Build No. 3 ... 2 way tower

[KiwiListener]

I posted this in the main forum before I realized it should have gone here.

The box design is one I have used before but not quite the same literage (smaller). The cabinet design philosophy is similar to the Kef Q series, but rather than rounded still has a squared front and tapering sides. The theory here is much like a pond of water and ripples from a pebble. The tapered shape breaks up the (sound) waves and reflects them away from the speaker and also cancels out the wave as well. Great in theory, and it does seem to work. All the interior sides have double layered acoustic felt, with a small amount of acoustic stuffing in the bottom chamber. The design is ported for extended bass.
Originally these cabinets were designed to take the Tronix 6.5 " woofer as shown.

This is an example of what can go wrong if you haven't done your homework right. I modeled the cabinet using Unibox and fitted everything up to air tightness for testing. They sounded absolutely dreadful, not mid or bass performance to speak of. WTF?
It turns out that I had inadvertently selected a box model that also included 2 drivers not one. Some how I had managed to change the parameters and not notice. Needless to say that wasn't the outcome I was looking for. So what to do with the cabinets? Simple, stick an 8" woofer in them and redesign appropriately.
The Unibox graphs now for a ported two-way using same tweeter and 8" driver is in the second post

[KiwiListener]

Re: Build No. 3 ... 2 way tower

This current project takes some of the ideas from Paul Carmody Amigas' and box styling from some mainstream manufacturers.

The design is a two way speaker capable of good range and big enough to fill a large lounge without having the amp work too hard. To a large degree this is experimental and I'm in the market for thoughts on a final configuration for the crossover.
The drivers are locally sourced Jaycar speakers. I did a little checking and it seems that these are a Peerless designed but Chinese manufactured. As to how accurate the information is is a little difficult to tell. Peerless wont confirm or deny this. In fact to date they haven't even responded to my inquires, so who knows.
The woofer and its parameters are here
And the tweeter information is here
I have used both these drivers in a sealed box design and they perform very well together. I made a simple second order crossover and attenuated the tweeters 1 db. It doesn't sound like a lot but it does control the natural the sibilance of this tweeters nicely. Theres been no indication of spittiness or other nasty byproducts, so I'm reasonably pleased with the setup.

The attached images show the results when the speaker parameters are fed into Unibox
Parameters


Box Design parameters


Port airspeed seems OK...


So that's the basis for the design.
In the next section I will detail a bit about the Box design/construction, but for now how would you see a crossover looking for this setup?

[KiwiListener]

Re: Build No. 3 ... 2 way tower

After discovering the small disaster previously mentioned I had to alter the cabinets to suit an 8" driver as well as a larger port.
The original port was 60mm dia but the new port was 69mm dia. Routing a new whole was easy, sourcing the correct tube was another matter. Our local version of Radio shack had the more standard port tubes, but nothing like I wanted. I was going past a plumbers yard on the way home and stopped in. It happens that they use a grey waste water pipe that is 68.5. Excellent. I routed out the hole for the port at 68mm and then carefully drove the tube into position. A extremely tight fit that doesn't require glue to set in place or seal. As the design was for one flush end I think I may well use this method again.

So how were these units put together?
Well construction of the case is done using 16 or 18mm MDF. In this particular case the MDF is 16mm and has 9mm Macrocarpa veneer added to it. This gives a wall thickness or 25mm (I inch) and a high/low density structure which works very well in reducing vibration and other nasty things from being heard. In reality this concept worked much better than I had anticipated. With the pair of bookshelf monitors I recently built external vibration was very well damped and this also makes for a heavy cabinet. With all things components being fitted these speakers will way approx 30 kilos. Not too heavy but a good weight for a mid sized floor stander.


Pre Cutting all the MDF and veneer. Note the outer and inner templates.



The basic carcasses showing bracing and glued support slats for the side of the cabinet.

[KiwiListener]

Re: Build No. 3 ... 2 way tower

Box construction.

I see people dealing with cabinet construction in various ways. As this design is a two part construction, basic carcass with overlayed outer veneer, there is a great deal of rigidity inherent in the process. I however am a little oldskool in my approach. While modern glues are very good, I'm not a fan of producing something that's subjected to long periods of stress or vibration without additional support. Therefore my basic premise is on of glue and screw. Especially when dealing with MDF. I want the inner part of the case to be as rigid as possible and this method most suits the design, as can be seen in the following photo.



As you can see, all mating surfaces are glued and then screwed into place. There is only one exception to this which I will cover later. Note also that even the battens that support the rear baffle will be treated the same, although only the centerline and pre-drilled holes are seen in this image.

[KiwiListener]

Re: Build No. 3 ... 2 way tower

Rear Baffle

The rear baffle retains the natural dovetail shape formed by the sides. I decided to make the rear baffle a fixed item and once cabinet construction was complete access to the inside would be through the speaker hole only. This does mean it can be a bit restrictive if changes to componentry are required but I want the rigidity factor this brings to the enclosure.
This is pre-glued then slid into place and screwed permanently in position. That now done, the battening, sides and rear baffle combine to form one very rigid unit.

As a footnote to the above. I have made a similar set of these speakers, but they hadn't as much internal support and rigid nature. I also made them out of 20mm heart Rimu. The finished look was excellent but unfortunately they resonate much more than I would have liked. They now perform the roll as my rear speaker in the H.T. setup I have. In this roll they work very well.

Rear Baffle, positioned, ready for glue up.

[KiwiListener]

Re: Build No. 3 ... 2 way tower

The Port

originally the port was to be 60mm diameter. After realizing the original drivers weren't going to work in this cabinet, I re-ran the Unibox settings for the 8" driver (200mm). This now changed to a 69.6mm tube which gives a diameter of 2.74 inches. As I mentioned above I was able to come up with a good result here. The first images below shows the rear of the enclosure and rear baffle in-place with the smaller hole.
Fortunately it was a simple matter to re-route the hole to the required size and then it was just a matter of press fitting the tube.


Bigger tube ready to be fitted, simply driving it into position for a very tight fit. No chance of movement or vibration here. As you can see I had already given the rear baffle its first coat of paint. I was really annoyed that I had missed something so obvious in the design.



Next up ...covering the walls and the front baffle.

[KiwiListener]

Re: Build No. 3 ... 2 way tower

Wall coverings.

The design calls for the walls to be covered. I would have done this no matter what as it supplies a measure of acoustic control.

The first image shows the inside of the front baffle lined with acoustic felt and more traditional stuffing in the cabinet. I did a test run at this stage to see how they sounded, not ideal when nothing quite finished. However it was worthwhile. The bass sounded flat and a little muted, so I removed the stuffing from the center chamber and the top chamber, and halved what was in the bottom chamber. The top two chambers were then covered with the acoustic felt.
The felt I refer to is a Dacron product that you buy by the meter (yard) off the roll, same as any curtain material. Its approximately 3mm (1/8) thick, medium density. Its the type of product you find as part of the lining in sleeping bags and snow jackets. It is however a very effect acoustic dampener as well.

At this point you will notice that I have strung the cables in the cabinet as well. These are hoop stapled to the cabinet sides to stop unwanted cable flapping around inside the cabinet.





Next up attaching the front baffle

[KiwiListener]

Re: Build No. 3 ... 2 way tower

Attaching The Front Baffle

This is the only part of the construction where I can't use the glue and screw method. Because of the shape of the box it is difficult to screw the front baffle to the carcass of the cabinet. I could be done but that would require more battens and therefore an even bigger finished size for the cabinet. Something I really didn't want to do.

I would therefore need a more mechanical process to do this. I have a biscuit cutter and could have slotted and biscuit joined the two pieces. The problem with biscuits is that they can move during the curing process even when well clamped. I have had a failure during colder weather and biscuit joints, because of the longer drying times, so I don't want a repeat.

The answer of course is good old spiral dowels. The spiral ones are best as they allow excess glue to escape and don't split the material being glued. Every surface is liberally coated with glue including the dowels and the front baffle is then tapped into place. Don't forget to use a slightly larger hole for the dowels too as this stops timber split as well. I used 6mm dowels and a 6.5mm hole.
It was then just a matter of rounding up every F clamp over 600mm (2 feet) long and clamping the whole thing together.





Next up ... The Grills

[KiwiListener]

Re: Build No. 3 ... 2 way tower

Grills
One of the easier parts of the build is the grills. These are made from 12mm MDF, Next time I will use 9mm , but as I already had some 12mm so be it.

The holes were routed out and rounded over with the router and router table, Having a separate dedicated router table is a plus and if you can afford one I would suggest its a worthwhile purchase. I have this particular model and while its not the most expensive it does work well. I had some 75 x 75mm aluminium angle, from which I made a separate full length fence which makes working with longer sections of wood easier, but the supplied fence does the job for most things.
A rounder-over bit the same as this sits in the router table most of the time, so that the inner and outer edges of the holes and the sides are all treated the same, then sanded with 240grit and painted chalkboard black. This is a flat, black acrylic paint that has the same color as the grill cloth, the grill cloth is acoustically transparent.
One of the best investments I made to go with my routers, (I have three) was a good quality half inch shank set like these, an investment I have never had any regrets for buying. WAF = Nil at the time

So here's the basic grill all nicely routed ready for sanding. I formed the bottom curve of the grill using a compass for the shape and then machining it using my disc/ belt sander the same as this one. I have over the last 5 to 10 years been investing in good quality woodworking machinery and now have a fairly well equipped workshop. There is however a couple of machines to purchase at some point and that also earns a WAF=0 as well.


You will note the holes in the grill plate. These are the location holes. Once the grill is shaped and the location holes drilled I lay the grill on the cabinet and align it to properly mark the cabinet using a sharp Bradawl This to locate the position for drilling the holes in the cabinet face to take the recessed plugs.
The holes in the grill plate are drilled out to 6mm on the under side to take the little lugs, that slip into the plugs in the cabinet face. All pretty familiar to anyone whose done a few enclosures in the past.



Pre-painted and pre-fitted, prior to having the grill cloth applied. The cloth is stapled on with the excess trimmed off and then covered with a black adhesive cloth tape to give a neat finish.


Next up the feet.

[KiwiListener]

Re: Build No. 3 ... 2 way tower

The Feet were a late innovation and came about because my local supplier no longer stocked the feet I wanted. Which led me to coming up with some sort of alternative.
I opted for a darker colored native hardwood for strength and color contrast. Its a 3 piece set, the two rear feet are angled and the front feet use a crossbar.
Isolation pad feet have been used for these but they are equally as able to accommodate varies styles of spikes. The bars for the feet are held in place using self tapping inserts and furniture bolts 60mm in length, these are slightly recessed into the underside of the bars to give a flush and hidden finish.

The RAW material complete with foam tape for vibration damping.



All external faces are finished with a polish oil for coloring and left natural.

Pre-fitting the feet, note I have now covered the grill plate and have it fitted.


At this point the enclosure has had the first two of seven coats of sprayed on gloss polyurethane.

[ReissM]

Re: Build No. 3 ... 2 way tower

Great writeup... I need to hire you to do mine.

Keep up the good work... it looks great! What's next?

[KiwiListener]

Re: Build No. 3 ... 2 way tower

Great writeup... I need to hire you to do mine.

Keep up the good work... it looks great! What's next?

Finishing Work
Actually not too much. I've finished these off with a total of seven coats of spray poly, using 1200 grit wet and dry sandpaper. Once the last coat had hardened off after 24hrs, being winter its taking soooo much longer to dry, I used my favorite wood polish with 0000 range steel wool just to smooth off any surface imperfections. I was using my new spraygun this time and found I was getting a lot better results.

The finish is a nice clear and deep gloss finish which brings out the natural figure in the wood. The color is rustic oak, one of the colors I find that suits the Macrocarpa, better than a lot of the darker stains. The look is recycled/retro so I have deliberately incorporated little things into the finish. The timbers is recycled Macrocarpa 8 x1 roughsawn planks from a cafe at a small seaside township, so its in keeping with the timber which has lots of small blemishes. In the photo following you can see I have set the veneer pieces in an offset manner Thats part of the theme and on the top of the other cabinet I went deliberately short on the wood and added in a piece and the sides have the same effect. It meant a lot of filling and smoothing with the orbital sander but I'm really pleased with the finish.

Top of speaker after initial sanding and stain applied.
Note all the old staple holes and nail holes. Filling all these took some time but is worth the effort.



Next ... Wiring up.

[KiwiListener]

Re: Build No. 3 ... 2 way tower

The Wiring,

When I had assembled the basic structure of the cabinet, I ran the wires as well so that once the front baffle was glued into place all that was required was a bit of soldering.
The cross over is a straightforward 2nd order Butterworth unit with a L-pad to set the Tweeter to the correct level. It only needed 1db to match the woofer, but the tweeter I used has a little bit too much sibilance with female voices and although 1dB doesn't sound much it has an excellent result with this tweeter. The polarity was reversed on the tweeter for correct phasing.

All components were sourced from our local Jaycar.



Crossover wired and set into place. The crossover was placed in the upper cavity mainly for the convenience of access. As it turned out it was fortuitous that I did this, as the only access is through the speaker holes. Note the patchwork of acoustic felt. I dont like to waste anything so it all gets used. A bit fiddly but a dollar saved...



The binding post are a face mounted unit with gold posts that accommodate both banana plug connectors or straight bare wire.

[KiwiListener]

Re: Build No. 3 ... 2 way tower

The Finish

I'm pleased with the final outcome of these, doing the finish as a recycled/retro idea seemed good at the time, but I was never quite sure how it was going to turn out. I wanted the look to be almost backyardish but with a professional look to the final coatings and by and large I think it comes close. I like things to not only sound good, but look good. The idea is to have people say that they think this style would fit with their decor. At least it fits with mine

So without any further ramblings, introducing the Aria2












Next...Listening Impressions and final thoughts.

[ReissM]

Re: Build No. 3 ... 2 way tower

Gorgeous! It was worth the extra work dude.