Impedenance in 2.5 way systems

[joekraska]

I'm scratching my head on this one.

I understand what 2.5 way systems are for, now, and have tooled around with the Diffraction & Boundary Simulator.

If you recall my original question on impedance in multiway systems with crossovers (to wit: why does a properly crossed over set of 2 4ohm speakers not present a 2ohm load?), you'll see where I'm going with this one.

The way I see it, for the 2 speakers that are "half way," you can wire them either in parallel or series. If you wire in parallel, I would expect half the impedance for the shared portion of the range (to 200hz or so). If you wire them in series, I would expect double the impedance for the shared portion.

But since wiring in series garners double the impedance for that portion of the range, isn't this pointless?

Am I thinking about this correctly?

Joe.

[Jeff B.]

I'm scratching my head on this one.

I understand what 2.5 way systems are for, now, and have tooled around with the Diffraction & Boundary Simulator.

If you recall my original question on impedance in multiway systems with crossovers (to wit: why does a properly crossed over set of 2 4ohm speakers not present a 2ohm load?), you'll see where I'm going with this one.

The way I see it, for the 2 speakers that are "half way," you can wire them either in parallel or series. If you wire in parallel, I would expect half the impedance for the shared portion of the range (to 200hz or so). If you wire them in series, I would expect double the impedance for the shared portion.

But since wiring in series garners double the impedance for that portion of the range, isn't this pointless?

Am I thinking about this correctly?

Joe.

Yes, you gain no senstivity gain from wiring the two speakers in series, so it is not a good choice for a 2.5 way design. And for the region that the two woofers share and are both operating in parallel the impedance will be half that of one woofer. This will clearly be seen at DC. However, keep in mind that the crossover contributes its own impedance to the system impedance so you may not see as much of a drop as you are expecting.

[joekraska]

Well I was merely mulling over going 2.5 way for my current design. It seems like you need a 4 ohm stable amp and 8 ohm mids to pull this off, however. The 4ohm stable amp--no biggie. But at least one of the speakers I was considering, the TB-1757SB, is 6 ohm...

Joe.