Help me defeat a 55Hz peak (>10dB)

[meuge]

I just received by new B&K amp, which made a huge improvement in sound. however, there is one more hurdle which I cannot seem to overcome.

Due to my room size i suppose, as well as the placement of the speakers, I get a huge peak of ~10-12dB between 54 and 59Hz, which I've dubbed the 'invasion of the plebeian bass'. It muddies up my music and causes me a ton of aggravation.

However, I cannot move my speakers much, due to the space constraints in the room. Its layout really only allows one placement for the speakers - down one of the long walls, with the listening area along the other long wall. The speakers are about 1ft from the wall.

I don't know what to do and I am really frustrated. I wonder if raising the floorstanders a few inches off the floor would improve the sound, or whether there is something else I could do which would not cost me a months' pay.

Please help

[damonrpayne]

How big is your room?

My first thought would be that this is the type of situation a multi-band equalizer might be usefull for but I've not experimented with trying to flatten out a room with an EQ. I assume you have an SPL that is showing you the bass peak? If an EQ isn't the solution artto can probably recommend the right bass traps or other room treatments.

I might be smoking crack on the EQ idea...

[meuge]

My room is 10x16 as seen in my sig. As for an EQ, I have really mixed emotions towards using it, especially since the peak is only >10dB at the listening position (next to the opposing wall), but only 3 feet away it is minimal.

[artto]

Keep in mind that the room, the speakers, your position in the room (more specifically your ears), as well as other objects in the room are all interacting with three-dimensional space. As such, it is often also beneficial to think in terms of the vertical (Z) dimension, not just the horizontal (X,Y) axis. Raising or lowering speakers, or ear level position can often have a dramatic effect regarding the perceived sound.

Since this problem is in the bass range, and supposedly in the 54-59Hz range, (I have no idea whether this was arrived at through measurement, how the measurements were conducted, or if this is simply a guess, etc.) the wavelengths involved are rather long. The wavelength of a 54Hz tone is about 20, 59Hz about 18.5, you can see, moving anything a foot or two will probably not have much affect as this is a relatively small percentage of the total wavelength. You usually need at least one-quarter wavelength to have any significant impact. As you can see, one of your room dimensions (10) nearly perfectly coincides with one-half the wavelength of 54Hz. This would cause a 54Hz tone being reflected from the depth of the room to come back to the speaker and coincide with the next 54Hz wave emanating from the speaker, thereby reinforcing it, especially if your listening position is near the rear wall.

Bass trapping may have some impact on this however, bass trapping is usually employed to increase the bass level at the listening position by reducing cancellations caused by these kinds of problems. Employing a bass trap along the back wall/ceiling horizontal corner would give you a bass trap that is 16 long which should be effective down into the 34Hz to 68Hz range. Something like Auralex LENRD is available from musiciansfriend.com for $219 plus S&H for 16 lineal feet. Similar, albeit, somewhat less attractive product (gray only) may be available from partsxpress.com.

If you dont want to go the acoustic route with its associated additional benefits, and can tolerate the potential added noise + distortion of inserting an additional component in the signal path, and this is your only frequency response problem that bothers you significantly, I would suggest using a parametric equalizer, one that has adjustable center frequency as well as adjustable bandwith. Musician.s Friend has a PreSonus EQ3B for $99, or you could go the used route. SAE made some decent parametric EQ. A few are up for sale on Ebay. http://search.ebay.com/SAE-EQ_W0QQsofocusZbsQQsbrftogZ1QQfromZR10QQsotrZ2QQcoactionZcompareQQcopagenumZ1QQcoentrypageZsearch

[meuge]

Do you mean something like this?

http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=305-120

I think I could afford a couple of these along the ceiling/wall border of the wall opposite the speakers. Do you think they could help?

As for the numbers, yes I arrived at them by measurements. Since I use digital SPDIF out of my PC for the majority of my music (and no it is not remixed to 48kHz before leaving) I have the luxury of being able to use a frequency generator (sine wave and multiple types of white noise) in order to do my measurements.

And some more info, just in case you missed it in my previous post - the peak grows as I approach the rear wall. It is noticeable about 2ft from the wall and is unbearable if sitting back on the couch maybe 1ft or less from the wall.

Another question - will these problems persist if I use a subwoofer for bass, located elsewhere in the room? Or are these effects independent from placement of the sub.

[artto]

Yes, thats the stuff. I couldnt find any NRC ratings on it so I dont know for sure how well it will work. I use the Auralex LENRD and Mega LENRD. Youll need a minimum of 5 of these (5x2'Long=1010=one-half wavelength @ 54Hz)

It is normal for the bass (peaks and all) to get louder as you get closer to the back wall. It will probably be even louder in the corners (vertical and horizontal). And this is also the reason bass traps are usually placed there.

One of the reasons I got rid of the large six piece sectional sofa in my listening room was so I could more easily move my listening position back & forth more easily using a leather swivel type arm chair, thereby changing the bass response at the listening position. If I want more bass and 'slam', I move back, closer to the wall. If the recording is bass heavy, I move forward a foot or more and the bass is not as oppressive.

A sub may compound the problems if not placed properly. Its possible that having multiple bass sources (like multi-channel might have), can produce alternate mode relationships between the speakers and the room and help smooth things out. This can be tricky at best. Running a separate sub handling the range below 100Hz may give you more flexibility in placement to negate some problems although I suspect it may also introduce some new ones. Much of this will also probably be recording and source (ie: LP vs. CD) dependent.

None of these effects are independent of each other. They are all interdependent and it ultimately it all goes back to the room. All you can do is try to minimize it.

Check the rear vertical corners too. If there is excessive bass build up there, they too may be candidates for corner bass trapping. The vertical corners typically have more bass standing wave problems since these more closely form a trihedral corner (3 intersecting planes, 2 walls and floor or ceiling) which causes more reinforcement than a long horizontal corner (2 intersecting planes).