February 20, 2016

Air tools vs electrical tools


Have you ever considered using air tools? Most DIYers only use mains powered tools and if you don't have a compressor then it's probably a good idea to stick to them. However, if you already have a compressor, this is something you might consider.

Now, of course every workshop should have a power drill, jigsaw and a cordless driver. But when it comes to these:

 You might think about some air tools.

Why air tools?

My interest in air tools began with a conversation with a factory worker who uses air tools a great deal. He was talking about some of the more expensive sanders and polishers like Festool. Outch - those are expensive! Yet in his opinion, in terms of professional heavy duty use, he describes them all as crap. 

The beauty of air tools is that they don't require an electric motor and they are inexpensive for their robustness, reliability and quality.  

Reliability and bang for buck are very good. 


The downsides are fairly obvious. They aren't mobile. You need the compressor, mains power and a hose. You probably don't want to take air tools on the roof.

When your compressor breaks down, all your air tools are useless. 

Reliability, robustness and value come into play with some tools more than others. My orbital sander and a rotary tool both get very hot with extended use. Often I've had to stop working when the tool gets very hot.

The Ozito has a great range of attachments. The air tool version is similar in price but it can handle more extended use.

What air does best

Very handy in the workshop is a simple blower:

Quickly and easily removes dust or sawdust. I use it all the time. You want to be careful you don't blow dust into your eyes. Once you have one it may surprise you how often it's useful.

Handy assembly and fixing

This stapler and brad nail gun are also very handy. If you want to temporarily hold an MDF brace in place, the brad gun is handy. MDF tends to split when you screw into it, but you won't have that problem with a brad. The stapler is handy for temporary attachment of rubber sheets to the inner walls of a speaker box, whilst the glue sets. I use this often in prototypes.

The Ryobi orbital sander shown above is another tool that is not very heavy duty. The air version costs about the same, but it doesn't overheat quickly.

 If you are a serious DIY enthusiast and you find one reason why you MUST have an air tool, you will quickly discover there are many more tools that will also work with your compressor.

February 14, 2016

30 Hz horn sub continues

Exposed edges of the formply are painted with Duratex and pilot holes are pre drilled. Chamfer bit to recess the heads:

This is the end panel near the mouth. Thickened on the far end. A little strip of MDF is also added where the internal divider meets the end. This ensures the divider will remain in the correct position.

 End panel attached to the sides. A little newspaper catches any glue ooze.

Next the other end panel is attached. Screws here clamp the panels together as the glue sets, however, clamping is used (not shown) and some care is needed to ensure the panels don't move. Tightening up the clamps and screwing both cause the panels to move. The trick is to adjust as you go, screwing the panels in with a clamp in place.

 The bottom panel comes next.

 Bottom panel now on:

Internal divider:

This is screwed in on the end near the mouth, and clamped on the other. The final side follows.

The braces are attached after all four sides. The taper allows them to slide in. If the angles are correct, this will work with ease. 

Notice how opposing sides are clamped? The panels can have a bow in them and this can create problems with the bracing. At this point, you have to ensure the width is correct so that when the last side goes on, these panels have not bulged out, especially when the bracing pieces have been done.

Completed box now standing:


Here you can see the raw unfiltered response and the response with DSP (crossover filters and 2 PEQ).

As expected we see ringing above the passband, common with all "small" low tuned bass horns. Subjectively it sounds quite tight and clean in the 30 - 80 Hz range with test tones. Yes - you can actually gain a basic appreciation quickly of the sound of a sub from test tones. 

This sub is 450 x 450 x 1800mm.

February 11, 2016

20 Hz home theatre horn sub

This sub is a custom design for one of our home theatre clients. The project commenced with a bass assessment where we tested for the best sub positions. In our analysis, we determined that two subs, one in each corner, would work best for the intended listening positions. As all seats were in one row, we didn't have to deal with row variation. This meant that two subs could achieve an exceptional result.

This client already had a sub with the Dayton Classic 12" sub driver. We determined that it would work well in a horn sub design. We used two per box but the client only had to buy 3. Using two drivers per box provides the option to reduce vibration with a dual-opposed design or to reduce distortion and improve linearity with one driver inverted. We chose the push pull configuration as we considered that the linearity aspect would be more important in this case.

Service offered

We offered a design service, delivering dimensioned plans only. The client then had sheets cut by a cabinet maker and built the sub from scratch.

Baffle cut outs with a DIY router jig:

This is an efficient folded design. Drivers can be installed via a hatch and the mouth fires into the corner. 

More build photos to come ...

30 Hz horn sub

Construction commences for a single fold 30 Hz horn sub using the Eminice Definimax 12" driver.

Testing out the circle jig on the new Triton 2.4kw Router. It works well.

Bridges are left at 3 points so that the centre cutout doesn't fall through when routing.

Build continues in part 2