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Bi-amping vs. bridging

Good day.  I am wondering what everyone thinks about bi-amping a dual port speaker vs. bridging the output on the amp to double the wattage.  I have a reasonably sweet Rotel 6 channel delivering 50 watts into all 6 channels (6 channels driven) but have the option of bridging the outputs and using a single teminal on the speakers.  I have a pair of Kef IQ5's, but will be taking delivery on some Martin Logan Motion 20's.  What do y'all think?  Best option?
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wisciman99 OP
75 posts
 
I appreciate the input from everyone. It sounds like I will stick to the bi-amping, especially with the 4 ohm ML's.  I have plenty of amp channels available, it should just be a matter of getting the right signals from the pre to the amp(s) from what I can gather.  What would the cons be for splitting the front L/R outputs at the preamp to provide the signal into the amp?  Is this also an impedance consideration?
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almarg
9,670 posts
 
What would the cons be for splitting the front L/R outputs at the preamp to provide the signal into the amp? Is this also an impedance consideration?
I suspect that won’t be a problem in this particular case, although I can’t say that with certainty because the output impedance of the AV-7005 is not specified.

As I mentioned earlier, driving two amplifier channels from the same preamp or prepro output stage will result in the preamp or prepro seeing a load impedance equal to the input impedance of the amp divided by two. Your Rotel RKB-650 amp has a specified input impedance of 20K, so two amp channels in parallel would present a load impedance of 10K. That would be a problem for many tube-based preamps, and for at least a few solid state components, but I suspect it would be ok in this case.

Also, to minimize the cable capacitance that would be seen by the prepro it would be preferable to split the signal using short y-adapter cables connected to the amp inputs, in conjunction with a single RCA cable for each channel, rather than splitting it at the outputs of the prepro and running two RCA cables for each channel. Although given the short lengths of the interconnects that appear to be required in your setup it probably won’t make much if any difference either way.

Regards,
-- Al


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wisciman99 OP
75 posts
 
I really appreciate you help, Al.  I think I am going to experiment with using the Front High outputs to use as the source signal for the tweeters.  This assumes the signal will be the same as the Front's.  It would then eliminate the potential impedance/loss issues of splitting the signal from just the Front.  I'll probably give that go tonight and post the results here for reference.
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wisciman99 OP
75 posts
 
Follow up:  I tried the Front High pre-outs as the source for the tweeters on the mains, and I was disappointed.  They sounded very muted and did not present musically as I had hoped.  Now, that being said, I was using the pre in stereo mode, so I presume there was some 'non-processing' going on if you will.  When I went to the All Channels selection, they did seem to wake up and became, at least to my non-audiophile ears, much brighter and clearer.  Again, I suspect it is a processing matter, so for the time being, I have returned to splitting the front mains into 4 channels for amplification sine I prefer to listen to my music in stereo mode.
auxinput
2,920 posts
 

I was just going to chime in here.  It really depends on how you are generating the signal for low/high biamp cables.  If you use the "special bi-amp" feature in most processors/receivers, they usually have a circuit that analyzes the actual signal that is played by the "low" part of the biamp.  It than uses another circuit to subtract the "used" frequencies from the unused.  It then outputs this "unused" signal to the "front high pre-outs" or equivalent.  The actual result is a significant loss in resolution and impact.  This explains why they sounded very muted and dull.  It is not recommended and I honestly don't know why these companies are trying to do this "differential subtraction" circuit because it just destroys the sound quality.  They really should have just output the normal "full range" signal on both low/high biamp outputs because the speaker would naturally play only what it needs to (based on internal speaker crossover).

It's probably best just to use a splitter cable, since you have the Rotel amp with 20k input impedance.  Al is correct in stating that splitting this into a 10k + 10k load will be fine for solid state components.  Actually, pro audio components usually have 10k impedances a lot of the time.  If you want a really good Y-splitter cable, check this one out (I'm assuming you're using RCA):

http://audiosensibility.com/blog/products-2/specialty-cables-occ-copper-and-occ-silver/#!/Statement-SE-OCC-Silver-RCA-Splitter-Cable/p/78179109/category=5528439

Or you can look for the Audioquest Y-splitter cable for about $20  or less, or something in between.

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