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View Full Version : How to compensate for room modes.



JuniorJBL
03-26-2006, 09:32 AM
I would like to hear how others have compensated for LF room modes.
My room has a -6 canceling mode about 30hz and a +3 bump about 60hz. Can anyone add their problem solving skills to this dilemma?:(

BTW this is at the listening position. 9ft back from the mains and 12ft back from the front wall.

Moving the listening position is not really an option.

Mr. Widget
03-26-2006, 10:10 AM
Moving the listening position is not really an option.Then move your washer and dryer into that room and move your audio gear....

Bass traps may help, but realistically moving things around is your best bet. Bass tends to load up on the back wall... so moving away from it or moving the wall are usually the best solution.


Widget

JuniorJBL
03-26-2006, 10:44 AM
Then move your washer and dryer into that room and move your audio gear....

Bass traps may help, but realistically moving things around is your best bet. Bass tends to load up on the back wall... so moving away from it or moving the wall are usually the best solution.


Widget

This is the biggest room in the house and I need to make it work. The reason the listening position is not movable is there are 2 rows of seating and my wife wants to keep it that way.
So I wonder if I can overcome this problem with other solutions.
I have read that it might be possible with Helmholtz resonators. Anyone ever tried these?
The room dimentions are 19.5' x 12.2' x 7.1'.
btw it is only in the center of the room that this happens.

Don Mascali
03-26-2006, 11:07 AM
Some of the guys on the HT forum have had good luck with a Behringer "Feedback Destroyer". It will find peaks in auto or manual mode and pull them down just like the excited frequencies on a PA rig.
Boosting nulls usually results in wasting amp power and making other locations terrible. Where are you taking your measurements? If you can get your primary listening position livable, call it good and let everyone else suffer. Most people don't listen critically like we do. They won't even notice.

Traps and speaker placement are the ticket...

One of the JBL white papers discusses the whole thing and makes recomendations. The search button is your friend.

Good luck,

Don M

Niklas Nord
03-26-2006, 12:04 PM
Itīs always better to use more than only one subwoofer. Two subs, one in each corner would be great in most rooms. One subwoofer in every corner - 4 subs, may be better in some rooms.

Ken Pachkowsky
03-26-2006, 03:33 PM
I would like to hear how others have compensated for LF room modes.
My room has a -6 canceling mode about 30hz and a +3 bump about 60hz. Can anyone add their problem solving skills to this dilemma?:(

BTW this is at the listening position. 9ft back from the mains and 12ft back from the front wall.

Moving the listening position is not really an option.

I have never moved into a house yet that did not have the issues you describe. Short of using traps, that have a low WAF, you are stuck with using an rta and good quality 1/3 octave eq. This is the easiest but not the best way to solve the problem. Traps and speaker placement are the right way to do it.

I had horrible bass cancellation in the listening position at our house in Palm Desert.

Our new home we are building in Nanoose Bay,BC was designed by an architect that has some experience with control room design. The dedicated listening room will allow the Westies to be soffit mounted where the wall meets the ceiling. They point down and are aimed at the listening position. The best thing is they will be enclosed in a concrete box that is reinforced with re-bar and runs down the wall into the foundation footings. This will eliminate any vibration anomalies in the wall.

The equipment will be flush mounted into the wall. We have allowed for a 3 foot wide closet running the full 16 feet of the wall so that all electronics and wires will be rear accessible. We included an independent air conditioner for that space. The house is only 1800 square feet but perfect for our needs. This could be the final one. I must admit other than dabbling with another preamp and Ian's completion on the crossover, I am pretty content and have reached my Nirvana. I will post some pics of the construction process. All the walls in the listening room run at odd angles including the ceiling.

Ken

boputnam
03-26-2006, 03:37 PM
Hey, Ken... :wave:

That "sounds" unbelievable! I really like the "access around the back" (had to be very careful with that syntax...!). Please do post some pics.

Got any of the surrounding area - your new hood - you could post in the "Off Topic" area? I'm sure many are curious... :yes:

btw, I think you are completely bullshitting about "reaching nirvana" - we all know you far better than that! :applaud:

briang
03-26-2006, 03:40 PM
It´s always better to use more than only one subwoofer. Two subs, one in each corner would be great in most rooms. One subwoofer in every corner - 4 subs, may be better in some rooms.

Uh, oh. Due to the nature of my house and it's floor plan, I only have one corner in the listening room...two are in the kitchen and one is in the entryway....:blink:

I found best placement for my single 12" sub was in the same plane as my loudspeakers, which puts it, roughly, in the middle of a wall that spans from my listening room to my kitchen.

I wonder what the WAF has to say about more subwoofers, and placing them in the kitchen....:D

More on topic, since I don't have any measurment equipment, I simply move the speakers, sub, (and sometimes furniture) in a weak attempt to tame room resonance peaks or nulls. But then I'm a rank amature at this...

boputnam
03-26-2006, 03:41 PM
Boosting nulls usually results in wasting amp power and making other locations terrible. Where are you taking your measurements? (and with what...?) Interesting points, Don.

Users of SmaartLIVE know that many points (segments, actually) in the measured frequency spectrum can be of low coherence. Adjustments made attempting to affect these areas of the response curve will: 1) not have the desired affect; 2) present a misleading "curve" on the front of the EQ, and; 3) sop power, uselessly.

JuniorJBL
03-26-2006, 03:50 PM
Itīs always better to use more than only one subwoofer. Two subs, one in each corner would be great in most rooms. One subwoofer in every corner - 4 subs, may be better in some rooms.

Subs are not the issue. I have tried 2 2242's 4 sub1500's this is something that I have tried and if I do play the 2 2242's in the front and the 2 sub1500's in the rear it does improve abit.
This is also the theater and to move to much will leave me with no room to get around in.

Mr. Widget
03-26-2006, 03:55 PM
It seems your best bet would be to bail on the real-estate hungry 2242s and use the 4 Sub1500s in 4 small cabs in 4 different locations. I really can't imagine you would need more bass than that... I use a single pair in a much larger room and they will scare you.


Widget

Ken Pachkowsky
03-26-2006, 03:58 PM
Hey, Ken... :wave:

btw, I think you are completely bullshitting about "reaching nirvana" - we all know you far better than that! :applaud:

Heh Bo, always nice to hear from you. OK, it was a weak moment!

Say HI to the gorgeous blonde! Julie came down with the flu/chest cold day before yesterday. Been rubbing Vicks into her back "and chest" for 2 days:bouncy: . The down side is fending for myself in the kitchen:banghead:

I will definately post pics.

Ken

boputnam
03-26-2006, 05:46 PM
Itīs always better to use more than only one subwoofer. Two subs, one in each corner would be great in most rooms. One subwoofer in every corner - 4 subs, may be better in some rooms.I am not agreeing with this.

I run into LF room node problems frequently as I move the system into rooms with troublesome resonances. I find that often even one sub is almost too much - and I'm not talking about gain, I'm talking about coupling and resonance. In those instances I unplug one sub and program the KT DN9848 so that the remaining one sub is receiving signal L/R at 50/50. Remember, most of this sub woof bandwidth is omnidirectional. If you are having node or comb filtering problems the last thing you want is more sources. Subs positioned in corners is particularly problematic.

I'm searching for a reference I was recently reading that reviewed sub placement - there was a great deal of discussion about 1/2 the wavelength of the node frequency relating to the sub separation (or something...). I thought it was in "Handbook for Sound Engineers, Third Edition" (Glen Ballou, ed), but I cannot find it!!

johnaec
03-26-2006, 09:03 PM
You could always build a custom EQ specific for your needs. Here's info on a custom 8-band constant-Q EQ for LF adjustments on 1/3 octave centers. He has info posted that would allow you to customize it for the specific frequencies and Q you need: http://sound.westhost.com/project84.htm#reference

John

Mr. Widget
03-26-2006, 09:03 PM
Floyd Toole's recommendation is for four subs placed at the mid point of your four walls... you won't get the additional room gain of corner loading, but you will have a more even distribution of VLF reproduction.

http://www.harman.com/wp/pdf/multsubs.pdf

Here are two other articles that may be of interest.

Widget

http://www.audioholics.com/techtips/setup/loudspeakers/SubwooferplacementP14.php

http://www.audioholics.com/techtips/setup/acoustics/BassTraps.html

boputnam
03-26-2006, 09:24 PM
Floyd Toole's recommendation is for four subs placed at the mid point of your four walls... you won't get the additional room gain of corner loading...:applaud:

With every band I work with - indoors - I beg to place the bass cabinet ANYWHERE else but the stage corner. Most doods are agreeable to place it Stage Left, facing across stage. That way, they get the dynamics they want, and I get the control FOH the audience needs. Far too-often, the bass cabinet is stuffed somewhere Stage Left facing out, on the high-hat side, and cranked-up so the bassman can get the groove. Far too often, that ends up in mud FOH. Zero tonality - everyone loses...

Robh3606
03-27-2006, 07:15 AM
That can be a tuff one. I have 3 subs, a stereo pair and an LFE. I have a placement issue with one of them. I have my mains stacked on the stereo subs and the right side is essential in the corner. The problem is I get room loading with the E-145 and I have a very hard time where the 2 drivers overlap. I also have a room mode right about where the crossover is. All 3 combine for a real mess on that side. I ended up going with steep 24db L/R to help reduce the overlap of the 145 with the sub and that helped quite a bit. It's still a juggling match though cause I still get room loading and have a hard time getting the balance good with the sub and the main. On the left side it works great, not in a corner.

Rob:)

JuniorJBL
03-27-2006, 08:58 AM
I have heard about mid way placement. This may be the ticket. Yes I could move the 2242's to a different system when it is done. It is not that I do not have any bass it is that the lower notes in the music are just not there. Woofers are a movin but cant hear a thing:blink:

Now this does only happen in a center strip about 8' long and about 2-3' wide. Once outside of this area all is good.

The sub1500's do not do this any differently then the 2242's. Yes the 2242's do want real estate but they are in the corner behind my mains and they really do not get in the way unless I need to move them to the side walls then this could be a problem. I may be able to make different boxes if this happens.

Thanks so far for all of your ideas and solutions.:D

JuniorJBL
04-15-2006, 08:15 PM
OK
Placed one 2242 RF pointing towards the rear of the room. Then pointed the LF 2242 towards the FR sub and.... well.... huge improvement!! now the 2242's just kick you in the chest!! also I do have some music content that goes somewhere in the 30 hz range and the whole back of the chair feels like an earthquake!! so just the placement of the subs was a good thing. I now want to build a twin pair of dual 2242 towers for the low level listening pleasure of impact.

BTW I really think they will look very cool.:D

SteveW
04-16-2006, 07:12 AM
JuniorJBL,
You may find this guy's solution interesting. It's a real-world application of Floyd's suggestions found in "part 3 - getting the bass right" and includes active cancellation too.
http://www.ultraaudio.com/twbas/twbas_20051215.htm

Here's the pdf of Floyd's paper 'Loudspeakers and Rooms for Multichannel Audio Reproduction - part 3 getting the bass right'.

http://www.infinitysystems.com/homeaudio/technology/whitepapers/inf-rooms_3.pdf

4313B
04-16-2006, 07:34 AM
It's great to see you posting Steve! :)

Thanks.

JuniorJBL
04-16-2006, 01:12 PM
Thanks you Steve!! These are good articles. I am waiting for a new rta and a tone generator. So I will most likely be using most of this stuff!!:D