bagdrew Posted April 28, 2002 Share Posted April 28, 2002 Hi there, I have a question for you experts. I have a Yamaha RXV 1105 that has an impedence selector switch. I am running a pair of RF3's on the "A" switch and just aquired a pair of KG2's that I want to run on the "B" switch. My manual gives me two options "If you use one pair of main speakers the impedence of each speaker must be 4 or higher. If you use two pairs of main speakers the impedence of each speaker must be 8 or higher. So what do I do? Will I destroy my reciever by running 2, 8 omhs speakers on "A" and 2, 4 ohms speakers on "B"? Please Help with any advice or ideas. Thanks Thanks for your replies, here is some clarification When I refer to A & B I am speaking of the speaker switches that activate a pair for A and a pair for B. The text in quotes is exactly as stated in my manual. It does not switch directly b/w 4 or 8 ohms but gives you the cryptic instructions in quotes above. This message has been edited by bagdrew on 04-29-2002 at 09:46 AM Quote Link to comment Share on other sites More sharing options...
WMcD Posted April 28, 2002 Share Posted April 28, 2002 Pardon me, the question is a bit ambiguous. Is there (1) a 4 or 8 ohm switch and (2) an A, B, and A + B speaker switch? I know in some amps these days there is a switch for 4 ohms or 8 ohms. They are probably trying to explain the following. If you have one 8 ohm speaker (per channel), set the amp to 8 ohms. If you have one 4 ohm speaker (per channel), set the amp to 4 ohms. That is easy to understand. The next question is, what is the function of the A, B and A + B switch. Answer: In A+B it just wires the speakers (for each channel) in parallel to the amp. That is the same as if you just took the wires to each speaker and hooked them up to the output of the amp. So, the question becomes, if I put two 8 ohm speakers in parallel (by use of A and B being "on"), what is the impedance? The answer is 4 ohms. You should be able to see that in such a case, they are saying to use the 4 ohm setting for the amp. Now, you need to appreciate the equation for parallel impedance loads created by the speakers. 1/R(total) = 1/R(one) + 1/R(two) with some algebra it also says. R(total) = (R(one) * R(two))/R(one) + R(two) Now this make sense in our example of two 8 ohm speakers. R(total)= 8*8/8+8 = 64/16 = 4 ohms. Okay that is bit complicated. You can see that two equal impedances in parallel equate to 1/2 the original. And if you had three speakers of equal impedance in parallel, the total would be 1/3rd of each. It seems that you have two speakers with impedances of 8 ohms and 4 ohms. What does that calculate to when they are in parallel? (8*4)/8+4 = 32/12 = 2.66 ohms That is well below the 4 ohm setting for the amp. Another way of looking at the equations is, what if we had three 8 ohm speakers in parallel? The total impedance would be 8/3. That = 2.66 ohms. Easy. But that is our situation. Consider that the 4 ohm speaker is equivalent to two 8 ohm speakers in parallel. (This may be deep water for some, but is my self check on math.) But getting back to the original question. Will you hurt the amp? I'd suggest that you keep the amp impedance setting on 4 ohms. You might well experience some distortion if you have them hooked up to A and B, and switch both on. If you drive the amp hard, it may shut down. I can't guarantee there will be no harm. Of course, everything is fine if you just use A or B without A + B. Others may wish to comment. Gil This message has been edited by William F. Gil McDermott on 04-28-2002 at 09:02 PM Quote Link to comment Share on other sites More sharing options...
USparc Posted April 29, 2002 Share Posted April 29, 2002 The impedance selector on amps is there mostly to protect the amp. The builders of the amp know that when 4Ohm speakers or 2 8Ohm speakers in parallel are used the amp would be stressed. To prevent that they implement a switch that limit the output of the transfo. ------------------ ------------------------- Receiver: Pioneer VSX-909RDS DVD: Pioneer DV-525 Screen: Thomson 46" RetroProjection Front: RF-3 tFTP Rear: RF-3 tFTP Center: RC-3 tFTP Quote Link to comment Share on other sites More sharing options...
boa12 Posted April 29, 2002 Share Posted April 29, 2002 when you run the a+b w/ two sets of 8 ohmers i think most receivers auto compensate - iow they handle as a 4ohm load to each set whether you put the switch on 4 or 8ohm. is that wrong? but if you run or will run any speaks w/ less than a 8ohm imped then i'd think you'd want the switch over to 4ohm. as always receivers do vary i'd think - heard of some that even use series for a+b (more in the past). ------------------ My Home Systems Page Quote Link to comment Share on other sites More sharing options...
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