connecting a tv audio 3.5mm audio out jack to 8 ohm speaker/s

Thread Starter

centroid

Joined Apr 21, 2018
3
I work in a hotel in Melbourne. We have phillips tvs in the rooms and there are remote speakers in the bath rooms. Sometimes there’s an extra speaker on the lounge room ceiling. There’s one room where the speaker is not working in the bathroom. There is no speaker on the lounge ceiling. On the wall in the bathroom there is a 100 ohm pot. I ‘m pretty sure the speaker is 8 ohm impedance. I did a measure with my ohm meter and it measured about 5.9ohm (ie/ purely resistive measure-I’m assuming that the impedance would then be about 8ohm)

first thing I checked was the outlet on the wall. I opened it and found the cable that goes to the pot in the bathroom not connected. so I thought Ha! this is the problem. I connected up this wire to the outlet, fitted it back on the wall but still no dice. the speaker in the bathroom did not work still.

measuring the ohms looking back from the tv I get about 10ohms with pot down low and about 100 ohms with pot up high. (this is comparable to other rooms that work). I’m not sure if the earthing matters as I think at the tv the tip pin is being used and the shield for the negative. and at the wall socket behind the tv it reverts to red and black travelling off to the pot in the bathroom. inside the cable from tv to wall socket two wires (looks like figure 8) are being used.

looking at my sony tv at home and putting a cable into audio out and then measuring between the tip and shield I get about 200ohms.

from memory at the hotel doing the same measurement I get 1kohm or more (maybe much more-again from memory-I’m at home)does anyone know what sort of ohms I should get looking back into the phillips tv?.

I was working with a specialist lighting tech and he said that “there should be a booster in the ceiling”, but I haven’t seen any booster regarding the output from the tv audio out. from what I have seen the tv audio out is directly driving the speaker/s







questions:

1/ could the issue be that I just have to select the audio out jack on this tv?

2/ could the audio out terminal be stuffed?

3/ does earthing/shielding matter or I just focus on the + and –

4/does polarity at the speaker matter?

5/ what should the electrical circuit look like if the one I present is incorrect?

6/does anyone have any other suggestions?
 

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wayneh

Joined Sep 9, 2010
16,155
I work in a hotel in Melbourne. We have phillips tvs in the rooms and there are remote speakers in the bath rooms. Sometimes there’s an extra speaker on the lounge room ceiling. There’s one room where the speaker is not working in the bathroom. There is no speaker on the lounge ceiling. On the wall in the bathroom there is a 100 ohm pot. I ‘m pretty sure the speaker is 8 ohm impedance. I did a measure with my ohm meter and it measured about 5.9ohm (ie/ purely resistive measure-I’m assuming that the impedance would then be about 8ohm)

first thing I checked was the outlet on the wall. I opened it and found the cable that goes to the pot in the bathroom not connected. so I thought Ha! this is the problem. I connected up this wire to the outlet, fitted it back on the wall but still no dice. the speaker in the bathroom did not work still.

measuring the ohms looking back from the tv I get about 10ohms with pot down low and about 100 ohms with pot up high. (this is comparable to other rooms that work). I’m not sure if the earthing matters as I think at the tv the tip pin is being used and the shield for the negative. and at the wall socket behind the tv it reverts to red and black travelling off to the pot in the bathroom. inside the cable from tv to wall socket two wires (looks like figure 8) are being used.

looking at my sony tv at home and putting a cable into audio out and then measuring between the tip and shield I get about 200ohms.

from memory at the hotel doing the same measurement I get 1kohm or more (maybe much more-again from memory-I’m at home)does anyone know what sort of ohms I should get looking back into the phillips tv?.

I was working with a specialist lighting tech and he said that “there should be a booster in the ceiling”, but I haven’t seen any booster regarding the output from the tv audio out. from what I have seen the tv audio out is directly driving the speaker/s







questions:

1/ could the issue be that I just have to select the audio out jack on this tv?

2/ could the audio out terminal be stuffed?

3/ does earthing/shielding matter or I just focus on the + and –

4/does polarity at the speaker matter?

5/ what should the electrical circuit look like if the one I present is incorrect?

6/does anyone have any other suggestions?
The owners manual for the TV can probably be found online and will describe the capabilities of the audio output and how to select it. I’m skeptical that it will drive an 8 ohm speaker load but I suppose some do. The output may only be line out.

Got any junk around? A speaker yanked out of an old radio or such could make for a very handy test device. You could check the TV output and the wiring at the pot to see where the signal is being lost.
 

Thread Starter

centroid

Joined Apr 21, 2018
3
The owners manual for the TV can probably be found online and will describe the capabilities of the audio output and how to select it. I’m skeptical that it will drive an 8 ohm speaker load but I suppose some do. The output may only be line out.

Got any junk around? A speaker yanked out of an old radio or such could make for a very handy test device. You could check the TV output and the wiring at the pot to see where the signal is being lost.
thanks, i will get a spare speaker at work and connect up a short 3.5m audio jack, plug it into the tv and see what happens. i will also check settings on the tv
 

Thread Starter

centroid

Joined Apr 21, 2018
3
The owners manual for the TV can probably be found online and will describe the capabilities of the audio output and how to select it. I’m skeptical that it will drive an 8 ohm speaker load but I suppose some do. The output may only be line out.

Got any junk around? A speaker yanked out of an old radio or such could make for a very handy test device. You could check the TV output and the wiring at the pot to see where the signal is being lost.
do i have to worry about polarity of an ac signal going to an 8 ohm speaker ?(i mean there is a + and - terminal on this speaker). i have swapped around the leads, making no difference. i mean does the ac signal ride on a dc "carrier" ?
 

BobTPH

Joined Jun 5, 2013
2,194
The polarity does not matter for a single speaker. It is there for multiple speaker systems to ensure they are in phase.

The audio signal is pure AC with no DC offset.

Bob
 
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