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In Reply to: RE: TAS Reviews the Magnepan 20.7 posted by hahax@verizon.net on November 26, 2014 at 04:33:35
The .7 series is an entirely different approach to crossovers for magnepan, which they had not done since the 80s. with 1st order XOs, the German tests show nearly no phase throughout most of the speaker's range above the mid high pass. An achievement all on its own.
I would be a believer that it is a breakthrough, but there is still the giant radiating surface of the bass panel which limits imaging precision. I wish they had the bass on a separate panel so you could time align and aim the center of the bass at the same distance as the mid and tweeter. Perhaps with the new aiming arrangement (on axis rather than face forwards) it is close enough to equidistant. It is similar to what I normally do with my Tympani/Neo8 (equidistant drivers and 1st order XO) and I find it difficult to find anything that comes close to its performance let alone betters it outside of bass extension and dynamics.
Follow Ups:
"The .7 series is an entirely different approach to crossovers for Magnepan, which they had not done since the 80s. with 1st order XOs, the German tests show nearly no phase throughout most of the speaker's range above the mid high pass. An achievement all on its own."
Not really. A first-order acoustic crossover has (inherently) no phase shift in its range. There's no special achievement there.
With the proper alignment, even the impedance phase angle will be level throughout the crossover range.
However, you are correct to note that the large radiating surface guarantee's less precise imaging than might be obtained with other (more conventional) speaker systems. This is another inherent trade-off in the design that can't be engineered out with crossover design or equalization or any other technique.
Time alignment is not is not an issue with regard to the bass panels because of the wavelengths involved and the crossover frequency chosen.
Cheers,
Dave.
Do you really think they left the LPs out of mid XO? If so, wouldn't the 1st order tweeter HP show up in the impedance and phase? Or do you think they put a zoebel network to iron out phase?
I have put my Tympani bass panels in equidistant arc setups with the mids and tweeters and used 1st order slopes in symmetrical and spaced alignments. It makes a very significant difference in image precision. It is very obviously lacking in the Limage setup where it turned out better to just cut it off with an LR4 and forget about time alignment. I trade off a bit of the fine imaging performance for an order of magnitude more bass.
Has anybody seen the crossover network for the 20.7? How do you know it's even first-order? :) How do you know if there's a Zobel in use or not?
As usual, your postings are full of speculation with no valid data points to back it up.
I was commenting on the theoretical alignments of generic first-order crossovers. However, I have no knowledge of whether the Maggie 20.7 employs this topology or not. It's very clear that no specific information will ever be forthcoming from Magnepan, so we're waiting on a knowledgeable user to divulge this at some point.
Cheers,
Dave.
Of course they didn't say. But the rumor mill keeps coming up with 1st order series XO. Also implying this is the new recommended aim for the 20.7 to be set on axis rather than face forward with minor toe in, as they had suggested for placing the 20.1.
There is no other option but to speculate since we can't expect anyone to void their warranty by looking inside. I know it gets on your nerves, but that is what is available to us, possibly not better than nothing.
You can't extrapolate on meaningless data. ;)
Regardless, a 1st order crossover with "no phase throughout most....." is not an "achievement"....that characteristic is inherent. It would be an achievement if it WASN'T a zero phase angle.
Besides, I think we've already found errors in the respective German test reports you mention. So, I wouldn't take it as a given their measured phase response is even accurate. :)
When the TAS 20.7 review appears online, I will be interested to read it.
Dave.
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