If they are new…yes there is burn in or more like stretching out the panel. I had 20.7s and Rel carbon subs matched well with them.
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When I got mine home they sounded like transistor radios. Speaker placement in the room is pretty critical. Where are they now?
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Room placement and amplification designed to play difficult loads make a big difference. Also, you could be suffering from bass node cancellation and may need bass traps in your room. I suggest you do some research on room acoustics and if you are able to implement some of the solutions, you should be rewarded with really good sound.
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Even the 3.7is are fussy about room placement. I’m still playing with mine after 3 years or more. M700s were a vast improvement over an Adcom GFA-555 and M1200s are better still.
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Thanks for answer. As a philosophy, I don’t want to complete a speaker with a sub, all the more that my room is not large (4,5m*8m). My concern is that I used 3.5 since 2005 in the same room, and the bass (down to nearly 40hz) was full and satysfying.
Buying 20.7 I hoped a gain in this bottom area, but in fact for the moment that is the opposite : quite nothing under 70hz, and under 150hz that sounds hollow, like an empty frame. I can just perceive this frequence by their harmonics, but the fundamuntal sound is lacking.
I do not think that my A-class amplifier is the prb for that, because it worked damn well with 3.5, thus I cannot imagine that it is unable to supply low frequencies. It works at low volume : never more that 1/5 of the whole, mostly 1/6.
I listen mostly classical music, where the lowest bass are expected on bass drum, and organ. Now with 20.7 bass drum sounds like bongo ; 16’ pipes are shy, and 32’ ghostly.
I wanted to get testimonies about “burn-in time” for 20.7. I can’t imagine that they at least do worst than 3.5, but how long would it take to gain low frequences ? Is there a technic for a quickier process ?
Actually I am worried because I read a review telling that quasi-rubbon is not a reliable technology for bass compared to the oldest technology in 3.5 (rear magnets). So I fear that notwhistanding the amp and the burnin-in time, I will perhaps never find the deepest bass I heard with 3.5.
Thanks for answer. Yes placement, orientation is very sensitive. They lies 40cm from the side wall, and 1m from the front wall. I sit 3m away, and behind me the back wall is more than 4m away.
I first tried to put the 20.7 closer to the front wall (50 cm), but no way : the low bass refuses to speak.
I must say however that the medium and the trebles are first class for dynamic, space construction, sharp details : far better than my 3.5 and far better I would imagine. The prb is just the low frequencies.
What do you mean “radio transistor” : narrow spectrum ? dirty or buzzing sound ? Are the results better now ? Do you managed to get deep frequencies ? how long the patience ?
I bought the 20.7 from a selective showroom, and the dealer told me that they only runned 30 hours in his shop since september. I owned them since beginning of the week, and now the total burning-in is about 45 hours including time at the dealer’s.
Thanks for answer. I know my room for many years. Sure it is always possible to improve the placement and to deal with acoustics properties, but actually the prb is not in the room but in the speaker itself. I don’t think it’s about my amp (please see supra my message to Minnesotafat).
Are your 20.7’s wired in proper phase (positive to positive, negative to negative). If they aren’t in phase you will definitely hear a loss in the lower frequencies.
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Thanks for message. The setting in my room was proceeded by 2 technicians from the dealer, so I dare to think that the cabling was properly managed. Anyway I am totally unskilled about electronics topics, I don’t even know how to do to check the phase as you told 
May I ask what makes up the rest of your system? It all matters. Can you attach a picture of your room???
Thanks for message.
sources : Marantz SA-10 (listened mainly for SACD), TECHNICS SX-X1000 (DAC, for CDs)
amp : ETALON Integral one
Technics is far better for larger scale listening, depth of space, transparency, and xlow bass
But even on my Technics, the sound in the bottom spectrum is flat and empty on the new 20.7, whereas it was blooming and deeping with 3.5
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Here is the Technics : https://www.hifi-wiki.de/images/d/d4/Technics_SL-Z1000-SH-X1000-2.jpg
As Kim mentioned, it could be your speakers are out of phase. It’s plausible the technicians made a mistake. If your not skilled enough to know if your system is connected properly, I would ask the tech to come black and check the connections. I would also recommend that you have him expain to you what he is doing, as he performs his work to make sure everthing is properly connected.
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The shop 200 km afar and I doubt they will come back for this. And he is more ok for selling me a new top-level amp, but I don’t have the money for now.
How could I do this myself ? Switching the two plugs ?
PS : the lack of bass involves each panel, so that would mean that the technician made the mistake twice, that would be so unluncky…
Not so. Only one bass panel would be connected out of phase with the other. If the positive and negative from the amplifier is connected correctly to the positive and negative of one speaker, and the positive and negative of the other speaker is connected in reverse at the amplifier then you would have an out of phase connection. In other words, positive must be connected to positive and negative must be connected to negative from the amplifier to the speaker.
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I have had my 20.7s for 30 months. It took 6 months to get complete burn in, but the problems you describe seem too severe to simply let time be the cure. I am also very puzzled you could make the 3.5s work in these positions in this room, while the 20.7s are failing so miserably. It makes me think there could be merit to the suggestion that they have been connected out of phase. Almost any test CD (including the PS Audio disc) has one or more tracks to test that the system is in phase. If you were to use such a test to verify that they are out of phase, anybody here could give you simple instructions to solve the problem. An objective result from a test CD might also serve to make your dealer come back and do the job right if you are afraid to touch the connection.
I do think you need to bring the speakers further out into your room, at least 2m, maybe 2.5 m from the front wall. Even if this is not practical from the standpoint of your other room furnishings, just temporarily testing the sound with the speakers further out might at least help you to narrow down the problem. However, these speakers are not easy to position and no single remedy is going to give you all the smooth bass you are hoping for.
My initial experience was the opposite of yours - I had too much bass. Installing bass traps (16 inches in diameter) in the front corners, plus pulling the speakers further out into the room solved that problem. I then had bass down to 25 Hz but a dip centered at 50 Hz. I had to use subs to smooth out the deep bass below 50Hz.
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So re transistor radio comment. Thin sounding … I would say it took close to 200 hrs or so to break in. The last thing to come in was the bass. Read the 20.7 review in The Absolute Sound by Jacob Heilbrunn?? It should be online.
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The phase thing. I mean how difficult is it to see if positive is hooked to positive etc… and the manual for your electronics doesn’t mention phase / connections and whether the product is non inverting ? I highly doubt this is an issue
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It is known that Magnepan speakers need amplifiers with high current capabilities and 20.7 is definitely even more demanding in that respect than 3.5.
Based on described lack of deep bass, I would not be surprised that your amp isn’t the best match for 20.7.
I believe that It would be good to try your 20.7 with some other amp, if possible.
As a guideline, amps that come close to doubling power at 4 ohms are usually a good choice.
Finally, I would also recomend to try with a placement of 20.7 further into the room (so that distance between the speaker and the front wall is increased).
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