Multiple speakers with Sonos Amp

In theory yes to the lower volume thing, but if you choose speakers that are an easy load, this will not be a limitation in actual use indoors. And easy load speakers are known by high impedance numbers in their spec - 8 ohm or more. Which is why Sonos recommends such where 2 pairs are to be used.

Thank you, that’s helpful. For the purpose of ensuring the 4 speaker set up works is it just the high impedance that matters or anything else? Could I extend to 6 speakers (8 ohms) do you think ?

The higher the combined impedance, the lower is the power demanded from the amp; hence the need to get high impedance speakers. For more on the subject see:

https://support.sonos.com/s/article/265?language=en_US

https://en.community.sonos.com/components-228996/connect-amp-with-6-speakers-39742

For 6 speaker, an impedance matching switch is highly recommended.

Thanks again. So does an impedance matching switch have any effect on volume? Ie do 6 speakers running off a single amp with an impedance matching switch play at the same volume as they would if they were running off their own separate amps ?

A speaker drops its impedance to draw more current from the amp when it needs the extra power - for example to play lower frequencies at high volume levels. The impedance matching switch prevents this from happening, and therefore also limits the volume levels to such that the amp can sustain.

Answer to your question therefore: No, they won't play at the same volume levels above a certain volume level. There are no free lunches here as well!

I thought the Sonos amp was a lot more powerful than the connect amp to negate the need for an impedance matching switch when connected to 6 speakers, any thoughts on the Sonos amps ability to drive 8 speakers with a switch in place

Power has nothing to do with impedance tolerance of an amplifier's output. You can have a 250 Watt amp that can't support less than 8 Ohms and a 10 Watt amp that is happy with 2 Ohms.

With an impedance matching unit in place (not all are switches) your amp will never be presented an impedance that is below what it can safely operate at.

When using an impedance matching unit it will use some amount of your amplifier power internally, that varies drastically among units.

Speakers hooked to an impedance matching unit split the available power between them, just how depends on the unit and the speakers.

Thanks for all the helpful comments. I’m now looking at four 6 ohm speakers running from one Sonos amp. I think this means that I will need an impedance matching unit. Do these units still allow the speakers to have a dynamic impedance or do they fix each speaker at a set impedance?

Power has nothing to do with impedance tolerance of an amplifier's output. You can have a 250 Watt amp that can't support less than 8 Ohms and a 10 Watt amp that is happy with 2 Ohms.

That is a curious statement, so I am going to ask why to understand it, with the following that may be questioned as part of the answer:
A speaker drops its impedance to allow it to draw more power from the amp, usually to produce lower frequency music that needs more energy to be delivered.

What would then be the reason for the amps quoted above to behave that way? Why would a 10 watt amp be able to meet the power draw from a speaker at 2 ohms, where a 250 watt amp would not be able to support impedances below 8 ohms from the same speaker? Is it not that supporting low load(speaker) impedances needs adequate power reserves in the amp to support the consequent higher power drawn from the speaker, power reserves that any 250 watt amp can deliver to at least the same extent that a 10 watt amp can?

As to impedance matching units, they still allow dynamic impedance in the speaker, but set a limit below which it cannot fall, thus limiting the power that the speaker will draw from the amp. This prevents the amp from triggering its self protection, or clipping, or getting damaged. It follows from this that the sound levels that are available from the speaker are also thereby curtailed, which in turn means that you will not be able to listen to all that is recorded as it is meant to be heard, where lower frequencies are concerned.

Power has nothing to do with impedance tolerance of an amplifier's output. You can have a 250 Watt amp that can't support less than 8 Ohms and a 10 Watt amp that is happy with 2 Ohms.


Hopefully I got the quotes right here, if not I'll try to edit them.

That is a curious statement, so I am going to ask why to understand it, with the following that may be questioned as part of the answer:
A speaker drops its impedance to allow it to draw more power from the amp, usually to produce lower frequency music that needs more energy to be delivered.

That is not what happens in a speaker, the impedance varies due to the capacitance, reactantance and resistance of the crossover network at various frequencies, not because the speaker needs more energy. It is a very complex relationship as the amplifier is usually feeding a variety of frequencies to the crossover and the impedance may be very low at one frequency while being much higher at a different one.

Longer: http://www.audiogurus.com/learn/speakers/speaker-impedance-rating/1092

What would then be the reason for the amps quoted above to behave that way? Why would a 10 watt amp be able to meet the power draw from a speaker at 2 ohms, where a 250 watt amp would not be able to support impedances below 8 ohms from the same speaker? Is it not that supporting low load(speaker) impedances needs adequate power reserves in the amp to support the consequent higher power drawn from the speaker, power reserves that any 250 watt amp can deliver to at least the same extent that a 10 watt amp can?

It is not about needing to meet the power draw of the speaker, the speaker doesn't draw power but rather allows power to flow into it. Better stated would be how can a low power amplifier be stable powering a 2 Ohm speaker when a high powered amplifier isn't. The answer is in the design of the amplifier's output stages and is an engineering decision.

You can design an amplifier to be stable into lower impedance but it usually costs more. Amp designers look to their target market and design to that, usually 4 or 8 Ohms, not matching the expected speaker impedance can be inefficient too. They do build in a safety factor as the amplifier's speaker impedance rating (as above) as it is an approximation that varies across the frequency range.

How loud the speaker plays is a different subject where available amplifier power and the speaker's efficiency are key players.

As to impedance matching units, they still allow dynamic impedance in the speaker, but set a limit below which it cannot fall, thus limiting the power that the speaker will draw from the amp. This prevents the amp from triggering its self protection, or clipping, or getting damaged. It follows from this that the sound levels that are available from the speaker are also thereby curtailed, which in turn means that you will not be able to listen to all that is recorded as it is meant to be heard, where lower frequencies are concerned.

Depending on the design of the impedance matching unit that can be correct or not. An impedance matching unit that adds resistance in series with the speaker does set a lower limit on the possible resistance. You can check this by measuring it with the outputs shorted. The problem you face with a resistance based impedance matching unit is the power it wastes in the resistors that is taken away from the power the speaker would use to make sound.

About half way down, after Fig 8, Impedance Matching: https://www.electronicdesign.com/communications/back-basics-impedance-matching-part-1

Transformer based matching unit: https://www.amazon.com/SVC100-Impedance-Matching-Theater-Switchable/dp/B0017K51WE/ref=sr_1_9

Resistor based matching unit: https://www.amazon.com/Impedance-Matching-White-Ivory-Almond-AVX-Audio/dp/B004TLAGQY/ref=sr_1_18

That is not what happens in a speaker, the impedance varies due to the capacitance, reactantance and resistance of the crossover network at various frequencies, not because the speaker needs more energy. It is a very complex relationship as the amplifier is usually feeding a variety of frequencies to the crossover and the impedance may be very low at one frequency while being much higher at a different one.

Speakers do draw power to produce sound - power isn't fed into the speakers in the absence of such a draw. For instance, when the speakers are silent, there is very little power being drawn by them even though the amp may be on and volume may be on full. The amp, using the common water analogy, is a reservoir of power, not a pusher of it. Of course, the amp, depending on what class it is, will have quiescent power consumption all the time it is on, but this will not be a large amount unless the amp is of the class A type.
And speaker impedance - resistance across the speaker terminals - does drop precisely because the speakers need more energy and the lower resistance allows for more to be sucked out of the reservoir - akin to increasing the size of the pipe.

So my thread has now become very theoretical. It’s interesting but hard to take practical guidance from. I’ve been recommended four Dali E80s (6ohm) with a Sonos amp. Is this a good combination, do I need an impedance matching unit and if so which sort? Or should I just choose 8 ohm speakers instead to avoid the inefficiencies of an impedance unit?

I surrender.

4 6 Ohm speakers are going to be roughly 3 Ohms, I wouldn't bet on them working particularly at higher volume levels. Why not contact Sonos support for an official answer? The twitter option is open 24x7 and the phones will be open Monday morning. Either option beats getting an unusable combo.

There is no dearth of very good 8 ohm speakers out there, so there isn't any need to be different except where one is looking at legacy/gifted units.

Ultimately, an amplifier is rated for a certain amount of output current before it burns up. An amplifier is really a constant voltage device. As you add more speakers the voltage output remains the same (for a given input voltage) and the individual speakers are not aware of the others. The output level of a given speaker does not change as additional speakers are added. This continues, as more speakers are added, until the current limit is reached. Beyond this point the amplifier takes protective action or burns.

It’s a similar situation for a lamp circuit, but we use different math. We keep adding lamps until the circuit limit is reached. Beyond this point a fuse will blow or the house will burn. Mercifly, we specify a lamp’s power draw at the rated voltage, rather than the lamp’s resistance.

The math for consumer audio speakers is contorted (for reasons that we don’t need to get into here). In professional audio the amplifier’s output voltage is specified along with a speaker’s power rating — just as our lamp circuit. One keeps adding speakers until the amplifier power rating is reached. It’s the same physics, just simpler math.

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An impedance matching device alters the voltage to current ratio for the circuit. If the current (and output level) is reduced for a given speaker, more speakers can be added to the circuit.