Sheilding requirements for a tube TV.

[Neandertal]

I will obtain a new (or used) center speaker and wish to use my 4 Heresy II's as the theater fronts and rears. Add to the setup a new sub-amp and I think I will have caught up to the year 2002. I would love to find an Academy for the center but will most likely find something easier to obtain. On the premise that one should always use the best possible speaker as the center...what can be done about the Heresy II and shielding problems with tube TVs? Can a Heresy II be shielded? How far away from a tube TV should a Heresy be kept? Will the new generation of HDTVs be effected by an unshielded Heresy in close contact?

[soundog]

I'd look for an older Heresy with Alnico magnet drivers which will provide the shielding required. I'll leave the discription of how to ID the right one to those more familiar with the history of this model.

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Soundog's HT Systems

[Ray Garrison]

Also note that different brands and models of direct view TeeVees (the kind with a picture tube) vary dramatically in their sensitivity to external magnetic fields.

At my house, I have an older Toshiba 35" TV (circa 1993) in the listening room, my wife has a 27" Mitsubishi, and my daughter has a 27" Sharp. The Mitsu and the Sharp are pretty much unaffected by speaker magnets as long as the speakers are at least 6" or so away from the TV. The Toshiba, on the other hand, is SOOOOOO sensitive to this magnetic interference that I had trouble find a location IN THE SAME HALF OF THE ROOM where my REL subwoofer wouldn't really screw up the picture.

It might be informative to take some speaker (ANY non-shielded speaker) and wave it around in front of, beside and above your TV, and see how much it affects the picture. If your set turns out to be quite sensitive to the magents, sheilding the set or the speaker "after the fact" by using Mu metal or something is (a) not always terribly effective, and ( will cost a large pile of $$$.

Soundog - I knew the Neodymium magnets, like Klipsch used in the Epic series, are self-shielding because they are so small they fit within the voice coil, which provides the shielding, but what is there about the Alnico magnets that makes them self-shielding?

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Music is art

Audio is engineering

Ray's Music System

[Neandertal]

Thanks for your responses.

I currently have a 27" Magnavox TV (about 5 years old) and when I attempted to put one of the Heresy II's within 3' of it the whole screen took on a very green tinge. So much for a Heresy center channel in my current setup. I will be moving soon and I plan on a new TV and expect it to be HDTV and in the 36"+ range. With a new A/V amp, new TV, and 6.1 DVD's I will absolutly have to find a good center. I am hoping a Heresy will be kind to the new TV I obtain and not force me into tracking down an Acadamy or using another center speaker that is not as matched to the Heresy II's.

[Michael Greenway]

My new to me KLF-30's caused a green tinge on one side of my Sony 27" Vega TV. I placed the KLF's in same place of my Heresy's and one speaker was at most about 6" from entertainment center. The tv was not centered in cabinet and if I tried to move speaker farther away it blocked hallway. Anyway I was toast if I could not make it work without a major re-arrangement of living room. I cut a piece of 14 guage steel the size of the side wall of tv enclosure, placed next to tv, and problem went away. This is just a temporary fix because the wife and I are house hunting and she has very high on her list of priorities a HT/listening room for me and her a formal living and dining room.

I bet MY room gets more use than hers!

[WMcD]

The factory might be of some help.

If your wed to a tube tv and the factory is no help . . . maybe a bucking magnet could be used on the woofer, which might be the biggest problem. A magnet from a similar woofer could be the ticket. But I'm guessing here.

I believe rear projection TV's have fewer problems because the tubes are in the base and people put the speaker on top. So there is several feet of separation built in to the geometry..

Gil

[soundog]

Ray-

You're the engineer, so correct me if I'm wrong but I beleive the older Klipsch speakers with horns with Alnico magnets are constructed in such a way so that the magnets are shielded. Something to do with the Alnico magnet being positioned inside the driver in such a way that the magnetic field is focused resulting in a sheilding effect. I know you can put a TV on top of an old LaScala with no effect on the picture.

Found this quote from a post by Tom Brennan who understands these things far better than I do:

"These (old speakers) use an Alnico slug magnet inside the driver, the iron return structure that forms the body of the driver focuses the magnetic field into the gap area and the result is a shielded driver (though the shielding was not the intent), a paperclip won't stick to one of these things". He was speaking of old Altec and JBL horns but I think this applies to the Klipsch (Atlas & EV) speakers also.

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Soundog's HT Systems

This message has been edited by soundog on 02-17-2002 at 08:44 AM

[Malcolm]

Bucking magnets should be available from Klipsch to minimize your problem. Reconvergence of the TV should help also. Any direct view (tube type TV) may be affected, HDTV capable or not. Rear projection sets are less vulnerable. Newest technology like RCA's LCOS based sets are not vulnerable but currently have their own problems.

Heresy for a center channel may not be a good choice to go with your Heresy IIs. It will have a different tonal quality in the midrange which you may or may not find objectionable as sound pans around the front speakers. Even the last of the original Heresys sound different than the earlier years. I think your best bet might be a KLF-C7, KV-4 or Academy. KLF-C7s are easy to find.

[Neandertal]

Thanks for the input so far. Malcolm; as far as the Heresy as a center channel... I got lazy and stopped using the II's at the end of each Heresy when I typed. Yes, I will stay with the best voice match which will mean a Heresy II or the rare (and nearly extinct) Academy.

Learning more about "bucking" magnets. Which of the Heresy II's drivers (mid or woofer) pulls the TV picture so bad? Can several small (1" donut Radio Shack) magnets work in combination to "shield" the drivers. Sounds like a Hersy II with proper bucking magnets would and will be my best choice. Anyone have an "orphan" Hersesy II needing a new home? I am good at cabinetry and would love to get ahold of the components to a Heresy II and build my own 'center'.

Thanks.

[Malcolm]

The speaker that generates the largest magnetic field at your TV is the biggest culprit. It depends on the size of the magnet, the shape of the magnetic field, and the distance from the TV. But it is usually the woofer, mainly because it has the largest magnet by far.

Don't know if you can do the job with the Radio Shack magnets. The best way would be to use the appropriate bucking magnets from Klipsch if they are available. As far as I remember, the parts list that used to be on this site listed bucking magnets for the woofer, squawker and tweeter for the Heresy II. You can find out if they are available by calling Klipsch tech support. I have seen bucking magnets advertised by other dealers that specialized in DIY speakers but don't remember which ones. They are just donut magnets that you glue, appropriately oriented, to the back of the magnet on the speaker. The size of the bucking magnet will depend on the size of the magnet on the speaker.

Your Heresy II center channel idea is interesting. Let us know what you are doing when you do it. Like you, I am going to build a Heresy center channel speaker when I get the time. I am going to use two 16 ohm CTS 10" woofers of similar vintage to the other components to get that center channel form factor.