I have after getting rid of one of my passive SVS subs I now have a couple of unused channels on my pair of 755 amps. I am considering biamping my two front channels (Klipsch RF-25 speakers). I also have a pair of RB-25 speakers (used to be for presence with Yammy 2500) I no longer use since I upgraded to the 990. I am also considering sitting the bookshelf units on top of the floorstanders and using one amp channel to power the three 6" drivers (2 from the RF-25, one from the RB-25) and one amp channel to power the horns (one horn in each of the speakers). I would toe the RF-25s in just a hair and the RB-25s in a little more. This way, I am thinking I could widen the sweet spot for the stereo imaging a little bit. Anyone see any problems with this or have any input?

Hi Doug, a couple of things to try:

I've been unimpressed with the results of passive bi-amping, so don't expect much -- but it costs almost nothing to try. You may decide differently. One Outlaw amp does pretty well on its own, so there's not much more to gain adding a second without altering the speaker, in my opinion.

Without knowing more about the speakers, I would be careful with this. If the net impedance of the drivers is different between the two speakers, connecting them in parallel to a single amp channel could do more harm than good. If the RB-25 drivers are lower impedance than the RF-25, it will mean most of your power is routed to the RB-25, which probably sounds worse out of the two. Even if the drivers are the same, the internal crossovers and cabinet geometry can change the total impedance. You can also strain the amplifier if the total impedance is too low. If you go this route, test it with low signal levels and a sound meter to make sure they're closely matched before cranking it up!

Instead of this, I'd probably drive the whole RF-25 with one channel and the whole RB-25 with another, feeding the same signal to both amps. I'm assuming the sensitivity of the two speakers is similar.

Yeah, that could work. You might want to experiment further with room placement too, in case this setup gives you diffraction effects. Sounds like fun.

-RM

Put the speakers in series instead of in parallel and you will not have an impedence problem (just a power one since you will raise the impedence instead of lowering it) if you don't want to use a separate channel for each speaker

Well, sort of. Series instead of parallel trades one problem for another. The higher net impedance is much less likely to send an amp into instability, yes, but you're still limited by the amp's ability to produce clean power, so your practical sound level limit is about the same. With parallel you'll pop fuses or get voltage droop as you pull too much current. Series, the amp will clip when you hit the voltage rails. I'm not sure which is worse.

Assuming you've got plenty of power, you'll still get lopsided power delivery if the speaker impedances are different. In parallel, the low impedance speaker will be louder; for series the reverse is true. I still think you'll get best results with one channel == one speaker without knowing more about the nature of the loads.

First, assuming that you are a careful person, “It ain’t gonna hurt to try it.”

But from my experience, there are several reasons why it might not work so well. On one hand there is the area already being discussed, the electrical signal path with potential impedance issues and poorly behaved crossover interactions, to name just two of the electrical issues.

On the other hand are some acoustic issues. Is the behavior of the disparate drivers going to ‘muddy’ the sound in the upper low, middle and high frequencies? Without getting into descriptions of the physics of acoustic propagation, ask yourself, do loudspeaker manufacturers construct systems where multiple drivers at the same location use uncorrelated crossover points and have multiple drivers responsible for the same regions of intelligibility haphazardly placed in relation to one another? I have some small experience with multiple cabinet and driver systems and know that the coordination of crossovers and driver placement is critical to maintain intelligibility and clarity.

I’m not trying to rain on your parade or be critical, I just saying that while you may find increases in acoustic output for certain locations in the listening area, you may find that the clarity suffers. Let us know how it turns out for you.

Thanks for all the replies. I am waiting for my acoustic panels to arrive, I am going to put them in place and then I am going to try a weekend of wome serious experimentation.

You can, indeed, hook two different speakers to a single channel of amplification either in series or in parallel.

Neither of these is likely to yield good sound reproduction. Connecting the two speakers in parallel would be better, though. Speakers are voltage driven devices and in parallel they should see the same voltage across their input terminals.
Separate leads from amp to each speaker would be a good idea. One danger of this is that the listed speaker impedance for most speaker is an approximation, as the speaker includes reactive (energy storing) elements that make the impedance frequency dependent. An 8 ohm speaker may dip to 3 ohms at certain frequencies and be as high as 70 at others. Trying to drive the combined curves may make life very interesting for the amplifier.


Hooking them in series is worse, because the changing (with frequency) impedances mean that the two speakers will share the available voltage/current/power unequally and neither will have a proper frequency response. In addition, if one speaker has capacitive reactance and the other has inductive reactance, at a particular frequency these will cancel, leading to an extremely low series impedance and the possibility of amplifier instability or overcurrent limiting. Most speaker do have inductive reactance but electrostatics (Dayton Wright, Martin Logan, Infinity Servo-Stat, Apogee among others) are generally a capacitive load.


Steve