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In Reply to: RE: Measurements on 1.7, 3.7 and 20.7 posted by Potrzebie on September 25, 2014 at 18:07:22
Before you and Davey come to blows, let's be sure everyone is on the same page. There is a lot of confusion among lay people and Audiophiles alike about the terms used to describe sound. Remember loudness is subjective and while related to intensity and SPL it is affected by human preception as well as duration of the sound and other factors.
While all Maggies may have the same sensitivity (I am not sure I agree with that), the maximum SPL differ. That's why the 20's can energize a larger space than the SMGa's.
Here are two references to clarify the terms used to describe sound:
Reference 1
Reference 2
Edits: 09/27/14Follow Ups:
There's no semantics here. :)SPL ratings are generally assumed to be free-field so it's generally accepted that sensitivity and SPL are directly related. So, if all Magnepan's have the same sensitivity then they all produce the same SPL at the 2 meter distance......at a given input.....in the free-field.
The point I am making here (that went completely over Potrzebie's head) is that the larger models CAN produce larger SPL's than the smaller models. It's common sense, you have a larger radiating area, you can move more air, but, you need more power to do it.
Cheers,
Dave.
Edits: 09/26/14 09/26/14
The larger Magnepans may be capable of higher SPL's (they handle more power) than the smaller ones, BUT NOT AT THE SAME WATTS IN!The larger panel just means lower bass and more resolution, at the same SPL.
That went over your head!
Edits: 09/27/14
In case you haven't noticed, I write my posts (on purpose) in a way that forces members to read them carefully. :)
Don't feel too bad....you're not the only who doesn't read them carefully. :)
Cheers,
Dave.
It is not semantics and each step up the price ladder in maggies leads to less sensitivity, as they increase the gap as they go up in price and active surface area. The SMG and later MMG are the most sensitive, Tympani and MG20.x least sensitive.
So, the Magnepan advertised (all the same sensitivity) sensitivity ratings for the various models are incorrect then?
And it seems like (at least a couple of) the German test report sensitivity ratings are way off the mark?Dave.
Edits: 09/27/14
Go try it yourself, but at least subjectively that seems to be the case. As to whether at a certain frequency they might all be within 1 or 2 db from each other is a possibility. Sensitivity ratings for speakers are a sensitive issue for manufacturers.
I have tried it myself. Not with X.7 speakers, but with MMG, 1.6, and 3.3 models.Magnepan's sensitivity specifications are well defined at 500Hz with a two watt input. That's an advertised specification that shouldn't be sensitive, or subject to subjective evaluation, or even frequency response. :)
I'm still looking for an explanation of the huge 6db difference (83db...77db) between the 3.7 and 20.7 (respectively) that you noted in the German tests. You seemed to accept that relative difference and commented that only a handful of power amps can drive the 20.7. Now you're backing away from that conclusion and seem to indicate they might be within 1-2db in sensitivity.
Dave.
Edits: 09/28/14
I am not taking the position that the 20.7 measurements in the German (stereoplay?) are correct. I believe that something is wrong there. Just that I can't know what without asking them.
I should perhaps have added a "if you believe they are correct then" qualifier.
As far as my own experience then 1-2 db was what I expected to see in the measurements. I see from their FR plots that the bass resonance does not show, which probably indicates a far field measurement If they were smart enough to do that for the FR then I would expect they did so for the sensitivity measurements, in which case they would have used some assumption to back calculate the representative figure for 1 m. My best guess - and that is all it is -- would be that the 77 figure is not back caculated while the one for the 3.7 was.
That said, "only a handful of high power amps" is still the case for an 82 db speaker. At least if you want to be able to reach the top capacity of the speaker to produce output.
As far as the spec. from magnepan - I think the choice of freq speaks for itself.
So in your own experience comparing those speaker models what did you observe?
The inherent sensitivity of all the Magnepan models is the same. This is primarily the result of the motor structure.
The magnets are the same, the distance from xducer to magnets is the same, the pitch of the transducer wires is the same, etc, etc. Thus, you have virtually the same amount of conductors cutting the magnetic lines of force in all the models. There's just no way to create significant transducer sensitivity differences in these models.
That's why the 6db relative difference measurement caught my eye in the German testing. Obviously it's an error in their testing, or arithmetic, or something else with the 20.7 system.
I think your subjective evaluation of the sensitivity differences is probably pretty good.
Cheers,
Dave.
I don't know that the distance between the voice coil and the magnets is the same on all maggies. It is definitely greater in the 20.x models. I suspect that was the case with the T-4 bass panels and midrange vs the III/A. It isn't easy to measure with accuracy with simple tools (micrometer) but it appeared so with the T-4 and 4A vs MGIII and later 3.3. the SMG appeared to have a really small offset in comparison. But these are finger touch observations, not measurements. It is easy enough to do in manufacture so it would not be an issue to implement.
Bottom line is that I don't know either way but strongly suspect that they are different. Definitely so in the MG20.x.
I think we're beating a dead horse. :)
The Tympani's are a long obsolete model, different scheme, and have a considerably different sensitivity rating from Magnepan. Those are spec'd at 87db at 1 watt. That's fully 4db higher than the X.7 models or most other "standard" models.
The push/pull 20.7 is quoted from Magnepan as exactly the same sensitivity as the 1.7/3.7 at 83db. Your subjective evaluation says otherwise. I'm fine with that. :)
However, it seems the 77db sensitivity quoted by the German test is way out in left field and incorrect?
Dave.
Yes, the horse is long dead but I am very curious to get a definitive answer on the standoffs for the various models.
The T IVa sensitivity spec is, shall we say, "in doubt". I don't have actual measurements but the T IV was not an 87 db speaker. The bass panels are 85 db raw (without the XO) so long as you don't reach levels where they compress. 85 db would be a very generous figure for the whole speaker (or actually the mids).
Stereoplay measured the Tympani IVa. http://www.forumbilder.se/DE2MF/tympani-20iva.jpg
It was found to be 3 dB more efficient than the Infinity RS1. 84 dB/W/m. Compression begins at 103 dB for both in the range 40-400 Hz.
Thanks Roger, also thanks for the scattered details on the differences in magnets wire/foil and spacer dimensions. If it isn't too much of an effort could you point to what models had which structural aspect?
I am thankful that someone stepped in with his observations of the differences, for a minute there I was thinking I may have been "seeing things" for 30+ years.
I think Magnepan speakers have sensitivity rating calculated "backwards" to 1 m. It is not a very good idea to measure them at 1 m, far better at 3 m or even more. When I compared with a conventional pair of speakers at my listening position (as mentioned earlier), I recorded a difference of 5 dB at a distance of 4 m to the 3.6. My conventional speakers are rated for 86-87 dB/m (real world numbers) and impedance is the same as the 3.6. The low rating for the 20.7 is really strangre but most reviews have no measurements at all.
I have also looked at the various Magnepan I have. There are partly different magnets and the distance to the conductors on the Mylar is also different. The differencies are small but they are there. Some speakers use heavier conductors, the old Tympani IIIA and the 3-series. The Tympani IVa has lighter conductors but as far as I can measure thicker magnets and spacers. Tympani IVa mids has curved back plates (allow for greater excursion), thinner Mylar and the diaphragm is partioned in smaller areas, low moving mass of these for sure.
Yeah, I can understand that the Magnepan sensitivity specifications would be extrapolated from a longer distance measurement. But you transition from the far-field to the near-field when doing that for most of the models. :)
I would feel better if Magnepan didn't publish sensitivity ratings for their speakers. It just creates more confusion than it solves for many users. :)
Cheers,
Dave.
Considering the difficulty of doing a "real" standard measurement, I think what they are doing is fine. The figure is a useful representation of output vs. power in the standard form we expect to see in a test or spec, even if it is a bit of an embellishment.
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