Does a 2441 affect a CRT Television?

[Harryup]

I'm thinking of building a new center channel. My Synthesis 3 center does affect my CRT a bit magnetically. Will a 2441 have the same charateristics as my Alnico 2405 which does not affect the CRT at all?

Thanks in advance

Bengt

[Mr. Widget]

All of the vintage alnico motors JBL developed years ago are magnetically shielded. The 2441 is another example of this design as are the alnico woofers. The 2441 will not send out stray magnetic fields to mess up your display.:thmbsup:


Widget

[Harryup]

Many thanks

[LE15-Thumper]

All of the vintage alnico motors JBL developed years ago are magnetically shielded. The 2441 is another example of this design as are the alnico woofers. The 2441 will not send out stray magnetic fields to mess up your display.:thmbsup:


Widget

How is it that the alnico stuff is inherently shielded ?

[Mr. Widget]

How is it that the alnico stuff is inherently shielded ?It is the physical design. The alnico magnet is placed in the center of the VC and the return casting completes the circuit. I doubt that Mr. Lansing cared about shielding, but rather wanted to design the most efficient motor with as little flux loss as possible.

This pic compares the JBL alnico motor to a typical ceramic/ferrite motor.


Widget

[clmrt]

...Alnico is the 2nd in the photo...right? I try to pay attention in class...:D

[Mr. Widget]

...Alnico is the 2nd in the photo...right? I try to pay attention in class...:D

It's in the one that looks like a woofer and not some Bose POS.:bouncy:


Widget

[Harryup]

Now I have bought a pair of 2441 for the center and they do affect the CRT very much. Not like the 2445 but about the same as the 2450. So my center project have to wait until I buy a Plasma in 2 to 3 years when they become more interesting.

So my conclusion is that treble horn like 2405 Alnico does not affect the CRT but anything else does. Or are there anyone out there that have other experiance with like 375 or ?

Bengt

[Mr. Widget]

That is odd...Just how close are you planning on putting the driver next to your CRT? I have had alnico motored JBLs "near" TVs on several occasions and never had a problem... with ferrite woofers, wow it's a psychedelic light show.

Maybe not all CRTs are created equally? Mine have all been Sony Trinitrons.


Widget

[Harryup]

Mine is a Loewe Articos 32", if I come closer than 3 feet from the tele it shows various colors. A bit odd to have the centerspeaker 3 feet of the center when you are sitting att a distance of 15 feet.

[Mr. Widget]

I guess the Loewe TVs are not well shielded. I have never had any driver of any type affect a Sony at 3'. I have even placed a raw LE15A right on top of a TV with no affect. The stronger ferrites will affect them at around 2'... This certainly isn't scientific, just anecdotal remembrances of forgetting I had a woofer in a box or some such event and noticing the TV or computer monitor going to hell.

I am sure that even the "TV safe" magnetically shielded speakers that are specifically designed to be near a CRT create a magnetic field to some degree. Have you been able to use other speakers?

Widget

[speakerdave]

Although the JBL Alnico drivers with the cast magnetic return pots have the least stray magnetic field of all the drivers I've checked, there is some field there. It is also true that different TV's seem to have different sensitivities. I doubt that it is the tube that makes the difference; it would more likely be the material used in the housing to shield the screen, if any.

With my TV I find that the Alnico JBL drivers can be much closer than the typical ferrite driver, but even they may cause a (small) problem when right next to the tube, whereas JBL woofers with the big ferrite magnets must be about three feet away. Also, remember, the 375/376/2440/2441 driver has a very intense magnetic field (20,500 gauss in the gap for the 2440), and so the same type of shielding will not be as effective as for lesser fields. Finally, with all of these JBL Alnico drivers the field extends more powerfully out to the front than to the sides or back, and the position of the 2441 behind a horn, next to a TV will bring that factor into play.

A while back one of our European members reported that a plate of iron or mild steel (don't remember which) between his drivers and the TV solved the problem. I'm not sure exactly why that worked, but apparently it did. The material would be very permeable to a magnetic field and so would act in exactly the same way as the cast pot return circuit of the driver itself. Ordinarily you would expect a magnetic material in a strong DC field to eventually become magnetized and have its own field. But a material of low coercivity index(?) would also loose its magnetism easily, and it may be that the plate is degaussed when the TV screen is degaussed on turn on. Anyway, it might be worth a try.

David

[B&KMan]

Mine is a Loewe Articos 32", if I come closer than 3 feet from the tele it shows various colors. A bit odd to have the centerspeaker 3 feet of the center when you are sitting att a distance of 15 feet.

Well,

In general Mr widget is solid information...

In Fact, the driver is affected the TV tube...
I have a couple old TV in relative close of my big 2231 15" LF. and no problem after 2 feets before the magnet is discernable on my TV

---But the Articos is equiped with the finest tube phillips : really sensitive system...

---the shape of the tv expose maybe thin or no farrad cage inside... for this reason probably the tube is more sensitive and more exposed at electro-magnetic field.

If you have a demagnetiser head-tape recorder, you just demagnetise your tube and shoot arround the driver cage for " maybe " reduce magnet inter-action...

good luck.

Jean.

[Roddyama]

Now I have bought a pair of 2441 for the center and they do affect the CRT very much.
Bengt

Check to be sure there are no cracks in the housing (outer magnet structure) of the 2441's.

[toddalin]

My center channel includes two 130As, an LE175, and an 075. The cabinet also served as a stand for my 45" Mitsubishi rear projection CRT. From my prior cabinet that the TV sat on (one 130A and LE175), I knew there would be some stray magnetic effects. Ergo, I mounted the components as low as possible in the cabinet (edge of the woofer frames are 7" below the top), and this still affected the picture quality slightly. At a foot or more there was no discernable interference.

Ultimately the Mit was replaced with an LCOS front projector and a Stewart screen now sits on the cabinet on a custom-made stand. As you would imagine, the magnets have NO discernable effect on the projector's light beam.;)

[Don McRitchie]

It is the physical design. The alnico magnet is placed in the center of the VC and the return casting completes the circuit. I doubt that Mr. Lansing cared about shielding, but rather wanted to design the most efficient motor with as little flux loss as possible.

I tend to agree, but it is interesting that even the 1945 JSMPE article by Jim Lansing on his new Altec 604 design describes one of that speaker's benefits being its shielding when used with CRT's. Since this was before the widespread consumer adoption of TV, I'm guessing it was in reference to military CRT devices like radar displays. Altec was a major military electronics contractor at the time.

[edgewound]

I just tried a little experiment a minute ago. I held a 2420 (not 2441)alnico driver next to my Philips 17" CRT computer monitor and noticed the following: The most stray flux field radiates from the loading cap side of the driver, and it's alot. you can actually see the flux field in the CRT screen when held infront of the glass. The stray field looks to be signifcantly less when the 2420 is rotated 90 degrees, but still enough to mess with the color....so I'm sure the 2440/41 would cause much more disturbance to the screen. You could fabricate a Mu-metal case to shield the driver..do a Google search for Mu-metal.

So..the alnico drivers do have enough stray field when VERY close to the CRT to upset the color/picture...even when off to the side or top/bottom

[paragon]

A distance of 6-8 " at the side (monitor) is enough.