Bi-amping and impedance

[limelakephoto]

I have a pair of RB61's I am thinking about bi-amping with my HTR as receiver allows it. (I only use L R C ). Now my question is the RB61's are rated as an 8 ohm load. Is this only when binding post straps are in place ? If straps are removed does the speaker become two 4 ohm loads ? I measured each set of posts and I cannot get a reading for the top posts, bottom posts read about 4.7 ohms, with straps in place it still reads about 4.7 ohms.

[Guest " "]

The reason you can't get a measurement on the HF section is becuase you are using a DC ohm meter which won't work on circuts with inline capacitors....DC can not pass thru a capacitor.

The 8 ohm number is an average number, as you found, at 0hz, you are at 4.7 ohms. You need to check your speaker documentation to find out if the terminals to your speakers are for bi-wiring or bi-amping.

[limelakephoto]

Thanks speakerfritz ! Duh ....I checked the manual and it says nothing about bi-amping...it just says bi-wiring is possible ! So i guess it's a no go for bi-amping ! Thanks again for the wake-up call !

[DavidF]

No, I think you may be coming to the wrong conclusion about the impedance. You don't sum the two individual driver impedance to get the system impedance. I would not anticipate you would have any problems driving the high and low drivers with different amps from a electrical point of view. That said I am not sure what your goal is by doing so on this two-way system.

[Guest " "]

Thanks speakerfritz ! Duh ....I checked the manual and it says nothing about bi-amping...it just says bi-wiring is possible ! So i guess it's a no go for bi-amping ! Thanks again for the wake-up call !

here's Klipsch's take on bi-amping and/or bi-wiring with their speakers.

http://forums.klipsch.com/blogs/andyw/archive/2007/09/07/bi-amplifying-or-bi-amping.aspx

[Chris A]

...here's Klipsch's take on bi-amping and/or bi-wiring with their speakers: http://forums.klipsch.com/blogs/andyw/archive/2007/09/07/bi-amplifying-or-bi-amping.aspx

I didn't know that article was out there--thanks!

An article on electrical impedance that discusses the DC and AC characteristics of the subject...

Here is another resource on bi-amping and tri-amping: Active Bi-Amping/Tri-Amping FAQ.

Chris

[Guest " "]

...here's Klipsch's take on bi-amping and/or bi-wiring with their speakers: http://forums.klipsch.com/blogs/andyw/archive/2007/09/07/bi-amplifying-or-bi-amping.aspx

I didn't know that article was out there--thanks!

An article on electrical impedance that discusses the DC and AC characteristics of the subject...

Here is another resource on bi-amping and tri-amping: Active Bi-Amping/Tri-Amping FAQ.

Chris

one of the items of interest is not to bypass the passives........the passives offer driver protection.

[DavidF]

Thanks speakerfritz ! Duh ....I checked the manual and it says nothing about bi-amping...it just says bi-wiring is possible ! So i guess it's a no go for bi-amping ! Thanks again for the wake-up call !

here's Klipsch's take on bi-amping and/or bi-wiring with their speakers.

http://forums.klipsch.com/blogs/andyw/archive/2007/09/07/bi-amplifying-or-bi-amping.aspx

Thanks for posting. Andy W. is an engineer at Klipsch, then? Not sure the connection with Klipsch.

I agree on the overall message that passive bi amping has limited benefits. Mixing "sounds" of amps is a common theme but then you have to deal with different gain between the amps and be sure they are the same polarity.

I have two amps that have bridge circuitry included to use as dual monos. I also use them stacked in stereo for passive bi amp specifically to alter the balance gain between high and low sections of the speaker system. The NAD preamp used has a potted output useful for this purpose.This alignment may also provide higher current overhead in the woofer section when I use JBL woofers. These units seem to soak up all the grunt the amplifier wants to give. I can't think of any other advantage as Andy mentioned.

[Guest " "]

have two amps that have bridge circuitry included to use as dual monos.

ok, then you need to remember that when you run an amp in bridge mode, each side of the amp only see's half the impedance. so if you use an 8 ohm speaker, and connect it to a stereo amp in bridge mode, each channel will see 4 ohms.....which is OK. BUT, if the speakers are 4 ohms...or have an impedance dip...each channel will see 2 ohms or half of the impedance dip. SO, you need to make sure that each channel is rated to provide power at the load it will see or half of the impedance dip of the speaker. AND, any amp problems with DC offset, are aggravated if run in bridge mode so make sure your amps do not have any DC off set problems.

[limelakephoto]

My amp is not rated to drive a 4 ohm load. The idea in bi-amping was a little more power and cleanliness. I am not sure....but I do assume that as I am able to control crossover frequencies to each channel(I don't know weather or not the crossover frequencies are applied before or after the signal is amplified I would assume before), that each channel would only be amplifing the necessary frequencies for each channel more or less. I would love to know the impedance curve for each section individually (binding post straps removed) and together. I have no desire to take chances with my amp or speakers.

[limelakephoto]

Okay....I read my speakers owners manual again. I have RB-61's, the owners manual for it says bi-amping is possible, but it does not give any more info other than that. The RB-61-II manual,(available online) says bi-wiring is possible. Knowing the minimum and maximum impedances for each driver section would help alot.

[Guest " "]

bi amping is driving speakers or drivers with different amps while at the same time segmenting the audio range feed into each amp.....HF to one amp...LF to the other amp, etc.

[Guest " "]

bridging is using two amp channels to drive a single speaker or
speaker system.....the speaker or speaker system is connected to the +
connection of each amp channel.....the - connection on each amp channel
is not used. the amp channels have to be fed an inverted signal and non
inverted siganl...both amp channels reproduce the entire audio
range....your speaker or speaker system has to be double of what the
minimum impedeance the amp channels can drive individually.

[Chris A]

I have two amps that have bridge circuitry included to use as dual monos. I also use them stacked in stereo for passive bi amp specifically to alter the balance gain between high and low sections of the speaker system.

DavidF,

I assume that you already know this, but for others reading this...

If you active bi-amp, then the need to bridge or strap the output of your amplifier(s) is significantly reduced for at least the midrange/tweeter channels, and reduced for the woofer channel. However, you'll need to use an active crossover to do this. If your speaker's drivers are already time-aligned and their FR is not significantly altered to achieve EQ via the Klipsch balancing network's (i.e., "crossovers") complex impedance response, then you can use an analog active crossver, such as a Rane, etc. to do the duty.

If you need to do EQ or time delay correction, then an active digital crossover is preferred.

Either approach (analog or digital active crossover) will effectively multiply the amplifier power that you do have applied to your speakers and audibly increase performance of your system. You will hear a significant difference if you take care in balancing, time-aligning, and EQing your speakers after going active.

Chris

[DavidF]

Okay....I read my speakers owners manual again. I have RB-61's, the owners manual for it says bi-amping is possible, but it does not give any more info other than that. The RB-61-II manual,(available online) says bi-wiring is possible. Knowing the minimum and maximum impedances for each driver section would help alot.

Back on the point of impedance. The impedance rating of the system takes into consideration the minimum values for the entire system. In this case both the high and low. Another way to look at it is if the amp won’t handle the high section or the low section individually, it won’t handle the system, either.

[DavidF]

Edited for duplicate posting.

[WMcD]

Further to Fritz. In the bridged set up the right "hot" has an output which is in reverse polarity from the left "hot". So I'm going to use "R-" to indicate that below. Assume the input to the amp is getting the top of a sine wave. The left hot is senting a plus. The right is sending a minus at the bottom of the inverted sine wave. We don't use the amps chassis ground.

However, we can imagine a 4 ohm speaker as being equivalent to two 2 ohm speakers in series. That what is in the [ ] below. .

L (+one volt)--------[ 2 ohms ---- virtual ground ----2 ohms ] -------- R (- one volt).

At the junction of the two speakers I've written that there is a virtual ground. This is because the voltage there has to be zero, and that is the same as the chassis ground (or the black output posts of the amp).

This is to say that the each channel of the amp thinks it is driving a 2 ohm load.

Generally, if the load is halved, the power is doubled, But that depends on whether the amp can supply the current demanded. 2 ohms is a heck of a load.

= = = = = = = = = =

There is another, very different, question regarding the parallel connection at the input straps. Assume the woofer and tweeter are both 4 ohms and the crossover is at 1000 Hz.

We see diagrams that the woofer filter sends 0 to 1000 Hz to the woofer and then nothing above 1000 Hz. Similarly, the tweeter sends 1000 Hz up to "infinite freq" to the tweeter. Of course there is typically an overlap and some blending around the crossover point.

The questions are: A) How does the passive filter work to accomplish that. And if the woofer and tweeter are both 4 ohms and they are in parallel at the input block, doesn't that work out to 2 ohms?

A) The filter works because below the crossover point, the input to the woofer filter presents a 4 ohm load. Above the crossover point, it presents very high or infinite impedance (ohms) to current from the amp (drawing no power). Therefore we see that the filter does not send power to its output to the woofer above the crossover freq because it has never absorbed any from the amp in the first place.

Similarly, the tweeter filter presents a very high impedance (ohms) to the amp below the crossover point and sends no power to the tweeter because it has never absorbed any power from the amp. Above the crossover freq, it is presenting a 4 ohm load.

This is just the logical result of A). Let us sweep up in freq. At all freqs the parallel circuits of the inputs to the two filters act like parallel resistors. Below crossover freq we have 4 ohms (from the input to the woofer filter) in parallel with infinite ohms (input to the tweeter filter), and that is 4 ohms. Above the crossover freq we have infinite ohms (from the input to the woofer filter) and 4 ohms (from the input to the tweeter.filter) and that is 4 ohms.

Therefore we see that even though we have two 4 ohm drivers (tweeter and woofer) in parallel the filters essentially turn inputs on (conducting) and off (not conducting current because infinite ohms is like an open switch).as we sweep up in frequency so there is no overlap.

Of course the above is a bit of a simplification because at the crossover freq, and nearby each filter is "half on" to present an 8 ohm load. In parallel that equates to 4 ohms.

It would be easier with graphs but I don't find any on the Internet.

The above is a vast simplification.

You could find a graph of the outputs of the filters and how they overlap and add in curves to something smooth in combined voltage output -- in perfect systems. If you invert the curves, you have a representation of the input impedances.of the filters. They follow parallel rules of resistors and work out to a smooth input impedance -- in perfect systems..

WMcD

[limelakephoto]

So basically.... The when the bind post straps are on, the total impedance averages 8 ohms. When the straps are removed each section would about 16 ohms. I assume that the drivers and there crossovers are connected in parallel to the inputs, not in series, as then the crossovers would not function properly. Just so everyone understands where I am coming from....I have a seven channel surround amp that I only use three channels of (L R C). I can control the crossover frequencies to each channel. The amp(s) say 8-6 ohm load. In the amplifier manual it does tell me how to bi-amp a speaker. The amp is a Marantz NR-1601.

[pzannucci]

So basically.... The when the bind post straps are on, the total impedance averages 8 ohms. When the straps are removed each section would about 16 ohms.

When the straps are on, the speaker presents a similar load as with the straps off. The crossover works by increasing the impedance and it creats the actual crossover point. So the impedance at crossover for a speaker system is many times much higher than at the normal operating (full on portion of the driver) function. Look at some graph such as http://www.stereophile.com/content/nht-classic-absolute-tower-loudspeaker-measurements figure 1.

So when you talk about strapping the two drivers together, their impendances when paired (overlapped or in parallel) for only a short portion of the frequency range. Where they are overlapped they could be 32ohms each giving you a higher impendance (when paralleled) of 16ohms as shown in the graph where it is 20 ohms. Not easy to see but the impedance is the inverse of the driver output. Driver output goes down, the impedance goes up.

[limelakephoto]

I due believe I have a fair understanding of what you have all so kindly shared with me ! I did try bi-amping them earlier before my first post, and they definately sounded better...without any doubt. The increase in sound quality started me thinking about impedences and crossovers. A then I began to question my thoughts ....and got myself in a tizzy. Just out of curiousity, does anyone know what order of crossovers each driver uses ? (1st 2nd ...4th). These speakers seem almost magical ! I have always found I liked speakers that used 1st order more. I actually these Klipsch so much they probably will end up as the main speakers on my old gem Levinson amp. My guess is the use a 4th order because crossover frequency is so low for the tweeter.