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EMIT magnets - difference?

repeater

repeater

New Member
Hello everyone. Very long time lurker, first time poster. I've done some looking here and there and can't seem to dig up an answer, and was hoping someone here could help.

I own a pair of RSII's and just acquired a set of RSIIb's that I'm currently restoring and modifying. My question is in the differences of early EMIT magnets.

The RSIIb originally came with a forward and rear firing EMIT with the 490126 PN on the back. They also have a front firing 490123 "super" EMIT as well, that uses the thin magnet. All use the same diaphragm. Two of my EMITs were damaged and when replacing them, I sourced a pair of the round front plate EMITs that look like those used in the InfiniTesimal. They also have the same diaphragm (which is all I wanted) but they used a 490124 thin magnet.

So now, I have both magnets in front of me, ready to put these EMITs back together with their new diaphragms. Which magnet should I use? The original 490126 "thicker" magnet, or the 490124 "thin" magnet?? Just for reference, the RSIIb's are going to be ran with an active crossover, so original crossover specs don't need to be the reason of using one or the other, I'm just curious because I'd assume there's some sort of frequency ability difference between the two magnets, as Infinity used the thinner magnet on the "super" EMIT in the RSIIb, but also used the thicker magnet as well, yet both have the same diaphragm. As you can see in the picture, the magnets certainly look like different material. Is the original, thick magnet Cobalt Sumarium? The thinner? I'm confused because they both have a different look and color (see pic) yet are both from roughly the same time period. Any help on these is appreciated, I'm just curious as to whether any particular magnet yields better results. More to come on these crazy RSIIb's I'm building.

2012-07-29_23-41-57_349.jpg
 
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The thicker one seems to be stronger. Then again though, I took the larger one apart much sloppier as it had a torn diaphragm in it anyways. The thin one I posted it up screw by screw and removed the two halves carefully. I haven't stuck them on steel yet to test...I guess I probably should have done that.
 
is the actual magnet thicker, or just the mounting for it? in the photo the magnets look the same. my understanding is that early emits used samarium cobalt magnets, and some later ones used neodymium magnets.


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No, the magnet on the right (the original one) is as thick as the white plastic casing surrounding it. Both magnets have the steel backplate on them that they are adhered to. The difference is the magnet on the right has the plastic spacer around it, where the thinner magnet doesn't. But yeah, the one on the right is 3...almost 4 times as tall.
 
Update on this :

I'm not sure why I didn't do this before, but I took both magnets to steel just to see which one was stronger, because when disassembling them, I didn't notice a difference. The thin magnet...holy...crap. That sucker is strong. The thicker one...not so much. I'm going to assume that the thicker magnet (the original RSIIb magnet) is NOT Samarium but the thinner one, the same magnet used on the lone "super" EMIT on the RSIIb is Samarium. So I guess the question is, if they had the technology to make the Samarium EMIT magnet at the time of the RSIIb...why didn't they make all the EMITs out of this material? Cost? Are there frequency difference implications between the two, despite having the same diaphragm??
 
the ribbon type emits never used "standard" magnets. they required a stronger rare earth magnet, either samarium cobalt or neodymium. judging from your reaction, i would suggest the stronger (thin) magnet is neodymium. neodymium is a stronger magnet than samarium cobalt. so i'm thinking the thick magnet would be samarium cobalt.

neodymium are so strong they will fly out of your hand when close to something they are drawn to, and require a great effort to get unstuck. i've actually had two of the magnets accidentally pull out of my hand and come together with so much force that they shattered each other.

it seems to me that since the super emit went into production later than the original samarium cobalt emit, the super would use the even more exotic neodymium, as that material was not commonly available when the "regular" emit was originally released. samarium was still used, even after the neodymium became available. whether it was because of a magnet related frequency difference i can't say for certain (but it seems logical if it was preferred for the super emit). i do know samarium cobalt was less expensive than neodymium, so cost could have come into play. samarium cobalt worked well for the "regular" emit, so they probably stuck with it for that application.

as for which to use, i'll leave that to those with more experience rebuilding emits to suggest. personally, i'd do what infinity did.


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Thanks! That makes good sense.

My initial thought was to stick with the original magnet as well...

I'm just real curious if there's really a difference sonically between the two...without listening for myself of course.
 
loquatious said:
the ribbon type emits never used "standard" magnets. they required a stronger rare earth magnet, either samarium cobalt or neodymium. judging from your reaction, i would suggest the stronger (thin) magnet is neodymium. neodymium is a stronger magnet than samarium cobalt. so i'm thinking the thick magnet would be samarium cobalt.

neodymium are so strong they will fly out of your hand when close to something they are drawn to, and require a great effort to get unstuck. i've actually had two of the magnets accidentally pull out of my hand and come together with so much force that they shattered each other.

it seems to me that since the super emit went into production later than the original samarium cobalt emit, the super would use the even more exotic neodymium, as that material was not commonly available when the "regular" emit was originally released. samarium was still used, even after the neodymium became available. whether it was because of a magnet related frequency difference i can't say for certain (but it seems logical if it was preferred for the super emit). i do know samarium cobalt was less expensive than neodymium, so cost could have come into play. samarium cobalt worked well for the "regular" emit, so they probably stuck with it for that application.

as for which to use, i'll leave that to those with more experience rebuilding emits to suggest. personally, i'd do what infinity did.


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Click to expand...

Often times, questions arise whether it is better to use Neodymium Iron Boron or Samarium Cobalt, which was used in all the pre-Kappa EMITs, they were used in all the early Infinity EMITs, which are basically the same, some have the magnet back with the magnet forming little pockets, the thinker ones, do not. There are minor differences, such that I prefer the half source square ones, used in the RS series. The Quantum series is fairly close, some having a bit higher impedance, why, I forgot and some think the round ones should not be mixed with the square ones, why again, I think this is more something to claim, than any real issue, fact is, the square ones look better in line source, or all round ones may do as well? Mixing them, for me, would look messy, and if I had to use some round ones, I would place them on the back.

Their are size differences, such as on some Q series. The small one may have a thinner diaphragm, however, I used them without the plastic cover.

The Neodymium magnets need a surface treatment. Options are nickel, which is what Infinity used and many came lose. I much prefer the Cobalt Samarium magnets, as they are free from dislocation of the magnet. Infinity changed because the Neodymium magnets were less expensive; they also claimed these reached frequencies of 45,000, I believe, yet I have no problem with the frequency of the original magnets in the older EMIT and EMIM, as they are less likely to come loose. Some change out the Colbalt Samarium, for the Neodymium magnets and you end up with a potentially bad driver. Oxidation is also a problem with the Neodymium magnets.

One advantage with Neodymium magnets; the diaphragm may be made thinner. This may be why the were rated at a higher frequency?

here is a link
 
Thanks for the info!

As of now...I changed out the two bad diaphragms and put the Neodymium magnets on in place of the Samarium ones.

What interests me is that by that claim, the Neodymium is what would be making the higher frequency. The diaphragms between all 3 EMITs I have are all the same part number. This being the Samarium magnet EMITs that were in my RSIIb's, the Neo magnet in the "super" EMIT in the RSIIb's, and the Neo magnet in the round front plate EMITs I picked up to rob the diaphragms.

I guess I always have the Samarium to change out should I need to.

So was Infinity's reason to use BOTH the Samarium AND the Neo on the RSIIb's a cost savings, or was the intent of the super EMIT truly to have a higher frequency? As far as I know, the Samariums in the RSIIb's were the last ones used and then phased out for all Neo EMITs.
 
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Yes, I like the samarium cobalt magnets and the round ones were this, until the Kappa K model. The gray ones, with blue or red print say they are samarium cobalt same with the older black ones, used in RS series. I have some NOS Kappa EMITs and they seem to hold up well. All the older ones are about the same, so, if you replaced a grey one, as you see is the later RS, with a black one, they will be the same. The Kappa are a bit different, and I do not know, or remember, but I would not mix them. I have modified Kappa 6.2i with two Kappa EMIT, front and back, the factory polydome and woofer, they are a more airy sound for HT fronts and the woofer goes well with my sub-woofers.

One thing about the poly-dome, if kept out of sunlight, they will not turn white, which is the first sign of the material breaking down. Mine are as old as the speaker, however old this is?
 
InfinityBob said:
Infinity changed because the Neodymium magnets were less expensive; they also claimed these reached frequencies of 45,000, I believe.

One advantage with Neodymium magnets; the diaphragm may be made thinner. This may be why the were rated at a higher frequency?
Click to expand...

It makes sense to me that Infinity would place a different magnet (Neodymium) on the Emit that was utilized as a super tweeter given the claim of frequency extension up to 45,000 kHz. Frequencies ranging well above what the average person should be able to hear have been reported (by some high end speaker manufacturers like B&W) to deliver a certain unique airy top end and enduce a larger more realistic soundstage hence B&W's decision to make the 800 series with diamond 'tweeter domes'.

Because diamond is rigid and very strong, the sound waves pass through the domes very quickly. But some tweeter domes made of traditional materials such as aluminium are susceptible to distortion at high frequencies. For example, aluminium tweeter domes break up at a frequency of around 30 kHz, whereas the diamond tweeter domes are stable up to 70 kHz. This is far beyond what any of us can hear, yet it has its effect.

My conclusion is that the Infinity S Emit with its Neodymium magnet offers listeners a similar experience as a result of these extended frequencies. :scratch2:
 
I'm a little late as usual but I'm sitting here with a box of emits and some are thick some are thin. I have three older round emits 2 are thick one is thin. And two square ones from the Qe or Qa. Those are thin. All these are Samarium Cobalt magnets. The RSIIb used one thick one thin because the rear emit and the front top emit are back to back and there wouldn't be enough room for the wires otherwise. The top front emit on the RSIIb is a regular thin emit which is crossed over at a higher frequency. Super emits came out later in the kappa line. Those are the zoomy 45k ones.
Jim
 
My two lower EMITs on my RSIIb's were both thick magnets on both speakers, back to back...all with the 490126 part number. All four EMITs (back to back) in my other pair of RSII's are all also the thicker 490126 magnets. The two upper EMITs in the RSIIb's (the super) that have nothing but a plate on the backside are the thinner 490123.

The 490123 thin magnets in my two super EMITs in the RSIIb looked exactly like the thin ones in the picture above, so I would assume those are also Neodymium.

So now I'm pondering whether to swap back to the Samariums on the two I changed. Oh...1st world problems....
 
Below is a link to the Infinity RSIIb. They are calling the the top (1/2 exposed diaphram) tweeter a UHF (Ultra high frequency) Emit and the one below it a LF (Low frequency) Emit. It's a very interesting shematic. As stated previously by another member the Emits are playing different frequencies. It looks like the UHF Emit plays from 8,000 kHz to 32,000 kHz and not the previously mentioned 45,000 kHz.

Link... http://www.infinity-classics.de/technik/manuals/RS_IIA_technical_sheet.pdf

Does anyone know if the thinner diaphram that the Neodymium Emit is capable of housing was used in the UHF Emit in the RSIIb? Maybe coupling the thinner diaphram with the stronger Neodymium magnet made the standard Emit more capable of the upper frequencies they were shooting for with the UHF Emit. I'm also curious as to why they blocked off half the diaphram on the UHF Emit. Maybe Arnie will chime in and clear the air. :D
 
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I'm not sure of your question about the diaphragms but I think the slots are blocked off because if they weren't the high freqencies may be over powering and unbalanced. Some guys pull that piece off to expose them. I never tried i like them the way they are. On the Infinity Classics wed site the IRS line up, Kappa, Rens, RS4000,5000,6000,5001 and 6001 had the emits that will go up to 45khtz. There may be some I missed.
Jim
 
I find the difference between the two interesting, because the only thing structure-wise different between the EMIT and SEMIT on the RSIIb is the magnet. The diaphragm is exactly the same, same part number and everything stamped on it. I'm guessing that the Neo magnet has the capability of handing higher frequencies better, therefore its used in the RSIIb crossover schematic as a higher frequency tweeter. Yet...in the model Infinities that use only 1 EMIT (same time period), the thinner NEO magnet is used, with the same diaphragm yet again...yet it is not called a SEMIT because it's crossed over back at a typical tweeter frequency.
 
From another vintage of SEMIT/EMIT.....

My IRS Gammas (1988) have an EMIT K, and a SEMIT K. They are different drivers with different diaphragms. The Betas are the same. I am certain the EMIMs from these are Neo magnets, but I have to check on the composition of the EMIT/SEMITs...
D
 
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