Axiom Home Page Forums General Discussion Home Theater ? on first reflections

Real80sman,

Is this finishing system CSA approved?

Just a quick note about reducing bass resonance in a room. Indeed ALL modes terminate in corners, and bass frequencies are dandy little culprits who end up there along with all of the others. The reason for bass trapping at all, is to reduce the resonance of the room, and to "decouple" (if you will) standing waves between parallel surfaces. One of the reasons I ask folks to consider using 4" thickness bass traps on the FRONT walls, is because speakers are often times situated so close to the front wall, (often times called a "boundry") that they help to resonate that wall easily and perhaps create a standing wave between that and another parallel surface such as the rear wall. Bass trapping on that front wall (and throughout the room in general) helps reduce overall resonances of the room. When you reduce the resonane and eliminate standing waves, your auditory senses can hear the clean sound from your sound source (speakers, sub) and not the additional resonance of the room. When the room is allowed to vibrate without treatment, it becomes part of the speaker system, thus creating that "whoom whoom" sound and destroying your sound system's full potential.

Using 4" thickness of rock wool (mineral wool) or mineral fiber (OC703) will go a LONG way to creating a more sound environment and much better sonic experience overall. And you don't need my products or anyone else's to make a HUGE difference. Placement is key as others have pointed out, but the "right" amount of absorption should not be overlooked.

I hope this helps?

Joel, that's one of the best down-to-earth, layman's explanation of room resonance, and what room treatments can do to help, that I've ever heard. Even I understood it. Bravo, and thank you.

What Jack said, very good indeed. I am now thinking about some corner traps.

Ditto what Jack and Rick said. Thanks for the input here, Joel--most of the time, I think, people don't spend enough time figuring out proper placement of his/her speakers and it may be the room that's the culprit of bad sound. The best part is that placement tweaking is free and can have the most profound effect on a system. I added some corner triangles to the top corners of my room, and those, too, had a significant impact on bass.

Thanks for your kudos gents. I appreciate them very much. I hope that information helps others as well.

I'll do my best to help however I can.

Thanks again,

I want to say thanks, too, Joel. I think we're going to like having you around.

Hi Axiom_man and all,

I want to issue a cautionary note here. While I don't advocate long stretches of bare, highly reflective walls to either side of your listening room, I want to point out that first and secondary reflections from the sides of a room, largely produced by the off-axis dispersion of the front left and right main speakers (and, to a lesser degree, the center channel) generate important psycho-acoustic cues that add a sense of spaciousness and breadth to the soundstage, whether it's multi-channel movie soundtrack playback or simple stereo.

Much of Dr. Floyd Toole's early work in speaker measurement and testing (I sat on the listening panels for lots of tests) at the National Research Council Acoustics lab indicated that in typical rectangular living rooms furnished with normal domestic objects--rugs on the floor, bookcases or the like on the wall, upholstered furniture--the smoother and wider the off-axis frequency responses were for a particular speaker, and the closer they reflected the on-axis response measurements (in anechoic measurements), the more "spacious" and "realistic" the soundstage was perceived in double-blind listening tests.

So leave those first and secondary reflections alone, and do NOT overdamp your room. You'll end up with a dead-sounding space. I've seen too many over-"treated" rooms that had a kind of dead, sucked-out quality that was almost akin to listening on headphones to a dry studio recording.
If you add a lot of absorbent panels to dampen and soak up first and secondary reflections, you'll lose much of the desired spacious quality that well-designed speakers like Axioms with wide laterl dispersion generate.

One room I recently visited that was "professionally treated" had exactly those dry, sucked-out qualities. It was almost like listening to music in an anechoic chamber (a room with no echos). Paradoxically, this prominent reviewer's family room, which had no special acoustic treatment delivered a much more satisfying listening experience. And the bass in that room (from one EP500 subwoofer) had greater extension and power than the over-treated listening room, where four subwoofers were operating.

There is a place for bass traps when you have impossible standing wave problems; however, more often than not, the addition of a second subwoofer will greatly smooth out deep bass distribution to multiple listening locations.

Regards,

Alan:

You might find this short article interesting which expounds on another element of Toole's recent work and the importance of NOT over treating small rooms with absorptive elements [specifically as such relates to speech intelligibility and center channels and more generally the inapplicability of paradigms developed for large spaces to small rooms].

http://www.audioholics.com/education/aco...ent-perspective

While I have long understood the importance of the caution to not over treat critical listening spaces with absorptive elements, I would object to the idea that early reflection control and similarly located absorptive placements implemented to diminish SBIR interference are in and of themselves bad ideas. Collaterally I would readily agree that modal resonances and early reflections are not bad things... its all about balance in my opinion, you can have too much early reflection input and garble the stereo image – you can have too much absorption and render the room dull. Neither is best practice.

We have found by that taking a broadband approach to absorptive treatment of small rooms [using absorbers on the order of 4” minimum thickness which work more or less smoothly at all frequencies – lows, mids and highs] one can greatly reduce the surface area of absorptive treatment used overall and in such cases yield a critical listening environment that does incorporate a modest amount of early reflection control but retains a stellar “spaciousness" and a “realistic the soundstage”. This approach also saves money in that you use fewer panels, and can achieve smooth low frequency response with fewer subs.

When properly balanced in a room with rational fixtures and finishes we find that modest early reflection control can enhance the depth and clarity of the illusion of the stereo image, diminish SBIR problems, and make for a larger “sweet spot” without killing the “snap and sparkle” of the room, or causing speech intelligibility problems.

Also, low frequency control through absorption is in our experience not simply a matter of dealing with “impossible standing wave problems”… but rather a means to smooth out the rough responses inherent to all small rooms arising form low modal density at low frequencies and unavoidable SBIR problems. Here is an example:



The above graphic is a series of 13 low frequency response measurements taken in a small room. The first frame is a bare room with no treatment. Each successive frame is the same measurement taken after the addition of a single 4” thick absorption panel. In the thirteenth and final frame a total of 12 panels have been added. Note the significant smoothing… this sort of treatment makes a profound difference in the accuracy of your system low in the band of audible frequencies.

Controlling low frequency distortion and smoothing the system/room responses at low frequencies and diminishing SBIR distortion can greatly enhance the listening experience – and diminishing strong early reflections can greatly sharpen and clarify the stereo image. In my view, the trick is to find ways to accomplish this without making the room exhibit “those dry, sucked-out qualities” you properly caution against.