Wednesday, August 28, 2013

Tips on Home and Project Studio Acoustics - F.I.R.S.T. Institute

F.I.R.S.T. Institute Course Director and Instructor, Rich Ott, has some tips and advice to share about home and project studio acoustics:

These days, all gear is acceptably flat over the most important parts of the audio range. Distortion, aside from loudspeakers and microphones, is low enough to be inconsequential. And noise - a big problem with analog tape recorders - is now pretty much irrelevant with modern digital recording. Indeed, given the current high quality of even semi-pro audio gear, the real issue these days is your skill as a recording engineer and the quality of the rooms in which you record and make mixing decisions.

What's the point in buying a microphone preamp that is ruler flat from DC to microwaves when the acoustics in your control room create peaks and dips as large as 20 dB throughout the entire bass range? How important really are jitter artifacts 110 dB below the music when standing waves in your studio cause a huge hole at 80 Hz exactly where you placed a mike for the acoustic bass?

Clearly, frequency response errors of this magnitude are an enormous problem, yet most studios and control rooms suffer from this defect. Worse, many studio owners have no idea their rooms have such a skewed response! Without knowing what your music really sounds like, it is difficult to produce a quality product, and even more difficult to create mixes that sound the same outside your control room.

Ethan Winer, co-owner of Real Traps, a well known acoustic panel and design company, gives us the details on construction of absorptive panels to help tame that home or office studio.
     

There are a number of ways to create a bass trap. The simplest and least expensive is to install a large amount of thick rigid fiberglass, spacing it well away from the wall or ceiling. As noted earlier, 705-FRK that is four inches thick and spaced 16 inches away from the wall can be quite effective to frequencies below 125 Hz. But many rooms have severe problems far below 125 Hz and losing twenty inches all around the room for thick fiberglass and a large air space is unacceptable to most studio owners and audiophiles.

Fortunately, more efficient bass trap designs are available that are much smaller. However, studios on a tight budget can apply rigid fiberglass in the room corners as shown in Figure 3a and lose only the small amount of space in the corners. Since bass builds up the most in the corners of a room, this is an ideal location for any bass trap.


Figure 3a shows the corner viewed from above, looking down from the ceiling. When the rigid fiberglass is mounted in a corner like this, the large air gap helps it absorb to fairly low frequencies. For this application 705-FRK is better than 703 because the goal is to absorb as effectively as possible at low frequencies. However, you can either absorb or deflect the higher frequencies by facing the paper backing one way or the other, to better control liveness in the room. Using 705 fiberglass that is two inches thick does a good job, but using four inches works even better. Note that two adjacent two-inch panels absorb the same as one piece four inches thick, so you can double them up if needed. However, if you are using the FRK type you should remove the paper from one of the pieces so only one outside surface has paper. Top
     
Besides the corners where two walls meet as in Figure 3a, it is equally effective to place fiberglass in the corners at the top of a wall where it joins the ceiling. With either type of corner, you can attach the fiberglass by screwing it to 1x2-inch wood strips that are glued or screwed to the wall as described previously. The 1x2 ends of these strips are shown as small black rectangles in Figure 3a above. One very nice feature of this simple trap design is that the air gap behind the fiberglass varies continuously, so at least some amount of fiberglass is spaced appropriately to cover a range of frequencies.
    

When mounting 705-FRK directly to a wall - not across a corner - you'll achieve more low frequency absorption if the paper covered side is facing into the room. However, that will reflect mid and high frequencies somewhat. One good solution is to alternate the panels so every other panel has the paper facing toward the room to avoid making the room too dead. Panels attached with the backing toward the wall should be mounted on thin (1/4-inch) strips of wood to leave a small gap so the backing is free to vibrate. For fiberglass across a corner as shown in Figure 3a, the backing should face into the room to absorb more at low frequencies.

For a typical unfinished basement ceiling you can take advantage of the gap between the support beams and the floor above by placing rigid fiberglass between the beams. Short nails or screws can support the fiberglass, making it easy to slide each piece of fiberglass into place. Then cover the fiberglass with fabric as shown below in Figure 3b. You can optionally pack the entire cavity with fluffy fiberglass one foot thick and you'll probably get similar results.
     
Hopefully this will get you started on your way to making your mixing and recording space sounding as good as it can. Remember the gear doesn’t make the room - the room makes the gear! Want to learn more about the Recording Arts? 

Consider attending F.I.R.S.T.! Request more info here


Written By Rich Ott, Recording Arts Course Director and Instructor

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