The Basilar Membrane and Crossover Distortion

[speakerdoctor]

Originally Posted by Scottmoose

As far as I can see based on this thread (I haven't had chance to look elsewhere), it seems to be an advocating taking a 1st order HP / LP & pulling them apart by x amount to introduce a large dip in the midband FR / power response. Shades of the so-called Solen-split variation on 1st order, where they've put the XO at the -6dB rather than the -3dB frequency, except there the object isn't really to cause a dip & what there is is relatively small, all other things being equal ~1.5dB.

Check out Mr. Knight's UK patent # 2445695 for a detailed explanation. I found the patent as written was dissapointing. How can one make a claim on a decades old method of calculating the mH valued on a woofer coil? How can an examiner award a patent when no utility is demonstrated? The only novelty (and that's a stretch) I found was a modified formula for calculating a tweeter's uF value included "CM" - a factor for adjusting the spread of the xover slopes.

[Scottmoose]

I had a few spare minutes, so I looked through the UK & US patent / applications. So, correct me if I'm wrong here, but essentially what we're dealing with is an extension of what Solen-popularised. Regular 1st order Butterworth has the XO at -3dB. Solen's 1st order variation (presumably also done by other people before them too, but a convenient handle) crosses at -6dB. And this one is at -12dB.

Quite easily re the patent grant etc. I've seen things that are a far greater stretch being patented. US Patents No. 6486750 and 6025810 for e.g. Or any patent produced by a hifi wire company come to think of it. I can't say the design philosophy advoctated here of deliberately creating an enormous hole in the midband frequency / power / amplitude / whatever response appeals to me, but live & let live.

[speakerdoctor]

Originally Posted by Scottmoose

I can't say the design philosophy advoctated here of deliberately creating an enormous hole in the midband frequency / power / amplitude / whatever response appeals to me, but live & let live.

Ahh, but Mr. Knight's contention is the dip counteracts the rise in our normal hearing profile shown to increase in the 1-3 kHz (typical 2-way xo) range by Flethcher and Munson. Other claims of lower distortion in the xo region caused by the Basilar 'beating' effect go unproven other than subjective assertions. The problem is - where's the test data to proove any of his claims of sonic improvements? No doubt the method claims to produce the dip are defensible, but the rest..... not so much!

[bwaslo]

But, how do you keep distorsion and dispersion under control, and still manage decent SPL? Has anybody made such a driver yet?

Sort-of someone has. Have you ever heard (or heard of) a Danley Synergy horn? Acts like a single-driver point source, but with constant directivity and high SPL capability. Can even be made to have linear phase (wavecom accurate) over wide range of frequencies. There are commercial ultra high SPL models and number of more tamed-down DIY versions around. Rather an ear-opener.

[Scottmoose]

Originally Posted by speakerdoctor

Ahh, but Mr. Knight's contention is the dip counteracts the rise in our normal hearing profile shown to increase in the 1-3 kHz (typical 2-way xo) range by Flethcher and Munson. Other claims of lower distortion in the xo region caused by the Basilar 'beating' effect go unproven other than subjective assertions. The problem is - where's the test data to proove any of his claims of sonic improvements? No doubt the method claims to produce the dip are defensible, but the rest..... not so much!

I know what the contention is regarding the hole in the FR / whatever you want to call it; I don't agree with it, but as I say, I take the live & let live view. As for the Basilar business, YMMV. Can't say I've ever had a problem along those lines myself, but I'll wait & see what data emerges.

[weltersys]

Originally Posted by speakerdoctor

Ahh, but Mr. Knight's contention is the dip counteracts the rise in our normal hearing profile shown to increase in the 1-3 kHz (typical 2-way xo) range by Flethcher and Munson. Other claims of lower distortion in the xo region caused by the Basilar 'beating' effect go unproven other than subjective assertions. The problem is - where's the test data to proove any of his claims of sonic improvements? No doubt the method claims to produce the dip are defensible, but the rest..... not so much!

If the goal of a speaker designer is to make a speaker that reproduces recorded music accurately, the last thing one would want to do is put a 12 dB response dip at the ear's most sensitive frequency.

It will be interesting to see how Ian defends his assertion that flat frequency response is not optimal.

[Pano]

Flat where, tho? At 1M, at the ears, at a mic? Somewhere in the room? As we know, it gets complicated.

[lolo]

flat on axis in a semi-reverberant field is not the best. I read the patent too, well, there are a lot of subjective assertions there, it's dissapointing. Proofs, any? Also it says in case of a 3 way, same crossover applies. Really? Another dip in the mid-bass? I guess people who have active crossover facilities can try and report.. but I am far from being convinced!

[lolo]

Originally Posted by bwaslo

Sort-of someone has. Have you ever heard (or heard of) a Danley Synergy horn? Acts like a single-driver point source, but with constant directivity and high SPL capability. Can even be made to have linear phase (wavecom accurate) over wide range of frequencies. There are commercial ultra high SPL models and number of more tamed-down DIY versions around. Rather an ear-opener.

Yes, you are right. But that's a speaker, not a driver, even if it behaves as a single driver. I'd love to check one sometimes.

[phase_accurate]

The patent's text starts with an IMHO completely wrong assumption: They suggest that one should have a hole in the frequency response in the area where the ear has increased sensitivity due ear canal resonance.

Well - we are used to hear like that ! We hear all unamplified and natural sounds including this hump in the ear's response. It is nothing more than natural. It simply doesn't make sense to "iron it out" in an artificial reproduction.

One of the most important things regarding the often cited Fletcher and Munson curves is the fact that every recording has to be reproduced by a linear speaker at the correct SPL level.

Regards

Charles