Bi-Amping Impedance

19ram98

I have the LSi15's and the LSiC and would like to use my receiver (Onkyo TX-SR800 100x5 full bandwidth) to power the high frequencies and a Onkyo M282 channel for the lows. My question is how does bi-amping affect the impedance each amp will "see"?From what I understand the factory jumpers place the two sections in parallel, if this is true and the the LSi's are 4 ohm nominal, then that would result in a 8 ohm nominal load for each amp. But something tells me my thinking is flawed as the other day, for the hell of it, I used an old Kenwood A/V receiver to bi-amp the LSi's. I kept the volume low in fear of damaging my three week old LSi's. Roughly 10 minutes into it the Kenwood shut off and went into protect mode. Onkyo says nothing about 4 ohm stability on their website for their stereo amps, mine have yet to come in and I was wondering if I should cancel the order because of the low impedance.

mantis

Thats a very good question.I'd like to know this as well.I would assume like you did about the impedance droping to 8 ohms when jumpers are removed,it make some sense to me.I'm not an expert on impedance in this matter,my logic tells me there is some truth to that.

organ

I've been doing a lot of thinking about it and I'm still a little puzzled. It's a fact that each amp will see the impedance of the driver(s) and crossover they are powering. The drivers are connected in series when the jumpers are in place. Using the nominal value of 4 Ohms with the formula for series resistors you get 2ohms+2ohms=4ohms nominal. But I don't think the speakers produce 2ohms nominal for one set of binding posts because receivers and even some amps would crap out if the jumpers are removed and they are bi-amped or bi-wired since bi-wiring is a parallel configuration. So if each set of binding post produce 2ohms nominal, bi-wiring will need a 1ohm load for each speaker from the amp. This is why I'm stil confused. Let's hope somebody here can help us out.

Maurice

19ram98

Maurice,
I am not sure I understand how the drivers/crossover networks in series? It seems to me a (+) to (+), (-) to (-) is a parallel connection. I think I might e-mail customer service with this one, I need to know the impedance before I can purchase an amp for bi-amping.

organ

I'm sure the drivers are connected in series when the jumpers are in place because there is only a single run of wire from the LF to the HF. If they were in parallel, there would be more than one path for the current to flow through(bi-wiring). Now that I think of it, the first +ve terminal may be connected in parallel to the second +ve terminal because the signal from the +ve end of the speaker wire is split into two when it reaches the first +ve side of he binding post. The single +ve end of the wire has to split to the +ve of the lower connection and the +ve of the upper connection(assuming we're not bi-wiring). I'm still confused because +ve to +ve will not conduct unless its in parallel.
I agree, I think it's better to contac Polk to get your answer.

Maurice

mantis

Nobody else???

Lsi9

Originally posted by 19ram98
for the hell of it, I used an old Kenwood A/V receiver to bi-amp the LSi's. I kept the volume low in fear of damaging my three week old LSi's. Roughly 10 minutes into it the Kenwood shut off and went into protect mode.

Dude DONT do this again...my friend did it with his polks and ruined a couple of the drivers...:o they tell you to take the jumpers off for a reason

briancs

Because Onkyo does not list low impedence specs for the M-282 on their website I contacted their customer service department. The person so graciously informed me that the particular amplifier is only recomended for 6 to 8 ohm use.

19ram98

LSi9,
Don't worry, the jumpers were removed. I am not quite that dense. :^)

Briancs,
Thanks for letting me know about the onkyo. Good thing I called and cancelled my order for those. Its kind of a let down as i would have liked to have the same brand of amps, oh well, the search continues.


Erik