When Bi-amping is there change in sensitivity
here's the earlier thread on bi-amping that Almarg was alluding to: http://forum.audiogon.com/cgi-bin/fr.pl?cspkr&1331402108&&&/Bi-amp-question and here is a really good article on real bi-amping: http://sound.westhost.com/bi-amp.htm |
Issues about wether it's actually beneficial or not aside, I am intrigued by a couple of the technical matters discussed so far. Great info from Al (as always) and Drew, BTW. Is it not true that of great importance is each amp's input sensitivity? And is there a correlation between an amp's power rating and it's input sensitivity as Al suggests? That has not been my experience. Also, while I understand that each amp would see a full range signal at it's input, I don't understand why the amp would not still benefit from not having to DRIVE a full range signal. What am I missing? |
Thanks, Frogman. Is it not true that of great importance is each amp's input sensitivity? And is there a correlation between an amp's power rating and it's input sensitivity as Al suggests? That has not been my experience.In referring to sensitivity I was referring to the sensitivity of the speaker, which is what I thought the OP was asking about. Now that you mention it, though, I'm not completely certain that I was interpreting the question as it was intended. In any event, I certainly agree that in general there will not be a high degree of correlation between an amp's power rating and its input sensitivity. The GAIN of the amp, though (the relation between output voltage and input voltage), will have a high degree of correlation with the relation between its output power capability and its input sensitivity. As I indicated, and as I'm sure you realize, the gains of the two amps must be closely matched. The sensitivity of the amps (the input voltage that will drive the amps to their maximum power capability) is indirectly relevant, because of its relation to gain. Also, while I understand that each amp would see a full range signal at it's input, I don't understand why the amp would not still benefit from not having to DRIVE a full range signal. What am I missing?That is all correct, and you are not missing anything. I was not implying anything to the contrary. In a passive biamp arrangement, each amp will benefit from a significant reduction in the amount of CURRENT and POWER it has to deliver. The point I was addressing, though, is that since the VOLTAGE that will be generated at the output of BOTH of the amps will correspond to the complete full frequency range signal, if there is a large disparity in the maximum power capability of the two amps it is likely that the lower powered amp will be driven into clipping at a volume level at which the higher powered amp is delivering far less power than it is capable of. And of course the volume level cannot be turned up beyond the point at which EITHER amp is clipping, or severe distortion will be heard. Therefore a substantial fraction of the power capability of the higher powered amp will not be able to be utilized. Best regards, -- Al |
In a passive bi-amp situation, where a preamp is feeding two power amps and the signal from those power amps are feeding a bi-ampable speaker where the connection between the bass and midrange/treble is removed, where does the excess signal go? The preamp is feeding the full frequency range to the amplifier, which is amplifying that full frequency range and feeding it to a speaker's woofer, for instance. What happens to the part that is above that woofer's frequency cut off range. Doesnt it just get absorbed in the crossover and turn into heat. If so, how does that result in a decreased load to the amplifier? Applying the OP's situation, where he wants to use an 80 watt tube amp on top and a 500 SS amp on the bottom, where does the 80 amps bass power go to? If it still has to produce that power, just to get absorbed in crossover, then your speaker is limited to what your lowest power amplifier can produce at the bass frequencies, even though the speaker is not producing that power from that amplifier. Usually, the point of using a lower power tube am with a higher power ss amp is to get the sweetness of tubes in the midrange and up, while getting the power and control of SS in the bass. Since bass notes require considerably more power for the same percieved volume, it would seem that the only way you could take advantage of the SS amps increased power is to direct frequencies before they get to the amp, so the tube amp never sees the bass frequencies. Then the tube amp can play very loud without clipping because the mid/hi range takes much less power than the bass. Reading the posts above has got me to thinking about this, and my prior approach using passive biamping makes little sense. |
