How to share one Stereo Input with several Amplifiers which would feed their own mono speakers.

Irving

Joined Jan 30, 2016
4,047
@BobTPH
- it seems like a good plan, except it would require providing 5v power supplies to each speaker in the ceiling (I don't want to do anything to the walls). Plus, if the amps are supposed to be attached to each speaker, then the input signal has to be traveling from the server room down to each room (diff. length wires, interferences or any other mismatch issues that I have no idea about). Perhaps there are products (perhaps headphone slitter boxes), which might be helpful in distributing the input signal in a balanced fashion to each room.
I think @BobTPH was advocating those amps as a cheaper, less powerful, version of what I proposed. They certainly would work but might be limiting on output level. On the + side they only need 5v so a much smaller power supply could be used. They are stereo amps, but whether the two channels could be paralleled to give more output.... needs investigating.
 

Thread Starter

deepmagenta

Joined Jul 26, 2019
73
I think @BobTPH was advocating those amps as a cheaper, less powerful, version of what I proposed. They certainly would work but might be limiting on output level. On the + side they only need 5v so a much smaller power supply could be used. They are stereo amps, but whether the two channels could be paralleled to give more output.... needs investigating.
@Irving : Some thing else just came to my mind, as regards amp input management and the required number of amps; what about dumping all the classical music pieces we play (about 70 of them in a loop), into a Digital Audio Editor such as Audacity/Auditon/Reaper etc. and convert them to Mono Tracks.
This way L and R channels from the input source will be the same signal (mono). So, if I use 4 Stereo-Amps, instead of 8 Mono-Amps, I will end up with 4-Left channles (mono) and 4-Right channels(mono) to be directed to 8 rooms. Does it make sense to you
 

BobaMosfet

Joined Jul 1, 2009
2,123
Hi all,
We have this Stereo Sound system which plays music in an office environment. With 8 rooms. In each room there is one 4 Ohm speaker. It is not working properly (long story).
What I need is as follows:
1- One Stereo Audio source (cell phone / SD card etc) shared with a bunch of (similar) amplifiers inside a box ( I see all sorts of Chines products available which I have purchased some already).
2- Each speaker in each room should get a mono signal.
3- Each speaker has to have its own volume control on amplifier-box (sitting in Server Room ), so that the level of sound in each room can be controlled independently from the server room.

What is the best practice to implement this? What are the potential issues:
- in sharing the same input for all those amps?
- in sharing the same power supply for all those amps
- in converting stereo signal, coming out of each amp, into mono signal.

I would appreciate any input on this. Naturally if there is a totally different approach to this, I would love to hear that too.
Cheers
Something like this might be more suited:

1594920836114.png

They work GREAT. Bluetooth.
 

MrChips

Joined Oct 2, 2009
31,073
Here is my two cents worth.

As already posted, the traditional way to install a PA (public address) sound system is with 70V transformers.

Judging that you want to keep this as simple as possible, the first attempt would be to wire up volume controllers and speakers directly to the output of the amplifier. The first consideration would be to install the highest impedance loudspeaker you can find. Unfortunately, you already have loudspeakers that are 4Ω each. That is too bad.

The next step is to match the load to the amplifier output. Eight 4Ω speakers in parallel gives 0.5Ω which is not good for the amplifier. Two parallel strings of four 4Ω speakers in series gives 8Ω. Four parallel strings of two speakers in series is 2Ω.
Hence the next step is to find out the range of load impedances that the amplifier can handle,

Finally comes the issue of level control. If you adjust one speaker volume level how much would this affect the volume at the others? Since your sound levels are low and they are adjusted once and left alone perhaps you can accept this drawback.

To do this you can simply put 10-50Ω 1W wire-wound pots in series with each speaker. This will give you some control on the volume level but you will have to put up with the other speakers having a lower level if you turn up the level at one speaker.

In summary, the simple solution is to put 10-50Ω pots in series with each speaker.
Set all pots to the lowest sound level. Adjust the amplifier volume until you get the quietest desired sound. Then adjust each room as desired. If the volume level drops in the other rooms you will have to adjust the amplifier level. It's a lot of running around but it could be a workable solution.
 

Thread Starter

deepmagenta

Joined Jul 26, 2019
73
Thank you @MrChips for taking the time to read prev. posts to see my requirement.
- What if I put each adjacent room ( because the are roughly at the same distance from the server room/amplifier), on a single Volume/amp, and make the speakers on those 2 room in series, hence 8 Ohm impedance. This way I would control the sound level of both rooms with one pentameter, which is not ideal but very acceptable in practice?
- in responce to @Irving above, I talked about making the music mono etc. If you have time please read that and let me know of you opinion ..... cheers
 

MrChips

Joined Oct 2, 2009
31,073
Take a look at your amplifier. Most home systems are dual channel, LEFT + RIGHT.
Therefore you really have two channels. Many systems have a MONO/STEREO button. Even if you don't have a MONO option, very often the music content between the two channels are acceptable for background music. So now you have two channels with separate volume control (BALANCE). Split your circuits into two groups of four rooms. Distance to the rooms are not significant at this stage.
 

BobTPH

Joined Jun 5, 2013
9,263
@BobTPH
- it seems like a good plan, except it would require providing 5v power supplies to each speaker in the ceiling (I don't want to do anything to the walls). Plus, if the amps are supposed to be attached to each speaker, then the input signal has to be traveling from the server room down to each room (diff. length wires, interferences or any other mismatch issues that I have no idea about). Perhaps there are products (perhaps headphone slitter boxes), which might be helpful in distributing the input signal in a balanced fashion to each room.
What makes you think these amplifiers have to be where the speakers are? I was suggesting that you use them to do exactly what you said you wanted, placing the in the central location and wiring them to the existing in wall wiring.

Bob
 

Irving

Joined Jan 30, 2016
4,047
@Irving : Some thing else just came to my mind, as regards amp input management and the required number of amps; what about dumping all the classical music pieces we play (about 70 of them in a loop), into a Digital Audio Editor such as Audacity/Auditon/Reaper etc. and convert them to Mono Tracks.
This way L and R channels from the input source will be the same signal (mono). So, if I use 4 Stereo-Amps, instead of 8 Mono-Amps, I will end up with 4-Left channles (mono) and 4-Right channels(mono) to be directed to 8 rooms. Does it make sense to you
That would work, but its a bit a faff for you...

MrChips has a good point and its a relatively cheap solution if your amplifier is upto it (and you actually have an amplifier). The pots are around £4 each.
 
Unless you are running the signal wires very close to mains wiring, a simple screened , unbalanced wire will work perfectly well at the 6 metres that you mentioned. You would need a balanced system only on long signal cable runs. Also, you could have the power supplies in the server room and just run 1mm twin cable and a signal cable to each amp, that way you have the volume controls in each room at the amplifier.
 

Thread Starter

deepmagenta

Joined Jul 26, 2019
73
Take a look at your amplifier. Most home systems are dual channel, LEFT + RIGHT.
Therefore you really have two channels. Many systems have a MONO/STEREO button. Even if you don't have a MONO option, very often the music content between the two channels are acceptable for background music. So now you have two channels with separate volume control (BALANCE). Split your circuits into two groups of four rooms. Distance to the rooms are not significant at this stage.
Yes, I see your logic, but I have decided not to use the Philips mini system at all. I have several of those Chines amps that I ordered in anticipation of this project several weeks ago, which have arrived. As I mentioned in one of my previous replies, I don't mind grouping rooms in pairs (4 Groups of 2 rooms), but not 2 groups of 4 rooms. It is not flexible enough in individual volume control.
In summary, I think I will use either 8-amps in a box (each room with its own Pot) or 4-amps in a box (each pair of adjacent rooms controlled by one volume) in server room...
 

Thread Starter

deepmagenta

Joined Jul 26, 2019
73
Here is my two cents worth.

As already posted, the traditional way to install a PA (public address) sound system is with 70V transformers.

Judging that you want to keep this as simple as possible, the first attempt would be to wire up volume controllers and speakers directly to the output of the amplifier. The first consideration would be to install the highest impedance loudspeaker you can find. Unfortunately, you already have loudspeakers that are 4Ω each. That is too bad.

The next step is to match the load to the amplifier output. Eight 4Ω speakers in parallel gives 0.5Ω which is not good for the amplifier. Two parallel strings of four 4Ω speakers in series gives 8Ω. Four parallel strings of two speakers in series is 2Ω.
Hence the next step is to find out the range of load impedance that the amplifier can handle,

Finally comes the issue of level control. If you adjust one speaker volume level how much would this affect the volume at the others? Since your sound levels are low and they are adjusted once and left alone perhaps you can accept this drawback.

To do this you can simply put 10-50Ω 1W wire-wound pots in series with each speaker. This will give you some control on the volume level but you will have to put up with the other speakers having a lower level if you turn up the level at one speaker.

In summary, the simple solution is to put 10-50Ω pots in series with each speaker.
Set all pots to the lowest sound level. Adjust the amplifier volume until you get the quietest desired sound. Then adjust each room as desired. If the volume level drops in the other rooms you will have to adjust the amplifier level. It's a lot of running around but it could be a workable solution.
What is the advantage of "10-50Ω 1W wire-wound pots" in series with each speaker. Why is it supposed to be wire-wound, is it for a better frequency response?
 

BobTPH

Joined Jun 5, 2013
9,263
Using pots will cost more than the amplifier boards I suggested, waste power, and are not much easier to hook up.

Don’t see much advantage in that.

Despite the fact that HiFi equipment industry wants to sell us all 300W amplifiers for home use, 15W will produce volume levels that will damage your ears and have your neighbors banging on the walls.

For the level you want, 1W should be more than adequate.

Bob
 
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Irving

Joined Jan 30, 2016
4,047
Using pots will cost more than the amplifier boards I suggested, waste power, and are not much easier to hook up.

Don’t see much advantage in that.

Despite the fact that HiFi equipment industry wants to sell us all 300W amplifiers for home use, 15W will produce volume levels that will damage your ears and have your neighbors banging on the walls.

For the level you want, 1W should be more than adequate.

Bob
I agree, and going with the cheap ones is a no-brainer - if the end result is not loud enough/ not good enough quality, there's a relatively painless fallback to more powerful amps.
 

MrChips

Joined Oct 2, 2009
31,073
If the amplifiers you have already purchased are 2-channel amps, then you only need 4 amps for 8 speakers.
Drive each speaker separately. You don't need the series pot at the speaker.
 

Thread Starter

deepmagenta

Joined Jul 26, 2019
73
If the amplifiers you have already purchased are 2-channel amps, then you only need 4 amps for 8 speakers.
Drive each speaker separately. You don't need the series pot at the speaker.
Totally agree....thanks

I hope everybody sees this. I would like to thank all of you, helpful generous souls, with imparting your experties and wisdom in this project. This is the second time I have posted a question in here and have been immensely impressed with the quality of interactions. My first post was about trrning our rice cooker into a smarter one, using Arduino. Many people helped me and that project was done beautifully, and in the process I learned about electronics. We are using that rice cooker pretty much daily and enjoy its enhanced functionality, display, playing melodies etc. All About Circuits is from Heaven, but Heaven without people like you guys and girls, is just a parking lot. Thanks again, your chivalry is much appreciated.
 
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