I'm never going to hear a megaspeaker in a good room am I?

Therefore in my opinion we want to minimize the early reflections but encourage the late ones.

@audiokinesis

Well, hmmmmm, I think in the context of what you posted above this makes relative sense, but don't most listening rooms have too long of an RT 60 to begin with, not to mention, it is usually pretty uneven.

So, you mean relative to early, coherent reflections, you'd rather have the energy come at the listener in the reverberant field time, but you are not suggesting the RT60 periods be made longer.

Is that correct?

Best,

Erik

For those who are curious, RT60 is the measure of reverberation time.  It answers "when does the signal decay 60 dB." and can be measured at different frequencies.

So an RT60 of 20 mSeconds at 1 kHz means that a 1 kHz signal will take 20 milliseconds to decay 60 dB.

Best,

Erik

Erik wrote:

"don’t most listening rooms have too long of an RT 60 to begin with, not to mention, it is usually pretty uneven.’

In general when we move into a larger listening room the RT60 will correspondingly tend to be longer, but the larger room STILL sounds better! So clearly RT60 is NOT telling us the whole story.

Making the RT60 more EVEN is of course desirable, BUT I have a question about the unevenness you mention: Is it based on measurements using loudspeakers whose off-axis energy is uneven? If so, is that uneven off-axis energy what’s showing up as "uneven decay"? If that’s the case, then the problem originates with the speakers, not the room.

The problem with a room acoustic approach which focuses on RT60 is that it does not target those reflections which are most likely to be detrimental (the early ones), but instead tends to have a heightened effect on the beneficial later reflections ("beneficial" assuming we’re talking about spectrally-correct reflections). This is because the early reflections will only be attenuated by the absorptive material ONE time, while the later reflections will bounce around the room enough that they may well strike the absorptive material MULTIPLE times, especially if there is a lot of it.

Imo minimizing detrimental early reflections is best accomplished by loudspeaker design and set-up, and if we still need to address the in-room decay smoothness, we can do so without the additional challenge of trying to compensate for the speaker’s uneven off-axis response.

Duke

@audiokinesis

The problem with a room acoustic approach which focuses on RT60 is that it does not target those reflections which are most likely to be detrimental (the early ones), but instead it has a heightened effect on the beneficial later reflections (assuming we’re talking about spectrally-correct reflections).

I’m not that widely read on the subject, but I have never read anyone suggest you should do an either or approach. Maybe if I worked more in the field I’d have a better understanding of the theoretical camps being promoted.

In my mind it was always both. Reduce early reflections, AND control the RT60. Now, here my experience is probably more biased towards motion picture auditoriums, as THX started promoting short RT60 times, so when I read about consumer listening rooms I’m probably assuming the same kind of thinking applies.

What I meant by uneven was having the decay times be different at different frequencies, and of course, eliminating echoes.

@erik_squires, in a big room like an auditorium, with listeners being far away from the speakers, the direct-to-reverberant sound ratio is MUCH lower than in a home audio setting, where we are much closer to the speakers. In a big room the reverberant field conveys so much more energy than the direct sound that intelligibility is an issue. The faster we can get that powerful reverberant field to die away, the less "noise floor" the direct sound has to overcome.

Also, in a large room the reverberant sound field is "statistical" - that is, the level of reverberant energy is effectively identical throughout the room. There are SO MANY reflections coming from SO MANY directions that WHERE we place our acoustic panels makes little difference on their net effect.

Concert halls, and larger ones in particular, have issues with excess reverberant energy, which makes seats near the back of the hall (where the direct-to-reverberant ratio is lowest) audibly inferior to seats near the front. The sound goes from "immediate and attention-grabbing" near the front of the hall to "muddled and less engaging" near the back of the hall. The cause is more complex than simply the direct-to-reverberant sound ratio (the earliest reflections are the worst even in a good concert hall!) but that’s still a major factor.

In our small rooms, in the absence of obvious issues like slap-echo, we have the opposite situation: Our direct-to-reverberant sound ratio is typically MUCH higher than in any performance venue. This is largely because we are typically within maybe eight to twelve feet of the speakers. The reverberation times in our small rooms are also much shorter because the reflection path lengths are much shorter, meaning that within a given time interval the sound will have been attenuated by room boundaries or room furnishings many times more often.

Ime there seems to be a "sweet spot" as far as how loud the reverberant sound is relative to the direct sound. The larger the room (the longer the time delay before the "center of gravity" of the reflections), the louder the reverberant energy can be before clarity suffers. Hence most good seats in a concert hall have a direct-to-reverberant sound ratio which would be WAY too low for home audio, but it’s okay because of the much later arrival times of the reflections.

You mentioned uneven decay times - how are you going to find out whether your room has uneven decay times, so that you can figure out what to do about them? You have to make measurements. And if the measurement process INCLUDES your loudspeakers, then inevitably it INCLUDES their off-axis response. Yes there are omnidirectional loudspeakers designed specifically to measure decay rates in large halls, but I doubt very many audiophiles have access to such.

Based on conversations with acousticians, it is much easier to fix the room with acoustic treatments than it is to fix the room AND the loudspeakers at the same time.

Duke