Nulls in bass

[Inu_Yasha]

Hey everyone, it's been quite the while since I've last posted. A lot has been going on; I finally graduated from undergrad and am getting my Ph.D. I just bought a new house and was setting up a room to be my designated theater room. I noticed that I was getting really bad nulls throughout the room. At some places, the bass was very nice and tight, others it was muddy, and in other places there was almost no bass. I was wondering what could be causing that? I'll post pictures of the room once I get my digital camera. Any help would be appreciated.

Thanks!

[bluewizard]

Just a preliminary thought, but if you are getting these nulls then it is probably because you are getting strong reflections off the walls and ceiling.

To sort things out, you need to add some acoustical treatments of some type. These could be curtains, rugs, etc.... Or you might have to go as far as bass traps, sound absorbing panels, and diffusers.

Here are some links I posted in another thread, that should help give you an idea of the possibilities.

http://www.avsforum.com/avs-vb/showthread.php?t=1003720

You can use real acoustical convoluted foam, but except that that is going to cost significant money.

A better compromise it to use convoluted packing foam as seen here -

http://www.uline.com/BL_8002/Anti-Static-Convoluted-Foam-Sets?keywords=foam

in pink or charcoal; I'm guessing you'll want charcoal.

Just one small note, the packing foam, is not specifically flame retardant the way acoustical foam is. Though acoustical foam is flame retardant to some standard, I have no idea how strict that particular standard is.

I did try burning packing foam (very old), upholstery foam, and some foam backed carpet. The old packing foam would sustain a slow flame on it's own. The upholstery foam, burned as long as I held a flame to it, but when out when I moved the the flame away. The foam backed carpet, would sustain a flame, but was slightly harder to ignite.

You'll have to use your judgment here.

For more professional room treatments, check out these links -

http://www.readytraps.com/

A DIY source for ridged fiberglass insulation.

http://www.realtraps.com/products.htm

Check out their on-line videos.

http://www.sweetwater.com/c669--Acoustic_Treatment__Absorption

Source of acoustical foam in several configurations as well has other products.

http://www.foambymail.com/Wedge.html

Another source of foam.

http://soundown.com/AI.htm

http://www.gikacoustics.com/

http://www.silentsource.com/index.html

Wide assortment of sound damping materials.

Steve/bluewizard

[minkuni]

Standing waves and room (eigen)modes are two names for the problem. It is related to the physical shape of the room and it is impossible to remove its effect in a normal room with realistic treatments. Correctly tuned Helmholtz resonators (bass traps) can help with the worst peaks, but ultimately you just have to find the best placing of the speakers and listening position in order to minimize the effect.

Try this calculator to see which frequencies your room has standing waves at.

Buy a copy of The Master Handbook of Acoustics and spend some time studying. The time and money invested in the book could save you some money which you otherwise might have spent on fancy cables :B

[ThomasW]

At some places, the bass was very nice and tight, others it was muddy, and in other places there was almost no bass. I was wondering what could be causing that?

Start here....

http://home.comcast.net/~thomasw-2/SubwooferSetupandEQpage2.html

here

http://home.comcast.net/~thomasw-2/SubwooferSetupandEQpage9.html

and here

http://home.comcast.net/~thomasw-2/SubwooferSetupandEQpage12.html