It’s taken me ages to get to the point of writing this Decware HDT self build project up. I ordered the parts almost two years ago! Since then it took me a year to motivate myself to get round to building the speakers and then I had a few problems with other things (like the amp) which prevented me from doing the writeup. But, now, it’s all done, apart from the veneer, the photos are taken and the speakers are wonderful. So here goes…

I wanted to build the HDTs as Decware previously described them as their top of the range speakers and they feature a single full range driver in a transmission line design. I originally purchased the plans online and then bought the kit when a good friend of mine very kindly gave me some money for doing their wedding photography. The kit was $394 which splits down as $295 for the two Decware-modified Fostex drivers and $99 for the plans and parts (such as spikes, binding posts, rubber bumpers etc). Shipping to the UK was $118 and with VAT and import duty on top I estimate the final bill was about $600 (or £300). Of course this didn’t include the cabinet material – I spent about £60 on MDF.

Cutting session

Having previously built the Decware WO32 “Wicked One” subwoofer with all its weird angles, cutting the wood for the HDTs was comparitively simple. It was extremely quick to cut all the pieces to size. I then used a router to rebate all the edges (if you look at photo 2 or 4 you can see the rebates all around) plus the rebate towards the bottom of the panels where the port plate is glued in).

The speaker driver and passive radiator holes are cut using a router and my “custom jig” which is just a piece of hardboard with holes to mount the router and then you drill a hole for the centre of the circle you need to cut, stick a screw in and rotate the router to cut the circle, routing about 4-5mm deeper each time until you’ve cut through the entire thickness.

Port tubes, port plate and starting cabinet construction

Not being able to find any speaker port tubes long enough I purchased 50mm PVC pipe to create the port tubes. The port plate has three holes for the port tubes (which I think we did with the help of my dad’s flying cutter on a press drill) and was extremely simple to cut the tube to length and glue it in place (photo 1).

Once the port tubes had been glued in the cabinet construction could begin. With the rebate in each of the panels for the port plate it was simplicity itself to glue the front on and then sides. Instead of having to check everything is square repeatedly, the rebate gives the knowledge that everything is aligned and true.

Alternative tuning

It is important to note that Decware changed the design slightly since I bought the parts, making the port tubes longer. I found this out before I constructed my port tubes and, as instructed, used 11″ ports in place of the 6″ ports and 17″ ports in place of the 8″ ports on my plans.

I haven’t put a photo here of the back of the cabinet glued on but, trust me when I say it was just as easy as the other panels! The top and bottom are just square and sit nicely in the rebate cut into the top and bottom of each main panel.

Internal dividers

With the outer part of the cabinet complete it was time to cut and fit the internal dividers which give the speaker its four chambers. The full (diagonal) width divider is cut first, carefully cutting one end in a “V” shape and then, even more carefully, the other end – so that the resulting divider fits snugly into the cabinet. In theory I could have used the table saw to cut the “V” shaped ends but I used a 45? router bit which gave me precise control. You end up with about a 1/8″ flat on the end of the “V” (see photo 9 below).

Once the full width divider is cut to fit, I then routed a rebate down the centre of the divider to accept the two other dividers (see photo 10 for a closeup). Again, using the router to cut this 1/8″ deep rebate was simplicity itself. I cut the two half-diagonal-width dividers and, again, used the 45? router bit to get the “V” shaped end perfect.

It was easy to get these internal dividers to fit really snugly, so I could get them out only by quite a lot of tugging). They are not glued in but screwed to the port plate from below. Photo 8 shows the dividers inserted all the way creating the four chambers of the speaker.

The oval holes in the dividers (between front and side chambers) are cut simply by drilling with a 1/2″ drill around the marked oval (actually I think I used a slightly smaller drill bit)and then carefully knocking out the shape. I tidied up the rough bits a little.

Bracing and foam damping

Although this was not part of the plans supplied, I’d read on the Decware Forums that it was a good idea to provide some bracing for the cabinet panels and, after initial listening to my HDTs before I finally glued the top and bottom plates on, I decided to follow this route. Whilst I couldn’t hear any cabinet colouration (or boxiness) to the sound the cabinet panels did “ring” when tapped and sounded quite live.

So I bought one length of “light” hardwood and cut and fitted internal bracing (as seen in photos 11 and 12). Because the long tubes (17″) would have meant a single piece of bracing below the driver would have been extremely close to the top of the tube, I decided to use two pieces of bracing either side of the long port tubes and one longer piece over the short port tube and also in the rear chamber.

With the bracing in place I cut and fitted the acoustic foam damping (purchased on eBay from Advanced Acoustics as I only needed one 30″ square sheet). One large piece is put opposite each of the passives and in the driver chamber a long strip is folded around all sides in a triangular shape both above and below the driver (see photos 13 and 14), plus another piece is glued to the top panel (so it sits over the speaker driver) (see photo 15).

Speaker drivers, passives radiators and binding posts

Mounting the speaker drivers was a piece of cake, using black hex-headed fixings. The supplied binding posts posed a little problem in that the posts were not long enough to go through the 18mm thickness of MDF so I just created a rebate for them (leaving the posts to go through only about 5mm of MDF) by using a big drill bit to take out the required depth and then a chisel to clean up. It might sound crude but the end result is extremely neat.

The passives (two per cabinet, on the sides of the cabinet) are basically a sandwich of 2mm foam, corrugated cardboard and felt which you glue together, cut into a circular shape and then glue on the supplied speaker driver surrounds (which are exactly the same as the foam surrounds on the main drivers). Once I’d made my passive radiators I glued them into the waiting holes on the speaker cabinets. One thing I would say is that I found it very hard to glue the circular foam surrounds onto my passives without getting some glue onto the passive itself – I used contact adhesive and it was impossible to get off the passive. So I actually binned my first passive and made another one.

Also, Decware now sell “alternative” passives which look more like a speaker cone (in that they are conical and have a cap in the centre) rather than the ones I made which are flat. Bob Ziegler at Decware says “since the passive are so close to the driver itself, there is a bit of midrange coming though the passives, not much, but if you get pretty close to a side wall, it could smear the mids, the ALT passives have a hard dome, which tends to diffuse the mids enough to make even close side wall reflections, from the passives, a non-issue.” My speakers are not near any side walls, but even so, I may get the newer passives at some point and fit those.

The only thing left to do was to wire up the speakers and try them out! I chose to go the shortest route, putting a hole right through the middle of the internal divider (making sure the hole is the same diameter as the cable). I used Chord Odyssey cable to wire the driver to the binding posts. Once I was happy with the sound I took off the top and bottom cabinet plates

I forgot to mention the top “dispersion” plate (as you can see below on the right hand cabinet). These are very easy to make, taking the pieces of wood cut at the initial cutting session I just routed the semi-circle out of them using the same technique as for the driver holes. Then I used a “rounding over” bit on the router which just whizzes around the top and gives that rather professional looking finish. The bit was so good it felt like I was going through butter rather than MDF! These top plates will eventually be spray painted black and the rest of the cabinet will be veneered.

Listening, at last!

I couldn’t finish off the project writeup without talking about the sound, could I?

I’ve been using these speakers for about two months now, but have had the ampplifier problems fixed for about a week, so everything is working just fine.

The thing these speakers bring to the sound is even more space and timing with a very neutral tone. I was immediately aware of definition around instruments giving them the space to breathe, and also the speaker’s ability to define the spaces in which the instruments are performing – I’ve suddenly become very aware of the ambience of drums, guitars, pianos, voices. The speakers are so good at helping to define this ambience that you really hear it on deep things too, like timpani, which is absolutely spine tinging.

Their tonal range is better, and smoother than my Parker Audio 98MkII speakers, with a deep bass, taut and fast, a nicer smoother midband and less “cutting” treble than my old speakers. This is only to be expected of this full range driver but it definitely suits my ears far better.

The fantastic speed really makes for some excellent dynamics and powerful leading edges to percussive sounds, I’ve never heard the track “Mid Town” on Calexico’s “Hot Rail” album like this before, with its massive drumming and thunderous final note.

I wouldn’t say the tiny micro-tonalities, the subtle nuances of timbre and texture where you really start to identify things like the individual trumpets of a brass section are really different to my old speakers but then that is where the Parkers really excelled – the HDTs are definitely no slouch in this area.

Lastly, the soundstage cast by these HDTs is by far the best I’ve ever heard though my listening room is not ideal so perhaps it’s not for me to comment on with authority but, again, these are the first speakers I’ve used in my system which deliver a really solid, wide and deep soundstage. Getting the Vertex Jaya mains conditioner and the Origin Live Silver tonearm really did enormous things to create space in the soundstage and placement of instruments – but these HDTs now use this to their full advantage positioning everything beautifully.

Without a doubt these are the finest speakers I’ve heard and I’m absolutely delighted to have made them because they are so good in so many areas. The first thing I thought when I heard them was, “I must buy another kit now, so I can make another pair”!

I’ll post a photo of them when they’re veneered.

Click here for information about the HDT speakers on the Decware site. If you want to see the photos larger I’ve posted them all into a set on Flickr.

This entry was posted on Saturday, August 9th, 2008 at 4:21 pm and is filed under Hi-Fi. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.