Product: Hawthorne Audio Silver Iris 15 inch coaxial drivers for use in open baffles
Manufacturer: Hawthorne Audio
Cost: 139$ (introductory price for one driver with coaxial tweeter and ready-built crossover)
Reviewer: Nick Whetstone - TNT UK
Reviewed: October, 2006

Fashions come and go and that's as true of hi-fi as any other part of our lives. When recorded sound was first invented, the sound was amplified by horns until somebody invented the moving coil type loudspeaker drivers that we know so well today. Those drivers were often placed in nothing more than a small shelf, perhaps part of a console or stereogram, or a plain baffle, until it was realised that there were advantages in placing it in a closed boxed. That resulted in more bass from the same driver because the front and rear waves produced by the drivers could not cancel each other out. Eventually, using drivers in open baffles was practically forgotten about, certainly by the vast majority of commercial loudspeaker manufacturers.

Now, who knows how any trend of fashion gets started. But in this modern age of easy communication, particularly now that we have the Internet, it's easy for somebody to have an idea and get others interested that idea. And over the last ten years, there has been a steadily growing interest in open baffle loudspeakers, mainly from those 'doing-it-themselves', and more recently, there have been several commercial open baffle speakers too.

I had read a bit about open baffle speakers on the Internet while researching the subject of full-range drivers. I had bought a pair of Goodmans 201s and successfully used them in very large ported boxes. I wondered how they would work in an open baffle, so one day, more or less on a whim, I constructed some chipboard (particle board) baffles and attached the 201s. I was immediately won over to the sound of open baffles. Sure, there was a reduction in the amount of bass, but the clarity, timing, and dynamics, were so enticing that I resolved not to go back to 'imprisoning' the 201s in a box. Since then, my open baffle system has evolved. First came some TL (transmission line) woofers that bolstered the bass frequencies down to 20 hz. Then I added a helper tweeter. But still the 201s were allowed to run 'full-range' ie with no crossovers.

This system sounded beautiful, but like all audionuts, I was always wondering how it could be improved. I took a close interest in anything to do with open baffles, and there was clearly growing interest in the subject from fellow audionuts around the world. One of the main topics of conversation was the search for suitable drivers for OB use. It seemed the choice was between some vintage drivers like the 201s, or drivers designed for use in automobiles where they may be placed in a parcel shelve, the equivalent of an open baffle. I did try one driver, originally intended for use in a car. The Ciare 250, a ten inch driver had a very good reputation amongst OB users. As good as it was, it didn't really come close to my 201s and after a few months, the Ciares were relegated to a shelf in the store room.

More recently, the Visaton B200 has become a big favourite with OB fans. Some describe it as the best driver that they have heard on a baffle. But it does roll off from around 200 hz making it (in theory at least) less than ideal for a full-range system. There are also one or two 'up-market' candidates for OB use from the likes of Supravox and PHL. But given that buying drivers, as opposed to finished speakers, means that you are experimenting, it's a lot to ask to pay out that sort of money in the hope that you will like the results. So where does that leave us in the search for an ideal driver for OB use? Well, it did leave us with very few options until recently!

One person who wanted to use open baffles and couldn't find 'the right driver' decided to take matters into his own hands. Off he went to Eminence, the world's largest driver manufacturer, and asked them if they would make a driver to his requirements. Full marks for his initiative, and credit too to Eminence who could so easily have said "forget it mate we're too busy to deal with individuals", but instead asked "what do you want exactly". To cut a long story short, the drivers were designed and produced, and the individual, Darrel Hawthorne, set up a small company with his wife, Diana, to sell the drivers and spread the gospel of the OB far and wide. And yes, you will find OB users do like to preach about the wonders of dipole speakers, and with good reason!

Hawthorne Audio haven't stopped with their first driver, the Silver Iris. They now supply a 15 inch bass augmenter, appropriately named the Augie, and are working hard on a 10 inch version of the Silver Iris coaxial for those looking for a more compact OB arrangement. But this review will audition the Silver Iris 15 inch coaxial driver and I'll cover the Augies later in part two.

So what's special about the Silver Iris (SI) drivers? Let's go back to the search for suitable OB drivers and ask what exactly it is that we need from a driver to work well on an OB. I mentioned above that when I took the 201s from their large 'boxes' and put them on open baffles that I noticed a reduction in bass. This is because on an OB, the driver can radiate its sound in two directions - forward and backward. At lower frequencies, the sound waves radiate out in a broader pattern. When they reach the edges of the baffle, the front and rear waves 'mix'. Because the rear wave is 180 degrees out of phase with the front wave, they partially cancel each other out, hence the reduction in the amount of bass. You may have guessed by now that the size of baffle has something to do with the amount of cancellation and if we have a larger baffle, there is less cancellation, ie more bass output. But most people don't want, or don't have room for, a massive baffle in their room and have to make do with smaller baffles.

One solution to that is to add some sort of 'help' in the form of a separate sub, or woofer, but let's stick with the idea of using just the one 'ideal' driver. If the driver has a high Qts (Qts is one of the driver parameters, ie part of the specification), it will have a sort of hump in it's lower response. In a boxed speaker, this hump would manifest as an annoying boom that we would want to get rid of. But in an OB, it will give the impression of the bass being boosted which is exactly what we want.

To produce more bass, the driver also needs a large radiating area, ie cone, and to be able to move that cone in and out a comparatively long way. So, we are looking for a large driver, with a good Xmax (sorry for the techno speak but that's another speaker parameter).

Now we need to think about the top end of the frequency range. There are drivers that will go up as far as 10 khz but those same drivers won't go down as low as we would like. So we need a tweeter and now we are back to using two drivers (yes - it's that old hi-fi compromise back to haunt us). But if a tweeter is necessary, we can do one thing to preserve one feature of a single driver speaker, and that is to mount it in the centre of the larger driver, thus preserving the single point-source advantage that will help imaging.

Having discovered that there wasn't such a driver, Darrel Hawthorne approached Eminence and they agreed to make one for him, subject of course to a minimum order quantity. And so the Silver Iris, 15 inch coaxial driver was born, and Hawthorne Audio was in business. Intrigued by the SIs, and the positive comments of the customers who had tried them, I asked if I could try a pair to review here. Hawthorne Audio not only agreed, but sent me their own pair of well run-in SI's so that I could immediately hear them at their best.

The SIs arrived in perfect shape having been very well packaged. On opening the boxes, I found the comparatively large 15 inch driver, the tweeter, and the crossover all neatly wrapped. Hawthorne supply the SI with a dedicated crossover making this an ideal way for even a beginner to get started in constructing their own high-end speaker. It really is easy to have the SIs up and playing music on a simple baffle in less than a couple of hours. That's exactly what I did, using some reclaimed chipboard. I recommend making your baffles out of scrap material until you are satisfied that you have your 'best' design. Then you can spend money if you wish on making the baffles look as good as they sound.

I started with the SIs on baffles 45 inches high and 22 inches wide. Why that size? Well it just so happened that I was able to scrounge two pieces of veneered chipboard that size, and I only had to cut the apertures for the drivers and add a base to support them. The centres of the drivers were about 30 inches up from the floor. I did find the sound a little lean for my liking, and having previously played around with some cheapo drivers in a very low baffle, I cut the SI baffles down and made a couple of trapezoid shaped wings for them such the drivers were angled upwards. The baffles are now 30 inches high with the drivers half way up the baffle. The change in sound was amazing. Not only was the 'lean sound' gone, but the timing improved as well. And of course, the visual impact was greatly reduced too! It's important to point out: the SIs don't require a huge baffle, they have been designed to work properly in a smaller baffle. This can be hard to believe for those used to other drivers in OBs but it's true. In fact, Hawthorne Audio warn against using the SIs in too large a baffle where the bass will then 'swamp' the mid-range.

Like any OB, the SIs need space behind them, about two to three feet from the wall is preferred, more if you have the room. A couple of feet from the side walls is also recommended. Don't be put off by these requirements, my room is only around 13 feet by 12 feet (3.9 by 3.6 metres) although there is a 4 foot opening to the next room. But I can accommodate the SI baffles easily. In fact after the combination of my 201 baffles and TL woofer boxes, the SIs seem positively compact! If having the baffles so far out in your room is a problem, you can put them against the wall and pull them out for critical listening.

The SIs are very efficient and you won't need a lot of power to drive them loud. But remember that you are also dealing with a bass driver here so any amplifier will need to have the necessary control. I tried running the SIs from a Gaicnlone and found it was more than adequate. I also tried an Autocostruire CT MC4x100 with the outputs paralleled for extra current. I'm sure that I read somewhere that open baffle speakers like plenty of current, but anyway, the combination worked brilliantly.

So how do they sound? Well they are a lot of fun! They are big drivers and you get a big sound stage. It stretches from wall to wall and is three dimensional, although not quite as deep as I get with my 201s. Despite those low baffles, the sound stage is at normal height and the only time I notice the height of the drivers is on those badly engineered recordings where part of the recording is recorded too quietly and the sound sort of 'sticks' to the speaker. I must clarify that this is the fault of the recording and not the speaker.

On good recordings, the performers and instruments are 'large' and with a lot of space between them. The SIs never sound 'flustered' even on complex recordings. With OBs, the music 'fills' the room in a way that it doesn't with boxed speakers. I watched an unsuspecting visitor turn his head in several directions when I started to play Roger Waters 'Amused to Death' with its Q sound special effects. He had heard that CD many times before on boxed speakers but was amazed how different it sounded through the OBs.

To be honest, having spent nearly three years listening to my own OBs, with their TL woofers going down flat to 20 hz, I was expecting to notice a lack of bass, at least until I got used to the SIs. But this wasn't to be. Instead I marvelled at not only the amount of bass that the SIs put out, but it's amazing quality. The TL design probably provides the best quality bass from a boxed woofer, but it doesn't match the quality of open baffle bass. I had read about it many times but still I was pleasantly shocked by what I was hearing from the SIs.

The clarity of the bass is the first thing I noticed. Each note is so clearly defined, it's almost like hearing it for the first time. The timing is superb and although each note is so clearly picked out, it is also perfectly integrated with the rest of the music. Listening to acoustic double bass, you can hear the strings vibrating. Electric bass is also much more defined than I have heard it previously. I have seen friends in bands learning bass lines from recorded music. How much easier the SIs would make things for them!

I also find that when listening late at night with the volume turned down, the bass is still prominent, rather like when using a loudness filter. That makes late night listening much more enjoyable. Let me make it absolutely clear here, the SIs on an open baffle, in a small to medium sized room, will produce more than enough bass! But at times you will think that there must be a sub woofer in the room too!

Percussion is another area where large OB speakers excel. Drums really do sound very real and with the right recording, a drum solo will give you a shot of 'adrenalin'. The big SIs portray the sound such that you can hear the hit of the stick on the skin, and hear each strike on the drum kit individually.

One trick the SIs do very well for a large coned speaker, perhaps because they have help from the coaxial tweeter, is to bring out details in the music that quite honestly, I hadn't been aware of before. In CD after CD, I was noticing something new. It really is like re-discovering your music collection. The SIs are very good at what I can best describe as 'magnifying' the sound stage, such that each element, each detail is brought clearly into focus.

The SIs create an atmosphere on some recordings that is quite eerie. For instance, listening to Nick Drake's 'Made to love Magic' late one night, I could almost sense the recording studio, see the musicians, cigarette smoke, and Joe Boyd at the recording console.

The SIs coped with just about everything well, whether it was listening to something quiet late at night, or turning up the Pink Floyd while the neighbors were out. I haven't tried it myself, but I am told that the SIs perform brilliantly out of doors. Perhaps I should organize a street party with its own open air concert!

If I can find any criticism of the SIs it would be with the mid-range. It's not bad by any standards but compared with the 201s, the SIs lack that ultimate "rightness', no doubt due to the crossover required between woofer and tweeter. But I'm being hypercritical here and possibly unfair in comparing the SI with another driver not encumbered with a crossover. And in some ways, the SI won out over the 201s. Male vocals were very well portrayed and if there was a roughness in them, the SIs let me hear it clearly rather than smoothing it.

And while on the subject, I did find the area around the crossover point just a little strident for my taste. I discussed this with Hawthorne Audio who said that I was the only user who had reported this. Perhaps it is system, or room related, but eventually I settled for a small notch filter using the Behringer DEQ2496 to tailor the response to my liking. If you find the same as I did, it shouldn't be very difficult to tweak the crossover.

And I should add a few words about that crossover. This is not the usual commercial offering, built on a PCB with cheap components. It's built with quality components that are cold-welded together and then mounted on a piece of solid mahogany. I'm not sure quite how this is possible for the price but another star to Hawthorne Audio for this attention to detail and quality. Hawthorne Audio have asked me to acknowledge the assistance of Dave (Hurdy Gurdy) Leonard in designing the crossover.

Summing up, the SIs are one of those speakers that just make me smile. I hesitate to call them a jack of all trades because that infers that they do most things well but nothing very well. In fact, they do bass brilliantly and the rest very well. No matter what you play through them, they bring it to life, and make it fresh. I'm not saying that they will make a poor recording sound good, but they may well make you re-evaluate some of your collection, and they will make your better recordings sound even better.

If you want to try OBs and see what all the fuss is about, the SIs provide a very easy way of 'getting it right'. It's not hard to design and build the baffles, and the SIs come with a ready-built crossover. In my opinion, the price of a pair of SIs with their crossovers, combined with the low cost of building a baffle, make this one of the best value-for-money high-end speaker systems! Even factoring in shipping costs, import duties and tax, the SIs with their crossovers, cost less than some entry level speaker kits! I appreciate that not everybody wants to, or is allowed to, have such large speakers, but if you are not restricted by space or 'co-habitational' pressure, I can thoroughly recommend the SIs. They don't have to be, or look that big either. Cover them in dark grill material and they really don't seem that large.

But it gets even better with the SIs! Hawthorne Audio have dedicated themselves to spreading the word about OBs and helping people get the best from them. Their support is second to none and they have their own forums where SI users (or users of any OB speakers) can exchange ideas, compare notes, and help newcomers. My usual advice on speaker building,is: stick either with a kit or at least a well-proven design. You can't build a good speaker unless you know exactly what you are doing. But OBs are the exception! You can easily get things 'right' straight off and it's no more than a matter of experimenting with different baffle shapes and sizes to fine tune an OB design and get the best sound from it. What you do need is the 'right' driver, and the SI certainly qualifies for that title!

Finally, if you would like to read more about open baffle loudspeakers, may I recommend the following:

Decaware Audio forum

Audiocircle forum

Hawthorne Audio forum

Manufacturer's comment

When asked if I would like to add a manufacturers comment section to the above review of our Silver Iris OB Coaxial's, I thought about this and one idea kept coming to mind.
I read the review over and over and I couldn't help but be moved by the time and effort that obviously went into writing such a detailed and informative personal perspective on the Silver Iris experience.

In the past several weeks it has been our pleasure to work with Nick and more than anything else we here at Hawthorne Audio would like to express our thanks and gratitude to Nick for taking the time to do this.

Perhaps some of you may not realize one important aspect of these formal reviews, that being the fact that the reviewers are for the most part not paid or compensated for all the time and effort that goes into these articles that we all enjoy reading so much.

I would like to welcome and encourage you all to join us in acknowledging the contributions to the audio arts that are being made day in and day out by reviewers like Mr. Whetstone.

If you enjoyed reading this review , please take five minutes and send Nick an E-mail and tell him so. Better yet, write to the Editor and tell him. Hug your kids, compliment your significant other, tip your waitress, and acknowledge the efforts of these fine reviewers... Thanks Nick.....
Best regards,
Darrel and Diana Hawthorne

Go to Part II