Last plea for a while: 1x8" or 2x6.5" SB woofers for a two-way?

[Apfelsauce]

As far as a mate for my NOS Focal TC90 TDX tweeters goes, I've narrowed down my choices a bit, but am still on the fence about one thing: should I go with one or two SB Acoustics SB17NRXC35 6 1/2" 4-ohm woofers, wired in series, perhaps in a 2.5-way, or one SB Acoustics SB23NRXS45 8" 8-ohm woofer? I'm drawn to the higher sensitivity of the 6 1/2" woofer(s), as the TC90 TDX has pretty high sensitivity itself, but I think I'd get better bass response from the 8" woofer, even in a sealed box. And I'm still unclear as to what the potential, audible advantages of multiple mid-bass drivers is, other than reduced excursion...?

Both woofers were reviewed quite favourably by Zaph, and according to both his and the manufacturer's published data, crossing them over 2k-2.5k-ish Hz shouldn't be an issue... Tweeter Fs is 950-ish Hz. Normally I'd balk at an 8" two-way, but I can't see any reason not to in this instance. Any thoughts? Thanks again for any input!

[weltersys]

Originally Posted by Apfelsauce

As far as a mate for my NOS Focal TC90 TDX tweeters goes, I've narrowed down my choices a bit, but am still on the fence about one thing: should I go with one or two SB Acoustics SB17NRXC35 6 1/2" 4-ohm woofers, wired in series, perhaps in a 2.5-way, or one SB Acoustics SB23NRXS45 8" 8-ohm woofer? I'm drawn to the higher sensitivity of the 6 1/2" woofer(s), as the TC90 TDX has pretty high sensitivity itself, but I think I'd get better bass response from the 8" woofer, even in a sealed box. And I'm still unclear as to what the potential, audible advantages of multiple mid-bass drivers is, other than reduced excursion...?

Both woofers were reviewed quite favourably by Zaph, and according to both his and the manufacturer's published data, crossing them over 2k-2.5k-ish Hz shouldn't be an issue... Tweeter Fs is 950-ish Hz. Normally I'd balk at an 8" two-way, but I can't see any reason not to in this instance. Any thoughts? Thanks again for any input!

The 6 1/2" woofers appear more sensitive because they are using 2.83 v, which is 2 watts into four ohms, so subtract 3 dB, then add it back for doubling of cone area, then subtract 3 dB for being in series and they are pretty close.
That said, the 8" has more low end, and more excursion, at Xmax it can displace 2808 cc, the pair of 6 1/2" 2596 cc. If low end is a concern, the 8 is a better choice. Of course, the 8 is moving 13mm to do just a bit more than the 6.5s at 11mm, it may have more intermodulation (AKA "Doppler") distortion.

Getting three speakers to "play nice" together is a bit more difficult than two.
Using the 6.5" in a WTW arrangement will result in symmetrical, but deeper lobes than than the 8 and a tweeter.

That said, the 8 inch has around a 6 dB on axis rise at 1K,and a huge peak at 2.5K making a passive crossover to a 950 FS tweeter in the 2K range a lot more challenging to get right than the 6.5".
Then again, the 6.5s have an 8 dB peak starting just below 4K, only an octave away from 2K.

In either case, the crossover will be the defining element as to the sound of the speaker, neither will be easy to get right.

I should get back to the dual Eminence Alpha 6/APT crossover design I'm working on. After 8 hours work (using SMAART, and substituting dozens of parts) yesterday, I got the passive crossover to work reasonably well. It only took about 10 minutes with a DSP to do a lot better though, out of band peaks and impedance changes are easy to deal with DSP, but very difficult passively.

Have fun with whatever your choice is !

Art

[Apfelsauce]

Wow, thanks for all that information! But you've only made my quandary deeper! In any case, I WILL have fun with it...

[weltersys]

Originally Posted by Apfelsauce

Wow, thanks for all that information! But you've only made my quandary deeper! In any case, I WILL have fun with it...

Always happy to help