21" scoop design

Dref wrote: That is going to be mad

The only input I have regarding design is use the VAS/4 rule and you probably already have an idea of what folding style you prefer the sound of. If you post a drawing of the design when you are done I will be happy to comment.

Problem with that rule is, it suggests scoop chamber for PD2150, should be 157L, which I don't think is quite right.

It would also suggest Scoop chamber for a Wembley Bline 18-800, should be 103L, which is also not quite right, as this driver is very serious in small chamber scoop.

Fane 18-XB has Vas of approx 246L, but performs great in reflex cab of 200L.

So slight problem with the Vas/4 rule.

I think that the VAS/4 rule is for the maximum chamber volume. And its only a rule of thumb. I have never actually put it to the test. Anyone have?

So he will most likely choose to go for a smaller volume than 96 L to get more sensitivity and sacrifice a bit of the extreme low end extension. Its also worth keeping in mind that the driver only has 9.5 mm Xmax.

Personally I still prefer to start by doing simulations instead of using rules of thumb. Even though I know its is not the preferred method for many when it comes to designing rear loaded horns. My guess is it is because of the unpredictability of the interaction between the low pressure & high velocity wave front from the horn and the high pressure wave created by the cone located outside the horn. I still plan to do some research on this when I get the time.(No idea when that's gonna happen )

What the absolute minimum space needed between the back of the magnet and the rear baffle?

In theory that should depend on the specific drivers displacement and vent hole shape.
But its not easy to say exactly when the problems arising from to little space is getting to much..

quick drawing-


seems ok so far, only am concerned about magnet being only 1cm from magnet to rear baffle. Is this enough to keep it cool? I could move it forward another cm if needed. As it is now, the chamber is 106L if I make the cab 600mm wide (unloaded chamber)
Thoughts?

This is the only pic I can find of the back of the magnet
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In the picture it looks quite tight, but I would think 1 cm should be enough.

If the chamber ends up being too large, then you can always ad a corner bracing in the chamber like Mykey does in a lot of his scoops. Maybe even a detachable one to do some testing/tuning.

Where are the narrowest point in the horn?

minimum of 10mm 1cm, 20mm is great..... the more air flow over the back of the magnet will help keeping it cool.......

to drop the volume down, use an angle section in the top of the back chamber......


this is the finished mini scoop with kicks.....

Thanks Dref/Bee I had the same thought.
Some better pics - SO FAR;