This Acoustic Panel Absorbs Down To 30Hz
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Are you going crazy trying to find a way to absorb low frequencies in your recording studio? Look no further. Finally there is a way to absorb low frequencies using a broadband absorber. Let's dive in!
1) The Genius of Philip Newell
If you haven't heard or read any of Philip Newell's books, I suggest you do. He has been building and designing studios for decades and has worked with some of the biggest names (The Rolling Stones). In his book Recording Studio Design 4th Edition he describes a panel wall absorber system that can absorb down to 30Hz. Let's go over the design.
This is my rendition of Philip Newell's design. He of course does everything in metric and uses cotton waste felt instead of my recommendation of Knauf ECOSE insulation batts. I would love to use cotton waste felt, but I couldn't find any good suppliers in the United States that were cost effective.
This said, let's dive into the design. A very important part of this acoustic wall is that it is built at least 2" from the isolation wall. 4" is better and one to three feet is even better than that. However, as Newell states in his book many studio owners do not see the benefit of better acoustics at the cost of floor space. For us home studio nuts we also need to find a balance between space, budget and our desire for pro level acoustics. I believe we can find that perfect balance and this design gets us closer to the truth we are seeking.
After the 2-4" air space we then have a 1" 3lb/ft3 Panel of Knauf ECOSE insulation. You can buy them in 2" panels and then cut them right down the middle for this design. Then Newell says to use a 5kg/m2 deadsheet (1lb/ft2). Now a deadsheet is really another name for a limp membrane having considerable inertia and little stiffness. In the United States we can use Mass Loaded Vinyl (MLV). Then we have another layer of Knauf Insulation. Then a 1/2" thick piece of drywall sandwiched over another layer of MLV and another 1/2" piece of drywall.
Finally, we reach the stud wall frame. Fill this with R13 Owens Corning unfaced insulation. Then seal the frame wall with a layer of 1 lb MLV and one last layer of 1" Knauf Ecose Insulation. Wow, that was a lot. You might be wondering why we need all these layers.
2) How this panel works?
Yes, it is more of an acoustic wall although you could build a panel out of this design if you wanted to save money. The key to this system working is the multiple materials working together to stop soundwaves through absorption and damping at different frequencies. Let's take a trip through the wall as a soundwave. Yay!!!
So we start off hitting the Knauf Insulation. This will absorb our mid to high frequencies from say 500-20K Hz. Then we will fly through a deadsheet and this will dissipate some of the mid and low frequencies through damping. Then we will fly through our Owens Corning Insulation and even more of the soundwave will dissipate as heat. Then the low frequencies that remain will hit the drywall - deadsheet - drywall and get absorbed in the pressure cavity of the mass spring mass system we created with the sealed framed wall. Lastly, any remaining sound would hit the insulation - deadsheet - insulation and lose even more energy. Finally, the sound will hit our isolation wall. Depending on the type of wall (drywall vs mortar) the energy may get absorbed again or reflected back and sent right back through the whole system again.
Needless to say, the low end frequencies really do get trapped in this system. Hence, it's ability to absorb down to 30Hz. In an ideal studio room you would line all four walls with this system. In a control room or a mix/production studio as is so common today you should use this system on three of the four walls and leave one wall and the floor reflective to keep the live of the room intact.
3) How much does this dang thing cost?
Great question! The total wall costs $8.65/sqft if you use the materials I mentioned above. That does not include the cost of the wood frame. To acoustically treat a room that is 15ftx20ft you would be looking at around $2,500 in materials. Yes, that is a lot of money, but honestly insulation panels that only absorb down to 125hz would cost you that much as well if you bought professional ones. We also did not look into the ceiling, that will come in another article, but that will add another 1,000-2,000 as well. However, if you have looked at Acoustic Fields then you know getting this type of acoustic paneling can cost 20-40 thousand dollars, so why not use basic construction materials and get the same if not better results.
Don't trust me, trust Philip Newell. He is the one who has taught me all these great studio design philosophies. Again, if you are serious about studio design I encourage you to pick up his Recording Studio Design book.
Work Cited:
Philip Richard Newell. Recording Studio Design. New York ; London, Routledge, Taylor & Francis Group, 2017.
