David,
You've opened up a 'can of worms' here that Tom and I went round and round on a while ago.
In this same paper, Allison shows a 2-pi curve of the 3a--with decorative molding and all the warts--and the curve shows the expected lift in the bottom end that one would expect from a 2-pi environment. As a matter of fact, the entire reason for Allison showing the 4-pi curve you reproduced was to show the effect of 4-pi on the woofer's response.
But, the thing Tom and I went around on was the fact that the 2-pi measurement showed considerably more upper-mid/HF energy that this 4-pi curve--even though they were identical speakers, both measured with the grille molding, through the x-o. But at those high frequencies, the 3a's baffle is large enough to be "2-pi" in the upper mid/HF region. So why the discrepancy? The 2-pi and 4-pi curves should have been identical above about, say, 8000, where the wavelength is less than 2 inches. The 3a's baffle is "2-pi" in either case above 8k, so the HF curves should be the same, no? But they're not.
I'll try to dig out the 2-pi curve (I have the paper somewhere), but if you have it, look and you'll see what I'm talking about.
Thoughts?
Steve F.
I'm not seeing any particular discrepency. I'm looking at figure 5 and figure 9 of the AES paper. It appears that there is a 10dB shift in chart level. Then the differences in the 4 pi curve relative to the 2 pi are: 4 to 5 dB less at 100, but a couple dB more at 500 (very typical of 2 pi to 4 pi change), upper mid response is much the same except 4 pi is a little rougher. The tweeter response is similar except, again, a little rougher in 4 pi (I read this as a greater dip at 8k and 15k rather than a treble level shift). Note that figure 5 has the picture frame lip added but the system is flush, from the picture frame level, with the wall. This means that the internal reflections are present but the external edge reflection is not present, hence the generally smoother curve.
The previous curve #4 is similar to the ones in the brochure that Howard submitted yesterday. Drivers and network as stock but mounted on a flush infinite baffle, so they are generally smoother as explained in the text.
This is a very instructional look at how the raw sections of a multiway system add up to the final 4pi response.
Note that these curves are with the mid and tweeter at max, rather than at recommended positions. You can picture what the mid prominence at 400 - 500Hz in 4 pi would be with the pots at nominal. I seriously wonder if this is part of the reason for the inductor increase that came later.
Of course, none of this is audible unless you are one of those direct field hoodlums that listens to non-serious music.
David
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