Almost every audiophile I have ever met wanted to design their own studio for either listening to, or recording music. Assuming that you have the appropriate equipment such as correct microphone(s) and audio to digital interface, you are “almost” ready to go. An audio to digital interface takes many forms but is essentially an external component that replaces the function of the sound card in your computer with one that is more linear in its response and has receptacles for both ¼” and XLR cables. (And we don’t really need to use XLR cables or expensive microphones, but that’s another blog, including what XLR stands for and its interesting history…)
Once we have the technology in place we can turn to the “softer” side of recording- the room characteristics. We would like a room that has minimal noise and interference from external sources and this includes the use of incandescent lighting (poorly designed fluorescent lighting can generate a low frequency 60 Hz hum). Other than minimal external noise, we would also like an optimal reverberation time.
An interesting observation when comparing “acceptable noise levels” and “optimal reverberation times” is that the two seemingly unrelated phenomena are related- specifically there is an inverse relationship. Music that requires a shorter reverberation time generally is more accepting of higher levels of acceptable noise levels. The table below show this interesting relationship between the two for some types of rooms and for some types of music.
|Room environment/music style||Maximum background noise||Reverberation Time|
|Concert halls/opera||18-23 dBA||1.3 – 2.1 seconds|
|“Large” auditoria and churches||< 28 dBA||0.9 – 1.4 seconds|
|“Small” auditoria and churches||< 38 dBA||0.6 – 1.1 seconds|
|Private or semi-private rooms||< 48 dBA||0.3 – 0.7 seconds|
These data are from a multitude of references but by far the best is a chapter written by William Gastmeier (an acoustical engineer) called “Room and Stage Acoustics for Optimal Listening and Playing”. This appeared in a book that I had edited called Hearing Loss in Musicians, 2009, through Plural Publishing. Its really quite a good book, but I suspect I am a bit biased.
But back to the inverse relationship- it’s really not all that surprising and says something about our preferences for different types of music that are played or listened to in different types of venues. Recall that Reverberation Time is the time is seconds for a signal to die off to a level that is 60 dB below its initial sound. Underground car garages have long Reverberation Times because there is very little in the way of damping material to attenuate the sound- it just keeps echoing off concrete walls, floors, and ceilings. In contrast, school libraries have a very short Reverberation Time since the carpeting, book shelves, books, and nicely padded comfortable chairs all absorb the echoes.
Reverberation Time then can be thought of as the amount of echoes (or unwanted background noise) that occurs a second or two later and we can actually measure the echoes or reflections in decibels (how intense they are). So, both Reverberation Time and the Maximum background noise columns in the table can be compared indirectly in terms of the same units… decibels.
Let’s look at the two contributions to background noise- the background noise level in dBA and the amount of undesirable echoes from a room with a longer Reverberation Time. If we assume that we will reject any background noise over about 50 or 55 dBA, part of this can come from the background noise and part will come from the undesirable echoes. In a large concert hall there is an acceptable maximum of 23 dBA in background noise but then we add the additional (possibly unwanted) reflections due to a 2.1 second Reverberation Time and we may be near our real maximum tolerable level of 50 or 55 dBA.
In contrast, let’s look at a small private studio room in our house- most of the acceptable background noise can be from the other occupants of the house as well as the furnace or air conditioner (around 45 dBA) but thankfully only a small contribution from the Reverberation Time (0.7 seconds or less).
So….. what does this mean for our home studio? We can spend the money ensuring that the room is very quiet or we can spend the money ensuring that there are minimal undesirable echoes. For a small studio or room, I would spend the time and effort to reduce background noises rather than minimizing the Reverberation Time.
However, as it turns out, environmental modifications that do one of the above, also has a side effect of doing the other. A book shelf with soft cover spines and bindings, and with occasional empty spaces between the books not only serves to baffle or attenuate the sound of the other residential background noises but also reduces the Reverberation Time- one change does two things.
Bookshelves, carpeted floors, insulated (or even carpeted) walls all contribute to a shorter Reverberation Time and a quieter room. But unless you are solely listening to your music through headphones you may want to ensure that the room is not too dead. Too low of a Reverberation Time is not great either. Experiment with having one unobstructed wall acting as an “acoustic mirror” to add to the Reverberation Time slightly. Trial and error is great (except when you are driving or having surgery).
If you are listening through loudspeakers place the loudspeakers aiming towards the least “conditioned” wall. After all, some reflections (off uncarpeted or untreated surfaces) can be good. And for small rooms, Reverberation Time is not as big of an issue as background noise reduction.