Room matters

Shadorne wrote: ".......... in theory there is no "purity" reason that DRC cannot be used throughout, however, from an acoustics perspective the ultra LF frequencies (below about 100 Hz) is the only area where DRC can effectively correct specific frequency related room modal effects. "

Agreed except for the frequency. From measurements, the upper limit of useful correction of standing waves and modes was defined by Schroeder as the point where still higher frequencies began to interact on a purely statistical basis. Above this threshold, one can best use a wider band "tone" control if room acoustics are poor. Of course, it is in this upper band that room treatments are practical, both physically and economically, for all serious listeners.

This creates a problem for us since applying correction only to the subwoofer (usually crossed over in the sub-100Hz range) leaves the bottom 2-3 octaves of the main speakers uncorrected and, imho, the problems here are more audible than those in the subwoofer range. Meridian's use of correction in the sub-300Hz range on all channels (optional and modifiable) is a great solution and one that should be an option on all other room EQ systems.

Kal

Meridian's use of correction in the sub-300Hz range on all channels (optional and modifiable) is a great solution and one that should be an option on all other room EQ systems.

My choice of 100 Hz may be a bit low and as you correctly point out - a lot of problems occur between 100 Hz and 300 Hz and, I might add, even further on up as far as about 600 Hz, as the sound goes from omnidirectional (bass) to directional (Lower midrange) and during this transistion the sound is affected at various frequencies by floor and ceiling and side walls until the sound becomes mostly of a forward direction (and the room becomes much less of a problem).

Roy Allison and many others are well aware of this problem with virtualy every free-standing speaker. However, this well known fact is hardly mentioned by the majority of speaker manufacturers these days...despite the fact that professional acousticans continue to take into account these very real acoustical problems in pro studio designs.

I decided to find out what was going on with loudspeakers and room interaction. I'd had a hint of it while doing some papers at AR. There was an unexplained phenomenon—nobody could tell me why it happened: a suckout in the middle bass range in almost every loudspeaker, almost every room transmission curve that we measured. That got my curiosity aroused. I wanted to find out what was causing it.

This transition zone from 100 to 600 Hz is often the most problematic. This is why studios tend to either

1) Use small monitors in near field close to the listener and away from walls/boundaries.
2) Use large main monitors that are built into a wall - a soffit mount

"My choice of 100 Hz may be a bit low and as you correctly point out - a lot of problems occur between 100 Hz and 300 Hz and, I might add, even further on up as far as about 600 Hz, as the sound goes from omnidirectional (bass) to directional (Lower midrange) and during this transistion the sound is affected at various frequencies by floor and ceiling and side walls until the sound becomes mostly of a forward direction (and the room becomes much less of a problem). "

I do not think this is true as stated. As the frequencies rise and pass through multiple reflections, their interaction becomes evenly distributed in space and their latency allows the listener to distinguish them from the direct sound. However, they still affect the soundfield and the decay of sounds but, fortunately, they are relatively easy to deal with. Acoustical treatments, absorption and diffusion, will do.

It is only below the critical frequency that spatial issues dominate.

Kal

Kal,

I may not have been clear enough or I oversimplified things too much but I can confirm we are in complete agreement.

It is only below the critical frequency that spatial issues dominate.

I very much agree with that and for the sake of a "critical frequency" Meridian's choice of 300 Hz is fair enough as a ball park number.

Here is an article which is based on Olsen's work that shows how a mere "baffle" can have some interesting effects. From this is follows that the effect of baffles and therefore room boundary surfaces can actually affect response over a "range" of critical frequencies - depending on the specific situation - leading to suckouts or peaks in what are sometimes broad frequency ranges.

These recent posts raise an interesting question: To those with experience measuring in-room FR, where do you find the most significant anomalies? I have experience with 4 rooms, and in all cases the issues below about 150hz to 175hz just dwarfed those above that frequency in my "normal", passively treated rooms. I've usually found significant elevation somewhere in the octave above 75ish cycles and a few severe suckouts scattered below app. 100hz. In any given room, these low end deviations have typically been 3 to 5 times as severe as anything I've encountered above 150hz to 175hz.

Kal notes that passive room treatments are effective for issues higher up in frequency. If you extend "passive" to include Hemholtz devices, I have found that these treatments can be effective in addressing that octave below 150hz. Below that, DRC (or possibly distributed bass generation with multiple subs...or maybe both) seems to be the best answer.

Even allowing for the ear's increased sensitivity to deviations in/near the mid-band, I find the deep bass issues much more vexing than those higher up.

Has your experience been different?

Marty

As an aside, I also stuck a bassbuster in the corner behind the piano in my living room and that now sounds a lot better, too. However, the piano sound would be most dramatically improved by advances in my operation of that exasperating user interface :<(