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Effects of Bi-amping on Speaker Impedance

21K views 38 replies 10 participants last post by  JBLsound4645 
#1 ·
Having trawled around the google for various phrases around this question, I have yet to find a conclusive answer regarding the effect that bi-amping might have on speaker impedance.


The most common answer is that bi-amping has not real effect - is this correct? So, when using 4 ohm speakers, separating the woofers from the tweeters still results in a 4 ohm load to the amp? Surely that is not correct?


I would have thought that the load would be less on the tweeter amps and greater on the woofer amps - but perhaps the difference is so slight as to lead people to say that there is no effective difference?


Any help?


Thank you.
 
#2 ·
It is, generally, correct. The impedance is not a pure resistance but varies with frequency. Thus, the LF end is 4ohms in its passband and has a very high impedance in the HF. Vice versa for the HF end. Put them in parallel and the net impedance is 4ohms. This is simplistic since I have not allowed for normal impedance variations but it should explain about what you asked.
 
#3 ·
Thanks for your answer, which is the first I have read that explained it in direct terms that even I could understand.



This answer is of real consequence when dealing with an amp that is nominally rated at 8 ohms but which is "known" to run 4 ohm speakers. Running two is one thing, but 4 (meaning 4 binding posts of 4 ohms each) could lead to a problem...


thanks...
 
#4 ·
Hmmmm


I have a pair of 4ohm speakers that are bi-amp able. I was considering a new receiver that allows bi-amping with the unused rear surround channels. For some reason I thought (or at least was hoping) this would lower the strain on the receiver. do I have this wrong?
 
#5 ·

Quote:
Originally Posted by Will-san /forum/post/15525647


Hmmmm


I have a pair of 4ohm speakers that are bi-amp able. I was considering a new receiver that allows bi-amping with the unused rear surround channels. For some reason I thought (or at least was hoping) this would lower the strain on the receiver. do I have this wrong?

Yes, you have this wrong. At least in regards to impedance. The impedance seen by each amp used will still be 4ohms. If anything, biamping with the extra amps probably adds more strain to the receiver.
 
#7 ·

Quote:
Originally Posted by Will-san /forum/post/15526110


So you would recommend against this?

I'd like to know what receiver you're considering to bi-amp a pair of 4 ohm speakers. It wont be one that you can purchase off the shelf at BB or CC Im pretty sure.
 
#8 ·

Quote:
Originally Posted by Yosh70 /forum/post/15526448


I'd like to know what receiver you're considering to bi-amp a pair of 4 ohm speakers. It wont be one that you can purchase off the shelf at BB or CC Im pretty sure.

Why? Even though they are not spec'd for it, many AVRs are robust enough to handle 4ohm loads. It also depends upon how low the impedance really drops with a particular speaker. And some speakers are conservatively (or would it be liberally?) rated as 4ohms.
 
#9 ·

Quote:
Originally Posted by sivadselim /forum/post/15526668


Why? Even though they are not spec'd for it, many AVRs are robust enough to handle 4ohm loads. It also depends upon how low the impedance really drops with a particular speaker. And some speakers are conservatively (or would it be liberally?) rated as 4ohms.

Again, you seem to post to bring your count up when the question is not directed at you. I asked Will.
 
#10 ·

Quote:
Originally Posted by Yosh70 /forum/post/15528166


Again, you seem to post to bring your count up when the question is not directed at you. I asked Will.

I could give a rat's behind about my post count.


What I said was pertinent to the thread, not just what you "asked Will".
 
#12 ·

Quote:
Originally Posted by soundlovr /forum/post/15528538


What would posses you to make such an outright wrong conclusion such as this?

Care to explain why you think it is "wrong"? Or maybe explain how using the unused surround rear amps to bi-amp a pair of speakers somehow reduces the strain on the receiver?
 
#14 ·

Quote:
Originally Posted by Yosh70 /forum/post/15526448


I'd like to know what receiver you're considering to bi-amp a pair of 4 ohm speakers. It wont be one that you can purchase off the shelf at BB or CC Im pretty sure.

The receiver I have in mind is a Marantz 6003. The speakers are Audio Physic Yara's which have a 90db sensitivity so they are pretty efficient.. and a lot of the bass is off loaded to a sub. My current receiver (an older BK) has plenty of power but none of the new bells and whistles, and well I like me some bells and whistles.
 
#15 ·

Quote:
Originally Posted by Denophile /forum/post/15528665


while it varies with freqnency, why not get the "nominal" impedance change by measuring impedance with a multimeter across the unconnected binding posts to see what nominal resistance load the receiver will be looking at in each case so we can all know for sure?

Sure. You could measure it but you should understand the rest of my statement about why it varies. Measurements of DC resistance, not nominal impedance, will be useless and not relevant.
 
#16 ·
I would assume that bi-amping with the back channels would put more overall strain on the receivers power supply but I wonder if by dividing the load between channels if there would be some benefit.
 
#17 ·

Quote:
Originally Posted by Will-san /forum/post/15529724


I would assume that bi-amping with the back channels would put more overall strain on the receivers power supply but I wonder if by dividing the load between channels if there would be some benefit.

Good choice on the Marantz, and those speakers look good too.

The more I read about it, the more I think about this "passive" bi-amping in that it just puts more of a strain on the power supply but the benefits are negligible.


If you want more power to those speakers Will, and money is a bit of issue, get the SR5003 and a good 2 channel amp. Just a suggestion.


And this thread is an interesting read on bi-amping.....little tussle here and there but interesting.
http://www.avsforum.com/avs-vb/showthread.php?t=794070
 
#18 ·

Quote:
Originally Posted by sivadselim /forum/post/15526668


Why? Even though they are not spec'd for it, many AVRs are robust enough to handle 4ohm loads. It also depends upon how low the impedance really drops with a particular speaker. And some speakers are conservatively (or would it be liberally?) rated as 4ohms.

Wow this is why I use separate stereo power amplifiers no issues with the DCX2496.
 
#20 ·

Quote:
Originally Posted by sivadselim /forum/post/15528660


Care to explain why you think it is "wrong"? Or maybe explain how using the unused surround rear amps to bi-amp a pair of speakers somehow reduces the strain on the receiver?

Sigh get a DCX2496 and load of stereo power amplifiers will you and knock yourself out please.


Don't forget to power each surround LF and HF you do know how to do that?
 
#22 ·

Quote:
Originally Posted by Kal Rubinson /forum/post/15529640


Sure. You could measure it but you should understand the rest of my statement about why it varies. Measurements of DC resistance, not nominal impedance, will be useless and not relevant.

surely there si a way to do this--still unclear how electrically this would be different but I believe you--if not with a multimeter then how would you suggest doing it?
 
#23 ·

Quote:
Originally Posted by Denophile /forum/post/15531744


surely there si a way to do this--still unclear how electrically this would be different but I believe you--if not with a multimeter then how would you suggest doing it?

You need to use a frequency generator, a voltage bridge and an AC meter. This allows you to sweep the relevant frequencies and measure the output with reference to a fixed resistor.


A standard multimeter will only give you the DC resistance, not the nominal impedance.
 
#24 ·

Quote:
Originally Posted by JBLsound4645 /forum/post/15530518


Wow this is why I use separate stereo power amplifiers no issues with the DCX2496.
Quote:
Originally Posted by JBLsound4645 /forum/post/15530524


Yeah its an announce when he quotes all the time to put his post count sky-high almighty.



So do you use separate stereo power amplifiers for B-chain?
Quote:
Originally Posted by JBLsound4645 /forum/post/15530527


Sigh get a DCX2496 and load of stereo power amplifiers will you and knock yourself out please.


Don't forget to power each surround LF and HF you do know how to do that?
Quote:
Originally Posted by JBLsound4645 /forum/post/15530561


Cinema B-chain diagram is stated in the pdf file of this users manual
http://www.jblpro.com/pub/cinema/cinedsgn.pdf

What, again, is the point of all this?
 
#25 ·

Quote:
Originally Posted by cctvtech /forum/post/15537505


Let me put it this way - say you drive a pair of speakers in a stereo configuration with 100 watts per channel. If you biamp those same speakers, you could feed 50 watts to each woofer and 50 watts to each tweeter. The resulting decibel output, and the load on the amp, would be the theoretically same either way.

You're not serious, are you?
 
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