Crossover point of 5.25” vs 6.5” in two way bookshelf

 @erik_squires  Yeah I enjoy Erin’s content but I’ve come to realize that what he likes I generally don’t. I’ve heard several of the speakers he liked in his reviews and I did not like them at all, and some of the ones he didn’t like I have liked…so 🤷‍♂️ His reviews are well done and very detailed but I can’t base my decisions off of them I don’t think.

@sounds_real_audio at what point is too high of a crossover for a 6.5” driver. From some of Erin’s reviews he talks about larger drivers “narrowing up” at higher frequencies, so I assumed you’d want to crossover a larger driver at a generally lower point.

OP: 

Not saying his reviews should sway you, but that the speaker reviewed showed optimal off-axis performance.   Also, take a look at the Stereophile Dynaudio review that just came out.  They used a relatively high crossover point without issues. 

For many years it’s been known that crossover in the 2000 Hz range can be very audible. Pushing above that to around 3000 Hz can be smoother, more “ideal”. Guessing also that the 6.5” driver is smoother out to 4 kHz than the 5-1/4” driver, and can maintain that smoothness at higher power levels.

If all else is equal, the 5" would tend to have better HF response, but it’s not an absolute.  It could be a typo or simply a variable due to other factors with the drivers.  Either way, to allow the sound waves to propagate as a single point source, a 3100hz crossover would ideally need the driver centers to be around 4.5" apart or less, which is a bit of a challenge.  A 2100hz crossover is a bit more generous allowing up to ~ 6.75" between the driver centers ideally.  There are always tradeoffs to consider between coherency, dispersion, frequency range, distortion, comb filtering, etc.  Hopefully they've done their homework and chose the best situation for both.  

All these 2 ways are a compromise for the following reason...

A small driver covering around ~1000 to 1300 hz and above is an important concept, as there is a lot a spatial information, resolution, detail, harmonics, etc that can be preserved by doing so.

Small drivers playing that low can only come from a compression driver/horn speaker or tekton style of small driver array. Some 3-ways also do it in an intelligent manner. For, example, a small ~3inch very high quality zylon mid driver takes over at approximately 750hz and above in a yamaha ns5000, etc. The PS Audio FR10 is another example, a low mass ribbon midrange taking over from 550hz onwards...

This can all be demonstrated in a a/b with what to listen for in tracks. (not just the science of small driver impulse, low mass, etc)

In general, it is best to avoid these 2 ways.