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speaker A,B or A+B?

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Old 2nd July 2011, 07:00 PM
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speaker A,B or A+B?


I am entirely in audio 2.0 set up. Most of todays stereo receiver includes speaker AB ports, I was wondering whats the difference between the playback mode: speaker A or speaker B and speaker A+B. Speaker A or Speaker B will not an issue - if the nominal impedance of speaker A/B is lower (compared to the amp) then they will draw more current, hence more power. Now if we run both the speaker simultaneously, i.e., A+B, there can be two possibilities

1.If A and B are in series the load increases, not a big issue for the amp as it is safe to run with higher impedance
2. But if A and B are in parallel load drops significantly, for example if A and B are 8 and 4 Ohm loads then the parallel load is around 2.6 Ohm. Now this should be a concern as with this load current flow will be much higher and the amp will run hot and if done for a prolonged period may damage the amp

so
1.In stereo amps the speaker ports A and B - are they in parallel?
2.As the manufacturers are suggesting both speaker A and B can be run simultaneously whats the safety involved in the design?

I myself have observed with speaker A+B the amp really runs hot within 1/2 an hour
so is it a safe recommendation that one pair of speaker be run at a time? i.e. is A or B is better than A+B?
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Old 2nd July 2011, 07:14 PM
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Re: speaker A,B or A+B?

In A+B mode, speaker systems A & B are in parallel. If A, B each has R Ohms nominal impedance, in the A+B mode their total impedance is therefore R/2, and hence the amp runs hotter. It should be clearly mentioned in the user manual. I have a very old SS 2-channel amp and its manual clearly mentions this so that there is no problem.

Regards.
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Old 3rd July 2011, 11:16 AM
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Re: speaker A,B or A+B?

most of user manuals say the same thing that two pairs of speakers can be connected. But do they really address the issue of connecting two sets of speakers of different impedance rating thereby reducing the overall impedance below the factory specification?

no one is interested??
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Old 3rd July 2011, 11:35 AM
 
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Re: speaker A,B or A+B?

Logically, if A=R1, B=R1, and A+B=R1/2, then if A=R1, and B=R2, will A+B be equal to R1/2+R2/2?

I don't think so. If we follow the theory that a speaker sucks power, when you connect two speakers of different impedances to the same amp, the power will just flow to speaker which is easier to drive. This is like trying to light two bulbs with different wattages through a single switch. The bulb with higher wattage will light up less efficiently.

I don't think amplifiers are intelligent enough to sense the impedance and resistance of a speaker pair and distribute it's power efficiently. That would effectively need two circuits and a feedback mechanism.

Cheers
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Old 3rd July 2011, 12:34 PM
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Re: speaker A,B or A+B?

Quote:
Originally Posted by venkatcr View Post
Logically, if A=R1, B=R1, and A+B=R1/2, then if A=R1, and B=R2, will A+B be equal to R1/2+R2/2?
If R1 and R2 are connected in parallel then A+B= (R1xR2)/(R1+R2)
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Old 3rd July 2011, 06:31 PM
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Re: speaker A,B or A+B?

Quote:
Originally Posted by venkatcr View Post
Logically, if A=R1, B=R1, and A+B=R1/2, then if A=R1, and B=R2, will A+B be equal to R1/2+R2/2?

I don't think so. If we follow the theory that a speaker sucks power, when you connect two speakers of different impedances to the same amp, the power will just flow to speaker which is easier to drive. This is like trying to light two bulbs with different wattages through a single switch. The bulb with higher wattage will light up less efficiently.

I don't think amplifiers are intelligent enough to sense the impedance and resistance of a speaker pair and distribute it's power efficiently. That would effectively need two circuits and a feedback mechanism.

Cheers
the equivalent impedance (R) is 1/R=1/((1/R1)+(1/R2)), what baijuxavior has written. this is the point I was wondering if the amplifiers don't hv separate circuits for A and B which is very likely then driving two speaker sets of different impedance rating would draw significantly more current as R will be less than the minimum of R1 and R2. Isn't that a point of concern in long run? moreover at such lower impedance THD is bound to increase significantly

so whars the word coming from manufacturer? is it safe to drive A and B simultaneously? logically it seems not unless there are protections in the power amplifier section

BTW impedance is different from resistance and the difference is not trivial, though helpful for illustration
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Old 3rd July 2011, 07:01 PM
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Re: speaker A,B or A+B?

I am using 2 pairs of speakers as A + B for a few months now. The only trouble I feel is that I have to take the volume higher quite a bit to maintain the overall volume in both areas.

1. The spaekrs are all impedance of 8 thus most probably it equates to an impedance of 4 overall. Is that OK?

2. Secondly is keeping the volume at around 70% level an isssue. Other setups of mine never even cross the 50% mark.

I am using the Marantz CR603 as the Stereo Receiver.
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Old 10th March 2013, 06:50 AM
 
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Re: speaker A,B or A+B?

I have an older electro brand stereo system in our mobile home it's an AM/FM Cassette stereo system it has a speaker selector switch that in the top position is A and the bottom position in A + B. I know the speaker are not properly wired and I was wondering if any one has a diagram of how they should be wired. I'd like to add a speaker selector to work with the A switch so I can add another set of speakers. Thanks for all your help.
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Old 11th March 2013, 12:01 PM
 
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Re: speaker A,B or A+B?

One use I have found for the A and B terminals is whle Bi-wiring. The bass section (woofers) can be wired to termnal A and the mid-hf (midrange-tweeter) section can be connected to terminal B. It allows for different wires to be used without having multiple banana plugs being plugged together.


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