ear speakers which made their debut at the Tokyo Audio Fair in 1959. Takeshi remembers the occasion even though he was still a boy: ”I was at junior high school but was already starting to help my father where I could,” he said.

The ear speaker

The original headphone was the SR1 ; it was the first electrostatic headphone in the world and set a pattern for the types that were to follow, coming complete with its own energiser unit. Gradually the headphone business took over, even though Stax continued making cartridges and tonearms, finally winding up production in 1977 when the company's last electret direct pickup cartridge was made. ”We'd still like to make a phono cartridge,” Takeshi said, ”but the problem is finding the time.”

Headphones now account for 70 per cent of the company's business although as Takeshi points out, products such as the loudspeakers and DACs are changing the ratio slightly says. The early headphones were soon followed by Stax's first full range floorstanding electrostatic loudspeaker, the ESS 3A , launched in 1960. The main reason for developing electrostatic products was to avoid the problems of magnetic hysterisis, something Takeshi views as one of the major disadvantages of traditional dynamic loudspeakers.

There are now three models of loudspeaker: the nearly two metre high elegantly proportioned ELS-F83, the shorter and slightly wider ELS-F81 and the colossal ELS 8X. The latter is also available as the ELS-8X BB (for battery box). The DC battery supply gives 4,000 volts to polarise the massive diaphragm; it's basically similar to a Stax headphone but with the polarising energy multiplied to compensate for its size. And with the powerful batteries lying on the floor next to the loudspeakers it's not the sort of thing you'd want with children crawling around, as Takeshi admitted.

”Electrostatic energy is getting force from plus and minus signals with a single diaphragm between electrodes,” he explained, ”if we apply DC voltage to the entire diaphragm and put a high voltage through the plus and minus sides the diaphragm is pulled by the opposites and pushed by the same polarity - that's the basic principle. But we need to polarise the central diaphragm and by using a powerful DC current from the batteries we can eliminate the noise, which is present from the rectifiers in AC systems, and so reduce the impedance factors.

”It's exactly the same with the ear-speakers. The regular system uses a 230 volt power supply and the professional series uses 580 volts - they have battery packs for DC and better sound.” This is why the ear-speakers need an adaptor (AC or DC) which raises the signal voltage from your amplifier to cater for the polarising energy needed by the diaphragm.

Takeshi joined the company in 1972 after reading Mechanical Engineering and Industrial Design at Sofia university in Tokyo and a short spell with the research and development team at Harman Kardon - in Long Island, New York. He worked on Stax's first stereo Class A DC power amplifier, the DA-300, a 150 watt per channel monster which was to provide the pattern for subsequent Stax amplifiers. ”The Mark Levinson company used it as its reference power amplifier until it had finished its own,” he told me with some pride.

A glowing reference Alongside the DA-300 sit a variety of valve amplifiers, built by Naotake in the Fifties for use in the listening room. Indeed valves are still very much in favour at Stax. The company's first digital to analogue processor, the DAC-X1T, uses a dual triode valve in the output stage, as does the new slim and compact version - the DAC Talent, which also uses a new American made ”glitchless'” chip to eliminate the need for de-glitching circuitry which degrades sound quality.

Valves are also in evidence in the SRMTI ear speaker energiser. Valves deliver superlative sound according to Takeshi, who believes that the simplicity of valve circuitry along with the perceived smoother or faster passage of electrons through a valve have kept it very much in the audiophile domain in spite of the greater availability, reliability and design attractions of the transistor.

Powering up The side-by-side development of both electrostatic loudspeakers and amplifiers led to one of the most powerful amplifiers ever made. In 1987 Takeshi unveiled his DMA-X1, an FET output monoblok that weighed a massive 101 kilograms and which could push 1,000 watts into a one ohm load. As Takeshi describes it, it was more like the power supply for a welding machine! When you consider two were needed for stereo it makes sense that the amplifier was fitted with castors.

Last year another power amplifier arrived. The DMA-X2 is a slightly smaller version, weighing in at a mere 47Kg, and with non negative feedback and Class A output stages. ”The power supply is A/B which reduces the problem of heat generation. It is balanced from input to output and is a traditional BTL (balanced transformer less) design,” said Takeshi. If all this implies that Stax is not primarily a headphone manufacturer then that is also what we discovered. However, the company is probably still best known for its electrostatic 'ear speakers'.

1977 saw the launch of the SR Sigma where the electrostatic diaphragms were angled slightly in front of the ear to make the listener believe he is hearing sound from in front. In 1982 the Lamda Pro and Lamda Signature followed the same design philosophy and incorporated high quality PCOCC cable and a thinner membrane ”for golden ears” as Takeshi describes discerning audiophiles.

Going digital

But by the mid Eighties Stax was heavily into digital electronics, releasing its Quattro CD player in 1986. The Quattro uses a Sanyo Fisher drive system and Stax designed electronics in the digital to analogue conversion process. The 18-bit CD player was followed by the DACs which also use multi (20) bit technology. Takeshi doesn't rate bitstream as highly as some: ”We have measured the new Philips one bit chip and we can see that noise levels are greater than with multi bit systems,” he said showing me graphs to prove his point.

Takeshi himself favours the analogue medium for its higher frequency range and more lifelike qualities: ”The problem with digital formats for high-end people (audiophiles) is that a higher bit or higher sampling frequency is needed. We don't just listen to music with our ears - we can also feel some frequencies with maybe our face or stomach. CD is still in its infancy and of course even four bit technology would be popular with most people. Denon has announced that it will making a higher density CD which will carry higher frequency sampling - that could be good for audiophiles.”

One can see that the making of Stax products is both exacting and painstaking. Takeshi said he spends hours every night listening and relistening to products with a view to improving them. And while the factory may not be as plush and clinical as some of the Japanese workplaces we visited, products are all hand-assembled and rigorously tested before leaving for Germany or the States, or any other of Stax's 20 marketplaces.

Stax engineers do clean clothing and masks to work in a dust free environment while assembling the delicate diaphragms of the ear-speakers and matching a left and right pair for efficiency.

Even though it's not a noisy factory Takeshi says he wants to extend it to incorporate a small concert hall and proper listening room where the engineers can play live music before listening to recordings on quarter inch tape. Whether this will be on the scale of the Nakamichi hall we visited last month remains to be seen, but if the company's previous exploits are anything to go by then you can rest assured that it will be more than a little out of the ordinary.

--from Hifi-Choice, 1991 © Copyright 1991 by Hifi Choice

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