How to correctly hookup multiple Ceiling Speakers in a zone?

xbmcgotham

Novice Member
Hi,

Hope someone can advice me on the following.

Firstly, I am new to this stuff and are not very advance if it comes to certain tech jargon, but happy to learn. :)

I have different music zones in a house, with mono passive ceiling speakers of 8 ohm each, and are hooking these up to RaspberryPi's with HifiBerry's, where there are only max 2 of these ceiling speakers for a zone as the RaspberryPi's will not be able to operate more. The RaspberryPi's will be controlled with Max2Play/SqueezeBox software.

The challenge I am facing to find a simple and affordable way to do the following:

1. As mentioned above, the RaspberryPi/HifiBerry unit will not be able to connect more than two 8 ohm mono passive ceiling speakers. But some rooms will have 4 or 6 of these ceiling speakers. How would I connect 4 till 6 of these ceiling speakers in a affordable way to a RaspberryPi? Is it as simple as getting 1 small amplifier (with its own power supply) per 2 ceiling speakers and than connect all of these amplifiers to a RasperberyPi? Or Maybe buy a bigger amplifier that can power 4 till 6 of these speakers and if it connect to a RaspberryPi?
2. And how do I hook up these mono speakers to each speaker in a zone so that each ceiling speaker will output both left and right audio? As separate left and right output is not really working for ceiling speakers in a room where people are changing position/movement. How do you make this? How do I connect the audio cables to the ceiling speakers and a RaspberryPi or amplifier? I was told its normally done for this kind of setup commercially, but I can't find any manual on how to do this correctly. Maybe its to simple to write about it. :)

Hope someone has some experience/advise on this.

Thanks for any assistance!
 

Gavtech

Administrator
Commercial mutli speaker PA systems normally use a 100V transmission system employing transformers. ... but I gather that this is probably beyond the scope of what you are trying to achieve.
But you can read about it here.

You will need to work in Mono throughout. If using a stereo amplifier it will have to be used in mono mode, or if that is not an option, the inputs should be shorted together so that each side of the amp is dealing with a mono signal.

I have no knowledge of the RaspberryPi or the amplification you may be using... but any speaker array must not present a lower impedance to any amplifier than it is designed to cope with.

The impedance can be balanced with mutliple speakers by the use of parallel or series connections , or a combination of both.
Depending on the combination this can result in differential dissipation in each speaker.

You can look at different arrangements and their implications regarding resulting impedance and relative power dissipations here which should give you a sense of what you are up against.
 

jamieu

Well-known Member
1. As mentioned above, the RaspberryPi/HifiBerry unit will not be able to connect more than two 8 ohm mono passive ceiling speakers. But some rooms will have 4 or 6 of these ceiling speakers. How would I connect 4 till 6 of these ceiling speakers in a affordable way to a RaspberryPi? Is it as simple as getting 1 small amplifier (with its own power supply) per 2 ceiling speakers and than connect all of these amplifiers to a RasperberyPi? Or Maybe buy a bigger amplifier that can power 4 till 6 of these speakers and if it connect to a RaspberryPi?

I'm guessing you're using HiFiBerry's AMP2 hat? If so you should be able to wire 2 x 8 ohm speakers in parallel (assuming they are genuinely 8 ohms) which will appear as a 4 ohm load at the amp — which is within spec. See this data sheet.

You might need to increase the voltage output of your PSU if you need to squeeze a few extra watts out of your amp hat. But for modern ceiling speakers 12v (15W/channel @ 4 ohm) or 18v (30W/channel @ 4 ohm) should be more than enough. You only really need substantial wattage if your speakers are hard to drive or you absolutely have to squeeze that last extra few DB's of SPL out of them. In short most speakers only need 10 to 30 watts to drive them to decent levels.

I doubt you'll need it, but HiFIBerry also now sell a 100W HAT.

I'd probably also drop HiFiBerry an email (or make a post on their forums) to check your current PSU is up to the job, I've always found them to be surprisingly helpful/honest.

6 speakers is tricker, as 3 x 8 ohm speakers in parallel (~2.67 Ohm) will likely be too low an impedance for the Amp HAT. You could, as you suggest, look at using a DAC HAT to supply an external multichannel power amp and then bridge inputs 1 and 2 to inputs 3 & 4 and 5 & 6 respectively. But if you don't already have the speakers in place I might keep things simple and just stick to 4 as it will make everything easier/simpler.

Actually it looks like HiFiBerry's BeoCreate Board might work for this kind of application (60W channels can drive 2 Ohm speakers aka 3 x 8 Ohm speakers in parallel). But it works out a lot more expensive than their other more basic Amp hats. Again I'd drop HiFiBerry an email and ask for their advice.

2. And how do I hook up these mono speakers to each speaker in a zone so that each ceiling speaker will output both left and right audio? As separate left and right output is not really working for ceiling speakers in a room where people are changing position/movement. How do you make this? How do I connect the audio cables to the ceiling speakers and a RaspberryPi or amplifier? I was told its normally done for this kind of setup commercially, but I can't find any manual on how to do this correctly. Maybe its to simple to write about it. :)

I'd do this in software, wire them up normally as stereo pairs and then in either in HiFiBerryOS itself (HiFiBeryOS can act as a Squeezelite endpoint) or in your playback software (LMS?) set the output to be mono on all channels. Although personally I'd do it in on the HiFiBerrryOS, that way it will also work if you just send audio to the RPi directly via AirPlay or Spotify Connect.

This is the tab (Sound->Channel Configuration) you want to access in HiFiBerryOS:

Screenshot 2021-11-01 at 13.47.27.png
 
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