Posts Tagged RT60
Ever wonder what gives us a sense of space? Obviously, our eyes visually tell us what’s going on, but there are other senses that contribute. Peak your head into a dark front hall closet, and even without seeing much, you can “feel” the close proximity of the walls and perhaps even the presence of the coats. Walk in to New York’s Grand Central Station, and you are confronted by a completely different sensation. Close your eyes, and the raucous environment tells you are in a large room with a lofty ceiling. Often times we take for granted the relationship that sound has to our spatial perception.
This sonic “sense of space” can be generally attributed to the room’s reverberation qualities. In simple terms, reverberation is the sound energy that remains in the listening environment as a result of lingering reflections. Reverberation time (RT or RT60) quantifies how quickly an impulse sound decays in a space. RT60 is how quickly the amplitude (volume) of short exciting signal decreases by 60dB in a large room. Reverberation time is dependent upon the volume and surface materials of a given room. Large spaces with hard materials (tile, drywall, etc.) like Grand Central Station have longer reverberation times, while small rooms furnished with “softer” materials, like the coat closet, sound much more “dead”.
Excessive reverberation is one of the most common acoustic issues that we encounter on a daily basis. As you may have experienced at some point, it’s difficult to understand what is being said when reflections from old information cover up what is newly spoken. In spaces where speech intelligibility is paramount, like classrooms or conference rooms, a short reverberation time (under 1 second) should be targeted.
That said, sometimes a long reverberation time is desirable. In spaces like cathedrals and orchestral halls, reverberation helps create ambience for the audience by sustaining musical notes, while allowing choirs and orchestras to blend more easily. These spaces may lack a sound system, and instead utilize the room to propagate sound. Rock venues, on the other hand, have amplified instruments, so a medium-short reverb time is needed to ensure that the music won’t become “muddy” and difficult to perform and enjoy.
There are a number of questions that an acoustician must ask when recommending appropriate treatment. These questions include, but are not limited to: Is there live music in this room? What kind of music is being performed? Is speech intelligibly important? What’s the audience size and where are they in relation to the sound source? So, the ideal amount of reverberation in a space is wholly dependent on the use of the space.
Listed below are the ranges of “ideal” reverberation times at mid-frequency (average of 500 and 1000 Hz) for a variety of rooms. The numbers are derived from David Eagan’s Architectural Acoustics (New York: McGraw-Hill, 1988), in which he breaks down rooms into Speech, Music and Speech/Music spaces. We hope you find this helpful.
Optimum Reverberation Times (T60)
Recording and Broadcasting Studio – .3 to .7 seconds
Classroom (elementary size) – .6 to .8 seconds
Conference/Lecture Room – .6 to 1.1 seconds
Intimate Drama – .9 to 1.1s
“Speech & Music” Rooms
Cinema – .8 to 1.2 seconds
Small Theaters – 1.2 to 1.4 seconds
Multi-Purpose Auditoriums – 1.5 to 1.8 seconds
Worship Spaces – 1.4 (Churches) to 2+ seconds (Cathedrals)
Dance Clubs and Rock Venues (w/ Sound System) – 1 to 1.2 seconds
Semi classical Concerts/Chorus (w/ Sound System) – 1.2 to 1.6 seconds
Symphonic Concerts (Classical) – 1.6 to 2.3 seconds
Liturgical (Organ/Chorus) – 2+ seconds
Contact Acoustics First to have our acousticians help you find the ideal reverb time for your space.
Yocumtown Church of God had a bit of an issue with their multipurpose room – They couldn’t understand anything anyone was saying.
While the space was designed well with a full court, dampers on the HVAC, a stage, movie screen and a good speaker system – they couldn’t overcome the poor acoustics of the space. A great deal of work had gone into the design and they wanted an unobtrusive way to treat the acoustic problems… enter Acoustics First.
We started the work of gathering information about the space; dimensions, some pictures and a few balloon pops.
Here’s what we got.
Wow! This room is big, all the surfaces are parallel and hard, there’s very little to break up the sound… You can almost imagine what it sounds like.
You actually don’t need to imagine. Here’s a balloon pop. CLICK HERE!
What you’re hearing is about 3.5 seconds of reverberation after the balloon pop. (Not good.)
So, whatever shall we do? How will we tame this space?!?!?! Will they ever be able to have movies for youth groups!?
Sure they will! We have Joe. You remember Joe from the Sabot School Big Room Big Boom Post?
Well, I would say that Joe has a 6th sense for hearing, but since that’s one of the 5 standard ones anyway, we’ll just say Joe has great ears – and they should be. Joe’s been using his ears as his primary tools for the past 40+ years; from Studio Engineer to Acoustic Engineer. His ears are tuned instruments, and we rely on his expertise with them to get the job done right – time and time again. (He also makes a mean spreadsheet.)
So after listening to the room, looking at the data, and running some numbers – Joe magically answers the question of what do they need? (Ok it isn’t magic – Joe’s just really good at this… did I mention his spreadsheet skills?)
So Joe says, “You put 280 – 4’x1′ Cloudscape®baffles up on that ceiling and you’ll bring that room down from about 3.5 seconds to about 1.5 seconds.”
Not only does it look great…
… But now they say that they can watch movies and it sounds just like you’re in a movie theater.
That’s about the best compliment you can give us.
(And the best compliment I can give Joe is, his calculation for RT60 time was about 1.5 seconds. When I ran the measurement of the “treated balloon pop” – I got 1.501 seconds. This is why we have Joe – he can tell you what you will get, before you even start!)