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202.4.2.36
This was quite an ambitious project, and by the looks of it, well executed. The builder's log is at the link. IMO, full marks for effort!
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The tweeter pod really is pretty bad but the midrange enclosure is worse.
Both pods only engage with B&W's findings on back wave damping.
They should resemble half spheres at the front.
For anyone here who wants to natter on about diffraction not being a big issue, please read Keith Howard's recent article/s at Stereophile?
Then rediscover Olson's (?spelling?) work at RCA.
And then listen to a pair of spheres in the near field.
If you've never heard a smooth-diffraction speaker, you just can't know how much it really does matter. (When it is also a dead / silent enclosure!?!? :-)!!!!) Hearing the effect of the felt pad idea around a tweeter/mid on your rectangular speakers gives only a hint of what good diffraction behaviour can do.
Real stereo recordings show it up _really_ well.
IMO most of us are USED to rough-diffraction designs. Some of you seem to LIKE them, ;-)!
This effort? And I do respect the effort! ..... Missed the integration that B&W achieved on most of what matters with enclosures.
Warmest
Timothy Bailey
The Skyptical Mensurer and Audio Scrounger
And gladly would he learn and gladly teach - Chaucer. ;-)!
'Still not saluting.'
http://www.theanalogdept.com/tim_bailey.htm
Hi, Timbo,
Interesting thoughts about a "smooth-diffraction speaker". Perhaps you could suggest some improvements I could make to my Maggies? :-))
Now, one has to live within the constrictions imposed by the type of drivers we like to listen to but I can understand how putting cone drivers onto a hemispherical baffle might be a very good thing, sonic-wise.
However, when it comes to a dipole planar driver that is flat and 1,600mm x 300mm, what more can one do to the frame which it is fixed to than round the vertical edges, front & back?
Regards,
Andy
The diffraction is less of an issue with the mid than with the tweeter. The mid is directional at a frequency below which the baffle comes into play. The tweeter, on the other hand, is still omni and thus illuminates the edge fully.
Bass is supposed to sound big. 6.5" is not a woofer size.
"Elsewhere, the major departures (shown more clearly in fig.3, which plots the difference between the blue and red traces) are found between 1 and 4kHz—about where we predicted on the basis of fig.1, although the details don't bear too close an examination. The largest departures amount to almost 3dB, and fall within a frequency range where the ear is acknowledged to be at its most sensitive."Taken from
http://www.stereophile.com/reference/704cutting/index1.htmlRead it, like I suggested, g'warn! ;-)! I found a coupla-three reads were necessary.
Warmest
Timothy Bailey
The Skyptical Mensurer and Audio Scrounger
And gladly would he learn and gladly teach - Chaucer. ;-)!
'Still not saluting.'
http://www.theanalogdept.com/tim_bailey.htm
Edits: 11/11/10
The baffle in that example is nearly 2x as wide as the driver, and 3x as tall. Very different scenario than an overall ratio of about 1.3 (and including rounding), as in the B&W clone.
Definitely not apples to apples.
Bass is supposed to sound big. 6.5" is not a woofer size.
B&W bothered to get it right for mid frequencies, with as small a driver, The distances involved / frequency? Diffraction happens at edges.If you look at this mid pod it's hardly any better than the tweeter pod, the curve radius at the edges, for the frequencies involved. The radius of the curve on that mid pod will not help smooth the pod's diffraction behaviour. It will be just as poor as the tweeter pod's, not enough of a curve.
On B&W's mid pods, a far greater radius curve begins at the driver's edge, and are you saying they shouldn't have bothered?
And, why didn't AR just restrict the blanket to the tweeter on the AR9 and all the later models? They did it to damp out the Mid (and HF) waves travelling towards the sharp edges, so that they would be weak at the edge, and their diffraction there less audible.
Lastly, the ear is much more sensitive at mid frequencies.
Warmest
Timothy Bailey
The Skyptical Mensurer and Audio Scrounger
And gladly would he learn and gladly teach - Chaucer. ;-)!
'Still not saluting.'
http://www.theanalogdept.com/tim_bailey.htm
Edits: 11/12/10 11/12/10 11/12/10 11/12/10
B&W bothered to get it right for mid frequencies, with as small a driver, The distances involved / frequency? Diffraction happens at edges.
Diffraction happens at edges, sure. But diffraction is frequency dependent. The smaller the baffle, the higher the frequency at which this occurs. The midrange is not only directional at the relevant frequencies here, reducing the intensity of illumination, but they are likely high enough in frequency to be outside the midrange passband.
If you look at this mid pod it's hardly any better than the tweeter pod, the curve radius at the edges, for the frequencies involved. The radius of the curve on that mid pod will not help smooth the pod's diffraction behaviour. It will be just as poor as the tweeter pod's, not enough of a curve.
You're not considering the operating bandwidth or directionality here. The tweeter pod is not the issue so much as the flange is. There is no corresponding flat section on the midrange mounting. This flat section creates the distance required to make diffraction an issue. Tweeters with tiny little flanges would be less sensitive here, as in the tweeters you see top-mounted on the Nautilus series.
On B&W's mid pods, a far greater radius curve begins at the driver's edge, and are you saying they shouldn't have bothered?
I'm not saying they shouldn't have bothered, but it's a design difference that doesn't really make much difference in the real world- both designs will be low diffraction, the B&W setup will have a little more on-axis output at the low end of its operational band as you're receiving reinforcement from the slightly larger apparent baffle size, but because it's so well rounded, it's a minimum effect. Fractions of a dB.
And, why didn't AR just restrict the blanket to the tweeter on the AR9 and all the later models? They did it to damp out the Mid (and HF) waves travelling towards the sharp edges, so that they would be weak at the edge, and their diffraction there less audible.
Yep, I like felt on baffles. The AR baffles had sufficient distance from the drivers to illuminate the edge. The transition from 2pi to 4pi is based upon the size of the baffle in traditional box speakers. With a "baffle" so small, the transition is determined by the directional characteristics of the driver itself, the edge diffraction is not an issue.
Lastly, the ear is much more sensitive at mid frequencies.
Yep. But since the "baffle" is not being significantly illuminated by the mid here, it's a non-issue.
Bass is supposed to sound big. 6.5" is not a woofer size.
The tweeter is the worst case scenario for diffraction and it doesn't seem that the mids/woofs are optimized well for the enclosure.
Bass is supposed to sound big. 6.5" is not a woofer size.
While they look wonderful, the standard sized tweeter face plate creates an acoustically large circular baffle that will cause polar response and diffraction problems absent in the original.
Now that's what I call a major DIY speaker project. Definitely not a casual weekend build. Looks like a hell of a lot of finishing/bodywork involved. Great results !
Looks fantastic but the "original" had a reason for the special shape like the loading of the drive units, it is obviously not the case here
as the tweeter is just a std Scan ring radiator, same for the mid and bass units but I am sure that it still sounds spectacular.
and I am sure sounding marvelous too.
Best Wishes
Bill
What a pleasure that was. Kudos to the team.
Regards,
Geoff
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