Friendly Ghost

Two sets of speakers

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7 minutes ago, MartinC said:

The OP isn't actually that explicit, which is why I've asked to clarify.

Ah, re-read again, OP says: “Good power supply as I will run both pairs of speakers together once in a while”

Edited by Headcoat
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3 minutes ago, Headcoat said:

Ah, re-read again, OP says: “Good power supply as I will run both pairs of speakers together once in a while”

Good spot :). When I checked back I didn't read that far down.

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Generally, running two sets of speakers both connected at the same time is not that good an idea. It has nothing to do with the power supply, but the amplifier's reaction to the load it is 'seeing'. Roughly speaking, solid-state amplifiers do not like very low resistance loads and valve amplifiers do not like very high resistance. A good solid state amplifier might be rated at, for example, 50 watts into 8 ohms and 75 watts into 4 ohms. However, run it into 2 ohms and it might be very unhappy indeed. You further have to take into account that the impedance figure for speakers is always 'nominal impedance' and changes with frequency. The long and short of it is that even two pairs of 8 ohm speakers in parallel may actually present a load significantly less than 4 ohms at some frequencies, though if the amplifier is quoted as being OK for 8 or 4 ohms, then it should be OK.

Some amplifiers can cope with driving even tougher loads, but not all. Certainly, not all will have been designed with this in mind. I'd be wary of running 8 ohm speakers in parallel with 6 ohms, and two pairs of 4 ohm speakers I personally would not connect to anything. All of these might be OK for short periods of time and low volume levels. However, if you're running two pairs of speakers, then you're going to have to run the amplifier harder anyway.

A switching box is by far and away the better option.

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9 minutes ago, rabski said:

Generally, running two sets of speakers both connected at the same time is not that good an idea. It has nothing to do with the power supply, but the amplifier's reaction to the load it is 'seeing'. Roughly speaking, solid-state amplifiers do not like very low resistance loads and valve amplifiers do not like very high resistance. A good solid state amplifier might be rated at, for example, 50 watts into 8 ohms and 75 watts into 4 ohms. However, run it into 2 ohms and it might be very unhappy indeed. You further have to take into account that the impedance figure for speakers is always 'nominal impedance' and changes with frequency. The long and short of it is that even two pairs of 8 ohm speakers in parallel may actually present a load significantly less than 4 ohms at some frequencies, though if the amplifier is quoted as being OK for 8 or 4 ohms, then it should be OK.

Some amplifiers can cope with driving even tougher loads, but not all. Certainly, not all will have been designed with this in mind. I'd be wary of running 8 ohm speakers in parallel with 6 ohms, and two pairs of 4 ohm speakers I personally would not connect to anything. All of these might be OK for short periods of time and low volume levels. However, if you're running two pairs of speakers, then you're going to have to run the amplifier harder anyway.

A switching box is by far and away the better option.

Thanks for clarifying. Two sets of speaker terminals on an amp is a good solution, IF only one output used at a time. Alternatively, have a greater choice of amps and use a switching box.

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3 minutes ago, Headcoat said:

Thanks for clarifying. Two sets of speaker terminals on an amp is a good solution, IF only one output used at a time. Alternatively, have a greater choice of amps and use a switching box.

Ideally.

For an illustration, if you look at amplifiers that have two sets of speakers and the ability to run both at once, they state the impedances. The Sony 730ES states 4-16 ohm speakers if it's one at a time, but 8-16 ohms if it's both together. And the 730ES has a repuation for being difficult to break.

Anyway, you can only be in one room at a time :D

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Thanks all for the suggestions! I was hoping not to need a separate box to do this, but will take this solution into account if I don't get on with the mentioned amplifiers.
It is weird that this arrangement used to be normal in vintage hifi and is now so uncommon.

I already have the speaker wire in the walls and ceiling, so my preference is to use one amplifier for both sets of speakers. Adding active speakers and a separate preamplifier is not my preferred option as I am trying to get the boxcount down.

Thanks for the suggestions, if anyone has more, keep 'em coming!
I stumbled upon the Marantz PM11 series yesterday, now discontinued but might be found somewhere ex-demo...

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Super Wammer
2 hours ago, Headcoat said:

Most amps with two sets of speaker terminals have an a / b switch negating the need for a switching box? 

The guy asked how when there was only one set of speaker outlets -  but as you did not notice all I said - you should note (as said above) even if there are two sets of speaker outlets, you need to be careful if you play both sets at the same time .. if they are 6ohm loudspeakers the impedance will drop to 3ohms and depending on your amp it could be severe damage time (most are not made to deliver below 4 ohms).     

So you may wish to negate the dual outlets in favour of a switching box which keeps the impedance above 4 ohms, if you intend to use two sets of speakers at the same time  ...

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24 minutes ago, uzzy said:

The guy asked how when there was only one set of speaker outlets -  but as you did not notice all I said - you should note (as said above) even if there are two sets of speaker outlets, you need to be careful if you play both sets at the same time .. if they are 6ohm loudspeakers the impedance will drop to 3ohms and depending on your amp it could be severe damage time (most are not made to deliver below 4 ohms).     

So you may wish to negate the dual outlets in favour of a switching box which keeps the impedance above 4 ohms, if you intend to use two sets of speakers at the same time  ...

Can you run both sets of speakers from a switching box at the same time, and if you did surely the nominal impedance assuming at least one pair is below 8ohm would drop below 4ohm and therefore creating the potential of amp damage?

Or have I misread your last paragraph quoted? 

Amp with two sets of speaker terminals or amp with one set and a switching box used, as long as only one set of speakers used, is the same thing surely?

Edited by Headcoat
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1 hour ago, Friendly Ghost said:

I already have the speaker wire in the walls and ceiling, so my preference is to use one amplifier for both sets of speakers. Adding active speakers and a separate preamplifier is not my preferred option as I am trying to get the boxcount down.

Just to clarify, using active speakers in the kitchen wouldn't mean you'd need an additional pre-amp, rather you'd need the amp you chose to have pre-amp outputs (so no extra box). You'd need a signal cable through the wall and a power cable to each speaker though.

How often do you think you'd really want to be able to play exactly the same music in both rooms? Or from the same sound source? I'm asking as I do think you're likely going to end up compromising your main system as a result of going down the route of shared use with the kitchen.

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28 minutes ago, uzzy said:

The guy asked how when there was only one set of speaker outlets -  but as you did not notice all I said - you should note (as said above) even if there are two sets of speaker outlets, you need to be careful if you play both sets at the same time .. if they are 6ohm loudspeakers the impedance will drop to 3ohms and depending on your amp it could be severe damage time (most are not made to deliver below 4 ohms).     

So you may wish to negate the dual outlets in favour of a switching box which keeps the impedance above 4 ohms, if you intend to use two sets of speakers at the same time  ...

ps I read the original post as looking for amps with two sets of speaker terminals.

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Super Wammer
23 hours ago, Headcoat said:

Can you run both sets of speakers from a switching box at the same time, and if you did surely the nominal impedance assuming at least one pair is below 8ohm would drop below 4ohm and therefore creating the potential of amp damage?

Or have I misread your last paragraph qouted.

The QED switch box ensures due to the electronics inside that the imepedance does not drop below that of one set of speakers .. what it does is when one pair is selected it is connected in straight in (as it is when you direct connect to the amp) when you switch to playing two pairs at the same time it connects them in series.  So if you have two sets of 4 ohm loudspeakers when playing both pairs the amp will see 8 ohms .   I did say earlier in my original post that the switch box provides protection.  This is how it does it 

Edited by uzzy
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4 minutes ago, MartinC said:

Just to clarify, using active speakers in the kitchen wouldn't mean you'd need an additional pre-amp, rather you'd need the amp you chose to have pre-amp outputs (so no extra box). You'd need a signal cable through the wall and a power cable to each speaker though.

How often do you think you'd really want to be able to play exactly the same music in both rooms? Or from the same sound source? I'm asking as I do think you're likely going to end up compromising your main system as a result of going down the route of shared use with the kitchen.

The last paragraph is a very good point. I opted for an amp with two sets of speaker terminals, later realising the issue running 8 and 6 ohm speakers, over 14 months I can count on one hand the number of times I have played music through both pairs speakers,

Opting for only using one set at a time opens up amp choices, regardless of switching box, or two set of terminals on amp, or a powered speaker.

If, like me, you won’t in reality play both sets of speakers then really you have more amplifier choice.

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7 minutes ago, uzzy said:

The QED switch box ensures due to the electronics inside that the imepedance does not drop below that of one set of speakers .. what it does is when one pair is selected it is connected in series (as it is when you direct connect to the amp) when you switch to playing two pairs at the same time it connects in parallel.  So if you have two sets of 4 ohm loudspeakers when playing both pairs the amp will see 8 ohms .   I did say earlier in my original post that the switch box provides protection.  This is how it does it 

I missed that part. It sounds really useful. 

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3 minutes ago, Headcoat said:

I missed that part. It sounds really useful. 

In terms of protecting the amplifier, it is, yes.

On the other hand, in hifi terms, running speakers in series is going to potentially adversely affect the sound. It won't do any harm to the equipment, but you're putting a frequency-dependent variable impedance (a speaker) in line with each speaker, and this is definitely going to change its response to an extent.

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