When BenQ invited us to take a look at their latest Bluetooth speaker, we were intrigued. Sure, we've seen some wacky speakers before, such as the Amazon Echo Show, or even levitating speakers, but an electrostatic speaker is an unusual and rare beast.

The treVolo S is a somewhat chunky speaker, with two large but thin "wings", which fold down for easy transportation, but is this enough to make it worth purchasing?

Watch our video review below, or read on to see our thoughts on this curious Bluetooth speaker.

Electrowhat What?

While we don't have time to get into the fine details of how electrostatic speakers work, we'll cover the basics.

Traditional speaker designs use an electromagnet and an enclosure to convert electrical signals into sound. This design works well, and is used in nearly every speaker from your car through to your alarm clock and everything in between.

Electrostatic speakers, on the other hand, run an electric current through a thin material known as a diaphragm. This in theory means that electrostatic speakers can be thinner, and lighter, and are less likely to suffer from cabinet resonance and other things that impact cheaper designs.

Don't worry if you haven't quite got all that. Put simply, electrostatic speakers have been around for ages, but they are not very common. They don't always sound better or worse than traditional speakers, but they have a distinct sound.

One of the biggest drawbacks of electrostatic speakers is bass -- or lack of it. While mids and mid-highs can sound wonderfully detailed, low frequency sounds can often be found lacking. To counteract this, BenQ have installed two small dynamic speakers into the front of the unit. This makes the treVolo S an interesting design. Not only is it practically the only Bluetooth electrostatic speaker on the market, but it's also a hybrid design.

Features

Electrostatic technology aside, the treVolo S has most features you would expect from a Bluetooth speaker. With an 18 hour battery life, Bluetooth 4.2, a 1/8th inch input jack, and digital audio conversion via the USB port, there's certainly no shortage of features.

On the top are six buttons for controlling settings and music. Most of these cover your standard play/pause/volume/power, but there is a button to enable or disabled 3D mode. 3D mode uses BenQ's proprietary settings to widen your music. This isn't the same as a bass boost or EQ cut, it adjusts the electrostatic settings to produce a wider and clearer sound stage -- and it works very well.

Measuring 3.8 x 6.3 x 2.5 inches when folded, or 3.8 x 6.3 x 8.3 inches when unfolded, this speaker is hardly small. Yes, it will fit into bags and suitcases, but it won't fit into your pocket. Not that you'd want it to -- it weighs about 2.2 pounds (1kg).

The treVolo S does look and feel like a premium device, and quite rightly as it sports a list price of $199. While its size makes it impractical to travel with, and the wings do appear slightly on the flimsy side, this speaker looks right at home on a desk or side table.

Like the Ultimate Ears Wonderboom we recently reviewed, the treVolo S supports "duo mode", where you can connect two units together for an enhanced stereo listening experience. While features like this are really smart, for the cost of two units, you may as well just purchase a higher quality speaker system to begin with. This linking does give you room to expand the system in the future, however.

Sound Quality

Listening to music on the treVolo S is a surprising experience. I was initially disappointed with the audio quality, but after extended listening, it grew on me. The more I listened, the better it seemed to get, and after several hours of listening, things sounded great! I had no ear fatigue, and I wasn't tired from straining to pick out details. Sure, this speaker has a distinctive sound, and it certainly won't suit every style of music, but if you get the genre and environment correct, the results are quite impressive.

As this speaker uses an electrostatic element, certain frequencies and specific styles of song do sound much better than others. To really try this out, I played a huge selection of different music, spanning many different styles, decades, and genres. I started with Stevie Wonder's Superstition, and then Iron Lion Zion by Bob Marley. Tracks like these contain a huge variety of instruments and melodies. From the first notes of the iconic Superstition intro, to Bob Marley's full band and vocals, each elements of these tracks is present and clear.

Switching to some heavier tunes, I played AC/DC classics T.N.T. and Thunderstruck. Each instrument can be clearly heard. From the thumping guitar, to the drums. The bass, and the screaming vocals of Bon Scott and Brian Johnson.

I was really surprised here. Music generally sounds excellent. Songs are easy to listen to, and there's no distortion to be heard, even with the volume nearly maxed out.

Switching it up a bit, I played a mixed variety of female vocalists. Holding Out for a Hero by Bonnie Tyler, Nutbush City Limits by Ike and Tina Turner, SIA's chandelier, Emeli Sandé's Read All About It, Pt. III, and Lullaby by Sigala and Paloma Faith. These tracks represent a huge variety of styles. From the 80s through to current pop and dance hits.

It's really amazing how well this speaker handles the high frequencies. Guitars in particular really pop, as do vocals from these spectacular singers. The piano in Read All About It, Pt. III really does sound very good. It's a testament to the capabilities of this electrostatic speaker just how good it sounds. You can hear the little details like the reverb trails on performer's voices, or the studio doubling on Sigala's latest track.

The treVolo S projects sound forwards and backwards. This means that you get an excellent spread of sound all around the speaker. Although this unfortunately means that music can sound somewhat unusual if there's not a large amount of space behind the speaker. BenQ recommend a distance of three foot, which is fairly significant.

Placing the treVolo S into a corner does help to increase the bass, but place it too near a wall or something like a computer monitor, and you'll start to hear unwanted reflections. While this can be said about any speaker, the electrostatic design means that this is more prominent than perhaps it should be.

While there's no doubt that the treVolo S can sound outstanding, it certainly has some big drawbacks. There's a "sweet spot", where audio sounds its best. This means that audio quality can sound fantastic, but only if you have your ears at speaker level. You'll want to angle the speaker on a book if you don't fancy resting your head on your desk.

While audio doesn't sound bad outside the sweet spot, there's a noticeable drop in quality. The treVolo S is certainly capable of filling a medium sized room, but the quality and bass drops off after about 3 foot. You'll also want to use this speaker in a quiet environment. It won't handle a noisy party, for example.

Due to the nature of electrostatic technology, changes in your environment impact the sound. Humidity is a big thing to watch out for. Large changes in humidity cause the distribution, quality, and volume of music to suffer. While this can be said for dynamic speakers, it impacts electrostatic speakers more than others.

Is It Worth It?

It's somewhat difficult to recommend the treVolo S. While it's certainly capable of sounding fantastic, it's a bit on the fussy side.

It boasts a great battery life, but you'd not want to take it somewhere like the beach. It's best to think of this speaker as a wired speaker. Keep it at home on your desk, and things will sound great. If you're wanting to travel with it, you may begin to notice the unusual sound pattern, the slightly flimsy design, or the reduced bass.

If you're listening to music in a quiet, roomy, home environment, the treVolo S sounds amazing. Use it in any extremes of noise, humidity, or in tight spaces, and you may be disappointed.

If you're looking for something a bit smarter, then why not take a look out our Sonos One review, or how about these Alexa compatible smart speakers?