September 29, 2012

S3 progress

Here is a sneak peek at the S3 throat:

In S2, this aspect wasn't modelled very carefully because I built it manually, using a combination of filling with bog and smoothing with a circular file and sand paper. S3 will be sculpted with a CNC router so it has to be right.

The profile is critical in this design.

I have a couple of goals here:
  • avoid diffraction
  • create the smoothest possible transition from the exit tube (circular cross section) to the horn where the midrange units come into play (rectangular)
  • keep the machining cost sane
  • retain constant directivity performance

September 8, 2012

Cheap self watering pots for sale!

Pickup in Melbourne:

$10 each or $100 for all 12.

They work exactly the same as any other you would buy from Bunnings, they are just a whole lot bigger! Made from large plastic drums, 600mm diameter, around half a metre high.

September 7, 2012

Goto SG38 WNS box sims

This post is in response to this discussion:

Tuyen has a Goto woofer in a 360L box originally intended for an Altec driver. I presume a tuning of 35 Hz here.

The Goto woofer has an extremely high BL of 37! As a result it has a very very low Qts of 0.15!

It is indeed a unique driver. This is how it models in the 360L box tuned to 35 Hz (I may be incorrect on the tuning). 

The existing box is shown in white. Do you see a problem here? The high Q peak there means that the box is too large, making the vent overly efficient. There is such a thing as "too much motor strength" - more isn't always better. This driver is very unusual, and certainly not intended for a box like this. The sensitivity is ultra high, but to get any extension out of this driver, some of it will have to be shedded. The blue line shows the same box sealed - no extension at all, however, in a small cavernous room it could actually have more extension than you think. The red line shows a more suitable box - 60L tuned to 40 Hz. In a room with lots of modes, this could work out. 

Here is the group delay:

 Notice how the large box has an ultra high group delay? It occurs are low frequencies, so it may not be an issue with most music, but this gives us a window to a problem, indicating a poor match.

September 2, 2012

FS: Aura 18" sub drivers

Quick heads up - some very nice Aura 18" subs currently listed on StereoNET:

SNA listing >

(No, these aren't mine)

From memory, they retail for about $900 each in the US, so they are a lot cheaper here. Located in Melbourne.