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In Reply to: RE: Measurements on 1.7, 3.7 and 20.7 posted by Davey on September 25, 2014 at 15:45:39
It is shown in the window between 3.5 and 4 msec. The start is something like 3.65 msec and the peak is at about 3.7 msec just left of center between the marks and the counter peak is just to the left of center at say 3.8 msec.
For comparison, here is the response for the Thiel 3.7 from Stereophile.
The scale is actually finer in the German audio rag.
It is entirely believable if you take what someone had measured here using his DEQX'ed maggies, which looked much the same. Damn quick speaker if the XO is done right.
Sensitivity measurements may have been done correctly with the 3.7 and too close with the 20.7 but the sensitivity is low in any case. If you use the measurement as if it were taken at 3m and back calculate to 1m using the linear drop assumption (rather than square) then you might have 82db ? That is one way to measure large planars for comparison to boxes.
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Does the data point spacing look consistent to you? There's something wrong with that impulse response, but I can't identify the exact issue without more information.
I question your "damn quick speaker" comment, but that's a subjective evaluation so can't argue with. Relative to conventional speakers which most likely use motor structures with much more power, Magnepan's do not have excellent impulse response. Much stored energy and ringing is noted with proper testing. However, that doesn't necessarily relate to a less than enjoyable listening experience, as has been noted by satisfied users for years. Objective testing is not where Magnepan's excel. :)
Dave.
I was thinking in terms of the settling back to 0. That makes it quick. I know that planars often have more ringing/resonances with transverse waves, and yes, the maggies have a lowish force/mass, but it looks good on this impulse test and the drivers have good impulse behavior on their own (without XO issues). The Neo drivers are better in this regard. The 20,7 also is supposed to have a thinner midrange diaphragm IIRC. I said damn quick because of the test. That is what I take from it.
These german tests does have a few faults, as there use to be about Magnepan speakers. The lowered moving mass etc. is really not there. Everyone seems to think the mass is lower for the foil conductor... The effiency is often measured in a more or less anechoic room and at 1 m. For large dipole speakers it is better to measure them at 3 m or even more. In these cases they prefered the speakers directed at the listning posistion. No wonder, as the frequency response off-axis is far from even. Frequency response measurements may also better be done in the listening room, like Stereoplay use to do, http://www.forumbilder.se/DE2A1/quad-20esl-20989-20measurement-1.jpg Sure the measurement on the right is closer to what the Quad ESL 989 sound like?Comparing just the size of the Mylar in the 1.7 and the 20.7 may not be correct. You need to know the tuning too. The larger area of the 20.7 bass driver will have to go lower. The lower resonant frequency use to have a very large peak reducing the maximum excursion of the diaphragm.
I also have some measurements of the MG II, 1.5, 3.5, 3.6, Tympani IV and IVa. Also some Apogees like Duetta, Fullrange, Diva, Caliper of different generations.For those of you reading german, I have scanned most of these reviews. Let me know if you want them.
Do you know why the http://www.twin-x.com/groupdiy/ is down?
Edits: 09/26/14
I don't see HOW the mass of the QR driver is less than the SAME driver in non-QR format.
IF the DCR of the drivers is the same, and the length of the serpentine is the same, than I'd say they used the SAME amount of wire per inch or CM. Just 'mash' it flat and you've changed from wire to QR.
Based on using LESS glue for the QR, and perhaps NO overcoat, you May get a few grams less weight for the QR driver, but measuring the material used, the difference should quickly be shown to be the glue / adhesives, NOT the wire/QR or mylar. That is, if my assumptions about serpentine length and DCR are correct.
Too much is never enough
I understand that different absolute sensitivity measuring techniques (other than a simple 1 meter measurement) might be more appropriate for Magnepan speakers, but I am only interested in the (German measured) 'relative' differences between models. It seems to me the German tests are showing different measuring technique when evaluating these models. That should have been explained in their testing. A 6db difference in sensitivity is a huge difference. :)
Dave.
I have compared the effiency of my MG 3.6 to a pair of conventional box speakers with a known effiency. I get about 5 dB difference at the listening position, 82 dB refered to 1 m.
That seems reasonable for a comparison to a conventional speaker.
However, I was referring to relative sensitivity differences of the Magnepan models quoted in the German tests and noted by Satie. A 6db difference there is considerable and there must be some explanation for it.
Cheers,
Dave.
I am not going to say that the actual sensitivity is 77 db and change, but I know from listening that it is lower. We compared them in the same setup and position with the same equipment and they produced lower volume but more substantial bass. When the dealer was done setting up the 20.1 (was a new model then) he set the vol. at 59 on the preamp which is the volume we were listening to with the 3.5 (IIRC) later I found mysef listening at 63 most of the time, but that was louder than how I played the 3.5. So I would guess that the sensitivity difference is something like 2 db. Could be as low as 1 db difference, but I don't think I would have picked up on that small a difference so readily.
In case you fellas haven't deduced this yet, I'm asking these devil's advocate questions to try and help you understand how difficult it is to characterize and measure these speakers.....for the German guys.....and even for Magnepan.
You don't mention whether the numerical readings on your preamp correspond to relative db levels. So, there's yet another confusing data point. :)
Dave.
I can't afford the white goods from Boulder. The blue flourescent display was on the dealer's preamp. Those are usually in 1 db increments. But I don't know that was the case, I never asked.
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