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Reverberation. I’m not going to get into definition, you can look that up on your own and obtain your own definition for that. But I want to focus on really what it does to our music and what it’s all about in terms of perception and the differences between the different parts of reverberation.

So it’s the most critical variable in any musical performance in a room. We all hear the term RT60 times. Well, this is what reverberation is all about. It’s the birth of sound, the decay of that sound and the death of that sound. And it’s cyclic. So we have kind of a journey of life, if you will, with each note. The note is born, the fundamental, it decays and hopefully it decays naturally and that’s what we’re going to talk about here. We’re going to talk about the differences when it doesn’t.

So reverberation does something that’s very unique. It increases the loudness which is a psychological term, not really a defined term, in terms of music and physics. So it increases the perception in the room of loudness, okay? It also gives us a feeling of envelopment, like the music is all around us. And this is the principle that these home theater systems are based on multiple sources, throwing lots of energy at you in different sound fields, will get that sense of envelopment. Well, that’s what you get also with RT60.

So when you have a balance, and this is really, really critical when you have a balance between the RT60 times and the individual notes. So if we’re looking at a graph, we see the RT60 times measured. But those times, the whole system, the whole room, all the fundamentals and harmonics that are measured. And then there’s a time signature between each note. And there has to be a correlation between the decay rate of the RT60 totally and the individual time signature of the individual notes that make up that whole curve.

So this is a real, real critical relationship. This is where you get the definition. Anybody can put a lot of absorption in a room and lower the RT60 time. But to match the rate and level of lowering with the time distance between each note is the critical part. Alright. Now, if you don’t do that correctly and the RT60 is too short the music lacks fullness and loudness, right? If it’s too long, individual notes, they blend together. So it’s a delicate – and you get loss of clarity and definition, so it’s a delicate balancing act between total time signatures of all the fundamentals and harmonics, the distance between each fundamental and harmonic and those time signatures have to match.

You also have to match to the usage of the room so that you get a nice time and tempo signature. So if you match RT60 times to the distance between each individual note and you make sure you have the proper room size and volume for usage you’re going to have a real nice natural sounding room.

Let’s continue our discussion of reverberation and look at some characteristics of a reverb. So we have to use subjective terms because human beings, we have a mind and a heart so it’s always this balancing act between thought and feelings. So some of the subjective terms we can use for reverberation: dryness, warmth, brilliance. Okay. So there’s some terms, some feeling terms that you could use.

Let’s get a little bit more technical. If we have a short RT60 it gets to be dead or dry. That can be good and useful in control rooms sometimes for improved definition. If we have a long RT60 time, it’s live sounding, it’s more enveloping and more lively, okay?

So it’s all – and this is so critical, most people when they have their rooms don’t realize, it’s frequency, time and space dependent. All of these variables – I mean, that’s just 3 variables that have an impact on RT60 time. And 3 variables that can produce all these subjective feelings. So it’s way more critical, it’s way more important than people realize. And when you design a room it’s way more important to keep all those things in mind. There is no one-size-fits-all. And I don’t care what you read in the literature. If you’re serious about the sound in your room you have to take all these variables into consideration or get somebody that knows them and hire them to do the work for you. Alright?

So let’s kind of break RT60 times down and see where the groups fall within the term. So RT60 is really a middle frequency, 500-1000. That’s really where the gist of everything falls. If it’s greater than 2000 cycles we have a lot of absorption in the air. So we have to be careful about what our air pressures are and things like that. So anything above 2000 really has a – the air can have a big impact on.

If it’s less than 250, if we increase it, we get a sense of warmth. If it’s below that, it gets colder in feeling, not so dry, not so warm and not so brilliant in terms of subjective. And it’s always – this is so critical, a relationship between the direct energy in the room and the reverberant energy or as we say the reflected energy. It’s that delicate balance and all of these things have to be taken into consideration. If your ratio of direct versus reverberant is low you get a full sound. If it’s high you get some clarity and definition.

So it’s a balancing act and everything in acoustics is balance. Balance, balance, balance. And there is no one-size-fits-all. There is no one size room that works for everything. There is no one sound absorption technology that works all the time for every situation.

This is an unedited transcript from our video series from Acoustic Fields. There will be some errors in grammar and sentence structure that occur during this translation process.

For complete understanding and comprehension, please view the video which is included in this text. For any additional information regarding this topic or others relating to room acoustics, please contact us directly at:

P: 520 – 392 – 9486

Dennis Foley

I am an acoustic engineer with over 30 years’ experience in the business. My technology has been used in Electric Lady Land Studios, Sony Music of New York, Cello Music and Films founded by Mark Levinson, and Saltmines Studios in Mesa, Arizona, along with hundreds of others.

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