Product: Arcadian Audio Pnoe Horn
Manufacturer: Arcadian Audio - Greece
Cost, approx: 24,000 Euro (introductory price now of 20,000 € (YMMV)
Reviewer: Geoff Husband - TNT France
Reviewed: February 2011

Background

For a small but increasing group of audiophiles the Holy Grail of speaker design is the full-range, single-driver, crossover-less variety. By using the single driver the various evils of crossovers are avoided. The downside is that of course to get a single cone to produce the entire audio band from say 20 Hz to 20 kHz is asking a hell of a lot and is why 99% of loudspeakers will use at least two drivers, one large for bass/mid and another much smaller for treble.

But it is possible to use one driver. To get the larger cone required for bass to vibrate fast enough to reach high treble requires a very light cone and a massive motor. Thankfully for us there are indeed such drivers – the Lowther being the oldest and most famous with more recent incarnations coming from companies like Loth-x (now defunct), Fostex, Supravox and AER. Now here I have to make a distinction – there are lots of drivers that claim to be full-range, but few do reach to the high treble, and many are very uneven. Generally those that do are expensive; to insanely expensive.

So you now have a driver that reaches at least most of the way to 20 kHz (hell my ears call time-out much over 14 kHz nowadays...), but the tricky bit now is the other end.

Now forgive the primary school explanation below, but I need to get on :-)

Take a small driver out of a box, say 3” and play a full-range signal through it. It'll have no bass at all. Now do the same with a 12” driver and what happens? You hear much more bass, but hell – not much for such a big speaker. Trouble is you are up against physics. High frequencies have short wavelengths and to put it at the most basic level – those wavelengths are smaller than the cone radius and so the cone can fire them into a room. Once the wavelength gets beyond the cone what happens is rather than being fired into the room, the wave of air (for that is what it is) 'falls' off the edge of the cone and goes round the back to cancel the output. That's why the bigger cone produces lower notes, but in the end even a 12” speaker will have very limited bass in 'free air'.

Now there are lots of ways to stop this – the most common being to put the driver in a box, and the simplest being to just put it on a big sheet of ply – a flat-baffle. But that driver that will go to 20 kHz just cries out for that most esoteric of designs – the horn.

Horns have been described as a kind of acoustic lever, but they are a bit more than that – rather than a lever that gains force by swapping it for distance the horn seems to be more of a piece of magic - giving something for not very much :-) To simplify (again) a horn uses the radiation (in this case from the back) from the driver which then travels along an expanding tube to the horn mouth. If you imagine the wave-front racing down this 'flare' you'll see no energy is lost sideways – each molecule of air moving the one in front and so on until it reaches the horn mouth and then the air right at the mouth acts as a large but unbelievably light diaphragm. The (for example) 8” driver may have grown to a meter across and therefore the bass cut-off frequency is much lower. Of course the bigger the horn mouth the lower that cut off.

Such a design is loud, because it focuses the sound towards the listener – when you cup your hands to shout to someone you do the same thing, a loud-hailer is a horn, a Tannoy is a horn, the whole design of a saxophone is a horn as is any brass instrument.

There are two snags to this wonderful invention. The first is that as with all those instruments and Tannoys, there is a very distinct character – the horn isn't just a wave guide, it's also a tube with resonances in it, and so some frequencies come out louder than others. The phase relationships of notes can change – in fact most are a very long way from hi-fi. What is a pleasant character in a French Horn is poison for reproducing a recording faithfully. So designing a good horn is not easy.

The second is that if you want the horn to reproduce bass it has to be B-I-G and therefore complex and expensive.

Which neatly brings us to the subject of this review – the Pnoe Horns :-)

Introduction

It's October 2010. A large container lorry pulls up outside the house. Inside are two enormous crates – each as wide as the full width of the container. The delivery man dumps these on the pavement outside my house. I knock up neighbours and we remove the speakers from each crate and stagger through the garden and into the back entrance of the listening room. And now folks, if your music room doesn't have double doors , or 8 foot headroom you can just forget it because these monsters are just not going to fit in. (correction – in fact they will fit through a standard 90cm door but you'll need to grease them first :-)

You can see the pictures – these look almost exactly like a giant tenor sax. Reading the above I hope you can see why.

I love horns, my own speakers are Polaris single driver horns and I wouldn't part with them for the world. But these make my Polaris seem like toys. The drivers are similar, both are 8” with a whizzer cone – both with lacquered paper cones, both beautifully made, though I'd give the prize for beauty to my Loth-x's Stamm driver over the Pnoe's AER drivers. And whilst on the subject of drivers, these AER's have gained a very good reputation in horn circles and are expensive enough (circa 1500 Euro each) to justify a large slice of the Pnoe's considerable price.

But what catches your eye are the monsters they are attached to. I knew they were fibreglass, but the finish is really good, in this case white, but I see no reason why the horns shouldn't go down to your local body-shop and be resprayed in whatever colour you wish – and when you change décor – sprayed again. After all it's the same stuff my Lotus is made of :-)

You might be forgiven for thinking that these speakers are a triumph of style over function, but nothing could be further from the truth – in this case form follows function - Louis Sullivan would be proud of them.

My own Polaris horns are classic, compromised bodges. Remember that 'flare' I talked about in the 'background'. Well in a perfect world it would be perfectly circular, gradually increasing in diameter and then folded back to exit as close as possible to the driver itself (which supplies the upper mid and treble while the horn provides the rest). The 'form' of the Pnoe is that 'perfect world'.

Now that's a sweeping statement but let's compare my Polaris with the Pnoe. The Polaris are designed to be domestically acceptable and reasonably economic/easy to build. Like 90%+ of large horns out there they are in fact a folded, rectangular-section pipe, the pipe being made up of pieces of MDF arranged to make an ever increasing cross-sectional area of the pipe itself. There's no smooth flair, rather a series of expanding sections each joined by a 180 degree turn as the next baffle turns the horn back on itself. Not only that, the section of the 'horn' is a rectangle of constant width (again for ease of construction) which becomes taller and taller until it finally exits the box.

So let's do a character assassination of the Polaris compared to the Pnoe.

1 – The Polaris horn is much shorter than the Pnoe's. This in itself gives a less flat frequency response.

2 – The flat baffles inside the horn will vibrate unevenly adding colourations.

3 – The horn is nothing like a smooth flair – bad...

4 – The horn path has several sections where the sound radiation has to swing through 180 degrees, and each folded section can act as a pipe to add yet more resonances.

5 – Compared to the smooth, circular cross-section of the Pnoe the ever changing rectangle of the Polaris' horn is just made for all sorts of colourations.

5 – The horn mouth of the Pnoe is much bigger (and circular) allowing a lower cut-off frequency.

6 – The horn mouth exits right next to the driver helping the two integrate far better than the Polaris, where by the nature of the folded horn the two are 50 cms apart.

You get the idea? The form of the Pnoe is as near perfect as you could get it without demolishing your house. 90%+ of commercial horns use a similar folded box to my Polaris. A few make the horn expand gently with curves but the section is still rectangular. Only a handful follow the Pnoe form or similar and some of them cost more than my house.

As for construction, as mentioned above the horn is made from fibreglass, I imagine using at least two molds and damping material (the joins are totally invisible), then all finished in gel coat and painted white or black. The finish is very good, not piano lacquer good, but better than a plastic bath. As already noted I see no reason why it shouldn't be painted to the same standard as any car body.

As is the nature of a horn the rest is very simple, the AER driver connected to binding posts (Eichmann Bullets) at the back. The horn molding includes non-spiked feet.

Size is especially important because you need to know if they will fit in your room – and they are 220x100x90 cms – i.e. huge, though at a surprisingly light 52 kgs they aren't that hard to move once you get them into your house. The light weight (relatively) down to the fact that you get the horn, but none of the extraneous woodwork around it that you'd get with more conventional construction...

The result is a speaker claiming to be full-range, 16 ohm and with 100 dbl efficiency, simply perfect for the single-ended valve amps that no doubt Arcadian Audio had in mind.

And here forgive a little aside. One well-known 'style' website 'reviewed' the Pnoe (actually a rewrite of the press release) and made the following comment...

“I was shocked upon reading the frequency response is only 42Hz – 21,000Hz, especially after I've seen horn design taking drivers to 65,000HZ or higher.”

Which shows the danger of allowing the ignorant access to the web :-)

In Use and Sound Quality

Having done a hatchet job on my own Polaris horns I need to make it very clear (as the politicians say) that despite the compromises involved they remain by some distance the most musical and pleasing speakers I've ever heard. That this performance is available given all their theoretical problems made me all the more eager to hear the Pnoe.

Of course when you set out to review a 20,000+ Euro speaker you really need to do it justice, luckily I had some serious front-ends to hand, and for most of the review the speakers were tested with my Opera LP 5.0 Droplet turntable whilst the matching CD 5.0 Droplet span the silver stuff.

But where it gets interesting is the choice of amplifier. With a power handling of 100 watts, an efficiency of 100 dbl and valve friendly 16 ohm impedance the Pnoe can be driven by just about anything. Many speakers with this sort of price-tag are multi-driver or flat panel jobs and demand seriously powerful amplification, and generally power+quality=expensive. In the Pnoe's case you could drive them with a 100 Euro digital amp and though you're not going to get the very best from them it'll be a good place to start.

More important you could drive them with a low-powered single-ended valve amp, and some of those produce the finest 'first-watt' you can buy regardless of price. One such amplifier is the Yamamoto A-08s and when it comes to transparency and sheer quality that little wonder is as good as anything I've ever heard at any price (including my own Ayon Crossfire). As the Yamamoto pumps out a huge 3 Watts a channel it'll drive the Pnoe to near threshold-of-pain levels. This quality comes at around 2000 euro and so assessing the price of the Pnoe + amplification as a package, provides a rather different value than might otherwise be the case.

With the Yamamoto I needed a fine preamp so wired in the Acousticbouy Scorpio with the Lehmann Black Cube Twin providing the phono stage.

I only measure speakers at the end of a review period, and then always in-room with my own crude equipment. I put this off to the last minute because I don't want my listening notes to be prejudiced by knowing the response curve. For example if I knew the Pnoe were 10 dbl up at 3000 hz you can bet I'd spot a mid-range bump:) But to be honest, after having done this many times I've now got to the stage when I'm rarely surprised by the measured performance. In this case the Pnoe showed one outstanding quality. They were flat +/- 3 dbl, in-room from 40 → 250 hz. This is an astonishing performance from a horn, easily bettering the Opera M15 speakers which use a 15” driver!

Usually with a horn you get hints of comb filtering as resonances add and subtract from certain frequencies. Likewise you expect a bit of a hump where the horn really sings and so-on - some notes get emphasized. One solution to this is making the horn mouth relatively small, and my own Polaris do trade depth for a more even bass response, giving up below 60 Hz. The Pnoe don't use this dodge. This is also done without any corner or wall reinforcement, just firing straight into the room – though the floor inevitably will add a little bass.

Above this all sorts of room reflections tend to show their ugly head so experience with my in-room plots helps separate the speaker from the room, and the result is a beautiful response with the high treble running easily up to 15 kHz and above. If anything the bass is a little above the mid and treble and this emphasizes the fact that the Pnoe are designed as a true free-space design – almost unheard of in the horn world. In my room there was about 50 cms between the speaker and side/rear walls so some corner reinforcement will lift that bass. Bringing the horn further from the walls – at least a metre - gave the speakers remarkably even response right across the range, but even in my large listening room this was a little impractical.

Of course this is all theoretical and very nice, but how do these characteristics manifest themselves in the real world?

To find out, my test of bass resonances - Simply Red's 'Sad Old Red' - produced a clean range of bass tones with no note singing out, at the same time the definition of the bass string and how it was played was spot on – the Yamamoto easily showcasing it's ability here. Horns, because of the huge 'air-diaphragm' at the horn mouth give lightening fast bass and great pitch, and my Polaris give a bass quality I find it hard to live without, but the Pnoe continued that for nearly an octave lower, right to the open 'E' of Tony Bower's bass. My Polaris I pair with a REL Stentor sub set just to tickle the very lowest notes – the Pnoe doesn't really need it.

Though I tend to use this track as a bass workout, it also does test pretty much everything else :-) Mick Hucknel's vocals retain an intimacy and detail that is easily lost, having both warmth, and an edge he draws on as he jumps an octave. And all the while the sound and size of ride and high-hat behind stay stable, realistically sized and with just the right 'strike'.

Speed and attack are there in spades with Nirvana's 'Nevermind' – massive crashing drums and the blood curdling crescendo of the opening of 'Breed' – who needs Ravel... This record shows some rather special, if artificial spacial effects, and the Pnoe show the advantage of the baffle-less design by producing a huge, overwhelming soundstage with big depth. Not only this, because of the directional nature of the treble reproduction, by positioning the speakers to cross over in front of the listener the Pnoe pull that lovely trick of having an image which is stable even if you move well off center. This also means that fine turning of the treble output is achieved by simply pointing the driver directly at the listener (maximum treble/midrange), or angling it further and further away. Personally I found the best balance and soundstaging with the classic X happening 1 metre in front of me.

This ability enticed me into digging out atmospheric records and one of the best is 'Bookends' by Simon and Garfunkel – though made in 1968 this has the simple care in production you usually only see on Jazz records of the period and just drips with ambiance. Very much a 'they are in the room' experience, such records are the best for the live illusion when played on very transparent kit and the Pnoe certainly didn't disappoint and as is often the way it took me down a particular path and I dug out Paul Simon's 'Rhythm of the Saints', the opening track of which is a mix of studio work backed by mass drumming recorded in a hard courtyard – the result was as spectacular as the producer intended.

As always my precious copy of 'King James' (Sheffield direct cut) came out and the band in the Wylie chapel, with its hard acoustic (again) gave the kind of sound-stage that demolishes the walls of the listening room.

And so it went on, and I began to take notes to pin down for myself (and you) exactly what the Pnoe offered for their considerable asking price.

My listening room is large – 6m square, but with a ceiling 7 metres at the point and a mezzanine extending back over the room there is a huge volume to fill. My own Polaris are lost in it, the Acuhorns even more so – only the big Opera M15 have really worked here. The Pnoe filled it with consummate ease, and that is just as well, because they really need space to work properly. Though my own Polaris have taken a hammering here it's the case than in my own living room (where they reside) which is 5x6m with a lowish ceiling, they work beautifully – the Pnoe, besides not getting through the door and being physically too large for the space, would be overblown. This though, means that given the space they need, they can drive areas well beyond most domestic horns.

Time and time again the Pnoe gave a scale to performances that even the M15 couldn't manage, leaving that excellent speaker sounding a a touch lumbering and slow, whilst at the same time a bit 'small'. King James' band really is a 'Big-Band' with the Pnoe...

This and the superb bass performance are down to that remarkable horn, and the way that the designers have integrated it almost seamlessly into the main driver - which inevitably flies solo for upper mid and treble. The AER driver in turn has an enviable reputation and the MD-3B is their top driver and certainly didn't disappoint. In some respects this even character could be seen as the one weakness. If you are looking for a more forward, sparkling, 'middy' sound many associate with horns then you will be disappointed. These are speakers that demand utterly transparent ancillaries. Anything that adds warmth (some EL 34 or Class A transistor amps for example) will push them from feeling even handed and utterly convincing, into something that steps you back from the music. Here the substitution of the Yamamoto with the Son of Pharao EL 34 valve Amplifier, (costing 4 times the price), pushed the Pnoe too close to 'easy listening' for my taste. But stick with components that open the window to the music and the Pnoe will make the most of it. What intrigues me is what would these horns sound like with other drivers? The horn should work with many different drivers with minimal modifications (mainly to the mount) and with some full-range drivers costing more (each!) than a pair of Pnoe equipped with the AER the sky is the limit, and I firmly believe the structure of the horn is up to getting the best from most of them.

Complaints

Nothing is beyond criticism, least of all a speaker costing 24,000 euro. As mentioned before the finish is very good, but 24,000 euro speakers are usually spectacularly finished, the black and white currently on offer are limiting and even as an extra cost option some very sexy paint finishes should be possible – I'm told this is in hand...

Handling is tricky as there's just nothing to get hold of. But sound quality? Hard to fault: fussy about placement: very. A bit 'laid back' for some tastes? Only if matched with the wrong amplifier. Not much under 40 Hz? True, but that covers the fundamentals of everything but the bottom key of the piano, the 32' pipe of an organ and whale song. Much better than trying to cheat and gain a few extra Hz at the price of an uneven response. Really good subs like my REL are at their best when asked to produce true sub-bass, the sort that just adds a hint of ambiance to a venue – not going boom-boom! to cover the bottom octave. So if you do want a system that goes down to 16 Hz there's a solution available.

Conclusion

The Pnoe are a brave and largely successful attempt to build a domestically acceptable, full-range horn with no compromises. Why don't other companies do this? Because it's difficult, expensive, and involves a shed load of prototypes, each requiring a mold to get right. No making a plywood box and playing with stuffing and baffles here. To get lower bass cleanly, from a single driver horn would take you to the world of custom horns built into a room. Its development must have been long, complected and expensive – bravo! to Arcadian Audio. It doesn't need expensive amplification but it does need a big room and space around it – people who's listening room is less than say 7x6 metres should think carefully.

To call a 20,000+ Euro speaker 'good value' seems insane, but looking at the competition I can't see anything less compromised at the price and if you believe in the single-driver horn it's hard to see how it could be bettered.

Manufacturer's comment:

© Copyright 2011 Geoff Husband - geoff@tnt-audio.com - www.tnt-audio.com