Theoretical - simple stereo amp into speakers of different sensitivity, impedance

[carpman]

I'm just trying to understand an effect on an amplifier (let's take as examples the recent Class-D, simple stereo amps like Fosi V3 or Aiyima A07) if you used a simple analogue source tone (same in each channel) into a stereo amplifier (RCA input) wired to two different (mismatched) passive speakers (i.e. L and R channel are feeding different speakers, firstly in terms of sensitivity then in terms of impedance):

1) Sensitivity (impedance = the same, say 8ohms):
a) LEFT channel speaker = 80dB (1w/1m)
b) RIGHT channel speaker = 90dB (1w/1m)

I'm assuming the amplifier will just supply the power equally and the right channel will sound louder and there will be no damage to the amplifier. Is that correct?

2) Impedance (sensitivity = the same, say 90dB (1w/1m)):
a) LEFT channel speaker = 8ohms (nominal impedance)
b) RIGHT channel speaker= 4ohms (nominal impedance)

I'm assuming this would damage the amplifier ???
Would it do anything else?
What would the effect be assuming all other variables outside those listed remained the same?

Any help and explanations would be very welcome -- just trying to understand how amplifiers are wired and would handle such situations.

Cheers,
C.

 

[Vladimir Filevski]

1) No damage to the amplifier, right speaker will be louder. But if there is a balance control, you can adjust both channel to be equally loud.
2) No damage to the amplifier, both speakers will be equally loud.

 

[carpman]

2) No damage to the amplifier, both speakers will be equally loud.

So if the amp (or perhaps PSU) is a cup and the two speakers are people sucking through different sized straws; the speakers are sucking from the same supply and the amp just gives each speaker what it's demanding. Is that how it's working. So the overall demand might increase if they were both 4ohms, but they're sucking from the same supply, so who cares? Is that basically it?

 

[Vladimir Filevski]

Yes, Power Supply and power output transistors are providing all the necessary juice. Pick your own straw.

 

[fpitas]

So if the amp (or perhaps PSU) is a cup and the two speakers are people sucking through different sized straws; the speakers are sucking from the same supply and the amp just gives each speaker what it's demanding. Is that how it's working. So the overall demand might increase if they were both 4ohms, but they're sucking from the same supply, so who cares? Is that basically it?

Yes

 

[solderdude]

1) Sensitivity (impedance = the same, say 8ohms):
a) LEFT channel speaker = 80dB (1w/1m)
b) RIGHT channel speaker = 90dB (1w/1m)

I'm assuming the amplifier will just supply the power equally and the right channel will sound louder and there will be no damage to the amplifier. Is that correct?

The right one will just sound about twice as loud as the left one.
A question would be why use 2 different speakers (other than differing in efficiency alone).
No amps will be damaged.
Amps don't care about sensitivity or power ratings of speakers but might not like impedances lower than they were designed to drive.

2) Impedance (sensitivity = the same, say 90dB (1w/1m)):
a) LEFT channel speaker = 8ohms (nominal impedance)
b) RIGHT channel speaker= 4ohms (nominal impedance)

I'm assuming this would damage the amplifier ???

The right one will just sound a little louder.
(Sensitivity is dB/V, efficiency is dB/W)
When you mean they have the same sensitivity then the speakers will sound equally loud but the 4 ohm one will draw double the current.

When the amplifier is designed to drive 4 ohm speakers the amp will not be damaged.

 

[DanielT]

...wired to two different (mismatched) passive speakers ...

And what is the purpose of your doing that?

By thw way the Ohm listed for a speaker is just an average value. In practice, the impedance flutters up and down through the frequency register. Check any review, test that Amir does on speakers and you will see it.

Edit:
The latest speaker Amir tested:

Tekton M-Lore Speaker Review

This is a review, listening tests, equalization and detailed measurements of the Tekton (Mini) M-Lore speaker. It is on kind loan from a member and costs $US 750 a pair. As you see, this is a mini-tower speaker if there is such a thing. I had to put a 6 inch stand under it to get the tweeter...

audiosciencereview.com

 

[carpman]

A question would be why use 2 different speakers (other than differing in efficiency alone)

A) Mainly, I'm really just trying to understand some basic concepts, BUT ALSO ....
B) I've got a spare centre speaker which fits nicely vertically in my kitchen and I'm thinking of using it to play mono. My understanding is that if you just run one speaker from a stereo amp you can damage the amp (perhaps I'm wrong about this). If that's correct you could in theory plug the problem with a spare satellite speaker that would be drowned out by the centre but the amp would be protected (and since you're playing a mono source, the mismatch is less of an issue). The alternative that I'm considering is the Aiyima MAX mono amp when it's available in the UK. Just playing around with ideas and seeing what I can use of existing gear that isn't being used.

C.

 

[carpman]

By thw way the Ohm listed for a speaker is just an average value. In practice, the impedance flutters up and down through the frequency register. Check any review, test that Amir does on speakers and you will see it.

Yes, I'm aware of that - but thanks.

 

[DVDdoug]

If you want to get slightly technical...

Amplifiers are "voltage sources". The voltage doesn't change with load (impedance). Sometimes the amplifier can't put-out as much maximum-voltage with lower impedance (because it can't put out the necessary additional current). But it the amp isn't clipping, the voltage will be independent of the load.

Resistance and impedance (both Ohms) is "the resistance to current flow". With a constant voltage, current is inversely proportional to resistance (Ohm's Law*).

Power (Wattage) is calculated as Voltage X Current.** When you cut the impedance in half, you get twice the current and twice the power.

...As long as the amp can put-out the necessary current you can get twice the power with half the impedance. But most amps can't quite do that. If the impedance is too low, the amp can overheat and burn-up, or hopefully just go into thermal-shutdown to protect itself.


* Ohm's Law says Current = Voltage / Resistance (It's a law of nature with man-made units-of-measure.)

** With Ohm's Law you can also derive: Power = Voltage squared / Resistance (often handy) and Power = Current squared x Resistance.

 

[solderdude]

I've got a spare centre speaker which fits nicely vertically in my kitchen and I'm thinking of using it to play mono. My understanding is that if you just run one speaker from a stereo amp you can damage the amp (perhaps I'm wrong about this). If that's correct you could in theory plug the problem with a spare satellite speaker that would be drowned out by the centre but the amp would be protected (and since you're playing a mono source, the mismatch is less of an issue). The alternative that I'm considering is the Aiyima MAX mono amp when it's available in the UK. Just playing around with ideas and seeing what I can use of existing gear that isn't being used.

Ah... you can use just one channel of a stereo amp and not load the other other channel.
Only some rare tube amps may not like that. So no worries about the amp and not loading one channel.

Besides... if your amp has a balance control you can set the balance to one side.
And if the amp has 2 RCA inputs you can also just only connect the input of the loaded channel.

 

[DVDdoug]

My understanding is that if you just run one speaker from a stereo amp you can damage the amp (perhaps I'm wrong about this).

Not a problem with "normal" amplifiers. It might be a problem with some tube amps or some "exotic" solid state amps, but I'd say that's a bad design.

A bigger problem with mono is combining the left & right channels. You should NEVER "short" outputs together so you can't combine the left & right line level signals with a "Y-splitter", and shorting the left & right speaker outputs together is even worse!

If you know how to solder you can make a fixed-passive mixer with two resistors. Or you can buy a little mixer for around $100 USD.

 

[DanielT]

But wait now you said Fosi Audio V3.It won't destroy the amp but it's a cheap class D amp so:
(if you're thinking about sound quality, that is)

Frequency response shows load dependency which all class D amplifiers in this price range show:

Fosi Audio V3 Amplifier Review

This is a review and detailed measurements of the Fosi Audio V3 stereo amplifier. It was sent to me by the company and costs US $89.99 with stock 32 volt supply. Price goes up to $109.99 with the 48 volt supply. There is a $10 discount coupon right now. Despite its budget price, the V3...

audiosciencereview.com

 

[voodooless]

In practice, the impedance flutters up and down through the frequency register.

That’s why there is a better efficiency definition: dB @1 meter @2.83V.

 

[carpman]

@DanielT: Whether I'd notice 1 db in those high frequencies I very much doubt (and in a kitchen -- it's not a big deal - nor is mono.).

@DVDdoug -- thanks that's a very nice summary. Also, I'm fine for the safe stereo to mono passive mixer issue.

And thanks everyone who chimed in on the single output from a non-tube amp. Very helpful (read some contradictory stuff online).

C.

EDIT: Added bit about passive mono mix.

 

[carpman]

I thought, rather than start a new thread on a somewhat inconsequential topic, I 'd add a minor tangent to this thread. Since it's on the topic of speaker mismatches and mono in a small and acoustically challenged kitchen.

My question: Is there such a thing as a passive (non-"audiophile" priced) balance control. I've seen passive volume controls (attenuators), passive channel mixers. Both of which could be used as a hack. Basically, as I pointed out earlier I've scavenged around and I have two speakers:

1 x MASS 10 (upside down Monitor Audio satellite)
1 x Monitor Audio Centre Speaker (in vertical position)

And these actually sound pretty good together.

I'm not a bass-head at all and I actually like that the MASS 10 speaker acts as a treble boost / bass reduction controller.

What I'd like to do is be able to change the balance (which in two channel mono would work as a subtle tone control as well as volume boost for the weaker MASS 10 speaker).

At present I'm running these off a cheap (Nobsound style mini amp) Fosi Audio ZK-1002D. Seems fit for the purpose.

I realise I could run a vol attenuator on one of the channels, but I'd rather be able to shift the channel weighting around like a balance control.
Do such things exist that aren't going to add a ton of noise or do anything stupid?

I'd rather avoid this kind of thing.

A simple dual RCA in / dual RCA out with a big round dial to balance the channels would be ideal.

Any thoughts most welcome.

C.

 

[kemmler3D]

I thought, rather than start a new thread on a somewhat inconsequential topic, I 'd add a minor tangent to this thread. Since it's on the topic of speaker mismatches and mono in a small and acoustically challenged kitchen.

My question: Is there such a thing as a passive (non-"audiophile" priced) balance control. I've seen passive volume controls (attenuators), passive channel mixers. Both of which could be used as a hack. Basically, as I pointed out earlier I've scavenged around and I have two speakers:

1 x MASS 10 (upside down Monitor Audio satellite)
1 x Monitor Audio Centre Speaker (in vertical position)

And these actually sound pretty good together.

I'm not a bass-head at all and I actually like that the MASS 10 speaker acts as a treble boost / bass reduction controller.

What I'd like to do is be able to change the balance (which in two channel mono would work as a subtle tone control as well as volume boost for the weaker MASS 10 speaker).

At present I'm running these off a cheap (Nobsound style mini amp) Fosi Audio ZK-1002D. Seems fit for the purpose.

I realise I could run a vol attenuator on one of the channels, but I'd rather be able to shift the channel weighting around like a balance control.
Do such things exist that aren't going to add a ton of noise or do anything stupid?

I'd rather avoid this kind of thing.

A simple dual RCA in / dual RCA out with a big round dial to balance the channels would be ideal.

Any thoughts most welcome.

C.

Well, I did not see anything like that on Amazon, although there are plenty of inline volume controls.

However, within a certain range of dB, these are almost the same thing.

 

[carpman]

Yes, likewise -- the only thing about a single inline vol controller is that it means (for my purposes) you're controlling one speaker - a balance would allow me to control both (turn one OR the other, down in essence). If it was a static issue -- set and forget - vol controller would work.

C.

 

[carpman]

I added "inline" to my searches and seem to have found some stuff on Ali-X. Aiyima seem to do one called W-10P Stereo Balance Controller (but the product page got mixed up with another of their products and resulted in terrible reviews because everyone got the W-10P but wanted something else). It states:

Due to the limitations of passive circuit conditions, the balance adjustment can only be adjusted below 80% of the main volume knob. The adjustment curve is relatively smooth.

Not sure I understand that.

There's another (below, left) which seems to be an input selector and balance controller, and then another which looks like a component from an old submarine (below right):

I might give the LINEPAUDIO (edit : corrected name) one a try --- it's cheap and 1/1 reviewers found it useful.

Balancing a mono signal between two mismatched speakers is clearly not something taking the world by storm - and I'm hardly surprised

C.

 

[K.Kevin]

I thought, rather than start a new thread on a somewhat inconsequential topic, I 'd add a minor tangent to this thread. Since it's on the topic of speaker mismatches and mono in a small and acoustically challenged kitchen.

My question: Is there such a thing as a passive (non-"audiophile" priced) balance control. I've seen passive volume controls (attenuators), passive channel mixers. Both of which could be used as a hack. Basically, as I pointed out earlier I've scavenged around and I have two speakers:

1 x MASS 10 (upside down Monitor Audio satellite)
1 x Monitor Audio Centre Speaker (in vertical position)

And these actually sound pretty good together.

I'm not a bass-head at all and I actually like that the MASS 10 speaker acts as a treble boost / bass reduction controller.

What I'd like to do is be able to change the balance (which in two channel mono would work as a subtle tone control as well as volume boost for the weaker MASS 10 speaker).

At present I'm running these off a cheap (Nobsound style mini amp) Fosi Audio ZK-1002D. Seems fit for the purpose.

I realise I could run a vol attenuator on one of the channels, but I'd rather be able to shift the channel weighting around like a balance control.
Do such things exist that aren't going to add a ton of noise or do anything stupid?

I'd rather avoid this kind of thing.

A simple dual RCA in / dual RCA out with a big round dial to balance the channels would be ideal.

Any thoughts most welcome.

C.

Sorry to resurrect, but why can’t you just handle this at the source/pre-amp level? When I plug in my phone or laptop to these cheap amps, I can simply use my settings app to change the balance of the sound. I can also set it to mono in there too. I also bought a 1mii bluetooth receiver that could probably be set to do the same thing.

This seems like a way easier solution than doing it at a hardware level. You will get the summed L/R content into a single speaker this way, and be able to control the L-R balance.