Stupid question on A+B settings

ematthews

ematthews

Audioholic General
Sorry I don't know this
Does it do any harm to run both A and B speakers at the same time? It's a Harmon Kardon HK 3490 two channel receiver. I was comparing two different sets of speakers and hitting a then b to compare. While running both A and B at the same time with all four speakers the sound is great.
 
Pyrrho

Pyrrho

Audioholic Ninja
In most cases, when selecting both A and B speakers, the receiver is wiring them in parallel (there are a few receivers that wire them in series; if when only one pair is hooked up and you select both A and B you get no sound, that is a good indication that one has a unit that hooks them up in series). Them being in parallel means that if they are both identical sets of speakers, the amplifier is being presented with an impedance of exactly half of just having one set of speakers hooked up. So it can harm the amplifier, if the resulting impedance is too low. Consequently, normally, next to the speaker terminals, it will tell you that the minimum impedance that you can use for both A and B is twice what the minimum impedance is that you can use for either A or B.

So, it really depends on what speakers you are hooking up to it, and also how loud you play it (as playing it louder makes greater demands on the amplifier).

There is nothing inherently wrong with using both at the same time, provided one pays attention to what the requirements are for running them at the same time.
 
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M Code

M Code

Audioholic General
The 3490 is very powerful and can drive (2) pairs of loudspeakers without any problem. Note that they are connected in parallel so it is crucial to note the impedance of each loudspeaker, if both are 8 Ohms than the actual amplifier load will be 4 Ohms. However if (1) is 8 Ohms and the other 1 is 4 Ohms than the actual amplifier load will be like 3 Ohms, lower than the lowest loudspeaker. The majority of loudspeakers are 8 Ohms so you should be fine but as the load impedance decreases the amplifier has to work harder and will run hotter. Just be sure to have at least 3" of free-air clearance for the L/R sides and top cover.


Just my $0.02... ;)
 
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