Frequency cancelation

[vaportoast]

Here's my problem-

When frequencies around 25-30Hz are played, where my chairs are located, I can't hear a darn thing or the sound is very weak. If I move slightly forward (or backward) I hear the frequencies again.

I have two sealed 15" down-firing subs for my home theater right now...

They're in the corners of a reletively square room.

My recliners are a little further back then center.

I was thinking maybe if I put some polyfill in the boxes it may work.

Or should I just move the darn chairs?

Or is it a sub-placement thing or because i have two?

Any help is greatly appreciated.

[Al Klappenberger]

I would try moving the sub to another location. My guess is that you are setting in the null of a standing wave. It's just a guess though.

AL K.

[j-malotky]

I also would try moving the subs. If you have a square room and subs on each side of the room, equal distantce from the walls on each side etc, I could see your delemma.

If your subs are on opisate sides of the room, try putting them both on the same side of the room. Maybe evan moving them so that they are not the same distance from each corner may do it.

JM

[vaportoast]

Thanks for the ideas.

I'll try them out and see what happens.

[justin_tx_16]

if you want to calculate your rooms peaks and nulls, click here. I made this page so you can input the demsinions and whatnot and find that kind of info out.

http://www.soundwise.org/beta/gethelp/peaksnulls.htm

[jnorv]

For the best start, put the subs where you sit and then move around the room until you find the best response. Then put the subs there. Never tried it with dual subs, but it should get you close.

Jim N

[Deang]

Jim's solution above is the best. Just walk around the room until you find the best bass -- then put your subs there.

Stereo subs are best placed side by side -- in the same general location.

[WMcD]

This is a matter of wave mechanics, not polyfill. This is to say, there is nothing wrong, or changeable in your speakers, or any speakers.

I'm a bit surprised that moving your head a few inches makes a difference at 30 Hz. Still, it is totally in keeping with my experiments with bass frequencies in a domestic room.

Essentially, at some combinations of wavelengths and wall spacing, and the relative positions, the echo from the walls will be out of phase from the speaker and cancel out entirely.

It is difficult to believe unless you have experienced this.

The experiment is to feed a speaker with a sine wave at about 100 Hz. Then walk around a room. At some positions, you'll find a null. It is as if someone pulled the power plug. Walk a bit farther, and it comes back.

If you do this, you'll find that if you change the frequency, all the nulls move.

Gil

[Manuel Delaflor]

If you can, put your sub right next to your listening position. Not very orthodox, but it will cure ANY room mode.

[Q-Man]

This happens a lot with two or more subs. Turn one off and listen. If this improves your situation then put them both in the same corner and try it again. You can also try having them out of phase with each other.

In most rooms one sub is better then two. This is why Horn ED stacked his SVS Ultras.

[Audio Flynn]

Human nature and influences of "stereo" lead us to make a room placement symetrical.

2 thoughts...

-non symetrical locations

-avoid corners

[vaportoast]

o.k.

i think i've tried everything i can as far as placement goes for the subs... i also tried everything with just one. i believe this room to be the devil. no matter where i put them i have this huge null kicking my butt! and i don't want to move the chairs any more than i have(i need about another foot to two) because my wife will freak. it's not that great of an improvement anyway. i'd love to do some remodeling but i don't think uncle sam would like that too much (military housing). well i'll be moving in 5 months anyway.

thanks to all of you who gave me advise.

vapor

[Ray Garrison]

vaportoast,

I have the exact same problem in my house. Where my couch is situated, I am sitting in a bass null. A *FIERCE* bass null.

As you discovered, if this is due to the relationship of your listening position and the acoustic parameters of the room, there is not a single damn thing you can do about it. One interesting way to tell if this is the case and avoid wasting a lot of time and effort in a futile attempt to cure this problem is to plunk a sub down where you sit. If putting the sub in your listening position results in little or no audible bass output into the room, then you are sol. Moving the subs won't help, changing to a bigger / better / louder sub won't help. The only thing that I found that helps is to put the sub real close to your chair (like, right behind it). This still doesn't fully solve the problem, but at least I got SOME bass that way.

Ray

P.S. Now that my entire loudspeaker system consists of a pair of Sennheiser HD600 earspeakers, to which I listen in the nearfield, I've found room interactions are *MUCH* less of a problem.