Vintage Find: Stax SR-40 Earspeakers with SRD-4 Adapter

A pair of thrift store finds recently came into our possession, impressing us with their capabilities despite their age: the Stax SR-40 Earspeakers and SRD-4 Adapter. We were cruising our local secondhand store and came across this pair of what some might consider, audio equipment history. We share what these old-fangled headphones offered while listening to newfangled audio sources when we got back home with our treasured finds below...

Someone who is looking for a random pair of headphones would be a fool to buy something so complicated, bulky and frankly, not so attractive. Whenever we see items like these, we immediately stuff them into my cheek pouches and find a quiet corner of the store to make sure everything is in order. We weren't able to actually use them while at the store, but for $5, WHUTEVER. To tell the truth, we have had these sitting around for years and never listened to them until we came across them a couple weeks ago.

Stax has been around since the early 60’s so it can easily be assumed that they are at least 50 years old. They've brought us a ton of unusual headphones and speakers that generally use electrostatic drivers.

In case you were wondering, electrostat’s work by sending a charge across what amount to two metal screens (about the size of the headphone earcup) sitting next to each other with a plastic film diaphragm between them. The film is what creates the soundwaves so the charge moving across it causes it to move air to the tune that is being fed to it. This is the reason for the need for increased voltage- to get enough charge to move across the whole screen. These are open ear elements so when there is no music playing, you can hear everything (almost) as usual. Another hallmark of the electrostatic headphone is low ear fatigue. This is a category we often forget we're wearing until we're several hours into an audition and discover we still feel like listening.

Let us tell you about our little listening adventure. We wrote a review about the Dayton Audio (DTA-1) reintroduction of the Sonic Impact T- Amp a long time ago and how super great it is and so we figured we'd would hook the Stax up to play some music for testing. Oh, that was good! First of all, the “amp” part of this package is not really an amp, as we're normally accustomed to dealing with. It takes the signal from your speaker outputs (on your amp) and turns up the voltage to a level the electrostatic elements can run on. There is no power cable or anything like that.

We tried the SR-40s out on all kinds of fun stuf, spending the lion’s share of our time testing with digital media. A fun thing we used to test soundstage was to watch exotic car paparazzi videos on YouTube. These kids chase Ferraris and Bugattis around London in the hopes of catching exciting cars in luxurious environments for their viewers. The cars pass by and slip away along crowded city streets so the sound can be spatially interesting if you have the right equipment and very accurate if they have good equipment. Think of it like a Hollywood movie with no post-production, so no artificial sounds...just the real sounds. You can really feel the location of events occurring on the screen – the sound of a W-16 engine burbling a block away as it approaches a left hand turn – the locations of teenage boys squawking out the model designation of their favourite obscure European hypercar in awkward, mid-pubescent tremolo. In short, it feels like a field trip to Harrods, sans the “Alms for the poor?” requests.

In music where spatial layout is well defined, these puppies shine. We guess that is what electrostatic headphones are known for, but the fact that these have been doing it so well for so long makes us wonder why sound reproduction is so uninspiring these days. It seems like things keep getting better and then they just drop off…only to reset the race with the same or lower goals.

[Oh wow, we just had a moment there whilst streaming some trance music...thought we had been picked up by an alien craft or something]

Overall the sound is very spacious and realistic. The bass isn't super deep and there seems to be lack a little "life" sometimes, but it is easy to get lost in what you are listening to. Dynamics were surprising, but this will likely depend a lot on your amp. Depending on your source, transparency can be excellent, as you are able to locate people who are 3 feet in front of you to the right versus those who are 30 feet to your direct right.

We like to write about obtainables around here whenever possible and vintage audio gear is often such a category. Sometimes you just need to know where to look (and what to look for). $5 is a steal for electrostatic earspeakers – even from 1975. If you had to, you could probably pick up a set for under a C-note, but you could also spend a few of those if you have obscure and good taste with a particular model in mind. We really enjoy listening to audio with the Stax Sr-40 Earspeakers with SRD-4 Adapter, and the tandem have quickly become our new go-to equipment for quite some time. If you can find some in a thrift store or elsewhere, we definitely recommend grabbing them.

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