Bi-wiring to 4 and 8Ω speakers

Hi Dbphd,

Sounds messy. 

Parallel impedance divides. When speaker makers do this, the crossovers prevent impedance dividing. That is, the tweet, midrange and woofer don't seem to be in parallel to the amplifier's sense of impedance (more or less). 

Without that, the basic resistance formula is like this R = 1 / ( 1/Ra + 1/Rb ...) so, roughly:

R = 1 / ( 1/4 + 1/8 ) = 2.7 Ohms. 

A pretty low value. 

Also, there is no level matching. Again, something crossover designers do for you. The level of one speaker may be far different than another. 

So, in general, I'd say no, don't do this.  If you were going to use a pair for say, one pair in your pool, another in your bedroom, this approach would be OK if the resulting impedance was high enough. 

What you really want to do in this case is use an active crossover, and separate amps for each speaker. 

Best,

E

Hello DB,

Since your amp is rated to work continuously into 2 ohms (with a power rating of 1200 watts for that impedance), I don’t think you’ll have an impedance problem. Looking at Stereophile’s measurements of impedance vs. frequency for the two speakers, the worst case occurs slightly below 200 Hz (just slightly above the low frequency crossover point of the 107/2), where both speakers have impedances of close to 4 ohms. So in the vicinity of that frequency the amp would see a load of 2 ohms.

HOWEVER, there are several other concerns with what you are proposing. A factor in some of these concerns is that the LS50 appears to provide just one pair of input terminals:

1)As Erik pointed out, levels would not be matched. And based on Stereophile’s measurements the 107/2 is about 4.5 db more sensitive than the LS50.

2)Most frequencies below a few hundred Hertz (i.e., below the point at which the response of the LF section of the 107/2 has rolled off to insignificance) would be reproduced by both speakers. Those frequencies would therefore be likely to arrive at your ears improperly aligned in time, resulting in comb filtering effects and compromised sound.

3)The fact that the frequencies referred to in item 2 would be reproduced by both speakers, while other frequencies would not be, will compound the frequency response issues caused by the differing sensitivities of the two speakers.

4)If the KUBE equalizer you may want to use with the proposed configuration is set such that it provides a bass boost (and I believe it may do so regardless of how it is set), the LS50 might receive more low frequency power than it can comfortably handle.

The bottom line: It doesn’t sound like a good idea, as Erik indicated.

Regards,
-- Al

Thanks guys,  I'm not sure what the hell I'm doing, running in circles trying to decided between keeping the 107/2s, buying 207/2s, or waiting for Blade 2s. The 107/2s sound very fine.  The real breakthrough for me has been Roon.

db 

So I've been doing some reading. Those speakers rely on an active EQ circuit, the KUBE, that adjusts the signal levels before the amplifier. 

Of course, this would make the resulting output quite unusable for other speakers. 

https://www.stereophile.com/floorloudspeakers/550/index.html

Best,

Erik 

Thanks for the link, Erik, it motivated me to reread the series of reviews, and made me realize I should quit messing around and just continue to enjoy the superb sound of the 107/2s as I have for the last decade.

db