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-   -   Minimum Bending Radius for Optical Audio Cable (http://www.avsforum.com/forum/19-dedicated-theater-design-construction/1387724-minimum-bending-radius-optical-audio-cable.html)

RamKat 01-16-2012 06:08 PM

Hi, I would like to route a 25' monoprice 8mm toslink audio cable through some walls in my basement. The ends of the cable will be terminated inside keystone toslink couplers that will be mounted in two wall plates. My question is, will the 4 inches behind the wallplate be enough to accommodate the required 90 degrees bend and the coupler/connector without attenuating the signal below the required levels. The routing in the wall will also require a couple of 90 degree bends. (the assumption is that there will be some signal loss in any 90 degrees bend) Is there some spec available that I could refer to (I could not find anything on the monoprice site)

jparr 01-16-2012 06:11 PM

Quote:
Originally Posted by RamKat View Post

Hi, I would like to route a 25' monoprice 8mm toslink audio cable through some walls wall in my basement. The ends of the cable will be terminated inside keystone toslink couplers that will be mounted in two wall plates. My question is, will the 4 inches behind the wall be enough to accommodate the required 90 degrees bends and the coupler/connector without attenuating the signal below the required levels. (the assumption is that there will be some signal loss in any 90 degrees bend) Is there some spec available that I could refer to (I could not find anything on the monoprice site)

That should be fine. Fiber handles a lot more abose than people think. You can test it by placing a strong flashlight up against one end and looking for light at the other.

gregzoll 01-16-2012 06:11 PM

90 degree bends for fiber is bad. Even with regular copper wire, 90 degree bends is bad. Fiber needs a long sweeping turn, not sharp. Even with copper, it should be a sweeping turn, so that the wires do not break inside the jacket.

jparr 01-16-2012 06:32 PM

Quote:
Originally Posted by gregzoll View Post

90 degree bends for fiber is bad. Even with regular copper wire, 90 degree bends is bad. Fiber needs a long sweeping turn, not sharp. Even with copper, it should be a sweeping turn, so that the wires do not break inside the jacket.

Idealy a sweeping bend is best, but certainly not required. In fact, when testing fiber the light meters require the fiber test lead to be wrapped around a drum slightly smaller than a wine cork. That is a bend radius of only a few mm.

http://www.aflglobal.com/Products/Te...-Test-Kit.aspx

RamKat 01-16-2012 06:33 PM

Quote:
Originally Posted by gregzoll View Post

90 degree bends for fiber is bad. Even with regular copper wire, 90 degree bends is bad. Fiber needs a long sweeping turn, not sharp. Even with copper, it should be a sweeping turn, so that the wires do not break inside the jacket.

Yes, the idea is to have a sweeping bend, not a sharp corner, however the direction of the cable has to turn by 90 degrees and I am looking for the minimum radius of this sweeping bend. The problem is that the 4 inch wall does not allow too much of a sweep when feeding into the toslink adapter. As an analogy. There is a similar issue when hooking RG-6 coax to a wall plate where a rule of thumb is to keep the bending radius above 6 times the cable diameter.

RamKat 01-16-2012 06:33 PM

Quote:
Originally Posted by jparr View Post

That should be fine. Fiber handles a lot more abose than people think. You can test it by placing a strong flashlight up against one end and looking for light at the other.

Thanks, that is a good idea.

Colm 01-16-2012 08:45 PM

The issue with bend radius for fiber is not when damage will occur. It is when internal reflections will cause a significant drop in signal. I have seen TOSLink cables with a specified minimum bend radius of 1" with less that .5dB loss. You are probably good to go, but you will have to check with the manufacturer of your cable to be sure.

gregzoll 01-17-2012 05:34 AM

Quote:
Originally Posted by RamKat View Post

Yes, the idea is to have a sweeping bend, not a sharp corner, however the direction of the cable has to turn by 90 degrees and I am looking for the minimum radius of this sweeping bend. The problem is that the 4 inch wall does not allow too much of a sweep when feeding into the toslink adapter. As an analogy. There is a similar issue when hooking RG-6 coax to a wall plate where a rule of thumb is to keep the bending radius above 6 times the cable diameter.

You should still be able to get a sweeping turn going up into the wall, from where it enters, or use a wall plate, with a right angle 90 attached on the back. http://search.yahoo.com/search;_ylt=...r=toslink%2090

RamKat 01-17-2012 03:38 PM

Quote:
Originally Posted by gregzoll View Post

You should still be able to get a sweeping turn going up into the wall, from where it enters, or use a wall plate, with a right angle 90 attached on the back. http://search.yahoo.com/search;_ylt=...r=toslink%2090

Thanks gregzoll - this is just what I have been looking for!

jparr 01-17-2012 04:19 PM

Quote:
Originally Posted by RamKat View Post

Thanks gregzoll - this is just what I have been looking for!

The extra connector losses will be higher than any loss from the bend. Either should be fine though.

RamKat 01-26-2012 05:40 PM

Quote:
Originally Posted by jparr View Post

The extra connector losses will be higher than any loss from the bend.

Yup, I have proven that. Received the cable earlier tonight and did some tests outside the wall with my current TV/ AV receiver setup. Bending the cable (on both ends) to allow it to fit inside a 4 inch wall results in a working setup, adding the 90 degrees couplers with straight cables does not work (even though I can see the red light at the other end)


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