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Audio Distribution

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premkumar9

Member
Hi,
I want to take the Audio O/P from a TV receiver and distribute it to different points in a hall. At each point there has to be separate volume control. The immediate solution came to my mind is to take the Audio O/P through a cable and use standard speaker system with amplifier (used along with PCs) at each point.
Here my doubts are
- What is the source impedance of the audio source from TV? is it 600 Ω
-What cable to be used? 600 Ω audio cable?
- What is the normal input impedance of the PC speaker system? is it 600 Ω.
- Should I use an audio distribution amplifier to give separate output for each speaker system.
-Or can I use passive tap off?
 

Nigel Goodwin

Super Moderator
Most Helpful Member
Only professional audio systems use 600 ohm feeds, and not really that much of those - you don't usually use impedance matching in audio.

The audio line output of a TV is a lowish impedance, probably a couple of kilo-ohms?, if you're using PC amplified speakers you need to check (or measure) their input impedance, as they are designed to be fed from a headphone output. Assuming it's sensibly high (10K or greater), you should be able to just tap off the TV using a resistor (say 5K) to each one.
 

premkumar9

Member
Only professional audio systems use 600 ohm feeds, and not really that much of those - you don't usually use impedance matching in audio.

The audio line output of a TV is a lowish impedance, probably a couple of kilo-ohms?, if you're using PC amplified speakers you need to check (or measure) their input impedance, as they are designed to be fed from a headphone output. Assuming it's sensibly high (10K or greater), you should be able to just tap off the TV using a resistor (say 5K) to each one.
Can these source and amplifier input impedance be measured with a multimeter OR multimeter reading may not give the correct value?
 

audioguru

Well-Known Member
Most Helpful Member
A multimeter measures DC resistance. Impedance is AC resistance and the amplifier probably has an input capacitor that blocks the DC from your multimeter but passes AC.
 

premkumar9

Member
A multimeter measures DC resistance. Impedance is AC resistance and the amplifier probably has an input capacitor that blocks the DC from your multimeter but passes AC.
So the practical method is to make connections and see the signal levels with an oscilloscope. Right?
 

Externet

Active Member
Hi,
I want to take the Audio O/P from a TV receiver and distribute it to different points in a hall. At each point there has to be separate volume control.
What will you feed that audio signal to? Speakers; recording inputs; amplifier inputs?

The immediate solution came to my mind is to take the Audio O/P through a cable and use standard speaker system with amplifier (used along with PCs) at each point.
Here my doubts are
- What is the source impedance of the audio source from TV? is it 600 Ω
From its earphone jack probably around 200 to 600 Ohms.
From its speaker probably 4 to 16 Ohms

-What cable to be used? 600 Ω audio cable?
Answer the first one

- What is the normal input impedance of the PC speaker system? is it 600 Ω.
PC speaker system? What is that ?. Are you planning to use PC speakers or PC amplified speakers at the 'different points of the hall' ?
Will that be stereo ?

- Should I use an audio distribution amplifier to give separate output for each speaker system.
Depends on how many and how loud you want them and how powerful the TV speaker amplifier is.

Miguel
 

premkumar9

Member
What will you feed that audio signal to? Speakers; recording inputs; amplifier inputs?



From its earphone jack probably around 200 to 600 Ohms.
From its speaker probably 4 to 16 Ohms



Answer the first one



PC speaker system? What is that ?. Are you planning to use PC speakers or PC amplified speakers at the 'different points of the hall' ?
Will that be stereo ?



Depends on how many and how loud you want them and how powerful the TV speaker amplifier is.

Miguel
1- Amplifier
2- from earphone
3-External speakers with amplifier normally used with PC. provision for stereo play back to be there.
 

Externet

Active Member
You may use two conductor + shield cable similar to Belden 8451 for L, R, gnd; from either the TV headphone jack or speakers outputs, and probably not from the TV L, R line outputs ---> feeding in parallel to several amplified PC speakers or to a distribution amplifier inputs.
Those amplified speakers should already have the volume control you want.

PC amplified speakers may have any input impedance the manufacturer decided to design, probably around 10K Ohm

Miguel
 

premkumar9

Member
You may use two conductor + shield cable similar to Belden 8451 for L, R, gnd; from either the TV headphone jack or speakers outputs, and probably not from the TV L, R line outputs ---> feeding in parallel to several amplified PC speakers or to a distribution amplifier inputs.
Those amplified speakers should already have the volume control you want.

PC amplified speakers may have any input impedance the manufacturer decided to design, probably around 10K Ohm

Miguel
Normally what is the impedance of head phones? Just to know the possibility of directly plugging in headphones in the place of PC Amplifiers if required.
 

premkumar9

Member
You may use two conductor + shield cable similar to Belden 8451 for L, R, gnd; from either the TV headphone jack or speakers outputs, and probably not from the TV L, R line outputs ---> feeding in parallel to several amplified PC speakers or to a distribution amplifier inputs.
Those amplified speakers should already have the volume control you want.

PC amplified speakers may have any input impedance the manufacturer decided to design, probably around 10K Ohm

Miguel
So what I plan is
- take out audio output from the AV output of TV (which may be a high impedance source).
- Give it to a distribution amplifier (which has to give a low o/p impedance)
- Take the signal to different locations (parallel tap off.)
- Sockets will be provided at these points where either the amplifier or head phone can be plugged in.
The above is OK? For your suggestions.
 

Mikebits

Well-Known Member
To feed the stereo input to a mono amplifier, can I connect the two inputs together and give?
Then you just have mono anyways. Also not a good idea to have to driving devices feed into each other.
 

premkumar9

Member
As long as they are line level signals it's pefectly fine, they are designed to be used like that - but NEVER do it with speaker outputs, as it's going to kill the amp.
So you mean L and R signals from high impedance sources can be connected together while from low impedance higher power sources should not be connected together. Right?
 

Nigel Goodwin

Super Moderator
Most Helpful Member
So you mean L and R signals from high impedance sources can be connected together while from low impedance higher power sources should not be connected together. Right?
Pretty well, 'high' impedance sources feed their output via a resistor, so joining two together makes a simple mixer using the two output resistors.

For example, a stereo keyboard - the line outputs will be fed from an opamp, but these will feed the socket via a series resistor (usually a few kilo-ohms), this is to prevent damage to the opamp should the output be shorted to ground.
 

Externet

Active Member
Line output level is not varied by the volume control and its impedance is typically 10K; much higher than earphone output.
Earphone output is typically 200 to 600 Ohms output impedance and its amplitude varies by the volume control
 
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