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Hawthorne Audio Silver Iris drivers - Part II

More bass Sir?

[Italian version]

Product: Hawthorne Audio Silver Iris Augie 15 inch bass augmenter drivers for use in open baffles
Manufacturer: Hawthorne Audio
Cost: v 165 USD (introductory price)
Reviewer: Nick Whetstone - TNT UK
Reviewed: November, 2006

In part one of this article, I wrote about the Hawthorne Audio Silver Iris coaxial drivers in open baffles. I will now describe my experience of adding the Silver Iris Augies, 15 inch woofers designed specifically for use on open baffles.

Hawthorne Audio were quite keen for me to try the Coaxial drivers on their own to see what they could do. And I found that on a low baffle, ie with some support for the bass frequencies from the floor) they performed very well. Indeed, I didn't think that I needed more bass and was intrigued by what the Augies could add to the performance. It may seem a drawn-out way of arriving at the same place, but building these Hawthorne Audio speakers this way helps in the understanding of what each driver is adding to the speaker.

For the coaxial driver review, I had done little more than scrounge some chipboard, cut the apertures, and add some small wings. I could easily have obtained some more free chipboard and built larger baffles to accommodate both the coaxial and Augie. But experience has taught me that we have to be careful with this type of speaker. The vibrations from the bass drivers (and we are talking large drivers here) can adversely affect the operation of the driver(s) handling the higher frequencies. And don't forget that although there is no 'box' to add sound, a baffle is also capable of making an unwanted contribution unless we take precautions. So I felt that something more sophisticated was required for this part of the review to do full justice to the drivers.

I've been building open baffle speakers for a few years now and have always liked to experiment. As already stated, the comparative simplicity of an open baffle means that they can be built much more quickly than a boxed speaker, and this should encourage us to try different types of baffle. One of the strangest designs that I have tried was an all polystyrene type with the drivers bolted to an MDF 'skeleton'. You can read all about that here. Although I only used a very cheap driver, the results were very encouraging, with clarity being one of the most noticeable aspects of the sound. I put that down to the polystyrene baffles having almost no mass, and therefore no stored energy, so they couldn't add any sound of their own. But those were only lightweight 8 inch drivers, and this time I was looking to support a pair of much heavier 15 inch drivers.

After thinking about the problem for a while, I came up with the idea of a wooden frame that would support the polystyrene baffles. The frame itself would be lightweight and the polystyrene would isolate it from the drivers. The next consideration was how to mount the drivers. You obviously can't bolt or screw anything to polystyrene so fixing the driver rim to the baffle is not possible. But I had already become interested in alternative ways of mounting drivers and read reports of people securing the driver by the magnet. That seemed like the way to go but I soon realised that drawing a suitable design on paper was one thing; actually building it was another. So it was back to the drawing board. Then I had the idea of mounting the driver by clamping the basket instead of the magnet. This would entail making some hooks to 'grab' the basket frame. And if the hooks were threaded, they could be secured with nuts that when tightened would pull the driver back into the polystyrene baffles, holding them securely in place.

[Basket mount]

In fact, this design turned out to be relatively simple to achieve and seems to work very well. The front of the driver (the rim) is held securely in a rebate in the polystyrene. Rebating the polystyrene with a router was very easy but I looked liked a snowman afterwards! (Never try this indoors unless you live on your own) By tensioning the securing bolts, the drivers are pulled into the rebates and held firmly. Only two 'hook-bolts' are required per driver making it quite a fast job to install or remove them. Each driver sits in its own piece of two inch (5 cm) thick polystyrene just to isolate them from each other a bit more. This may be overkill but it wasn't very much more work to do so I went for it as it also allowed a brace across the middle of the frame to increase rigidity. And that's about it. Six pieces of timber for the frame, two upright posts at the rear to bolt the drivers to, top and bottom decor pieces, and some polystyrene. The front of the baffle was covered in some thick carpet underlay-felt and then some thin black felt was wrapped right around the baffle. The grille cloth is then attached to two batons and stretched around the whole baffle. Some rear grilles would finish the job nicely! For the amount of work required, and the cost of materials, I think you will agree that it looks quite classy (a bit like a Quad ESL63?). Although I was only reviewing the drivers, I felt obliged to present the product as well as possible (and uphold the high standard of TNT reviews).

Before we get on to how it all sounds, I had better tell you about what I used to drive the new baffles. Hawthorne Audio call their baffles with the two drivers 'Duets', so that's what I'll call the review baffles for the rest of this review.

As stated in part one, the SI coaxial drivers come with the their own crossover. However, the Augies require that some sort of crossover by used to roll them off, either the passive type (an inductor between power amp and driver), or the active type, (used between pre amp and power amp). I am much more of a fan of active crossovers and fortunately, my own open baffle set-up uses an active crossover for the bass woofers that has a variable setting for the crossover point. As I also had the four channel Audiodigit CT MC4x100 amplifier 'on review', it seemed sensible to use that too.

[Finished Duet]

I thought that it may be a good idea to see how the coaxials sounded on their own in the new baffles so I didn't connect up the Augies. The coaxials did sound quite different on the higher baffles and this brings me to an important point. Changing the shape, size and construction methods of an open baffle speaker nearly always changes the sound in some way. That's the reason you will often hear the advice to experiment when you build this type of speaker. With the coaxial drivers further off the floor, the sound went back to sounding a bit on the thin side. In addition to that, the baffle was clearly adding less sound than the simple panel of chipboard that I had used previously.

Turning on the signal to the Augies, I immediately noticed that the 'thin' sound disappeared. I played around with the active crossover, settling on a cut-off point of around 55 hz. At first I had the level control for the active crossover turned nearly to maximum but as I played more and more music, I found myself reducing the level quite a bit. I find for this type of job, using my ears and playing a wide variety of material is the best way to get everything set up optimally.

When I was happy that I had got the settings more or less spot on, I sat down to listen. And straight away, I could see the advantage of using the two drivers together. With the coaxials raised further off the ground, they seem to gain a little more clarity. Perhaps this is because they are not producing so much bass. Anyway, with the Augies 'helping' with the lower frequencies, there is still that very tuneful, solid, bottom end. Even more so than with the Coaxials on their own, the Duets, produce wonderful bass even at low volume settings.
I have found myself listening to CD's that I had previously reserved for day-time listening, when I could play them louder without worrying about the neighbours. With the Duets, I can play them late at night, still enjoying the bass lines, and not worrying about upsetting anybody else.

I'm not sure if it is connected with adding the Augies, or some other factor, but listening to the Duets, I didn't get that impression of the slightly rising response (that I had noticed using the coaxials on their own). No longer did I feel the need for a bit of a notch filter on the Behringer DEQ2496! The Duets are wonderfully 'even-handed' right across the frequency range. Even playing loud, there is nothing 'offensive'.
I'm not sure exactly how low they go, I don't have accurate enough equipment to measure them but I did do a room correction on the DEQ2496 and apart from the usual room suck outs, the DEQ2496 didn't need to boost any frequency down to 30 hz. (Please note, all the comments about the Duets are made after listening without the DEQ2496 and in fact, I prefer the sound without the room correction). The impression that you get with the bass is that it is lower than it actually is. And of course, being dipole bass, it's remarkably clear and well defined, and doesn't cause any room problems, even in my moderately sized sitting room. On 'Sister drum' by Dadawa, the bass literally 'thunders' but is always well-controlled.

Timing is also very good. Paul Simon's 'Graceland' had my foot tapping right through the album. If you thought that large drivers could not produce 'speed' then the Duets will really enlighten you. It's hard not to get up and dance sometimes!

What you get with the Duets is a 'big' sound. Sound stage is large and individual performers on a good recording are life size. When the recordings get complicated, the Duets just sail on, keeping everything where it should be. When there is a lot of bass content, that is portrayed clearly without affecting the clarity of the mid range and higher frequencies.
Percussion is brilliant, with the passive crossover showing no signs of dulling the dynamics or transients. Vocals are clear and natural. Everything I have played through the Duets sounds great; this is not one of those speakers that excels at say jazz but not rock. It compels you to rediscover your (whole) music collection.

Perhaps the only thing I can 'criticise' the Duets on, is that vocals are not quite as good as with my Goodmans 201s. But it's worth repeating, the 201's run without a crossover and don't have quite as wide a frequency range as the Silver Iris coaxials. If I am totally honest, the mid-range aside, the Duets better my own open baffles over-all, and take up less space!

[A pair of Duets in room]

Before I conclude a review, I usually ask myself if I have covered everything, particularly the negative points. This time, I honestly can't think of anything negative to say other than this type of speaker may be physically too large for some people/rooms. Remember that apart from the size, an open baffle speaker really likes at least a couple of feet (60 cm) between it and the adjacent walls. I'm not saying that these are the best speakers in the world, they are not but they are much nearer the top end than the bottom!
For their cost, and the relatively small amount of work to build them, I can't think of anything at (or near) the same price that can produce the same quality of performance. At the current price, a set of drivers and the passive crossover are comparable with what we could consider 'entry-level' kit speakers. Given that the Duets sound like high-end speakers, I know what I would spend my money on! And going back to the size issue, when they are finished in that grille cloth, they almost blend into the room like a piece of furniture.
They are certainly far less obtrusive than my open baffle speakers that use smaller drivers! Personally, listening to them, I wouldn't begrudge them the space even if they didn't look so good!

Summing up, this is possibly the best way to DIY open baffle speakers for anybody, regardless of their previous experience. It's really not that expensive for what you get. You don't need to design or build a crossover.
Even if you have zero DIY skills, a local carpenter should be able to make you baffles at a reasonable price. I'm forwarding full details of my baffle design to Hawthorne Audio who will make them available as part of their excellent customer service. (Of course, there may be an even better sounding design) Hawthorne are a tiny company looking to further the cause of hi-fi as much as make their fortune.
To that end they really go the full distance in looking after their customers to the extent that even if you have no knowledge of building speakers, you needn't worry about tackling something like the Duets for yourself! If you have been intrigued by the idea of open baffle speakers but didn't know how to get started, going the Silver Iris route is as good as any!

Copyright 2006 Nick Whetstone - www.tnt-audio.com

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