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.

[prodj101]

I have had the same prob. Some area's it's extremely loud, and than you walk a few feet away and nothing at all. I have 1 RSW-15, so I can't say if it's the fact that you have 2 subwoofers or not, but I think it is just the placement of the subs.

[boa12]

vap, EQ, sub placement, & crossover settings can help some, but its mainly a factor of the room & where you listen in it. here's a site explaining sound pressure peaks & nulls:

http://www.soundstage.com/synergize/synergize081998.htm

[boa12]

oh & here's the rest of the articles from that mag including the follow up in Sep/98 that has some room fixes:

http://www.soundstage.com/synergize/synergize.htm

[justin_tx_16]

Here is a way to calculate your rooms peaks and nulls to find the best placement, or approximate placement etc.

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

[Dustin B]

You'll find this educational I think:

http://www.harman.com/wp/index.jsp?articleId=122

Adding polyfill to the subs won't help. Adding bass traps to your room will help. Changing seating and/or sub placement will help, but can also create other problems.

Trying to EQ out a null is an exercise in futility. Nulls are like black holes. You can keep throwing more and more power at them, but you won't get anything back out.

[boa12]

dustin, this seems like deja vu. you can eq down the peaks though for a smoother response, like i do w/ my notch filter but just for one peak around the 50hz crossover point.

i agree though eq won't do much if you have bigtime nulls. i'm not big on eq at all either 'cept figured i'd use the notch filter some because its there.

room work seems like the best route. i'd just like to get a new house w/ a nice big finished basement w/ the right room.

[vaportoast]

Cool, thanks for all the suggestions.

I have a lot of reading to do

Hopefully I will soon find a solution.

Thanks again for all the help.

Vapor

[TheEAR]

Late to the party

Fully agree(well its logical)any sub filling or EQ will NOT solve this problem.The best thing to do in this case is find the perfect spot for the first sub and then try to find a spot in the room that works in a team with the first and not againt it.This is done with placement and I am sure a great compromise can be found where there is vast output with only minor dips in the frequency response.

It can be done since I work with three large subs and five small ones in each room and they work as one.Not competing against each other.This took me some experimentation and tweaks(placement here,nothing magical).

[Colin]

ear, how did you end up placing them in the room? how many are stacked up on each other and did you run them in parrallel or series?

[TheEAR]

Colin,

You are lucky I am still not in the dream land its 3:06AM here! LOL

The smaller room(Klipsch/Sunfire/ATI) the Sunfire Sig.,Mark II and Junior are alongside the front wall.And the two Carver Knight Shadow are in corners,two front corners.Where I sit there is no bass cancelation and the output can reach over 120dB with ease at 31.5Hz.My ears start to fail before the subs.

In the larger room the Velod HGS18,Revel B15 and Aerial SW12 are also alonside the front wall.Again this solution works like a charm,output and no nasty dips or bumps.In the larger room I can hit about the same SPL level at 31.5 but get a good deal more output at 20Hz then the Sunfires/Carvers.