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In Reply to: RE: Measurements on 1.7, 3.7 and 20.7 posted by Satie on September 25, 2014 at 13:56:08
The low sensitivity is not as bad as it seems. Stating the obvious, these are planar speakers and the fall off is proportional to the distance unlike point source speakers where the fall off varies with the square of the distance. Off-hand I would have expected the sensitivity of the 20's to be higher because of the push-pull magnets -- so much for common sense. Regardless Maggies like "kick sand in your face" Charles Atlas amplifiers.
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I think they used up the doubling of the magnets by increasing air resistance from the second perforated plate and increasing the depth of the gap(s) to allow greater xmax. Besides, magnepan's philosophy is that the higher the cost of the speaker so is the importance of sensitivity is reduced since "power is cheap" at least relatively.
And by using a cheap high powered amp be guaranteed to never hear what the speaker is capable of sonically just to pursue high volume listening...
That is the problem you can solve with biamping. Though it persists with a low sensitivity midrange and tweeters that require over 100W for some listeners such as myself.
If you want to use a high quality amp with limited output on the upper end then you can replace the midrange in a large maggie with a line array of Neo8 or Neo10 drivers. The ribbon tweeter is more sensitive than the bass and mid. On the 20.x models you need to build a new frame for the Neo drivers and tweeter to accommodate them and to separate them physically from the bass, creating a two panel speaker.
I'd figure some way to Biamp the 20.7 with a QUAD of JC-1 or perhaps a PAIR of Magtech. Than call the electrician out to install a 20 amp service x2…..one for each amp or amp-pair.
Too much is never enough
If you are willing to open your 20.7's and sketch out the wiring with the values of the caps, coils and speaker resistances (you can get a cheap LCR meter for around $30), I will come up with an equivalent parallel crossover and its active line-level equivalent.
Unfortunately they don't make that easy with the 20.7, but go to your dealer and try it out with the same electronics and see the difference between a small maggie and a big one. I think it is a sensible approach and it is not much of an issue to make the claim that they all have the same sensitivity rating. In the bulk of measurements in S'phile the speakers come in short of their sensitivity ratings - sometimes seriously so.
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