STAX (part of Edifier), a leader in the implementation of Electrostatic audio technology in headphones, has announced the latest version of this classic SR-009 electrostatic headphone platform, the SR-009D. This latest version of the standard setting iconic SR-009 and the intervening SR-009S is a direct response to overwhelming demand from audiophiles and music lovers.
What Are Electrostatic Headphones?
An electrostatic headphone uses drivers similar to those used in electrostatic speakers, but on a much smaller scale.
An electrostatic driver for headphone applications employs a very thin diaphragm that is placed between two perforated metal plates. The diaphragm holds a constant electrical charge as a result of a conductive coating. The membrane is firmly attached in place with “spars” that allow it to move back and forth freely to produce sound.
Electrostatic drivers are noted for their exceptional accuracy, very low distortion, and quick response. However, to operate electrostatic headphones, an external amplifier (sometimes referred to as an energizer) is needed that can supply the needed power – one external amplifier option is the STAX SRM-400S. You just don’t plug an electrostatic headphone into your typical headphone output. Electrostatic headphones are typically not only more expensive than other types, but are also more expensive to operate.
There are more details, but the above description gives you a basic idea of how electrostatic drivers work in headphones and what you need to hear what they can do.
Pro Tip: STAX refers to their Electrostatic Headphones as Earspeakers.
SR-009D Improvements
The SR-009D has been updated with modern features for enhanced usability and longevity. It preserves the same groundbreaking technology that made the original SR-009 a headphone benchmark, while incorporating key improvements that fit in with the current STAX lineup.
MLER (Multi-Layer ElectRodes): The SR-009 and 009D both utilize MLER (Multi-Layer ElectRodes) technology, which uses photo-etched metal plates bonded at the atomic level. MLER was introduced on the SR-009, which provided speed and “see-through” clarity that was not available at the time.
The SR-009D retains the core MLER architecture of the SR-009 but with modern refinements. Instead of the gold-plating of the SR-009S that was released in 2018, the “D” model uses a refined version of the original SR-009 stainless steel plates that maintains the classic, lightning-fast 009 sound signature.
Detachable Cable: The SR-009 incorporated a fixed, non-removable cable. If the cable snagged or failed, it meant a costly and stressful trip to a service center. To make life easier and connectivity more flexible the SR-009D provides a detachable detachle cable.
Build & Comfort: One of the most significant physical changes is the housing material. The SR-009 had a heavy, all-aluminum frame, which resulted in a heavy overall weight. The SR-009D incorporates an injection-molded unit case. This significantly reduces the weight (down to roughly 452g without cable), resulting in more comfortable long listening sessions
Sound Profile: The SR-009D smooths out the mid-range frequencies over the original 009 for a more balanced sound listening experience.
Earpad Materials: Genuine sheep leather earpads provide a luxurious and comfortable listening experience.
Headband: Instead of a friction slider used in the original SR-009, the 009D incorporates a 10-step headband click mechanism.
Aluminium Carrying Case: This provides a lightweight, durable, and secure protection against impacts, weather, dust, heat, and wear, ensuring the long-term preservation of headphones
From Douglas Ip, Sales & Marketing Head, STAX Limited. “The SR-009 has always held a special place in the hearts of our customers and in the history of STAX,…With the SR-009D, we are thrilled to bring back that legendary sound, updated with the features that our customers have long asked for. It is the perfect gateway to the world of high-end electrostatic audio, offering an unmatched listening experience at a much more accessible price point.”
Comparison
| SR-009D (2025) | SR-009S (2018) | SR-009 (2011) | |
| Product Type | Over-ear Headphones | Over-ear Headphones | Over-ear Headphones |
| Price | $2,890 | $4,545 | $5,250 |
| Headphone Type | Push-pull electrostatic sound element. Open-back type enclosure. Large round shape | Push-Pull Open Back Circular Electrostatic Headphone | Push-pull electrostatic circular sound element. Open-air type enclosure |
| Frequency Response | 5 – 42,000Hz | 5 – 42,000Hz | 5 – 42,000Hz |
| Capacitance | 110pF (including cable) | 110pF (including cable) | 110pF (including cable) |
| Impedance | 145 kΩ (including cable, at 10kHz) | 145 kΩ (including cable, at 10kHz) | 145 kΩ (including cable at 10kHz) |
| Sound pressure sensitivity | 101dB / 100V r.m.s. 1 kHz | 101dB / 100V r.m.s. 1 kHz | 101dB / input 100Vr.m.s / 1kHz |
| Max sound pressure level | 118dB / 400Hz | 118dB / 400Hz | 118dB / 400Hz |
| Bias voltage | 580V DC | 580V DC | 580V DC |
| Earpad | Genuine sheep leather, artificial leather (surrounding portion) | Genuine Lamb Leather (direct skin contact), high-quality synthetic leather (surrounding portion) | Genuine leather (Lamb) |
| Cable | OFC parallel 6-strand, low-capacity wide cable 2.5m | Silver-coated 6N (99.9999%) OFC parallel 6-strand, low-capacity special wide cable, 2.5m full length | Silver-plated 6N (99.99999%) OFC low-capacity wide cable 2.5m |
| Weight | 580g, (452g without cable) 1.25 lbs (1 lbs without cable) | 596g, (454g without cable) 1.3 lbs (1 lbs without cable) | 596g, (454g without cable) 1.3 lbs (1 lbs without cable) |
Bottom Line
Electrostatic headphones are in a different class, using technology that might you find in select speakers from MartinLogan and Final Audio, only in a much smaller and portable form factor. STAX is the “king of the hill” in the electrostatic headphone category, and their new 009D continues the legacy of their celebrated 009 series.
However, as dominant as STAX is in electrostatic headphone category, there is competition from Audeze, HiFiMAN, and Warwick Acoustics at higher price points.
Electrostatic headphones are not for the casual or budget-minded music listeners as in addition to the cost of purchasing them, the cost of operation has to be taken into consideration, as they require an additional external amplifier to access desired sonic results.
On the other hand, if you aren’t satisfied with your current headphone listening experience and have extra cash, the STAX SR-009D might be just for you. There is even hope for more budget-minded headphone fans as STAX also offers the SR-X1 for the “low price” of $535!
Price & Availability
The SR-009D is available now directly through STAX, Authorized Dealers, and Distributors. North America Pricing is $2,890.
Note: The SR-009S is still available for $4,545 and the original SR-009 has been discontinued for some time.
Related Reading
- Meet the STAX SR-007S—Electrostatic Tech So Next-Level, Your Old Headphones Are Jealous
- Stax SR-X1 Earspeaker Review: Can a $535 Electrostatic Headphone Convince the Naysayers?
- Stax SR-L700 MK2 Open-Back Electrostatic Earspeaker Headphone: Review
- Audeze CRBN2 Electrostatic Headphones Review: Is it Time to Sell Your Loudspeakers?
