Residential home theatre

[infinity]

Semantic, really. Since most houses are fed from a single phase service, what's inside must be single phase, but it does have two different ungrounded leads. I'm poking at the sound techs that insist on "using only one phase" for their supply.

This is quite common when using three phase systems.

 

[mxslick]

This is quite common when using three phase systems.

Rob are you referring to the use of the term or the practice of wiring?

Like I said before, if the tech doesn't know how to properly wire his signal wiring then yes it is important to stay on the same phase or leg, whichever you prefer. It minimizes (but does NOT eliminate) possible noise issues. If the signal wiring is not done correctly, then you'll still get noise and hum.

I have wired literally hundreds of sound systems for cinemas and live performances and have always used ALL THREE of the phases (or BOTH LEGS of single phase) and have NEVER had hum or noise issues. It's all in how you connect the shields of the signal wiring to avoid noise problems. :grin:

At one of my current contract venues the company who installed the "smart classroom" A/V gear tied into my screening room system and created a bad hum in the left and right channels. (The system had been in place for 8 years before with no issues.)

My investigation has found that the shields of the audio lines are NOT connected at all!! They used (it's Belden 8723 2 pair cable) Red as +, Black as - and green(!) as the "shield".

I will be correcting the problem this week after a huge fight I had with the A/V department head (he would not allow me to fix the problem for the last 5 years!!) where I threatened to disconnect their system from mine if it wasn't fixed now.

Why the long delay? Because that other company was under obligation to fix it, and they still haven't done it.

 

[kwired]

Ok, so is a theater a room that is similar to those listed in 210.42(A)?

210.52(A)? I'd say so.

I think it is open to interpretation. There are some "dwellings" that are not really much different than a hotel. If this is a large mansion with separate areas that in themselves are not the typical dwelling areas I don't know if you have a dwelling anymore. You may have "dwelling units" within the entire structure. Building codes and how things are constructed may help determine this easier.

 

[infinity]

Rob are you referring to the use of the term or the practice of wiring?

Like I said before, if the tech doesn't know how to properly wire his signal wiring then yes it is important to stay on the same phase or leg, whichever you prefer. It minimizes (but does NOT eliminate) possible noise issues. If the signal wiring is not done correctly, then you'll still get noise and hum.

I have wired literally hundreds of sound systems for cinemas and live performances and have always used ALL THREE of the phases (or BOTH LEGS of single phase) and have NEVER had hum or noise issues. It's all in how you connect the shields of the signal wiring to avoid noise problems. :grin:

At one of my current contract venues the company who installed the "smart classroom" A/V gear tied into my screening room system and created a bad hum in the left and right channels. (The system had been in place for 8 years before with no issues.)

My investigation has found that the shields of the audio lines are NOT connected at all!! They used (it's Belden 8723 2 pair cable) Red as +, Black as - and green(!) as the "shield".

I will be correcting the problem this week after a huge fight I had with the A/V department head (he would not allow me to fix the problem for the last 5 years!!) where I threatened to disconnect their system from mine if it wasn't fixed now.

Why the long delay? Because that other company was under obligation to fix it, and they still haven't done it.

I recently spent 2 years building a new theater on Broadway and the audio consultant, who is an engineer, wanted all of the AV IG receptacle power on the same phase. 42 circuit panel with about ten circuits being used, all on the black phase. He has been an audio engineer for twenty years and insisted that it was necessary. Didn't really matter to me. I have no opinion as to whether or not it makes a difference.

 

[dbuckley]

There is no need (or indeed benefit) to having any or all of the supplies to an audio system on the same leg, phase or even the same transformer.

What does help enormously is a decent grounding arrangement, whereby all the grounds of all the outlets go back to one single point.

Unfortunately, many (most?) sound people dont understand this, but have noted that when everything does run off a single panel (like Rob's example above) then the audio system has a lower noise floor. Its not the legs or phases, its the grounding!!!

Electricians in general understand enough to be annoying in this situation - they believe that the leg / phase of supply makes nom difference (in which they are correct) but they also think a ground is a ground, and thats when the audio troubleshooter gets called, usually when the sockets at the back of an auditorium run off one panel and transformer, and the sockets on stage off a different panel and transformer, and there are whole volts between the ground pins of the socket at the back of house and the sockets on stage. Whole volts that appear across the audio wiring and cause mayhem.

it is much easier to explain to an electrician that what you want is all the recepticals off a single panel on a single phase (just like Rob's installation above) and then you get... common grounding, and thus a quiet installation. So Rob's audio consultant is wrong but for the right reasons...

 

[LawnGuyLandSparky]

The problems all relate to defective input cables and connectors. And when hundreds of cables are employed tracing the ones with bad shielding is next to impossible.

Just understand their handicap and deal with it.

 

[SAC]

The problems all relate to defective input cables and connectors. And when hundreds of cables are employed tracing the ones with bad shielding is next to impossible.

Just understand their handicap and deal with it.

Well, when you are being paid to "delight the customer", spending the extra bucks to make the system foolproof isn't viewed as a handicap. Why bother doing something like this (custom theatre room) if it isn't done "right"? If I had the luxury of something like this, the $$$ spent in the power distribution to reduce potential problems related to differential mode power supply noise would be the least of my concerns. Yeah, the other components should filter it - but why not just eliminate that concern? Putting the drops on the same phase like this in a home shouldn't push the service drop up a notch (can't get away with something like that in a commercial install) - if not, the $$$ are peanuts compared to the overall $$$ of the project.

 

[LarryFine]

I thought I already posted in here, but I guess I didn't.

In my HT, I have a typical 4-sp/8-ckt 120/240v sub-panel on a 50a 2p breaker and 6-3 NM from my main panel, and all wired as usual. I used all 15a tandem breakers and 14-2 for all circuits.

The distribution is as follows:

1A Future lighting (or etc.)
1B Future lighting (or etc.)
2A Unswitched electronics
2B Switched electronics
3A Sub-woofer amp receptacles
3B CRT projector receptacle
4A Stereo amp (main spkrs)
4B 5-ch amp (ctr, sides, rears)

By "switched" and "unswitched" electronics, the preamp/processor has 12v trigger outputs, one of which triggers a 4p contactor in the panel, which switches circuits 2B, 3A, 4A, and 4B.

I even have 120v in NM, speaker wires, and shielded cables for the sub amps, all fished in each wall-stud bay to supply the speakers with power, bi-wired mids and tweeters, and lows, respectively.

So, while the source electronics are all on one phase, the sub amps (and projector) are on the other, but, the entire system is dead quiet with no signal, and there is no video noise, either.

Maybe I'm just lucky, but I just wired as normal, I use good-quality audio and video cabling, and keep the power cords at right angles to the rest on the shelves, and bundled vertically.

Here are a couple of pix:

I'm expecting a question or two, so let 'er rip.

 

[kwired]

I thought I already posted in here, but I guess I didn't.

In my HT, I have a typical 4-sp/8-ckt 120/240v sub-panel on a 50a 2p breaker and 6-3 NM from my main panel, and all wired as usual. I used all 15a tandem breakers and 14-2 for all circuits.

The distribution is as follows:

1A Future lighting (or etc.)
1B Future lighting (or etc.)
2A Unswitched electronics
2B Switched electronics
3A Sub-woofer amp receptacles
3B CRT projector receptacle
4A Stereo amp (main spkrs)
4B 5-ch amp (ctr, sides, rears)

By "switched" and "unswitched" electronics, the preamp/processor has 12v trigger outputs, one of which triggers a 4p contactor in the panel, which switches circuits 2B, 3A, 4A, and 4B.

I even have 120v in NM, speaker wires, and shielded cables for the sub amps, all fished in each wall-stud bay to supply the speakers with power, bi-wired mids and tweeters, and lows, respectively.

So, while the source electronics are all on one phase, the sub amps (and projector) are on the other, but, the entire system is dead quiet with no signal, and there is no video noise, either.

Maybe I'm just lucky, but I just wired as normal, I use good-quality audio and video cabling, and keep the power cords at right angles to the rest on the shelves, and bundled vertically.

Here are a couple of pix:

I'm expecting a question or two, so let 'er rip.

I've seen old houses with less receptacles than this in the entire house

 

[dbuckley]

the entire system is dead quiet with no signal, and there is no video noise, either. ... Maybe I'm just lucky

You're not 'lucky', you've done it right, albeit possibly more by accident than design.

All your grounds go back to one bar, in the dedicated panel, and there are no other nasty loads on that ground bar injecting noise along that bar; the entire ground is single pointed, because of the run of #6 away from the main panel.

Nice.