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Subwoofers, and standing waves...

I've noticed that placing my Servo-15 at the side of the room (facing the back of the room) produces a smoother room response than placing it conventionally between the my main speakers.
I believe this is due to my main speakers(B&W CDM9NT) reinforcing a different set of room nodes than the subwoofer.
ie: at the side of the room, the sub is within the "anti-node" of the mains at the front of the room, and therefore does not excite the same set of standing waves as the mains.

The difference is fairly significant:
With mains and sub at the front of the room, there is a 6db peak at 40hz and 80hz, and 6db nulls at 60hz and 30hz.
(+/- 12db variation and a rolloff below 40hz)
With the sub at the side of the room(with the phase set to 30 degrees), the peak at 40hz is reduced to 3db, and spreads downward to 25hz, and the 80hz peak is eliminated.
The 60hz null is reduced to 3db, and the deep bass below 40hz is essentially flat to 20hz.
The character of the bass response is dramatically improved, with no subwoofer localization or bottom end thumping.

I'm amazed that this is not mentioned in the manual, or considered an axiom for subwoofer placement.

Cheers
snickelfritz
4 responses Add your response
gunbei
2,327 posts
 
Thanks for the update. I asked because I have my sub along the right wall facing inward about midway between the main speakers and my listening position.

I find that when the speaker is located further away from me closer to the mains the sound becomes very boomy and loose. Having it closer to me along with a little crossover and phase adjustment I find the bass reproduction to be fast, tight and well balanced. This set up is very good for 2 channel music and movies, and it's noticeable only when needed.

I'll try your rearward firing position too.
snickelfritz OP
42 posts
 
The sub is actually along the sidewall, halfway between the listener and the mains, forming a "+" configuration.
The subwoofer driver is facing the back of the room.
ie: the sub is sitting "sideways" against the sidewall, with the driver being equidistant from the sidewall and floor boundaries.

BTW, I tried corner placement as well, with results similar to placement bewteen the mains, except that the 40hz peak was much larger(+6db or so), the rolloff below more pronounced, and the trough centered at 60hz much larger.
Very tubby sounding, with little impact in the midbass.
gunbei
2,327 posts
 
Byron, are you saying you kept the sub along the same wall as the mains, but moved it closer the corner, or that you relocated it to one of the side walls so it's actually now closer to your listening position? Thanks.
sean
6,231 posts
 
I don't doubt your results at all. The problem is that most people buying subs simply want to tuck them in a corner or somewhere else out of the way and forget about them. As such, the manuals typically state something to the effect of "experiment with placement". Posting the info that you have may help others to experiment and obtain better results than what they currently are. As you mentioned though, you will have to play around with the phase since the arrival times from the sub(s) to your ears may vary drastically from that of the mains. Sean
>

PS... Yes, the difference that you hear is due to the varying loading conditions / nodes present in various locations.
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