Monoblock or Bi-Amping?

Nico72

This is a theoretical question.
Let's suppose one has speakers with two binding posts that allow bi-amping.
The choice of amplification is between two monoblocks outputting 100 W each, or two stereo power amps outputting 50 Wpc each, to be used in bi-amping configuration (passive bi-amping, without external crossovers). So the overall power is 200 W for nominal 8 ohms in all cases.
Assuming that the quality of the components is comparable between the amps (transformers, capacitors, transistors...), what are the advantages and drawbacks of monoblocs vs bi-amping?
I would guess (but I may be wrong) that the impedance of the single drivers in bi-amping is higher than that the speaker with the links fitted? Does that mean that bi-amping delivers less power by seeing higher impedance?
Does bi-amping bypass the crossover inside the speaker? If so, is there any advantage in that?

One more question: Can one use four channels of a multi-channel power amp to bi-amp the front channels? And is there any advantage in doing so, given that the power supply in the power amp is shared among all channels anyway?
Thanks

mushii

What would you be HOPING to achieve by bi-amping. You are still going to be using the same crossover in either scenario.
Unless the crossover is particularly poor in design and assuming that there is adequate power available, is it not better to let the crossover determine which driver the power goes to, as the designer intended, rather than just splitting the power in half and sending half to each driver?
Much will depend on the efficiencies of the amps themselves and how well they can handle the power transients. For me I would use 2 x 100 watt monoblock amps over 4 x 50 watt of the stereo amp channels (on paper) just because there is more theoretical power available where it is needed, but again it would all depend on the amps themselves.

3rdignis

I think bi-amping is not cost effective.

Although if you did have 2 identical stereo power amps, I would use extremely short speaker wires 6 inches or so.

This would be a better use of the power supply as the small demands of the tweeter would free power for the woofer.

Ugg10

I had two Rotel RB850's that were nominally rated into 8 ohms as 2x50w or 1x150w - this was achieved just using a switch on the back so the same power supply in both cases.

I tried them with
- One amp for woofers, one for tweeters (horizontal stereo biamp)
- One amp for Left and Right stereo  (vertical stereo biamp)
- One amp for left, one amp right bridged (bridges mono)

......and there was not much difference but preferred the bass definition on the mono bridged version (this was into B&W CDM1SE's).

3rdignis

I use bridged monoblocks in a true balanced system.

Bridged amps generally offer more power but are not recommended with speakers that drop too low on the ohms.

Nico72

Ugg10,how does the “vertical strereo biamp” works?

Ugg10

You connect the left/right from one stereo amp to the tweeter/woofer of one speaker. This is slightly less advantageous beacause if there are slight volume or tonal differences in the two amps one speaker will be slightly different to the other which is more noticeable than differences between tweeter and woofer in a horizontal set up.

In fact some use a tube amp on the tweeters and solid state for the woofers but they should have the same amplification factor (gain) otherwise the tweeter will change volume differently to the woofer.

                                                                                                                                                                                                                                                                                                                                                                                                                                Bi-amping: Vertical vs horizontal - av2day.com                                                                                                        By Lam Seng Fatt Since Victor Pheh of hifi creations liked...                                                                                                                                                                                                                                                                                                                av2day.com

Mark.Yudkin

Biamping with 2x50W effectively gives you 50W of amplification, not 100W. Using 4x50W amplifiers to power two speakers also gives you an effective 50W.

IOW, you'll get more volume (  3dB) by using 2x100W than by using 4x50W.

Antiquarian

Unless you are a lottery winner where money is no object, one £500 amp will always sound better than 2 x £250 amps.

dannnielll

Taking it at face value.  Monoblocks are just another method of packaging amplifiers. The very powerful amplifier needs ample cooling and putting the beasts in different boxes sorts that out. The biamping concept is that ideally the frequency response crossovers for the different drivers is carried out electronically in the amplifier rather than by using passive components in the speaker cabinet. The advantage of this is that the corrections can be more accurate as higher order filters can be used, and because the power levels are much lower ,there is little waste. It also means that there is a lower impedance driving the individual drivers which improves transient response. All of these advantages are lost with passive speakers with internal crossovers. Ordinary copper  or aluminium or silver cable, is incredibly linear and even the presence of a high frequency tone intended for a tweeter will not interfere with the bass tone intended for the woofer.  In the case of passive biwirable speakers it makes more sense to just parallel the cables.
Now the prospect of parallelling the signal into multiple channels of an AVR ,is intriguing and then driving the same speaker in parallel .. and might have merit. I might think about doing that with my HK..except I have no use for 800 watts of RMS power.  Potentially there would be value, as the drive capabilities would allow 200amps per microsecond slew rate.  If however anyone were to change the operating mode, by say clicking a button on the remote to 5.1 ,the entire amplifier would be destroyed as each output would be trying to drive other outputs of differing polarities.