John Brandt


    Your question is very common and I hope that many people will read this:

    1 and 2" treatment on the walls can reduce the RT-60 (reverberation time) quite substantially, but only effectively from about 1.6 - 3 kHz and up. This leaves the rest of the musical spectrum untouched. 8" deep 1/4 wave trapping works down to 423 Hz!

    Bass trapping is critical in order to be able to hear the bass that is on your track. Otherwise the frequency response will be very lumpy around the room. Boomy here, thin there, etc.

    The most important part played by bass trapping is that the trapping added to a room reduces or eliminates the diffuse field which, in turn, broadens the ‘sweet spot’. The free field that is created by trapping has everything to do with the Critical Distance of a room.

    Critical Distance (Dc):

    The ratio of direct sound to ambient sound is dependent on the distance between the source and the listener, and upon the reverberation time in the room. At a certain distance the two will be equal. This is called the "critical distance." So this is basically defined as; the distance that a sound ceases to fall off at -6 dB per doubling of distance from the source. (Inverse square law) The source sound goes constant volume at the Dc (Critical Distance) of the room. Once the listener is at the Dc from the source sound, the perceived level is the same everywhere in the room. This point in space can translate to ‘MUD’ in a studio room where you must record many instruments at once.

    Control Rooms are heavily trapped to create a large free field. A control room being trapped is not an unusual thing and most people assume that it must be done, but tracking rooms – often called ‘live rooms’ – also need good low frequency trapping. You won’t be able to work multiple instruments or vocals in the room at the same time unless you have to have a decent amount of trapping in the walls and ceiling. Without the trapping, you will need to use close-miking techniques, and then why do you need such a large room?

    Note that the term ‘live room’ is not so named because the room is ‘lively’ or ambient. It is simply the room where ‘Live Performance’ occurs. I prefer to call them ‘Tracking Rooms’ so as not to confuse.

    I hope this is helpful.