Most home or project studios are located in smallish rectangular rooms, creating a real challenge in creating a relatively accurate listening space. Parallel walls reinforce and nullify harmonic frequencies, creating peaks and dips in the frequency response, particularly between 50 and 250Hz. A common mistake is the overuse of thin acoustic panels (50mm and less), which provide virtually no absorption of frequencies below 200Hz. This is not a balanced acoustic treatment, and makes recording and mixing music a nightmare.
Every small room requires bass trapping, but how much? There are many different bass traps on the market, the most common being semi rigid fibreglass traps, membrane traps and acoustic foam traps. Which is best? In reality, all well designed traps are effective. The real question is, how much trapping do you need?
Much of my work is acoustically measuring recording and listening rooms. Many of these rooms already have well regarded (and expensive) bass trapping in place, but still exhibit a very lumpy frequency response.
The problem is, there simply isn’t enough bass trapping in place to overcome the acoustic characteristics of the room. It’s often a matter of experimenting with as much bass trapping as practical and measuring the impact it has. In some cases, it’s just not possible to get a room within plus or minus 15 db, due to the dimensions and construction of the room.
A good place for bass trapping in small rooms is the ceiling. The RAM400-1000 traps are ideal for this application, as they can be easily installed with a staple gun.
The reality with bass trapping is that it’s often a case of experimentation, and small rooms generally require a substantial amount of trapping.
I recently had the opportunity to pre and post test a room that had been treated with the CSR Soundchek plaster system which involves hanging plaster on channels supported by a rubber insulation system. It’s a very easy system to use and reasonably economical. While it won’t completely soundproof a room with high SPL’s, such as a drum room, it certainly reduces transmission of sound significantly. http://www.gyprock.com.au/resources/filemanager/datasheets.aspx?fileIteration=155
The alternative to this system would be to use Green Glue with plasterboard.
I recently visited a very well equipped home studio (more like a professional studio built on a home!) which consisted of a control room,a drum room, an iso booth and a vocal booth. The client had noticed that low frequencies were an issue in the vocal booth. That is, certain frequencies taking off, and an overall sense of “boxiness” in the room. When the vocalist backed off the mic, the take was virtually unusable. The dimensions were 1 x 1.5 x 2.4m. The booth was mostly brick and glass, and about 75% of the walls had been treated with 50mm Sonex acoustic foam. Sonex is good quality foam, but like all relatively thin acoustic foam, the Sonex was absorbing virtually none of the low frequencies. This is a very common scenario, and when you buy an acoustic product make sure to look at the absorption coefficients across the spectrum. Total NRC rating is pretty much useless for audio applications. A 50mm product will typically absorb around 25% (.25 AC) at 200Hz and 10% (.1 AC) at 100hz, which is pretty much ineffective. We tried a few thicker panels, but ended up installing the SA600/150 (600 x 600 x 150mm) acoustic panel. We only needed to install three of these panels on the door to effectively control the low frequency resonance. The SA600/150 absorbs at 100 % at 200Hz and 60% at 100hz. This is a good example of how bass absorption should be considered a necessary part of vocal booth acoustic treatment. A brick or concrete voiceover booth will be more reflective than a plasterboard booth, but both situations require bass control.
The control room at Incubator studios already had some polyester built in panelling that wasn’t quite doing the job. Initial measurements revealed some significant “lumpiness” below 200Hz so we decided to install some of the BT600/150 bass traps in some of the available ceiling corners. This is where the staple gun channels in the BT600/150 come in very handy. After the initial treatment the room was greatly improved, with Adrian noticing an immediate improvement. Post measurements revealed a flatter response, but there was still a persistent dip at 180Hz. As a trial we loaded the rear wall with 6 x BT600/150 which totally dealt with the issue. It’s always nice when the first option works!
