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I have a pair of Magnepan 1.6qr and 1.7i speakers. The .7 iteration of the Magnepan lineup was of course when the transition from the use of round wire conductors to flat foil conductors was made in the bass/mid frequency portion of the driver. This got me thinking about the differences between the two different conductor characteristics recently and why this change was made.
I seem to remember reading something along the concept that the foil (quasi-ribbon) conductor had a lower mass, making it closer to the ideal material for exciting the Mylar membrane truer to the actual audio signal. In other words, it sounded better.
I also think there was some discussion about the physical traits of the two materials and that the foil had much better adhesion to the Mylar. This made the drivers way less prone to delamination issues, something the wire drivers were notorious for having.
What ever the reason, this brings me to my question. Given the same input signal to the drivers, one with wire and one with foil conductors, how does the change in conductor material change the response characteristics of the driver? Has anyone actually measured the raw drivers and their differences without the effects of the crossover circuit?
-Joe
They're not that big!
Follow Ups:
I think that the foil will be less likely to come loose from the diaphragm over time, as there is more area upon which the glue will be bonding it to the mylar.And, unless the panels wired with foil have a different DC resistance than the panels made with wire, then the mass will be the same. Unless they have to apply more glue to the foil due to the larger surface area of the foil vs round wire...
You could argue some things about skin effect being different in the two, but skin effect isn't all that important in such small conductors until you get up into high RF frequencies. If you are using your speakers for an antenna.... well then maybe.
The shape of the magnetic field around a flat foil might differ slightly from a round wire, but it's unlikely this is a large enough difference to affect the sound.
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Science doesn't care what you believe.
Edits: 12/27/22 12/27/22 12/27/22 12/27/22
I think that would be true about delamination, but it really hasn't been a problem since they introduced the new adhesive 20 years ago. (My bass wires are starting to come loose again, though -- #*(@&.)
One thing I haven't seen mentioned is diaphragm damping. There is less diaphragm noise from the foil. Parts of the diaphragm are less likely to go out of phase, too (Mylar dragged behind the conductors).
The main differences in the XO were because they went from higher order parallel to first order series crossovers, not because of the foil.
"The main differences in the XO were because they went from higher order parallel to first order series crossovers, not because of the foil."
What I find interesting is that the 1.6 has a very distinct 4dB dip centered at 600Hz, while the 1.7 has a 2dB hump centered at 425Hz. Of course that is the electrical response based on a computer circuit analysis and how that translates to the in room acoustic response I haven't tested. Maybe I'll get a calibrated mic and give it a try.
All the factors discussed in this post could certainly be the reason there is such a different shape to the filter in the ~500Hz (about a 6dB difference) region.
I haven't opened up the 1.7s, but if I did it would be interesting to measure the response of the two different raw bass drivers of wire vs foil for comparison. I'm just not sure how I would do that to get any accurate data below ~300Hz. Using a calibrated mic and something like REW do you have any suggestion on how I would do that with a big dipole driver? Thanks Josh.
-Joe
They're not that big!
Speakers like Magnepan need to be measured at a distance. The response varies a bit over the driver(s). Measuring at a distance will include the room... You will need to measure the two speakers in exactly the same spot and with the microphone in also in the same spot.
"I think that the foil will be less likely to come loose from the diaphragm over time, as there is more area upon which the glue will be bonding it to the mylar."
That has certainly been my experience with the 1.6s. The tweeter section (foil) has never exhibited any issues related to delamination. On the other hand, the bass section of the panel (wire) developed the classic "banana peel" delamination when they were around 15 years old.
"And, unless the panels wired with foil have a different DC resistance than the panels made with wire, then the mass will be the same."
Makes sense. The same amount of aluminum, just a different cross sectional geometry.
"Unless they have to apply more glue to the foil due to the larger surface area of the foil vs round wire..."
Very interesting point! So, the composite foil driver, (conductor, adhesive and Mylar) would most likely have a greater mass than its wire conductor counterpart because there is more adhesive material used with the larger surface area of the foil bond!
"You could argue some things about skin effect being different in the two, but skin effect isn't all that important in such small conductors until you get up into high RF frequencies. If you are using your speakers for an antenna.... well then maybe."
I do remember there was some discussion around here many years ago about the RF/antenna effect of Maggies in general. The idea being that RF "recieved" by the "antenna" was interacting with the audio frequencies causing subtle, but audible distortion. The proponents of this theory advocating the use of an RF filter (choke) on the speaker input terminals. If I remember it correctly it was mostly an anecdotal position with little to no measurements/science to back it up. I'll go with your engineering knowledge on this one. This is not a factor to be concerned with.
"The shape of the magnetic field around a flat foil might differ slightly from a round wire."
This gets my attention the most! This could go a long way in explaining the differences I have experienced comparing the two 1.x series speakers firsthand. I'll go in to more detail on that in another post.
Thank you so much for the detailed point by point explanations. This was exactly the kind of information I was interested in.
-Joe
They're not that big!
triamp wrote: "The shape of the magnetic field around a flat foil might differ slightly from a round wire, but it's unlikely this is a large enough difference to affect the sound."
It does effect the output of the speaker as the foil is not sitting in the highest magnetic field like a round wire. The flat foil seems to stiffen the diaphragm and that is positive for higher frequencies. Comparing the magnets of the LRS with my old Tympani, shows far thicker magnets for the LRS. Probably because the distance between magnets and the diaphragm is larger.
"It does effect the output of the speaker as the foil is not sitting in the highest magnetic field like a round wire."
Thanks for the additional clarification on this concept Roger. This goes a long way in explaining what my experience has been comparing the two 1.x series speakers. Like I mentioned in my reply to triamp, I'll get in to that in another post soon.
-Joe
They're not that big!
Comparing two generations of Magnepan where one has round wires and the other flat wires is not that easy. It is often more than the type of wires that separate them. Comparing the look of the naked 3.6 with the 3.7, you will find many details that are changed. The layout of the tiedowns is very different, the number of magnets is changed and we do not know much about the tension of the Mylar. Then we have the crossover which is very different between the two. It surprises me that people think the wiring/foil has little mass. For the bass section of most Magnepans it is about 40 gram, some Tympanis is about 20 gram.
Spot on Roger! The crossover circuits are very different between the .6 and .7 iterations. Besides the obvious switch from a parallel to series circuit, the shape of the two 1.x series crossover responses is so different too. I thought it must be compensating for a difference in the efficiency of the foil conductor, I just wasn't clear as to why. The explanation from you and triamp about the difference in the magnetic field using the foil conductor vs wire has cleared that concept up! Thanks.
I somehow bought in to the idea that foil was "better". I just didn't question better for what? I assumed it was for a sonic improvement, but my own listening experience has not proven that out.
-Joe
They're not that big!
I can't give you any measurements, but the foil conductor has significantly less mass. It will start and stop in response to a signal quicker as compared to a wire conductor.
The foil has the same mass! For a given resistance it does not matter if the wire is round or flat.
Assuming the round and flat wire are made of the same material. :)
The difference between Maggie foil and wire configurations is not just the conductors, but also the layout on the Mylar.
Dave.
There are many more differences between the older generation (3.6) and newer generation (3.7) than just a switch from wire to to flat foil.
The original question asked, though, was simply "Foil vs Wire: What difference does it make? " not "how are the newer magneplanar speakers different.
One thing that I had not considered in my original reply was the change in diaphragm stiffness that the foil / glue / mylar "sandwich" would impart to the speaker. Yes that would change frequency response, all other things being equal. But the "other things" were also changed so I assume some one of those changes compensates for this somewhat stiffer diaphragm. ( Really I'd like to measure the stiffness of an old diaphragm vs a new one...yes there is more glue surface area, but wire is stiffer than foil....)
Science doesn't care what you believe.
Round vs. flat wire in a planar has been investigated by Joppe Peelen. As the diaphragm gets stiffer with the foil it also changes the frequency response. Slightly better for higher frequencies but not for lower, the Mylar cannot stretch the same way.
Yep, I'd expect the compliance would go down, meaning resonant frequencies would go up given the same tension and geometry. They'd have to be tuned differently.
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