Axiom Home Page Forums General Discussion Technical Questions EP500 Magnetic Interference

Aloha. Wondering if any owners of direct-view CRT's have experienced interference from the EP500 subwoofer? I use the SONY KD34XBR970, and have experienced bending of both horizontal and vertical lines from my sub which is 10' away but directly off to the right side. I've pretty much concluded that the sub is the root issue, as I can see interference when viewing the OSD from my Outlaw 990 pre/pro and the sub kicks in. Also, I've had the service guy here twice now, and each time the line bending returns in the direction of the sub (down and to the right).

The driver is not magnetically shielded so you'll need to move the sub away from any CRT display.

Thanks, I'm guessing you mean further away, and that's kind of what I'm trying to poll here. How far away are other owners of larger CRT's finding they need to put the sub...?

My EP500 is only about 4' - 5' away from my 32" Sony CRT and I have no visible distortion. Here's how they are arranged.

When I was tweaking the location for the EP600, I had it within 2ft of my 27" CRT Sony, with no problem. And with the drivers location in the cabinet being so high, it was RIGHT beside the picture tube.

In re-reading your post, I have a few questions.

Are you saying that you can only see the bending when you have the OSD on and the sub is running? Does the bending change with the sound emitted?

If it was a magnet issue, the bending would be there constantly, regardless of what was audibly playing, or visually on the screen. Usually it is accompanied by discoloration as well. (Even with the sub OFF)

Shawn makes a good point.

Are you certain that the vibrations of the sub playing are not just wiggling a video cable connection, or even a loose internal connection in the pre-amp?

Thanks for all the diagnostic help. I'll be more specific: Line bending is noticeable on the tv with the cable input when viewing the "Guide" function or "Program Information" overlay from the DVR box. It is not noticeable within the underlying video. The same bending can be seen with DVD input when using callibration screens from Avia, but I know for a fact that the service guy did not adjust this input. So, I'm left wondering if the cable input just needs further adjustment, or is something causing the adjustment to change over time, with the sub being the most likely source. I've read over at AVS that owners of this tv have also experienced this line bending problem, which in some cases has been corrected via the service menu and in other cases required magnets to adjust the yolk or some other technical components. As for the interference, I have to date only seen it with the OSD input from my Outlaw 990, where the screen will show obvious distortion similar to when you vacuumed too close to older tv's - in this case when the sub kicks in. I have not seen this distortion when other video inputs are playing, but I'll pay closer attention as I try to diagnose further. The Outlaw connection to the sub is with an unbalanced new cable from BlueJeans - no obvious physical defects. At least it's heartening to hear that several of you have placed the sub very close to your CRT's without incident. I'm going to have the service guy come again, and adjust the cable and dvd inputs further, and confirm with a good source like Avia. Hopefully then I'll be better able to determine if there is drift over time. As for the interference seen from the Outlaw OSD, it's not so much a viewing problem (the osd is only for setup changes), but I would like to diagnose if there is a problem with either the cable or pre/pro. Again, thanks for all your help.

Woah... how did you NOT shake the tree off the sub? I'm sure a few ornaments came close to rattling off!

OK. So, the distortion you see when the sub kicks in, is definitly a separate problem from the bending.

I *think* I can confidently say that the bending is NOT the subs fault, but an issue with the TV/tube itself. At 10' away, the sub can't magnetically affect the TV. As a test, take a small magnet and bring it close (not too close) to the tube. Notice how the image bends and discolors? Notice when you pull the magnet away it goes back to normal?

Regarding the distortion when the sub "kicks" - This is either a loose connection or cold solder joint in the video path of that particular input. (Either in the cable itself, or on one of the circuit boards)

Thanks again for the help. Unfortunately, looks like you're on the mark real80sman. The line bending will hopefully turn out to be an issue for fix via the tv's service menu. Sadly, the issue with the video distortion is turning out to be problematic. Based upon your feedback, I tried video switching for the first time, and the distortion was severe, again when the sub kicked in. I tried switching my sub cable, but the distortion is caused using either balanced or coaxial connections, and also occurs when I switch the connection to the tv between composite and component. Have contacted Outlaw to see how to proceed, as it does seem that therein lies the issue, rather than with the EP500.

Hi. My EP500 is right next to my Sony 32XBR CRT, approximately 1.5 ft to the lower righthand corner. I have never noticed any interference.

Thanks for the feedback maphiker. Yes, it appears that I was confusing two separate problems I'm experiencing in my system. The line bending appears to be a calibration issue with the tv itself - whether or not something is causing drift over time is unclear, but I'm now confident that the sub has been far enough away to not be the root cause. I had assumed that it might be as I have also experienced noticeable distortion of the video picture on my crt when the sub kicks in, and having ruled out cable issues, it appears to be a problem with my outlaw pre/pro.

Hi,

Real80sman is correct. It would be impossible for the EP500 at that distance to cause magnetic interference to a CRT set, because the inverse square ratio law applies. All this means is that when you start moving a source of magnetic interference away from the CRT set, the magnetic field dissipates extremely rapidly.

In all my experience with large unshielded floorstanding speakers and subwoofers close to a CRT, a separation of 2 to 3 feet from the speaker or subwoofer and the CRT set completely removes the interference.

I also have a gut feeling that there may be a ground-loop issue operating between the Outlaw, the Sony CRT, your cable-TV input and the subwoofer.

Have you tried using a ground-isolation transformer between the cable input and your set-top box? Try disconnecting your cable-TV input from the box and see if the issue with the subwoofer disappears. . .

Regards,

Thanks for the suggestion Alan. Will try that after work today. Would this still explain the distortion seen with other inputs, such as my dvd?

Yes, because if there is a low-level ground-loop issue, it will operate between any interconnected components, whether or not they are powered on or off. The "ground loop" voltage differential is conducted through the shield connection of the incoming RF cable from the cable-TV supplier, the outer shield of any RCA cables, the chassis grounds of the TV, the AV receiver, DVD player, subwoofer, etc. and your ground connection of the house wiring, to which every component is also connected through their AC power cords.

Ground loops are frustrating and difficult to track down and are pervasive in their effects on audio and video performance. But all such grounding issues can be resolved with persistence and/or isolation transformers.

Thanks Alan. Looking forward to checking it out after work today.

Alan, you're the Man! Unplugging all the cable tv connections and power didn't solve the issue, but plugging the sub into the same surge protector as the tv and other a/v components did. The sub was originally on the same circuit but a different outlet and surge protector. So the question now, given the sub's power cord length, is whether there is a method of isolating this voltage differential so that I can again move the sub further away if better frequency response dictates. I'm not familiar with the isolation transformer electronics - is there a type that can be put in the path of either the coax or balanced cable that might do the trick?

Mark, there're isolation transformers that'll do the job, but the simpler solution would appear to be extending the sub power cord(the EP500 cord is impressively thick, but it's unnecessary for the extension to match it; common cords have more than enough capacity).

Awesome, I didn't realize that was an acceptable solution. Thanks so much for everybody's help - was so glad to solve the issue I cranked the Cream DVD to insane levels and it was great to watch and hear at the same time. Aloha.

Just 'cause I'm paranoid, and I've seen burned up extension cords, I wouldn't use one of those little 18 gauge cords. 16 or better!