custom home theatre/entertainment center

[BJ_M]

you can't shield a speaker.
'shielded' center channel speakers have a different type of magnet and a different magnet configuration than "normal" speakers.
there is no "shield" in the speaker's box or case
steel is magnetic and will not block or alter a magnetic field.
aluminum is not magnetic and will not block or alter a magnetic field.
(i've looked into this quite a bit already )

i'm sorry - but you are wrong -- it is not hard to shield speakers and ive had to do it 100's of times in some of our installations:


Conventional speakers incorporate both a permanent magnet and an AC magnetic field to produce sound. The field from the permanent magnet is present whether the speaker is active or not. The AC magnetic field is only present when the speaker is activated, and varies in frequency and strength with the pitch and volume of the sound produced. The magnetic field from the two sources can deflect the electron beam in a cathode ray tube monitor (TV) causing distortion of the image, sometimes called jitter (and possible damage to the equipment).

You will have to use magnetic shielding alloys to shield these magnetic fields and you have a choice of several methods. Keep in mind that with magnetic fields, you can either shield the source of the offending field, or shield the thing(s) that you wish to protect.
Note:Unlike the bucking magnet method, these shielding methods do not alter the sound quality of the speaker.

1] Method for maximum aesthetics

To achieve maximum aesthetics you will need to be able to open the speaker cabinet and get access to the back of each speaker. There, you will find a donut shaped magnet, proportional in size to the size of the speaker, over which you will place a cup shaped shield.

Because you will be placing the shielding material in close proximity to this strong magnetic field, you will have to take saturation into account. This means using at least 2 layers of shielding.

For the layers closest to the magnet, choose a high saturation material such as MagnetShield. This material has the ability to "absorb" the initial blast of the field without saturating and becoming useless, but it will only give a limited attenuation. It is very low cost, so 2 or 3 layers are practical.

The outermost layer should be a high permeability material such as Joint-Shield. This outer layer will "absorb" much of the field which has evaded the first layer and yield a very high degree of attenuation. Note that attenuation will be greatest close to the speaker magnet, where the field is strongest (most interfering) anyway.

MagnetShield and Joint-Shield are both offered in a convenient 4 inch wide strip. The material is thick enough to provide good shielding, but still can be cut with a scissors and shaped by hand. For especially strong magnets, you may need more than one layer of each material.

Here is how you do it: Inner layer

Wrap the MagnetShield around the speaker magnet (notice that it is attracted to the magnet) in a cylinder shape. Cut it so that you have about 1" of overlap at the seam. Use duct tape to tape the seam securely. Cut the material which extends backward at several locations so you can bend these "tabs" inward to form the "bottom of the cup" shape. Leave this layer in place.

Outer layerJoint-Shield is provided with a peel-and-stick adhesive on one side. Before removing the adhesive backing, cut and shape the material just like the first layer, but on top of the first layer. Remove the adhesive backing and press the second layer onto the first layer. You are done!

Just be careful not to disturb or allow the shield to touch the electrical contacts on the speaker.

2] The Quick and Easy Way (and Maximum Field Reduction!)

Flat Foil ShieldIf you need maximum field reduction, or cannot open the speaker cabinet, or you simply want to take the easy route, you can simply place flat magnetic shielding alloy between the speaker and the TV.

The magnetic fields at the side of the speaker magnet have different characteristics compared to at the back of the magnet, and different shielding materials are required. Take this into account when considering where your speakers will be positioned relative to the TV.

Shielding the side of the speaker:
Most times you can get away with one or two layers of Magnetic Shielding Foil. On each speaker, place the foil flat against the side of the speaker cabinet which faces the TV, or place it against the side of the TV. A good, inexpensive way to check for shield performance and the best position for the shield is to use a Pocket Magnetometer. You can get additional attenuation by using multiple layers of foil, especially if you use a spacer (such as cardboard) in between the layers. This may offer some aesthetic challenges, but you don't need much technical expertise.

Shielding the back of the speaker:
A high saturation material of significant dimensions such as 36"x15" MagnetShield Plate is required here. If your speakers cabinets are small, you can cut the 36"x15" sheet in half to get two 18"x15" pieces. Note: There will be a position somewhere between the back of the speaker magnet and the front of the TV which will yield "near perfect" shielding. Move either towards the speaker or towards the TV from this point and you will loose shielding effectiveness. Therefore be sure to check the position with a Pocket Magnetometer or digital DC Gaussmeter. Naturally, some situations may require shielding of both the back and the sides of the speaker cabinet.

3] The Third Alternative

You can always place the TV or monitor inside a shielded enclosure. This will protect the monitor from external fields produced by the speakers and any other sources.

where to get supplies:
http://www.lessemf.com/mag-shld.html

or other dealers pretty well everywhere (radio shack even carries some of this)

[Xylob the Destroyer]

fantastic!
these must be some (relatively) new products.
when I first purchased these speakers a few years ago, none of this was available (at least not to the "ordinary" consumer).

[BJ_M]

no -- we were doing this back in the 1970's

[Doramius]

sounds like 10 or 12 stranded with a braid. Just make sure it doesn't cause more resistance than your amp can handle.

[BJ_M]

amps cant handle low resistance (impedance) 9most of the time - some amps can run down to 1ohm just fine) , high resistance is not a issue - just power loss at that point

for short runs - even 18awg cable really works fine , 16 is really really common to wire whole home systems ...

[Doramius]

high resistance is not a issue - just power loss at that point

That's basically what I meant to say. You just don't get the sound coming out that you'd like.

for short runs - even 18awg cable really works fine , 16 is really really common to wire whole home systems ...

I agree! If you're running 10-12, that's some mighty big cable for what you're doing if it's over short distances. Even BOSE gives you a 16 wire for their speakers that's only <25' ft. long.

[Xylob the Destroyer]

one of the houses that we looked at on Sunday is very nice and the basement is totally unfinished and wide open.
if we decide on this one, the point becomes moot, as we will be building a custom home theatre in the basement
including in-wall speaker wiring and custom electrical -- at least 3 dedicated circuits for the electronics and another for lighting.
double-thick walls with sound-proofing/insulation
and of course an access room behind the electonics wall.

all of course dependant on which house we wind up buying.

[Doramius]

It's still worth finding out some of these tips. Also if it is unfinished, use any means necessary to wall fish lines from rooms upstairs and put in LAN, speaker, phone, & cable ports in each room. It's not that expensive and boosts the value of the house as more people are looking for fully wired homes like that. Basically run everything to a main controll area in the basement where you were going to have the back wall access to your entertainment system.

We were able to sell our last house for $5000 more because I had redone all of the rooms so they all had cable, LAN, & misc RCA connections. They all had phone jacks & cable already, but the dickhead who built the home daisy chained them. It's okay for code, but you lose signal the further away you get, and you don't have as much control over which ones you get to turn on or off. I basically ran lines for each room directly back to the master bedroom (because we don't have a basement). I put a main access panel in the Master closet. It has 2 coaxial cable/antennae in and 4 telephone in ports. It also has the phone, LAN, Cable, & 2 RCA ports for each room. I can set a router and modem in the closet and wire any room I want for internet & LAN. Also turn on or off phone in any room, or if I had multiple phone lines I can give each room their own phone line. I can wire it so my room plays a video and the TV in my son's room will show it. Or I can just run cable TV to all of the rooms. The RCA jacks are rarely used, but are there just in case I decide to wire something else. It had only cost me about $250-$300 to setup and several hours of personal labor. Worth it though.

[Xylob the Destroyer]

I like your line of thinking!
I had already planned on LAN, but the way you did yours rocks!
Where did you get the access panel?

[Doramius]

Home Depot. They have the nice wallplates that have the small square holes. You can pick and choose what modules you want in each room. The Plates I have are 6 holed. The top are LAN & Phone. The middle is Cable & blank. The bottom are the RCA ports. The main terminal in the bedroom is also from Home Depot, but is special ordered. I think you can get it from True Value & Lowes too. The main panel reminds me more of an electrical panel and works similarly. Very modular. Just pop out the plastic blanks of areas you're going to use. The input side has 12 blanks and the output side has 30. As you can see I used all the holes on the output side and only a few on the input side. I couldn't find the panel online anywhere, or I would have posted an actual picture. The Panel box is about 10"x10". You can get a larger one that's 10"x20". It has 70 outputs and 18 inputs.

Here's a picture that's close to the style of wall plate I used. Mine is a 6 hole module. The Main panel has the same holes in it. You just need to buy the # of modular pieces you want to use. It looks so much better than a patch panel too.