bi amping

tajanes

My issue/ question is with bi amping: aren't the amps still doing all the same work of producing the full range in any event with the crossover (acting as a filter) just burning off via heat the filtered out frequencies? Or is there an advantage to the amps by not ‘seeing’ the driver on the other side of the filter?  If not, it seems to make sense to put in a pre-amp filter of some type- i.e. for a three way, wherein using one amp for the woofer and a second for the mid/tw combo where crossover to mid is say 400Hz, putting in a preamp filter at ~200Hz so that a) the second amp is not dealing with amplifying the low bass frequencies and b) not interfering with the speakers internal and specifically designed filter? 

Some high end speakers have their own built in powered subs, so similar question- does this help the amp by delinking its need to drive a woofer/sub?

(yes, using a dsp/mini is an option, but for systems not wanting to bring digital conversion into the mix....) 

Thanks,

Andy

Killa

My understanding is you can passively filter the signal before it arrives at the amps. If I remember correctly you need to know the inputs impedance to calculate the filters.
 As far as amps driving speakers directly goes it is suppose to be better to directly drive a speaker. Anytime there is less stuff between the amp and speaker the amp will be able to control the driver better. How much affect this may have on sound is debatable.

Ron_E

Crossover filters don't work by burning off frequencies via heat. They work by increasing the impedance at certain frequencies and shunting some frequencies to ground. There is heat generated when you use resistors to pad a drivers level down. I've never seen much advantage to driving separate crossovers with separate amps.

Subs with their own amps and filters help by off loading bass frequencies from the mains which lowers IM (doppler) distortion. It also lets you easily match levels between the woofer and mains.

You can go fully active using analog solutions. You can even get tube crossovers if you want.

http://www.marchandelec.com/xovers.html

Ron

PWRRYD

I never really understood the purpose.

Wolf

Here I thought you'd be all about tube xovers, Craig...

PWRRYD

Nah...  need too many tubes and high voltage rated caps to do exactly what a couple of op amps and low voltage caps do better

Wolf

I didn't say it would be 'rational', but the warm glow that you so desire I figured would tip the scales...

tajanes

A goal being using a tube amp for the mid/tw and limiting its ‘work’ to those frequencies, and driving the woofer with a higher powered amp. 

I've read, but am questioning, claims of advantages of bi-amping (w/o add'l pre-amp filtering).  Several speakers are offered with bi-wiring posts, and I'm curious of the affect on an amp running through say just the high pass half of the speaker’s crossover- is there an advantage to the amp when set-up in this format? 

Killa

Not really much of any advantage IMO other than being able to use different types of amplifiers for different sections. An example would be a high powered cass-d amp for the low end. Some class-d amps don't do well with the high end (aren't accurate depending on design) but they tend to do really well with the lower stuff. Then you could use a smaller class-a for the high end if you wanted.
  Of course this all depends if you believe in amps sounding different. (I do)