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In Reply to: RE: Early reflections and comb filters posted by KlausR. on December 13, 2007 at 00:14:24
Hi Klaus,
Of course I'm aware of Toole's paper, but I disagree with that particular conclusion regarding comb filtering. In my own 25 by 16 foot living room I've tried absorption, diffusion, and nothing at the side-wall first reflection points. Absorption won hands down. If you want hard evidence in the form of graphs, see Figure 1 in THIS article on the RealTraps web site. The horribly skewed response from untamed early reflections is undeniable!
This came up a while back in one of the other forums, and I wrote the detailed "rebuttal," if you will, quoted below.
--Ethan
=========================
Folks,
Floyd is brilliant and I agree with most of what he wrote. I enjoyed the article tremendously, and learned a lot too.
Perhaps the most important thing I learned is that "Generic 'good' listening room ratios are a myth" for which he makes a compelling argument. However, his point does not seem to apply for a playback system having bass management if the subwoofer is in a corner, as in my living room HT. I never experimented with four subs, one in each corner, but I suspect the same thing applies there too. If all the modes are activated equally, their ratio should indeed still matter.
I did find a few more things to comment on. In the opening Floyd wrote:
At low frequencies the long-standing problem of room resonances can be alleviated substantially through the use of multiple subwoofers, thereby providing similarly good bass to several listeners in a room.
If you define "good bass" as a flat response, I agree that multiple subs can help. But that does nothing to reduce modal ringing which is at least as damaging as a skewed response, so having multiple subs is not a complete solution. I'm still waiting for proof that modal ringing can be reduced by EQ for an area larger than one cubic inch.
I also think his comparison of music in a concert hall in the context of why we don't mind longer reverb decays is flawed. That's fine for opera and symphony concerts, but it's not relevant for pop music or jazz where the bass instruments are recorded either direct or with a microphone very close. In that case you do not want excess ringing or decay because bass notes can run together losing clarity and articulation.
Likewise, he seems to equate "good" but very late reflections in a concert hall that make the orchestra appear wider than it is, to side wall reflections in a home listening room. This defies my own experience, where absorbing those reflections makes the sound stage wider, rather than the other way around.
Strong directional features were associated with early reflections.
Sure, and this returns us to whether the listening room should impart its own character onto the playback, versus all desired ambience is already in the recording so the room should add nothing further. The latter approach is the only way a recording can be heard as intended in different rooms. I contend that all needed and desired localization is (or should be) already present in the recording through the use of panning and reverb and ambience effects added by the mix engineer.
All of this is clearly relevant to localizing the real sources - the loudspeakers. However, success in doing this may run counter the objectives of music and film sound, which is often to "transport" listeners to other spaces.
Exactly. In a listening room you do not want to localize the sound as coming from the loudspeakers. Untamed reflections defeat this goal. It is very easy to demonstrate that in my own living room, and I do this all the time for visitors. If you stand behind the couch outside the Reflection-Free Zone you can clearly identify the speakers as the sound source. If you then lean forward over the couch the sound stage opens up, becomes wider, and you no longer hear the speakers as the source. (Except maybe for instruments panned all the way left or right.)
Another thing he seems to miss is why a small room seems to sound better than the measurements would imply. As I see it, the reason we can enjoy music in a room that measures excessive comb filtering is because the comb filtering is very different for each ear. He keeps trying to make it sound like the brain is some mysterious processor that is able to make sense of sound even when the comb filtering response is so poor. As Occam would say, I have a simpler explanation: The frequencies missing in one ear due to comb filtering are mostly present in the other ear simply because the ears are far enough apart. Later in the article Floyd seems to recognize this because he observed:
Gilford ... concluded: "The fact that the listening room does not have a predominant effect on quality is very largely due to the binaural mechanism." ... we measure differences that we seem not to hear.
Were we to measure at two locations six inches apart (ear spacing) and combine the results, I believe that would more closely resemble what we hear.
--Ethan
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