Bi-amping, "What amps would you use"

Actually Greg, i would be "dodeca-amping" as i have twelve active channels being driven. To make things understandable, i have six stereo amps set up as monoblocks with all 12 of their channels being used. In other words, i have both channels of Amp A driving the left tweeters, both channels of Amp B driving the left mids and both channels of Amp C driving the left woofers. There is an identical set of amps ( which would be Amps D, E & F ) set up the same way for the right tweeters, mids and woofers. Even though i am using both channels of each amp, they are still only seeing a mono signal ( left or right, but not both ).

I've done it this way as i have multiple low impedance drivers in each frequency range. By splitting the drivers between multiple channels, i've reduced the low impedance load on each amp and increased the available power for each frequency range. In effect, none of the amps are pushed as much, they operate in a range that is Class A for the mass majority of time, damping is improved, dynamic headroom is increased, etc... to top all of that off, using the "monoblock" approach offers the ultimate in channel separation.

As Bear mentioned, i chose amps that i thought excelled in specific frequency ranges. Getting everything dialed in and gain matched was a "bear" to say the least : )

The drawback to all of this is that i have more cabling in this system than what most audio shops have in their demo rooms i.e. twelve interconnects from the active crossover to the inputs of each amp channel and twelve sets of speaker cables. Needless to say, it is next to impossible to make this installation look "clutter free" :( The fact that i'd like to move into a bigger house sometime in the near future does not make me happy either :( Sean
>

Sean, you just blew me out of the house! Indeed, this looks (and probably sounds) like an ultimate system i.e. taking available products & implementing the most sonically efficient set-up... bending the limitations of the products to serve the system sonics.
Another A'goner has a similar concept, it seems, with a different approach: being discontent with the reproductive range of speakers (i.e. none satisfied his ear as full-range players), he relegates part of the output frequency to the "appropriate" speaker -- hence a speaker or "sound-wall".

I would assume that your primary limitations now can only come from speaker drivers & cables. (I discount digital source technology because we can't control that other than tweak the cdp's a bit -- we can't change the s/ware).

Impressive! Proof that it pays to be a music-phile & an EE at the same time!

Sean,
Whant kind of amp are you using .

Greg & Trandanny: I am using a vertical line array of very small surface area E-stat panels for tweeters. The line array offers better vertical dispersion and offers sustained output into the farfield. This helps to overcome some of the limiting factors in terms of problems that people run into with limited SPL's with panel type speakers. The use of multiple panels of limited surface area also helps to minimize the effects of beaming that one gets when using one larger panel to do the same job. I have appr 800 wpc driving these arrays with the impedance that they present to the amps.

Mids are handled in a similar fashion. I'm running E-stat panels that are 12" wide by 36" tall. There are two of these, one stacked on top of the other. As mentioned above, this acts as a line array and helps with maintaining a higher SPL at the seated listening position. It also minimizes the problems associated with limited vertical disperion i.e. changes in sound when you move your head, or the differences that you hear when laying back, sitting up straight or standing up. Once again, i have appr 800 wpc driving these arrays with the impedance that the amp sees.

Lows are handled by four woofers per channel. These are configured in a rather unique array. In order to duplicate the radiation pattern of the panels and achieve proper blending, they are configured in a bi-polar arrangement and are running in a push-pull configuration. The cabinets are both sealed and stuffed with a low Q design. The stuffing helps reduce the impedance peak at resonance making the drivers far more controllable. It also helps to minimize cabinet vibration. Using fiberglass adds apparent volume to the internal size of the box, increasing low frequency extension. Use of a low Q in the tuning means that the bass is phenomenally tight and well controlled with no ringing.

Bi-polar bass designs reduce room loading effects to a great extent ( as mentioned by Duke / Audiokinesis in many of his posts ). It can be tricky to set up though as anybody with bi-polar or omni speakers will tell you. When you do get it right though, bass response sounds phenomenally clean and natural.

Using a push-pull configuration in the manner that i am lowers distortion by appr 50% at low frequencies and slightly increases bottom end extension. Since the woofers are working in a push-pull configuration, each "motor" shares the load. While one woofer is pushing air away from the box, the other is compressing air within the box. As such, the work load on each voice coil is reduced and transient response is increased. This also reduces distortion to a great extent.

If you've ever read any test measurements on speakers, the woofers are typically producing somewhere in the area of 5% - 10% distortion under load at low frequencies. I am probably at less than 2% due to the approach that i'm using. Part of this is due to the push-pull arrangement and the other primary reason would be the fact that i have multiple woofers sharing the load. As such, none of them are ever "pushed".

The drawback to this approach is that you need two drivers to do the work of one i.e. one produces a positive wave while the other a negative wave. Since you are running two identical drivers in parallel, the impedance is cut in half. That is why i have four drivers, in effect giving me the output of two "super duty, low distortion" woofers. In order to overcome the amount of reflected EMF ( ElectroMotive Force or "voltage" ) in such an arrangement, you need to have a lot of muscle. As such, I have an easy 1000+ wpc driving these.

The tweeter and midrange amps are products of the "old" Threshold Corporation. I don't know anything about the new company at all. While both the tweeter and mid amps are rated for the same amount of power, they are different models. One has more "air" and i use that for the tweeters. The other has slightly increased warmth, so i use that for the mids. The woofer amps are Perreaux's and seem to work quite well for this application. I am running Goertz MI-2's for the tweeter and mid panels and i am have two runs of Fulton Gold for the subs. For those of you that have never seen Fulton Gold, it is made up of fine strand four gauge conductors : ) Sean
>