Speaker Asylum

Really?!!!!!!!!!

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"you'll find that the responses in figure 15,16, and 17 (the rectangular box) have the best response. The sphere with offset tweeter (figure 6) is not a practical design and you didn't specify an offset driver which makes a significant difference as the centered driver on a more practical circular baffle (figure 8) is the worst case (which is what I was referring to). "

You are correct that offset, baffle width and driver's bandwidth/coverage play a role.

But you have made a significant error about spheres in the Olson paper.

The reported tests used a single WR/FR driver, no tweeters. The sphere in Fig.6 is itself offset so that you can see the single WR driver clearly.

But the driver IS centred. And why is that?

Put a single driver on a sphere - anywhere - and it will be centred on the sphere by definition (as would any infinitesimal dot be,) no!? And, you would measure it on axis, as with all the other shapes covered.

So, you were wrong, and

Fig. 6 - the sphere with a single - centred - driver, has the smoothest FR / best diffraction behaviour. Despite the driver being - inevitably - centred. So that 'rule' about centred drivers falls away in this case.

A sphere is not a circular baffle as it does not have any edge.

A circular flat open baffle does have a sharp edge, and would be pretty awful with a centred driver, also by definition!

Just by the way - there are no Figs for a circular flat baffle on that page - for two conics? yes.

And, the paper is about enclosures not open baffles.

Even a truncated sphere with a small sliced (circular) baffle is measurably superior to a 90-degree edge box and audibly so. In the late 1970 enclosures of the same Vb, same tuning, stiff laminated walls for the box (3mm hardboard pressure glued to the inside walls) same amount of BAF. Gave the box every chance by offsetting the driver (not done on the sphere) and making the baffle area narrower than that of the sphere, and maximally dissimilar dimensions. The mass of the enclosures were matched using a concrete block glued underneath the box encl, so motor reaction effects were similar. Same screws, same plastic rawl plugs. The same WR 5inch Coral Flat 5 was used.

Measured FR? no contest. Listening? not in the race. Measurements done at ANU. More than 30 years ago.

Offsetting the driver on even a small circular baffle - on a sphere - does help a bit, so the production model 2's had that as well.

Now, this audible superiority may have an additional cause - that curved surfaces suppress bending waves / are self damping.

Practical / real spheres are truncated and thus do not have the predicted single/audible internal standing wave either. Just in case you want to bring that up.

Mind how you go. Especially with your commitment to particular points of view, eh? :-)

Do read the paper by Olson, all of it, twice.

LBNL John Dunlavy respected both the Model 2 Audiosphere with the Coral Fl5, and the 2-way Model 3. Told me so himself.

And you know more about wave launch than 'THE wave-guide man' did?



Note that a post in response is preferred.

Warmest

Timothy Bailey

The Skyptical Mensurer and Audio Scrounger

And gladly would he learn and gladly teach - Chaucer. ;-)!

'Still not saluting.'



Edits: 04/18/12   04/18/12   04/18/12   04/18/12   04/18/12   04/18/12

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