Axiom Home Page Forums General Discussion Technical Questions Bi-amp question

When biamping as in the picture, for example where you are using the SL to drive the woofer section of the speaker and using the FL to drive the tweeter section (all channels driven, 200W into 8Ohms) are you actually driving the speaker with 400W?

Thanks.

Nope. Partially because if you were putting 400 watts of signal to a speaker, it would be really, really, really loud. But mostly because it doesn't work that way electrically. I'm sure someone who actually understands that bit will be along to explain shortly...

You are not able to add the power of both channels together to achieve 400 watts, you are simply driving each section of the speaker with 200watts, this makes it better for the low frequncies, as you have a full 200W available to the woofers instead of a portion of the 200Watts when single amped, other than that there is no advantage.

Conversely, wouldn't you be wasting almost all of the 200 watts going solely to the tweeter? I can't even imagine what level of volume would possibly ever require that much power solely when driving a tweeter... (but this isn't my area of expertise either).

Jason

Thing is, that kind of power isn't used if it's not used, ya know? If you're playing something that requires .5 watts of power, it's putting out .5 watts of power, whether the amp's rated at 20 watts or 2000. And, at least according to certain people around here, .5-1W of power puts out about 70-80dB (he says, pulling numbers out of his ear...)

Without an electronic crossover to separate the woofy parts of the signal from the tweety parts I don't think you get any real benefit at all (other than lots of cool points). Since both the woofy and tweety amplifier channels are getting the same signal as before they are going to clip at roughly the same volume setting as before.

Now, if you were running 4 ohm speakers and the amp hit current limits before voltage limits (which is not unusual AFAIK) then (a) you could run at slightly higher volume levels before clipping and (b) you could, to a certain extent, clip without guilt because the harmonics from clipping would only go into the woofer not the tweeter, so not only would you not hear them as much but they wouldn't be able to damage your tweeter since it would be the woofy side of the amp clipping.

Back when I used to play with professional sound systems (and I stress the word "play" ;)) I remember the nice thing about bi-amped systems was that you could drive them hard into clipping and they didn't sound so bad 'cause the midrange and tweeter were still getting clean signals. You could also get more effective power but that was thanks to the electronic crossover before the amps. Also, the amps tended to be different sizes, usually with a big honkin' bass amp and a much smaller mid/high amp.


Eww !! Did you wipe those numbers before posting ?

This is not true Biamping, even if the AVR manufacturer says it is...

Bobby, there's no "biamping as in the picture" going on; there's only one amplifier shown there, with several channels of output transistors(which have no power of their own)to meter out the power from the one main power supply section to the connected speakers. The maximum power output(200 watts or whatever)that the amplifier is capable of isn't doubled or increased by any amount. Biamping requires separate amplifiers with external crossovers preceding them so that the amplifiers only have to amplify a limited frequency range.

Almost nobody goes through the expense and complication of true biamplification for home use, and there's no need to. Axiom, for example rates the sensitivity of their various speakers at around 90dB(quite loud)for 1 watt of input. 1 watt is all the power that's used for that sound level even if a 1000 watt amplifier is connected. Brief peaks on highly dynamic material, such as some classical recordings that I have, can use much more, of course, but the typical modern receiver with a rating somewhere in the 100 watt area is entirely satisfactory for nearly all home audio requirements. Relax.

That illustration is straight from the Sunfire TGA-5200 manual.

Bobby Page 13 in their manual shows true biamping(external crossover), but either way, you are not able to add the power of the 2 driven channels on the speaker to achieve 400W, you are simply running 200W for each section of the crossover you are feeding the power to. Bridging the amp is how you achieve double the power or 400W/channel. I didn't look, is this amp even capable of bridging?

I also wonder how Sunfire/Carver is able to claim/achieve a true doubling of power into 4 ohm loads when nobody else appears to be able to?

I don't know the hows, but that kind of increase is common[ly claimed] in the mobile AV industry when moving from 4 to 2 ohms or to 1 ohm. Funny to hear all the issues with 4 ohm loads in the home AV side when DC amps run down to 1 ohm pretty often. I'm sure I'll get slammed with a ton of tech-speak as why this is wrong, but 2 ohm loads are stable in my car - yes I used a meter not a manual to make that claim.
But that is not what is diagramed here. Using separate channels you would not get the resistance decrease of adding more or lower ohm speakers as I am describing above. That picture should be 200 to each channel as the amp will just push the 8 ohm load it has in front of it, regardless of whether that load is in the same box as another 8 ohm load (or whatever the loads are). Of course, separating out the speakers may mean you have higher loads, thereby reducing the power output to each…in my weak theory anyway. (Let the tech slam begin.)

Thanks sirquack, that is a very clear and understandable description of what true bi-amping actually is

I think JohnK gave me the link.

car amps have WAY large capacitors in them (i think)... maybe that lets them handle lower impedances easier?

Most car audio is set up for 4 ohm loads, so a dip into the 2 ohm range is not uncommon. I have always considered running a car amp to drive the M80s, because they are built , or at least appear to be built, stonger and cheaper than home audio.

Yeah, I had noticed that. Do they mean to bypass the speaker internal crossover and then set the external crossover to the same freqs as the original internal was?

That is correct. Or adjustable external crossover. A whole lot of trouble for a dubious possible improvement.

I agree. It had better make a MAJOR improvement for all that