Effects of Bi-amping on Speaker Impedance - AVS Forum
Forum Jump: 
Reply
 
Thread Tools
post #1 of 39 Old 07-06-2008, 01:27 PM - Thread Starter
Member
 
NeedingInfo's Avatar
 
Join Date: Jun 2008
Posts: 24
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
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.
NeedingInfo is offline  
Sponsored Links
Advertisement
 
post #2 of 39 Old 07-06-2008, 03:28 PM
AVS Addicted Member
 
Kal Rubinson's Avatar
 
Join Date: Mar 2004
Location: NYC + Connecticut
Posts: 28,486
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 95 Post(s)
Liked: 141
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.

Kal Rubinson

"Music in the Round"
Senior Contributing Editor, Stereophile
http://www.stereophile.com/category/music-round

Kal Rubinson is online now  
post #3 of 39 Old 07-06-2008, 05:16 PM - Thread Starter
Member
 
NeedingInfo's Avatar
 
Join Date: Jun 2008
Posts: 24
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
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...
NeedingInfo is offline  
post #4 of 39 Old 01-11-2009, 12:42 PM
Senior Member
 
Will-san's Avatar
 
Join Date: Oct 2003
Location: Los Angeles
Posts: 363
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
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?

"I was just reading here on my internet that Tofu is made from little baby seals". - Strong Bad
Will-san is offline  
post #5 of 39 Old 01-11-2009, 01:27 PM
AVS Addicted Member
 
sivadselim's Avatar
 
Join Date: Oct 2004
Location: CO
Posts: 16,085
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 54 Post(s)
Liked: 69
Quote:
Originally Posted by Will-san View Post

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.

"All men are frauds. The only difference between them is that some admit it. I myself deny it."
sivadselim is offline  
post #6 of 39 Old 01-11-2009, 01:37 PM
Senior Member
 
Will-san's Avatar
 
Join Date: Oct 2003
Location: Los Angeles
Posts: 363
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
So you would recommend against this?

"I was just reading here on my internet that Tofu is made from little baby seals". - Strong Bad
Will-san is offline  
post #7 of 39 Old 01-11-2009, 02:20 PM
AVS Special Member
 
Yosh70's Avatar
 
Join Date: Mar 2002
Location: Sask. Canada
Posts: 2,023
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 3 Post(s)
Liked: 20
Quote:
Originally Posted by Will-san View Post

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.
Yosh70 is offline  
post #8 of 39 Old 01-11-2009, 02:46 PM
AVS Addicted Member
 
sivadselim's Avatar
 
Join Date: Oct 2004
Location: CO
Posts: 16,085
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 54 Post(s)
Liked: 69
Quote:
Originally Posted by Yosh70 View Post

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.

"All men are frauds. The only difference between them is that some admit it. I myself deny it."
sivadselim is offline  
post #9 of 39 Old 01-11-2009, 06:10 PM
AVS Special Member
 
Yosh70's Avatar
 
Join Date: Mar 2002
Location: Sask. Canada
Posts: 2,023
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 3 Post(s)
Liked: 20
Quote:
Originally Posted by sivadselim View Post

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.
Yosh70 is offline  
post #10 of 39 Old 01-11-2009, 06:14 PM
AVS Addicted Member
 
sivadselim's Avatar
 
Join Date: Oct 2004
Location: CO
Posts: 16,085
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 54 Post(s)
Liked: 69
Quote:
Originally Posted by Yosh70 View Post

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".

"All men are frauds. The only difference between them is that some admit it. I myself deny it."
sivadselim is offline  
post #11 of 39 Old 01-11-2009, 06:58 PM
Advanced Member
 
soundlovr's Avatar
 
Join Date: Mar 2006
Location: Canada
Posts: 610
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 16
Quote:
Originally Posted by sivadselim View Post

If anything, biamping with the extra amps probably adds more strain to the receiver.

What would posses you to make such an outright wrong conclusion such as this?
soundlovr is offline  
post #12 of 39 Old 01-11-2009, 07:16 PM
AVS Addicted Member
 
sivadselim's Avatar
 
Join Date: Oct 2004
Location: CO
Posts: 16,085
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 54 Post(s)
Liked: 69
Quote:
Originally Posted by soundlovr View Post

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?

"All men are frauds. The only difference between them is that some admit it. I myself deny it."
sivadselim is offline  
post #13 of 39 Old 01-11-2009, 07:17 PM
AVS Special Member
 
Denophile's Avatar
 
Join Date: May 2005
Location: New Hampshire
Posts: 2,297
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 11
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?
Denophile is offline  
post #14 of 39 Old 01-11-2009, 09:33 PM
Senior Member
 
Will-san's Avatar
 
Join Date: Oct 2003
Location: Los Angeles
Posts: 363
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
Quote:
Originally Posted by Yosh70 View Post

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.

"I was just reading here on my internet that Tofu is made from little baby seals". - Strong Bad
Will-san is offline  
post #15 of 39 Old 01-11-2009, 09:36 PM
AVS Addicted Member
 
Kal Rubinson's Avatar
 
Join Date: Mar 2004
Location: NYC + Connecticut
Posts: 28,486
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 95 Post(s)
Liked: 141
Quote:
Originally Posted by Denophile View Post

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.

Kal Rubinson

"Music in the Round"
Senior Contributing Editor, Stereophile
http://www.stereophile.com/category/music-round

Kal Rubinson is online now  
post #16 of 39 Old 01-11-2009, 09:51 PM
Senior Member
 
Will-san's Avatar
 
Join Date: Oct 2003
Location: Los Angeles
Posts: 363
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
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.

"I was just reading here on my internet that Tofu is made from little baby seals". - Strong Bad
Will-san is offline  
post #17 of 39 Old 01-12-2009, 12:51 AM
AVS Special Member
 
Yosh70's Avatar
 
Join Date: Mar 2002
Location: Sask. Canada
Posts: 2,023
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 3 Post(s)
Liked: 20
Quote:
Originally Posted by Will-san View Post

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
Yosh70 is offline  
post #18 of 39 Old 01-12-2009, 01:10 AM
 
JBLsound4645's Avatar
 
Join Date: May 2006
Location: Bournemouth, Dorset, United Kingdom
Posts: 5,409
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
Quote:
Originally Posted by sivadselim View Post

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.
JBLsound4645 is offline  
post #19 of 39 Old 01-12-2009, 01:12 AM
 
JBLsound4645's Avatar
 
Join Date: May 2006
Location: Bournemouth, Dorset, United Kingdom
Posts: 5,409
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
Quote:
Originally Posted by sivadselim View Post

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".

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?
JBLsound4645 is offline  
post #20 of 39 Old 01-12-2009, 01:14 AM
 
JBLsound4645's Avatar
 
Join Date: May 2006
Location: Bournemouth, Dorset, United Kingdom
Posts: 5,409
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
Quote:
Originally Posted by sivadselim View Post

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?
JBLsound4645 is offline  
post #21 of 39 Old 01-12-2009, 01:29 AM
 
JBLsound4645's Avatar
 
Join Date: May 2006
Location: Bournemouth, Dorset, United Kingdom
Posts: 5,409
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
Cinema B-chain diagram is stated in the pdf file of this users manual
http://www.jblpro.com/pub/cinema/cinedsgn.pdf
JBLsound4645 is offline  
post #22 of 39 Old 01-12-2009, 08:01 AM
AVS Special Member
 
Denophile's Avatar
 
Join Date: May 2005
Location: New Hampshire
Posts: 2,297
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 11
Quote:
Originally Posted by Kal Rubinson View Post

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?
Denophile is offline  
post #23 of 39 Old 01-12-2009, 05:09 PM
AVS Addicted Member
 
Kal Rubinson's Avatar
 
Join Date: Mar 2004
Location: NYC + Connecticut
Posts: 28,486
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 95 Post(s)
Liked: 141
Quote:
Originally Posted by Denophile View Post

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.

Kal Rubinson

"Music in the Round"
Senior Contributing Editor, Stereophile
http://www.stereophile.com/category/music-round

Kal Rubinson is online now  
post #24 of 39 Old 01-12-2009, 07:26 PM
AVS Special Member
 
whoaru99's Avatar
 
Join Date: Dec 2004
Posts: 6,960
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 1 Post(s)
Liked: 67
Quote:
Originally Posted by JBLsound4645 View Post

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

Quote:
Originally Posted by JBLsound4645 View Post

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 View Post

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 View Post

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?

Just because there is a knob doesn't mean you should turn it.
whoaru99 is offline  
post #25 of 39 Old 01-12-2009, 08:13 PM
AVS Addicted Member
 
sivadselim's Avatar
 
Join Date: Oct 2004
Location: CO
Posts: 16,085
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 54 Post(s)
Liked: 69
Quote:
Originally Posted by cctvtech View Post

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?

"All men are frauds. The only difference between them is that some admit it. I myself deny it."
sivadselim is offline  
post #26 of 39 Old 01-12-2009, 08:14 PM
AVS Addicted Member
 
sivadselim's Avatar
 
Join Date: Oct 2004
Location: CO
Posts: 16,085
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 54 Post(s)
Liked: 69
Quote:
Originally Posted by whoaru99 View Post

What, again, is the point of all this?

LOL. IGNORE LIST.

"All men are frauds. The only difference between them is that some admit it. I myself deny it."
sivadselim is offline  
post #27 of 39 Old 01-12-2009, 08:34 PM
AVS Addicted Member
 
sivadselim's Avatar
 
Join Date: Oct 2004
Location: CO
Posts: 16,085
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 54 Post(s)
Liked: 69
Quote:
Originally Posted by cctvtech View Post

Yes, are you? What's wrong with the logic? Or do you not have a legitimate argument with my points?

That is not at all how it works. Passive (nor active, for that matter) bi-amping doesn't double the effective power that is driving the speaker. Nowhere near it. And that seems to be what you are implying.

"All men are frauds. The only difference between them is that some admit it. I myself deny it."
sivadselim is offline  
post #28 of 39 Old 01-12-2009, 09:16 PM
AVS Addicted Member
 
sivadselim's Avatar
 
Join Date: Oct 2004
Location: CO
Posts: 16,085
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 54 Post(s)
Liked: 69
Quote:
Originally Posted by cctvtech View Post

So, explain it for us dumb folks.

Do some reading. There are plenty of threads regarding bi-amping here in these forums. And sorry if I've offended you. That was not my intent. Frankly, in the context of your post, I was startled that you thought the power was simply additive. You do not seem "dumb".

Biamping a speaker with 2 100watt amps is not the same thing as driving that same speaker, conventionally (mono-amped), with a 200watt amp. At all. If you feed a tweeter 100watts and a woofer 100watts, in a passive bi-amp situation, you are not now driving the speaker at 200watts. The tweeter does not receive the 100watts. Nowhere near it. Tweeters do not require nearly the wattage that woofers require. Likewise, if you conventionally wire (mono-amp) a speaker to a 200watt amp, the woofer receives considerably more than 100watts of power. Considerably more. A speaker's crossover does not simply split the power evenly between the woofer and tweeter. One of it's functions is to properly parse the power, as is necessary and as designed, between the two. And even when passively bi-amped, the crossover still parses the amount of power between the woofer and tweeter identically to the way it would were the speaker not bi-amped. In other words, you do not use a whole bunch of the power of the amp that is being used to power the tweeter when you passively bi-amp. One might even say that you waste it.

The power is not additive. If you bi-amp a speaker to 2 100watt amps, you are not now driving it at 200watts. I can't give you an exact figure, as it is going to vary from speaker to speaker, and the math is not at all so straight-forward, so let's say for simplicity's sake that it would be more like driving it at 110watts.

Now, there MAY be other benefits of passively bi-amping that do not have anything to do with increased power. But these are arguable. And only barely so. I think the consensus would be that you'd be better off buying a more powerful amp and conventionally wiring a speaker than passively bi-amping with lesser powered amps. Everything else identical, a 200watt per channel amp, conventionally wired to a pair of speakers, is a much better choice than passively bi-amping the speakers with 4 100watt per channel amps.

"All men are frauds. The only difference between them is that some admit it. I myself deny it."
sivadselim is offline  
post #29 of 39 Old 01-12-2009, 09:18 PM
AVS Addicted Member
 
Kal Rubinson's Avatar
 
Join Date: Mar 2004
Location: NYC + Connecticut
Posts: 28,486
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 95 Post(s)
Liked: 141
Quote:
Originally Posted by cctvtech View Post

So, explain it for us dumb folks.

It has been explained many times on AVS. Basically, due to the power demands for bass frequencies and the common spectral distribution of most music, the LF leg will draw the majority of power. Thus, feeding a speaker with the full output of a 100w amp (assuming the speaker can handle the full output) will have an acoustic output limited by the bass output.

Now, biamp (passively or actively) this speaker with 2 100w amps and how much louder will it play? Well, the bass speaker will play just slightly louder since its amp no longer has to drive the HF but that was minor to begin with. Depending on the speaker (and the music), it may only be 1db. (If the HF and LF drew the same power, the improvement would be 3dB.)

HF output is not an issue since you cannot play the HF louder than the LF anyway.

Kal Rubinson

"Music in the Round"
Senior Contributing Editor, Stereophile
http://www.stereophile.com/category/music-round

Kal Rubinson is online now  
post #30 of 39 Old 01-12-2009, 09:35 PM
Advanced Member
 
EnergyOwner's Avatar
 
Join Date: Aug 2008
Posts: 952
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
IIRC, the pivot frequency for most content is around 350Hz where half the power goes to the lf and half to the hf.

The sleeper must awaken.
EnergyOwner is offline  
Reply Audio Theory, Setup, and Chat

Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page


Forum Jump: 

Posting Rules  
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off