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powered towers and standing waves/room resonance


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8 replies to this topic

#1 of 9 OFFLINE   john doran

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Posted February 07 2002 - 07:04 PM

i've been having an ongoing problem with a mid-bass standing wave at my listeniong position that i'm hoping one (or more) of you might be able to help me with: i've got def tech 2000tl's for my fronts (clr 3000 for the center channel), firing down the long axis of a rectangular room that's about 20w x 30l x 8h. the wall opposite to the speakers is actually floor-to-ceiling windows - an acoustic nightmare, i know. there's a particular mid-bass frequency that has to be about +6db or more that shows up every now and then in movies and music. it's particularly bad in "atlantis the lost empire". all the other bass frequencies are ok - astonishingly fast and clean - down past 20hz (my couch and chest go nuts, e.g. during the opening of gladiator and the pod race in episode 1, and when the train is about to crash in unbreakable, i can't hear anything, just feel my floor and chairs shaking shaking shaking). i've tried everything i can think of: toed in; not toed in; subs on; subs off; speakers set to small (with sub); speakers set to large (with and without sub); speakers inward, outward, side to side; subs firing outward; subs firing inward; socks in the ports; ports open. and every combination and permutation of these - and no matter what, the room resonance persisted. have i missed anything? i can't change the listening position, and i can't bring the speakers any further from the wall than about 1.5ft (that would put the left one smack in the middle of a doorway. incidentally, the gain was pretty bad on one cd i have, and ever since i hooked up both the full-range inputs AND lfe, and set the subwoofer to "on" and the mains to "large", it has vanished. but not in the movies. weird. (not only does the music no longer have any standing waves, but it sounds much cleaner all around, something i'm going to go out on a limb and attribute to the new RhinoCables i just got...) i know you guys are probably sick to death of dealing with questions like this, but i'm hoping you'l take one more kick at the can... any suggestions?
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#2 of 9 OFFLINE   john doran

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Posted February 07 2002 - 07:08 PM

an afterthought: is it possible (something i haven't really considered before) that some dvd's are actually recorded this way?
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#3 of 9 OFFLINE   Paul Clarke

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Posted February 07 2002 - 07:30 PM

There may well be a frequency 'push' on some material which gives untoward effects. I think we have all experienced this to some degree or other. I listen to a lot a light jazz---Sade, Metheny, you name it---and I encounter this kind of phenomenon all the time. After awhile you get tired of reaching for the remote to hand select settings for individual recording material. Certainly the standards for LFE content is an open question on some sources. Question: are there drapes of any kind on the glass?
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#4 of 9 OFFLINE   john doran

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Posted February 07 2002 - 07:52 PM

no, there aren't, just vertical blinds made of some kind of thin metal. we'll be moving soon, so i plan on investing in some room treatments if the house we move into has the same unfortunate acoustic properties.
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#5 of 9 OFFLINE   Bob_A

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Posted February 07 2002 - 09:45 PM

Hi John!



Which movies, and with what specific scenes, do you find this problem? How does it sound to your ears when the problem is evident?



Did you use new Rhino cables for the full range low level in AND lfe hookups?



It is very possible that the recordings were mixed to emphasize these frequencies.



Would it be possible to use an equalizer to tame this frequency if all else fails...?



I guess we'll have to wait and see how it goes in the new room.



By the way, I completely agree with you...the bass on these speakers is astonishingly fast and clean Posted Image

#6 of 9 OFFLINE   john doran

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Posted February 08 2002 - 05:18 AM

Bob, I have found, most recently, that the whole opening scene of Atlantis: the Lost Empire has the offending frequencies, as well as when milo drops the shield in the following scene, and when the leviathan attacks the sub; pretty much in any scene whenever there's sustained low end in that movie. i'm afraid i can't think of other movies right now, since i've been running through that movie as my test disk for all my speaker modifications... and it feels uncomfortable (very fatiguing) both for its volume as well as for the fact that it feels as though the sound is pushing in on my eardrums (which, presumably, the air in the room actually IS). yes, i used the Rhinos for both full range and lfe. i was thinking about an EQ, but i think i'll live with it (the room gain) until i move into more permanent digs, at which time, if the problem persists, i'll consider the investment in an EQ well worth it. thanks for the reply, Bob. i hope you're well.
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#7 of 9 OFFLINE   Bob_A

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Posted February 08 2002 - 10:00 AM

Hey John, Hopefully I will have a chance to rent this movie someday...and I'll let you know how it sounds (but I am only using the full range low level in). Take it easy John...have a nice weekend!

#8 of 9 OFFLINE   john doran

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Posted February 08 2002 - 10:33 AM

There's not too much difference between the full-range alone and the full-range-with-lfe - if anything, the bass is slightly more aggressive, or forward with the lfe. which i like. At any rate, the resonance is the same with both configurations. And I swear, that movie has to have the most brutal low-end I've ever heard, Episode 1's Pod Race notwithstanding. It's really nutty. Thanks, Bob, and I hope you have a great weekend, too.
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#9 of 9 OFFLINE   Michael R Price

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Posted February 08 2002 - 01:53 PM

I think that many have peaks in the 30-50Hz region because at that point their room is entering 'pressure zone' (below or at the lowest mode) and the large tower speakers have not yet begun to roll off the bass. In this case you may be experiencing +6 dB or more in that region. Sometimes this might be hard to fix without an equalizer, since the room response under a certain point tends to rise evenly at most positions inside the room (whereas the standing waves would have different effects, and you could fix such problems by changing placement.) While the mid and upper bass sounds different as I move around the room, the lower bass sounds the same. So you should probably try an equalizer... or maybe it's just inherent in the source. Try measuring your bass response with an SPL meter. If you have a good (+/- 2-5 dB) response, the problem is likely the source... if you have significant peaks, try changing placement (maybe move the speakers farther out into the room and closer to you) or an EQ.




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