ISOLATING BASS FORM MY STRUCTURAL CORNERS

[DAX616]

I have true false corners for my k horns the wall extends at least 4 ft to either side. It seems the bass couples with the corner walls. I would like to bring more of that bass energy forward. If I built stout false corners away from the wall and employed bass trapping in the upper corners above the speakers, would this help?. I realize the room has modes acting on it, but it seems the direct connect makes this worse. What happens to the inch or two gap between the true corner and the offset corner. Should I use an isolation attachment to the original studs in the corner and try for an air tight seal?

Dax

[artto]

Try using bass trapping in the rear room vertical corners first. This is the farthest point that is a trihedral corner, 3 surfaces, to reinforce reflected bass frequencies with those coming directly from either speaker. You'll also be able to use a 'taller' bass trap which has a larger cross-section making it more effective at lower frequencies. And don't forget about the horiziontal corners. While there is not quite as abundant bass frequency buildup in these areas, providing bass trapping here can still be quite effective even if the traps are not as deep (thick) as can usually be applied in vertical corners because the traps can be much longer & still have an impact on the longer wavelengths of lower frequecies.

An inch or two gap between the false & true wall corner is not enough to affect bass frequencies (500Hz=2'+ of wavelength).

Using an isolation attachment to the original studs in the corner and trying for an air tight seal has nothing to do with what you're trying to achieve.

Let me explain what is at work here. A Klipschorn, by it's very design, is required to be in a large corner to achieve maximum performance. This location (without false corners) is obviously the room corners. From this location its possible to excite any & all room modes. The modes are caused by a situation where the dimensions of the room coincide with certain frequency wavelengths of the sound coming from the speaker. The reflected sound winds up coinciding with subsequent 'waves' or cycles, of those frequencies. Consider that even a 16Hz tone 'cycles' 16 times per second. So it takes some time for the buildup, or 'standing wave' to actually reach maximum amplitude.

What happens is that these standing waves, or pressure buildup areas in the room corners tends to cause quite the opposite effect in other parts of the room. It produces a cancellation of those same frequencies. By putting large bass trapping in the room corners you are reducing the amplitude of the standing wave at that location, and in doing so, you are also reducing the cancellation effect in other areas. It's basically cancelling the cancellation. It's sort of counter-intuitive.

As an example, I had always thought that it was a good idea to have the large 6 piece sectional sofa (4 seat sections + 2 large ottomans) in my room, located near the center of the room. I thought this would help break up standing waves. WRONG! Thats not where the standing waves were occuring. In fact, this large absorbent 'structure' was actually compounding problems by absorbing low frequency energy precisely where there were already cancellations occuring! I've since removed the 2 ottomans & 1 seating section. Bingo. More low end! Eventually I'll replace it with something more 'acoustically appropriate'.

Another common misconception is that you should have as few 'modes' as possible. This is also somewhat counter-intuitive. What you really want is as many modes as possible. Many modes, closely spaced, produces a much smoother low end response. It's when you have a few modes that the modes are at widely spaced frequencies and consequently have higher amplitudes that you wind up with a bumpy low end frequency response. As the room dimensions get larger, to the point where any of the room dimensions are much longer than the wavelengths of the lowest frequencies to be produced, you no longer have any 'mode problems'. All the frequencies essentially get reflected equally. As the room dimension become smaller the modes become more prominent, and in poorly proportioned rooms, the problem becomes exaggerated even more as multiple dimensions, or their derrivatives (2x, 3x, .5x, etc) coincide to reinforce certain frequences at room boundaries, especially corners.

In my room I recently installed 3 stacked Auralex MegaLENRD bass traps (6' high, 2' deep) in the rear vertical corner. I have them pulled about 6" away from the side walls so that the rear surfaces are exposed to provide a larger surface area for absorption. It seems this increases the effective size of the stack even more. The impact on the low end was truely remarkable! I've measured nearly flat response with both broadband white noise & sine wave tones down to 16Hz at the listening position (room has a fundamental resonance at 19Hz).

[DAX616]

Unfortunately my far corners are a fire place and then a hall way leading to a stair well. My room dimensions are about 28' x 26' and 93" high. And according to the formula I believe I start around 19 hz between my farthest walls. Half my room is carpet the other is a hardwood dance floor. The room is now untreated. I've been reading the "Master Handbook of Accoustics" and researching my approach, before I go get free accoustical advice from that company mentioned in previous threads.Thanks for the advice artto it seems your the patron "saint" of the architectural forum, Please feel free to add more.

Dax

[artto]

Well DAX, then I'm afraid you're at a disadvantage in your present situation. Thats why, as I've said before, in order to achieve maximum performance from any speaker system, but the Klipschorn in particular, you really need to start with the room itself. I even declined putting a fireplace in my room when the house was built even though I would love to have one. It's just another source of potential noise infiltration & living about 10 miles from the O'Hare airport runways I deemed it not a good idea if I wanted a very quiet room. I even closed off the stairway & hall to the room, putting the room entry near the middle of the rear wall so it would interfere as little as possible.

We all have different situations & priorities in life. I guess I was fortunate enough to have interests in both architecture, music & audio at a point in my life long before the more usual priorities take over in our lives. That, coupled with the good fortune of Mrs. Belle Klipsch sending me a complimentary copy of the Klipsch Audio Papers early in my "audiophile career" (1973) enlightened me at a relatively early stage and encouraged me to do much more research on acoustics & audio while I was attending U of I (Urbana). I was planning for this situation years before it came to fruition. And I still made so many mistakes along the way!