SR-L700 MKII Earspeaker Review and the SRM-D10 Portable Driver Unit for Earspeakers Review

That’s the case with the latest incarnation of the Stax SR-L700 MKII Earspeakers, a reference design which is one of the most impressive devices for listening to music that I’ve ever heard.

This latest ‘earspeaker’ from Stax, who feels that the term ‘headphones’ doesn’t do justice to their products, impressed me and every audiophile that auditioned my review unit. They are comfortable, highly revealing, and really require the best quality program material. Playing some garden variety CDs will immediately make it clear that the recordings are not the best. Even little details in the recording room like the HVAC or the movement of music stands are quite apparent. This is both a blessing because the Stax SR-L700 MKII Earspeakers are so revealing and a curse because you will hear ‘everything.’ Stax headphones will spoil you for anything else. While expensive, they deliver, and people who enjoy listening to headphones in a serious way will want to audition them.

First off, what is an electrostatic driver and how is it different from other headphones?

I’ll give you a simplified explanation of the differences.

Most headphones use dynamic drivers. They are basically a scaled down version of the speakers that might be powering your desktop speakers. A small coil carrying the signal moves the driver and produces music.

Planar drivers are now getting very popular among discriminating listeners. They are similar to dynamic drivers, but instead of focusing the magnetic field on a small section of the driver, a planar driver is wired to work on the whole panel of the driver, using more points of contact and more magnets.

Electrostatics have a long history, and Stax was a pioneer in the design. Koss also offered, and still offers, some electrostatic designs. Simply put, electrostatic drivers are usually a thin mylar that is sandwiched between two conductive plates. Electrostatic headphones require an amplifier or energizer box to set the drivers in motion, so we’re reviewing the Stax Headphones with the required accessory amplifier. Stax has a variety of amplifiers at different price points, but I liked the idea of a portable driver unit so that’s what I’m evaluating here.

The SR-L700 MKII Earspeaker has the classic Stax electrostatic sound, and by that I mean smooth and extended high frequencies, fast transient response and deep bass. The company has been in business since 1938 starting with the design and sale of condenser microphones and then moving on to electrostatic tweeters and then finally to headphones – aka Earspeakers in the late 1960s. Stax has also produced Electrostatic speakers and even an amplifier.

I owned a pair of the Stax electrostatic Lambda Earspeakers many years ago when I was in college. Sadly, the driver box went out after a couple of years, and I was a poor student and couldn’t afford to fix them. I sold my Stax as-is to a more well-off student, and he enjoyed them for many years after that. I envied him.

When I heard that the descendant of that very Earspeaker was alive and well in a much more evolved product, the SR-L700 MKII, I just had to hear it.

While Stax makes many driver units that will power their headphones, I was most interested in a portable unit that did not need to be plugged into house power. The SRM-D10 is a rechargeable unit. You can listen anywhere without need of AC power. It seemed like the way to go for my lifestyle.

Externally, the Stax headphones on review look very similar in design to the Lambda headphones I owned more than 30 years ago. However, there are many changes and all are for the good. The cable, which was formerly permanently attached, is now unplug-able and easily replaced. Headphone cables get strain during their daily use, and this is a most welcome change.

The headphone structural elements are now made of aluminum. In the MK2 models, changing the case holder design from conventional linear style into moderate curve form produces the effect that ear pads fit more naturally on both-sides-of-the-head part. Moreover, the curve form gives high rigidity and prevents the headphones from generating unnecessary distortion or twist at the time of wearing, resulting in the great improvement of fit and feeling.　In an open-air type earspeaker, which these are, the degree rise of adhesion at the time of wearing greatly contributes to the improvement of low-frequency reproduction.

The headband (ARC) assembly of the SR-L700 MKII is equipped with 10-click slider mechanism for head pad height adjustment adopted from the older SR-009 Earspeakers. Once adjusted, the slider always maintains its optimal position to make readjustment unnecessary. It makes for a very comfortable fit.

High performance pure copper HiFC™, developed by Hitachi, is used in the core wires on the Earspeaker. HiFC™ has various stated advantages, including low capacitance 6N high purity 99.99999% copper wires. The entire cable is then arranged in a flat, wide format configuration to lower the capacitance between each wire and then enclosed in a durable plastic covering.

The ear pad design is carefully hand crafted with genuine lamb leather for good comfort, even during long listening sessions.

This portable, rechargeable unit is something new for Stax, and I think it makes life easier if you are a traveler or multi-room user. The SRM-D10 can also function as a very high quality DAC that can play high resolution files up to DSD128.

It features a micro-USB input for using this device as a DAC and a 35mm analog input to get audio from your source device. The unit is powered by Lithium Ion batteries, and it can be fully charged in about 3 hours. The amplifier comes with its own AC charger.

Getting started with the headphones is simple enough. First, charge the SRM-D10 Amplifier. A small LED glows red when the unit is charging, and turns off when charging is complete. Unattached to its charging cable, the LED glows green while it is in use. There is a power/volume control which feels high in quality.

On the back of the amplifier is the DC in port, the USB DAC port, and the analog input. A switch lets you select between use as a DAC and as an analog input to drive the Earspeakers.

In my tests, I provided the Stax Amplifier with the output of a FiiO M15 Digital Audio player for music, and also plugged a stereo to 3.5mm mini cord into one of the Zone outputs in my Emotiva processor.

The Stax D10 Driver was fully charged before listening. It kept working through sessions that were many hours. Generally, I recharged at the end of each day. Once charged, it’s just a matter of finding somewhere comfortable to sit and adjusting the volume to taste.

This was the part I was looking forward to. Would these super expensive Earspeakers blow the headbands off some really high quality planars and dynamic headphones I had on hand? Like much in life, the answers are a bit complicated.

In general, the high frequencies are superior on the Stax Earspeakers. It’s more than high frequencies though. Transient response is lightning fast. Quick percussion hits, plucked strings, acoustic guitars are all very clear and involving. On my planar headsets those transients aren’t as well defined, although when not comparing them to the Stax, they sound just great.

Bass is another story. Electrostatic headphones like the Stax aren’t historically thought of as really deep bass reproducers. I find the SR-L700 MKII Earspeakers have greatly improved in low end from the Lambda’s I had years ago. Bass is tighter. It’s very clean, but still doesn’t reach quite as deeply as some of my planars. If I listen for a few minutes to the Stax phones the low end sounds just great. I let a few audiophiles audition them, and all liked the bass, and were over the moon with the high frequencies and transients.

We all agreed that while the bass on the Stax was not quite as deep as some of the headphones I compared them to, they seemed cleaner and more effortless. Without strain, I think, are the best words to describe it.

Here are some of the things I tested the Stax Earspeakers with:

I have to spend a little more time than usual discussing the Value of the Stax SR-L700MKII Earspeakers. At a total of $2468 for the headphones and the drive unit, the package is almost 3 times the price of some of the excellent headphones I now own, are they 3 times as good? It depends on what you value. In high quality audio equipment, small increases in quality and accuracy can cost a lot of money. It’s the nature of the cost of engineering products beyond the usual mass market equipment. It’s clear these Stax Earspeakers are built to the highest standard. The quality of materials, with robust connectors, switches and the volume control didn’t come out of some bargain parts bin.

If you seek a quality of audio some steps above the usual, then this Stax Earspeaker should be auditioned with first rate music files. They are breathtaking. Everyone who heard them at my home wanted a pair. I felt the same way. They deliver fine audio in a way other high quality headphones I’ve owned and heard simply can’t. But like all ultra-quality audio equipment, the price is higher than many will want to pay. Some will say diminishing returns sets in at this price. Others will want the spectacular presentation of music the Stax SR-L700MKII Earspeakers offer.

The Stax SR-L700MKII Earspeakers are an absolute revelation to listen to. On any kind of music from rock to opera they are a unique listening experience. The better the program material, the more you will enjoy them. You will hear everything on your recordings; not always a good thing if you are hearing HVAC equipment or rattling music stands, but that’s the level of the detail presented.

The Stax Earspeakers were very comfortable on my head, encouraging long listening sessions. The rechargeable energizer/amplifier made it easy to listen in my office, in the living room, or in the bedroom without having to hunt for an AC outlet and worrying about tripping over the cord.

The SR-L700 MKII Earspeakers are the best sound I’ve heard from any headphone. But that doesn’t mean the headphones I own are suddenly of no value. My HiFiMAN and Sennheisers sound as great as they always have. It’s a bit like having a wonderful dinner at a terrific restaurant. It simply doesn’t negate all the other great meals you’ve had. But the Stax Earspeakers are ‘ear opening’ and standard setting, and I had to keep telling myself that cost-wise these are about the middle priced offering in the Stax line, where their top Earspeaker and Energizer can run about $10,000.