(SOLVED -for now-)Subwoofer Crossover Setting Advice

[mdiemer]

Awhile back I added a Mackie 10Smk3 subwoofer to my M-audio BX5a speakers. These monitors are rather small. They have a frequency range of 56hz to 22Khz. They have an active crossover freq. of 3khz. (That is, the built-in crossover between the tweeter and woofer). The tweeter draws 30 watts, the woofer draws 40.

The subwoofer is also not a large one, and should match OK, although it's a different manufacturer. It has freq. range of 35-180hz. The crossover range is 40-180. It draws 120 watts.

I've been researching this, and see that the usual suggested crossover on the sub is 80hz. But I have also seen recommendations which are much higher if your monitor speakers are small, and don't have much bass response . Some as high as 150hz. The BX5a monitors are pretty weak on bass.

Does anyone have any thoughts on this? Even ballpark numbers would be helpful. I'm not sure I can trust my aging ears like I used to.

 

Edited January 17, 2021 by mdiemer

[Glenn Stanton]

i have the SP-5B and a Sony sub (120W) and i set the crossover to 90hz and because it has a frequency bandwidth setting as well i allow up to 150hz ( a slight bump in EQ) to compensate for a room mode. but the main crossover point on my x-over unit is 90 and the setting on the sub is 90. that seems to produce a fairly even response. even with the Avantone Cube, 5.1 JBL satellites, and my Bose 901 as well.

best bet - make sure the sub is well-placed and run a series of noise and frequency sweep tests to iron out the best crossover for your room and system. i would say it took be probably 2-3 hours of testing and tweaking to get it just right for me.

Edited January 14, 2021 by Glenn Stanton

[mdiemer]

Thanks Glenn, I appreciate the advice. I'll  see how 90 sounds. Right now I'm all over the place. I forgot to point out that I'm doing classical, orchestral stuff, in case that makes a difference.

[mdiemer]

Well, setting the crossover to 90 hz does make it sound better. I have tried 80, 100 and 120, but not 90. There is a definite improvement at 90. not overwhelming, but it's there. I'm going to compare it to 80 and 100. It looks like this is the ballpark I'm hitting in. 90 may be the sweet spot, If not it's very close.

[Glenn Stanton]

it may but i'd start with a more clinical approach to get the balance then tweak if needed - based on your experience with a given piece and how it should sound - i find usually this is done with some final monitor positioning and perhaps some very small monitoring EQ movements.

[mdiemer]

My current thinking with this: using the "10hz" rule, since my monitors go down to 56hz, the lowest I should set the sub would be 66hz. That does seem pretty low. So, is the "10hz" rule valid? does this at least give me a lower limit? If I could then decide on an upper limit, it would help narrow things down.

I'm going to test some settings out with a string passage that starts low in the bass and goes up well into the high-mid range, then back down to the bass. If I can find a setting where there is a seamless transition, that may be a good way to nail it down.

[Glenn Stanton]

never heard of the 10Hz rule... in general, a LF spec of (for example) 50Hz on a speaker may be the -6db roll-off point or a -12db roll-off point where the manufacturer felt comfortable making the claim about 50Hz... so in general, see if they have a publish frequency response chart you can validate it and also keep in mind that speakers are generally tested in an "infinite baffle" type of configuration to reduce or eliminate baffle step and refraction impacts on the response. if they're honest they'll also publish a polar distribution chart or two to show how it acts in a free space. and some even go so far as to show how the speaker reacts in wall and corner scenarios. (reference: https://www.trueaudio.com/st_spcs1.htm)

[mdiemer]

Wow, that's pretty complex stuff. Not sure I understand it. My latest thinking on this: If mid-range speakers start at about 110hz, then if I set my sub at 110, I am freeing my monitors to only deal with the mid-range. Below 110 the sub takes over. so far, results are good. Still not sure I have the best setting, however.

[Glenn Stanton]

there is a "slope" in the response, so no setting is generally a perfect "cut" or "boost" at a given frequency (hence "cross over") and determining where on the slope to transition from one driver to another has plagued acoustic transducer design since time immemorial ?  (well, since at least 2000BC)...

[mdiemer]

It is indeed somewhat bewildering. Like the strike zone in baseball. It's supposed to be fairly exact, but in fact is very subjective, a fact which leads to frequent ejections of players and managers. 

At this point I am thinking the ballpark is between 80-120 hz. somewhere in there is the wheelhouse (to stick with baseball metaphors, although a bit out of season). 

[mdiemer]

I'm putting it at 90hz and calling it good for now. The reason is, I have discovered other problems with my sound, resulting from the use of samples from several different libraries, and conflicts arising from differences in panning, room impulses, etc. For example, the basses in Vienna Special Edition are panned left of center, while East West and Cinematic Strings basses are panned right. I kept wondering why there were basses on the left. I even checked my wiring to see if I had reversed some connections. 

Anyway, you can see that writing for full orchestra, and using multiple libraries, creates all sorts of problems. I need to get these sorted out before worrying about crossover settings! But at least I have learned some things from this thread. I also put a thread on Tom's Hardware forum (you might be surprised at that place; they have a zillion subforums, and very knowledgeable and helpful people. I learned a lot there, too. For example, someone directed me to this place: 

https://www.avsforum.com

I found some very interesting threads there on subwoofer issues, among other things.