Stealth Acoustics

LRX-83 Speakers

AUD $2,599 RRP

The Stealth Acoustics LRX-83 is a so-called architectural or installation loudspeaker, designed to be installed in a wall. That doesn’t mean flush with one, but actually inside it! Made to be placed inside a wall cavity, it can then be painted or even wallpapered over – making for true invisibility, assuming your tradespeople’s skills are up to the job…

Sold in pairs, it comes in the form of a rigid ABS panel that is reinforced with ridges. Over the face is the paintable, wallpaper-able diaphragm which delivers the sound. The whole panel is 403x559mm while the required mounting depth is 63.5mm. As is common with installation speakers, the rear is exposed. Back boxes are available as optional extras – the MDF one costs $199 each, while a metal variant is $299.

On the back are three drive units. In the middle is a 203mm low profile woofer with a 38mm voice coil and 0.6 kg ceramic magnet, which is acoustically coupled to the front panel. In other words, it apparently doesn’t touch the front diaphragm. Note though that I’m largely going on Stealth Acoustics’ description here; the speakers were delivered in sturdy demo boxes, and it was in those that I used them. I removed them from their boxes for inspection but didn’t feel confident that I could dismantle the speakers themselves without inflicting damage.

On the bottom left – as viewed from the front – is the midrange driver. Stealth Acoustics simply describe it as a 30mm neodymium driver and says that it is direct-coupled, suggesting that there’s a 30mm voice coil behind that section of the panel. At the opposite – top right – corner is a direct-coupled 25mm neodymium tweeter, according to the company.

The frequency response is 40Hz to 20kHz, according to the supplied on-axis response graph of the speaker, done with no less than four coats of latex paint! This shows a fairly prominent bass (+ 6/7dB) around the 90 to 100Hz region, with the output gradually diminishing to an even upper midrange, a small peak around 10 to 12kHz and then a falling away to around 10dB down above 16kHz. Bass was around -6dB from the average at 40Hz. I ran a quick test myself, measuring in-room at 1 metre; it was largely comparable to those results, except that high frequencies were much stronger, around +8dB at 20kHz.

Each LRX-83 needs lots of power – there’s a cost for driving sound through a wall, it seems! The company specifies a power handling of 160W RMS, or 320 watts peak into its nominal 8 ohms. Nothing too unusual there I guess, but what is unusual is the minimum recommended power specification of 80W – reasonable considering the sensitivity is rated at a low 83dB/1W/1m. A typical high fidelity loudspeaker has a figure of around 89dB, so for the same output level, you’re going to have to provide four times more power.

SOUND QUALITY

First, a caveat. The sound of any custom installation loudspeaker will be affected by all manner of things. For example, are you using the optional back boxes or not? With a back box, you’ve basically got a small infinite-baffle loudspeaker. Without, you may have somewhere between modest and almost zero acoustic loading. Bass will differ accordingly. Also, where you place the speakers in the wall will make a huge difference to the sound. I remark on that below to some extent, but installation locations depend on various practical considerations, such as other furnishings within the room. How much paint, and what type will you be applying?

Finally, this kind of speaker is often intended principally for a home theatre system. My listening impressions below are based primarily on music. But if you’re going home theatre with a suitable receiver, you will be calibrating the system using its DSP. Or you may be using Stealth Acoustics’ own SA 2400 MKII amplifier, which includes DSP optimisations for several of the company’s speaker systems, including the LRX-83. I used a high-quality 100W RMS per channel power amplifier.

The main effect of the high frequency drivers being hidden behind, and actuating a section of a large panel was not – as you might expect – a diminution of the high frequencies. Stealth Acoustics appears to have more or less balanced the drivers to account for that possibility. Rather the result was a slight disembodiment of the sound; it wasn’t quite the attractive airiness which is often delivered by panel speakers. 

That effect is only partially due to the panel, and mostly down to the dipole functionality – in which as much out-of-phase energy is being delivered from the rear of the panel as in-phase from the front. That’s clearly not the case here since all sound is from the front. One would expect the high frequencies would be beaming quite tightly directly to the front (an inevitable result of the wavelength of the sound being much shorter than the size of the driver.) That was not immediately obvious when playing stereo music. So, ever the good reductionist, I unplugged the left speaker and tried listening to regular music on the right channel alone.

The first obvious thing was that there were two styles of sound. With my head on-axis with the tweeter – or, really, directly in line with any part of the panel – there was a solid, well rounded and integrated sound. But as I moved to around twenty degrees off-axis to the side, treble softened markedly, and the entire sound lost coherence as though its constituent parts weren’t entirely connected to each other. There also seemed to be some ‘lobing’ response patterns depending on the angle. I stood directly in front of the speaker, with my ears some 300mm above the tweeter, and moved slowly towards it from about three metres away. At several points, the sound was fine, and at others, it was delivered with a kind of hollowness.

Okay, enough of that reductionist stuff – with both speakers running, little of that was really noticeable. What remained obvious though was a marked difference in stereo imaging depending on height, and impact depending on the distance. Listening to Master Hunter by Laura Marling, I was leaning forward and tapping out some notes on my computer, and the impact of the clattery drums was excellent, verging on thrilling. I leant back by half a metre into the couch, and sthat edge and attack was softened, taking the excitement with it – then I leant forwards and there it was again, and back and it was gone. Perhaps it was the large tweeter radiating surfaces exhibiting variable time coherence, depending on the relative position of speakers and listener.

Having my head well above the level of the tweeters also weakened the impact of the sound and reduced the coherence of the soundstage. Both of these effects say something about installation and furniture arrangement. It would be a good idea to have them installed so that the tweeter is at ear-level for your normal listing position. Later, after installation, experiment with different listening positions if possible, closer to or further away from the speaker pair.

All this is assuming that you’re using these speakers for stereo listening. The fact is, the Stealth Acoustics LRX83 can, with a little bit of care, sound remarkably like a good quality standalone bookshelf loudspeaker. For instance, as I’m writing, they’re doing a credible job on Brahms’ first piano concerto (Haitink/Concertgebouw/Ashkenazy on Decca). Tonally, there’s something of an emphasis on the upper bass. It remains clean, so isn’t boomy, but it does give a weight that hides the relatively limited deep stuff. The violin section is restrained and with no hint of screechiness, which is in part a characteristic of Decca classical recordings. There is little layering of stage depth, except for the piano initially sounding a little distant.

Finally, that occasional disembodiment which I mentioned early was manifested in an unusual way. When Laura Marling got to the track Little Love Caster, my attention was attracted by low-level creaky noises coming from behind me, near the door of my office. I paused the music and looked, but there was nothing there. Once the music was going, I realised that this was low-level stuff within the music itself. Somehow it was being projected down the length of the room and reflecting from the surfaces back there.

THE VERDICT

The trick in making a loudspeaker invisible isn’t just painting it over, as Stealth Acoustics knows all too well. The LRX83 has been carefully engineered to give a good result despite the sonically adverse locations it is likely to find itself in. Although I’d still prefer a good pair of standalone speakers at this price, if invisibility is a requirement, it’s hard to see how it could be done much better.

For more information visit Stealth Acoustics