This is what has made me wonder about the freestanding waveguide. Don't we have to treat the woofer with the same care as the CD? Is the freestanding WG going to cause diffraction problems for it? Sorry to keep pounding on about it. They just almost seem to good to be true, I want to be as excited as the data suggests...
Genelec has basically improved upon the technology of the 8260, by carefully integrating the woofers behind the (optimized) waveguide panel.
From 6moons:
"Besides the usually cited advantages for a coax (lower interference, point source dispersion, potentially superior group delay) there are obviously disadvantages too. Midrange cone travel modulates tweeter output for Doppler distortion and undesirable edge disturbances from surround, basket and mounting screws aren’t uncommon. Those will cause a certain ripple effect or response irregularities as the Finns admit.
Their solution for the first problem is basic. Restrict excursion of the midrange by crossing it out sooner. Genelec does so at 490Hz to have the 10-incher handle all bass and the lower midband. Sorting out the second issue required more brains. We’ve seen similar addresses from KEF whose Uni-Q dual-concentric sports a very shallow geometry to avoid jagged transitions whilst their baskets hide behind trim rings. Genelec skins this cat differently. They’ve moved the midrange surround to the inside for a perfectly seamless transition between midrange diaphragm and box and thus also tweeter. Due to the company’s trademark wave guide, the tweeter ‘sees’ a perfectly smooth clearly defined transition which supports its homogenous dispersion. In Genelec jargon that becomes a Minimum Diffraction Coaxial driver with Directivity Control Waveguide. MDC, DCW… the attached picture says more than a thousand acronyms."
From 6moons:
"Besides the usually cited advantages for a coax (lower interference, point source dispersion, potentially superior group delay) there are obviously disadvantages too. Midrange cone travel modulates tweeter output for Doppler distortion and undesirable edge disturbances from surround, basket and mounting screws aren’t uncommon. Those will cause a certain ripple effect or response irregularities as the Finns admit.
Their solution for the first problem is basic. Restrict excursion of the midrange by crossing it out sooner. Genelec does so at 490Hz to have the 10-incher handle all bass and the lower midband. Sorting out the second issue required more brains. We’ve seen similar addresses from KEF whose Uni-Q dual-concentric sports a very shallow geometry to avoid jagged transitions whilst their baskets hide behind trim rings. Genelec skins this cat differently. They’ve moved the midrange surround to the inside for a perfectly seamless transition between midrange diaphragm and box and thus also tweeter. Due to the company’s trademark wave guide, the tweeter ‘sees’ a perfectly smooth clearly defined transition which supports its homogenous dispersion. In Genelec jargon that becomes a Minimum Diffraction Coaxial driver with Directivity Control Waveguide. MDC, DCW… the attached picture says more than a thousand acronyms."
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I think you got the general idea: the maximum score would be reached when everything is “flat”. That's what I interpret from the model predictions. However, it is not clear whether this type of speaker was tested and validated though actual listening tests, you are correct.
Actually, in anything but the idealized limit case, the model would rate a speaker with a steeper (see the SM definition) slope for the PIR higher, everything else being equal, and this leads to an observation.
Keep in mind That the PIR and ER are so similar that one can be used as very good estimator of the other. In my graph I show both but the PIR is not shown in the CEA2034/Spinorama.
Going by the measured performance of the Revel speakers, as an example the Revel F228 spinorama
To my eyes, the ER/PIR/DI targets seems to be closer to a flat line, the DI is flat from 200 to 8000Hz and the PIR/ER is matching the Harman preferred in-room response over the same range. This is consistent across the current line of Revel tower speakers which are supposed to be double bind tested for best performance and hopefully up to date with their more recent findings.
That is rather different from the Kef state-of-the-art speaker measured performance:
Kef R5
which seems to follow the ER/PIR slope target and is consistent with the earlier Harman findings on the preferred in-room response i.e. a “pure slope" PIR, see the Harman in-room EQ study.
I have generated a comparison of the spins, it is attached.
The SM PIR data, what I want to highlight, it show the issue of the model vs the preferred in-room response in the general case:
F228Be: 0.830
R5: 0.986 (max and desired is 1) which show that Kef PIR is almost a perfect line with a slope rates higher on this parameter while the NBD PIR are nearly identical.
Note: the score are not actual scores as I am missing the LF extension of the F228Be. I used the normalized 14.5Hz LFX extension to enable the comparison nonetheless.
From these examples there is one instance (F228Be) in which the flatter DI provides a better approximation of the preferred in-room response.
The game could then become to get a reasonably flat ON/LW while engineering the directivity of the speaker to achieve the preferred in-room, somewhat disregarding the model SM_PIR parameter.
It seems to me that it makes more sense to see the issue this way rather than trying to reduce the design process to the design of a certain DI with little consideration for the other parameters. it sounds like oversimplification to me, not saying that it is what you or others are doing...
Whether this design ethos is the most constraining (and the target to shoot for) might be true but I feel that it is an incomplete image of the actual target which seems to be the PIR itself.
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And this is exactly what I would try to do. I already did, actually, with the newest designs presented here. We have now all the machinery to optimize a waveguide for virtually any DI slope we desire.
The point is that if the power DI curve is smooth (e.g. a tilted line) you can be almost sure the other curves are smooth as well, the PIR included, so I still see it as a natural optimization target but it could easily be some different (integral) curve. To get a flat ON/LW is then a no-brainer. I only don't see a reason why would be the SM_PIR disregarded - it would be still there (and smooth as well), IMO.
- I'm pretty sure that the new waveguides optimized for the following DI targets would behave as desired in all other aspects as well:
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Looks really nice.Here's another one measured
Looks also very similar to that previous measurement where I mentioned that 2.x kHz and 4.x-5.x had some weird dips, it's more clear here. I know that the off-axis is affected the same way so active EQ easily fixes it, but I still don't have a clear idea what's happening in these regions.
Acoustic Horn Design – The Easy Way (Ath4)
Acoustic Horn Design – The Easy Way (Ath4)
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I still believe that the waveguides (per se) are not to blame. The waveguide was virtually the same here: #3796 and #3792
Not only active. In a typical situation where you have sensitivity to spare, this could be equalized passively without much struggle (if the driver was the culprit).
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- Give this waveguide a perfect driver and it will work perfectly. Anyone?
How would you (personally) define "the perfect driver"?
On paper (and imo), the hf1440 seems to largely comply with the definition.
Really? With passive EQ, my best guess is a low-Q notch around 3.8 kHz and a shelf between (low end of passband) and 2.0-2.2 kHz with pelanj's example, and I'm not sure that would be good enough to give a "flat" on-axis or averaged response.