Mono'd sub and mid bass question for crossover sound system

[Nick Birkby]

Im wondering what difference (if any) it would make to the stereo image if I made my sub bass and "mid bass" mono up to 800hz? At what point does it start to matter?

Im mulling over a 4 way crossover with two subs on the floor 40-100hz and then mid bass/ low midrange 100-800hz followed by a 4" diaphragm horn and tweeter 800 upwards.

I have a powerful Crest 9001 amp and it occurred to me that running one channel to bass and the other to midbass might work well. It wouldnt be for very high spl so the 4 ohm load should be ok.

Id be curious if there are any conventional "rules" to doing this? Im assuming the overall mix and stereo spread should be ok (unless of course with some very wildly panned source material).

Thanks for any comments or insights.

[Drew Stephenson]

Edit - ignore all that, I'd missed that this was in the live sound forum.

[James Perrett]

I'd agree that 800Hz is too high to run in mono unless the whole system runs in mono.

[Sam Spoons]

If this is for a live sound rig then most would be run in dual mono anyway as there are significant disadvantaged in running in stereo*. Basically any audience members on the right hand side of the room will not hear any instruments panned too far left and vice versa. So I'd suggest doing the same with your rig, as James says, just run in mono and all will be well.

* There are some advantages to running stereo too but mostly to do with stereo fx rather than panning individual instruments. If instruments are panned it will likely be fairly close to the centre and sometimes to the opposite side to compensate for a loud backline rig offset to one side of the stage.

[Nick Birkby]

Ok, thanks. My apologies the question should have been clearer- its primarily for prerecorded music. I put the question in live sound as it was more PA related.

[Wonks]

Any hard-panned instruments, are going to sound really weird, with the treble to the sides and the mids and bass in the middle. 100-800hz covers the fundamental frequency range of most instruments in their lower to middle registers, so you'd certainly make a smeary mess of almost anything that's not centre panned.

80Hz and below is basically omnidirectional, above 150Hz is certainly directional and 80-150Hz is the transition area between omni and directional sound dispersion. So it really helps to keep any pure mono signals to as low a frequency as possible. Your 40-100Hz subs are OK for mono, but you wouldn't really want to extend that 100Hz upwards by much.

[Hugh Robjohns]

Im wondering what difference (if any) it would make to the stereo image if I made my sub bass and "mid bass" mono up to 800hz? At what point does it start to matter?

Roughly 100Hz. 150Hz is definitely directional.

I'm mulling over a 4 way crossover with two subs on the floor 40-100hz and then mid bass/ low midrange 100-800hz followed by a 4" diaphragm horn and tweeter 800 upwards.

If you're running a notionally stereo rig then I certainly wouldn't mono the 100-800Hz boxes. Most of the musical content fundamentals are in that region. The subs (<100Hz) can be run in mono in an otherwise stereo rig, but nothing higher than that.

If you're limited to that amp for subs/mid then I'd run the whole rig mono. Otherwise, use a stereo amp for the low-mid boxes and a (dual-)mono for the subs.

[Nick Birkby]

Ok, thanks everyone, that clears it up for me.

[Sam Spoons]

Ok, thanks. My apologies the question should have been clearer- its primarily for prerecorded music. I put the question in live sound as it was more PA related.

To what audience? If a single listner or a few people in the sweet spot then stereo will work, if a club/concert hall full then mono would still be better (for all bar the few in the sweet spot).