November 16, 2012

S3 integration

How do you fit a bit horn into a small room?

November 15, 2012

Bathurst room treatement video - measurements

Here are the measurements that go with the video demonstration at Bathurst of acoustic treatment.

Frequency response:

Untreated: red
Treated: grey

You can see the bass range is similar, but in the midrange we see more differences due to the treatment.

Unsmoothed version:

Untreated: red
Treated: grey

Below 200 Hz (smoothed)

Untreated: red
Treated: grey

 Perhaps the most interesting result is the reverb time:

Untreated: red
Treated: grey

In the untreatd room, the reverb is quite high, with an average above 0.7s and this drops off at higher frequencies. In the treated room, the reverb time is more flat, and averages around 0.32 s. 

By 100 Hz, both rooms are similar in reverb as the treatment is midrange focused. 



90L sealed 18" woofer flat pack - assembly

Suggested construction sequence for 90L woofer flat packs.

Much quicker and easier to assemble!

You can see here how the trench has been machined around the edge so that the pieces can slot in easily. The corners are at 45 degrees to allow the box to go into the corner on an angle, as a base for horns. The terminals are on the back flat section.

I prefer to use PVA glue generally, as it sets fairly quick. Expanding poly glue is stronger, but greater care is needed and it takes longer to set. The extra strength isn't required and I tend to use it where I need its gap filling properties. 
Front baffle sits on top of the base, side sits on the trench. A small clamp holding the side to the front baffle is suggested.

Now add a vertical brace.

The first horizontal brace slots into the groove of the side panel. The CNC flat pack is designed to minimise the need for a lot of large clamps. (Yep, a shameless plug right there!)

For this step, you may want to use one of these:

 You can buy 30 of them in varying sizes for $10, they are dirt cheap and very handy.You can use a pair on the right edge of the front baffle, to secure the second horizontal brace. You can use them to secure the vertical also from sideways movement. Place one either side of it on each horizontal brace.

Right side piece

Angled side.

Back end is best added last of all sides.

Top panel.

And finally the outer baffle.

90L woofer flat pack

This is a flat pack for an 18" woofer - sealed 90L box. It is designed to go into a corner under a horn, but it could be used for other systems as well.

CNC machined for easy assembly, with trenches machined so pieces fit together nicely and bracing also slots in. 

The design is similar to my prototype:

The prototype above was built manually. I no longer have time to build things this way, everything now with CNC. 

Shown with a smaller Unity horn.

November 12, 2012

S3 revised sims

S3 shown in black compared to S2 (simulated response).

You can see that S3 allows a higher crossover point than S2, which is one of the design goals. The response is also smoother, meaning a simplier crossover should be possible.

S3 in progress

I'm currently getting the S3 design ready for a CNC quote, lots of checking to make sure all aspects are correct - quite a meticulous process. For example, I found that I had an incorrect model of the Celestion midrange driver. The area in front of the cone forms part of the acoustic chamber, an important aspect of the design. I've had to model it again to work out the volume precisely and ensure the driver slots right in.

Here is the render of the 3D model:

I could model it with even greater precision than shown, but this is as good as it needs to be.

Unfortunately I also thought I had the throat profile design complete, then found it didn't model as well as I'd like. The process takes a lot of time, due to all the twists and turns, and ideas that in the end don't work!

The goal is to have S3 up and running as a Christmas project. Drivers for the current batch are now on their way and we have a couple of places left.