Audio 101 – Acoustical Treaments
Studios & Small Rooms – Part One
Churches and recording studios must consider sound quality. This is part one of a two part article on Acoustics.
This article is a bit technical, but it is a primer for people interested in creating their own recording studio or practice room.
A common misconception is that electronic mastering and equalization can fix all sound and recording problems. In reality, the most common sound issues for small studios must be addressed in the design and construction to ensure the space provides the performance you need. The question is what performance do you need?
A recording studio needs to have an adequate amount of sound absorption to address sound reflections within small rooms, and sufficient sound reduction to control outside sound sources such as traffic, televisions, and heating/cooling systems. If these issues are not effectively addressed, your recordings will have issues that cannot be easily fixed with post-processing, and can create frustration and stress.
To address these three common issues, I discussed some of these common challenges and approaches with two professionals, Erik Miller-Klein, PE, an Acoustical Consultant and Associate Partner at SSA Acoustics, LLP based in Seattle, Washington, and John Ark of ATS Acoustics located in Piper City, Illinois. An acoustical consultant or engineer provides design assistance for architects, engineers, and homeowners to ensure sound and vibration is considered before construction. He or she provides cost effective diagnosis and mitigation for acoustic issues in existing constructions.
Let us begin with room finishes and shapes. Mr. Erik Miller-Klein from SSA Acoustics notes, “The most challenging interior condition for small studios is room modes. Room modes are natural reflections of sound waves within a small room. Depending on the dimensions of the room, these reflections create loud and quiet spots for certain frequencies. The low end of the piano or bass instruments has frequencies that go down to 30 Hz with bass lines in the 50 Hz to 100 Hz range.”
“For example, the wavelength for 63 Hz is about 17-feet long, and in most small studios this frequency, and other low frequency energy, is not effectively scattered within the room. This creates the high-amplitude hot spots called antinodes, or lower amplitude, cold spots called nodes, which will make the room sound uneven; this phenomenon can be picked up by one’s microphones. To effectively absorb a frequency you need a fibrous absorber that is one quarter of the wavelength, which for the example would be a sound absorptive panel that is over 4-feet thick. That is not practical, but there are other materials and options. The walls and corners experience antinodes and these frequencies can be efficiently absorbed with bass traps and specialty designed low frequency absorbers placed on the walls or in the corners. With adequate sound absorptive finishes, one’s recordings will be true to one’s sources, and this gives one the ability to add in one’s effects during post-processing without trying to fix residual sounds in the mix.”
I asked John Ark of ATS Acoustics about speaker placement, he said, “most manufacturers offer recommendations; however the rule of thumb is to set your speakers as an equilateral triangle toward the listening position. We can recommend placement, but most manufacturers will recommend best placement practices.”
Erik said, “The two most challenging components of small studio design are associated with the impact of noise sources such as traffic and other outside sound sources, and heating/cooling systems. I personally experienced excess heating/cooling noise, often referred to as HVAC noise, within my own small studio. I did not have the benefit of talking to an acoustical consultant and completed a trial-and-error approach that eventually mitigated my furnace to an acceptable level.”
Erik said “… that to address these issues you need to understand the location and potential impact of these sources. Many companies and products promise ‘Sound-Proof’ materials, but this is a marketing term, and the realistic goal is to have high enough sound reduction that outside sources do not impact your space. Some sound will be transmitted through any assembly, but if that sound is less than your background levels, it will be inaudible, giving you the perception of sound-proof. Be skeptical when someone uses that term to try and sell you a product. To treat outside sound and HVAC noise, the location and source sound level must be clearly identified, and then a cost effective solution can be designed.”
With respect to HVAC noise, Erik said “Duct liner (fiberglass or specialty foam) on the inside of the duct can reduce some fan noise, but duct liner is not thick enough to efficiently attenuate low frequency sounds below 125 Hz. In order to attenuate low frequency sound, a silencer may be necessary, but these can be expensive for home studios. A silencer is specially designed to attenuate low, mid, and high frequency sound, and can be selected based on your system type, sound reduction requirements, and space constraints; it is important to note that silencers go in the air stream and often need to be discussed with a mechanical engineer prior to installation to ensure it will not negatively impact your heating/cooling performance.”
Erik recommends hiring an acoustical expert when you have questions or challenges. Potential mitigation can be much more expensive if you do the trial-and-error construction approach. Acoustical consultants can save you many hours and considerable money by quickly getting to the root cause of your issues, and let you focus on recording. At the time I built my studio, I had no idea I could hire someone to help. Erik recommended http://inceusa.org/ as a resource for finding people with acoustical backgrounds.
What is the problem with most small studios? According to John Ark of ATS Acoustics, “They don’t think they need any sound absorptive finishes. They think they can fix every sound problem electronically. Rooms don’t have a flat or even frequency response across all the frequencies. They usually suffer in the low frequency range.”
What about speakers which self-adjust to a room? Both engineers agree they are effective but limited. Some low end frequency peaks (Spots in a room where frequencies bouncing off a wall actually enhance each other) may enhance a frequency as much as 10 to 15 dB (50% – 75%). Self-adjusting speakers have a limited amplitude and frequency response, and cannot fix major room issues.
ATS Acoustics offers a room analysis and helps guide you through options within their catalog to fit your needs. They offer customized panels which are not only effective but which would be very cool looking with your CD cover or studio logo. I wish I knew of their panels when I built my studio.
SSA Acoustics is an acoustical engineering firm that provides design and mitigation support for architects, engineers, and owners throughout the United States. They focus on the design of schools, multi-family buildings, medical environments, churches, commercial/civic buildings, and noise control for manufacturing environments. Erik states: “Most acoustic consultants often save you money by guiding you to find the most cost effective solutions to your issues, and assistance during design often saves up to four times the construction cost compared to post-occupancy mitigation.”