Acoustics Myths and Misconceptions
In this post I’ll be dispelling some common acoustics and isolation (soundproofing) myths I get questions about and see others discussing online. Feel free to reach out if you think there’s anything I should add.
Green Glue is generally not worth using. Yes, it can be beneficial by damping the walls (“constrained layer damping”) but adding more mass with something like an extra layer of drywall will improve the isolation and cost a fraction of the price of Green Glue. Green Glue will mostly improve transmission loss (how much sound gets through) at upper frequencies. In studios, what matters most is the transmission loss at lower frequencies and adding more mass is what will improve this the most. Damping the walls is beneficial but there as significantly cheaper alternatives to Green Glue. From what I’ve heard, the formula of Green Glue has changed in recent years with no lab testing done on the new version so it may or may not behave as it should.
Mass Loaded Vinyl (MLV) has some applications in soundproofing (such as isolating machinery and ducts) but in general should not be used in walls. Again, it’s a big waste of money. MLV doesn’t dampen the walls like Green Glue does. It simply add mass. A significantly cheaper alternative is an additional layer of drywall. The only time I’d recommend using MLV for isolation would be if space is at a premium and you’re willing spend thousands more to make the room 1/2” bigger. When it comes to acoustics, MLV can may be used for things like membrane absorbers.
Putting a floor on rubber pucks or insulation is not a floating floor. Doing so will introduce more problems than it solves by making your floor act like a giant drum as well as potentially being “squishy” which will negatively affect your monitoring. A floating floor requires mass and springs. This is generally done with a concrete slab which sits on spring isolators (literal metal springs or a material like sylomer which behaves as a spring). The system must be engineered so that the springs have the correct loading and resonant frequency. It’s not a guessing game or simply buying piece of rubber.
A room within a room has nothing to do with acoustics. It’s used for the isolation and sits outside of the inner shell of the room (i.e. drywall). A room within a room involves framing 2 separate structures so that they are decoupled from each other and you don’t get structure borne transmission between them. You have your drywall attached to one framing structure, a small air gap, and then another framing structure followed by drywall. The acoustic treatment starts after that. The acoustic treatment may be “framed in” meaning additional walls are framed in the room which are used to hold the materials for the acoustic treatment and subsequently is covered in fabric. This framing inside the room used for the treatment is not a room within a room.
Rockwool should not be used in your walls for isolation. Yes, in a standard residential wall with 1/2” ultralight drywall rockwool may provide better isolation than fiberglass but for the purposes of building a studio or home theatre, the walls will be significantly more massive. At that point, the slightly higher mass of rockwool compared to fiberglass will not improve the isolation. The insulation is only in the wall to dampen resonances inside the wall cavity. The insulation itself is not there to stop sound directly. Any insulation material will suffice so fiberglass should be used as it’s cheaper than rockwool.
Owens Corning 703 and 705 are not materials to use for acoustics. For the purposes of building a studio (or home theatre, practice space…) it will perform worse than using cheaper common building materials such as rockwool and fiberglass. The standard soft batts used in walls. Not rigid batts used for exterior or duct insulation. Compressed products like 703 don’t allow the air to effectively travel through it an get absorbed. It reflects the sound back out with the sound travelling through it making it less effective. The only reason 703 was used for building studios is it’s easy to stick up on a wall, cover in fabric, and have a space that looks like a studio. It won’t sag or need bracing and if someone pushes on it they won’t fall through the wall. It has nothing to do with its acoustic properties. Many specialty stores sell 703 because of the cult following it has from being an elusive and expensive material that was used in such and such’s studio. There are some useful applications such as when dealing with ducts but if your acoustician/studio designer proposes covering your walls with it, run.
Using speakers with phase correction such as the D&D 8C or Kii Three and a Trinnov makes no sense and will be introducing problems. The magic behind systems such Trinnov, DEQX, and Dirac is phase correction which makes your speakers play all frequencies at the same time instead of delaying some speakers more than others which is what all speakers do if they don’t have built in phase correction. I don’t recommend using those systems and instead doing a “manual” calibration but that’s beside the point. If the speakers already have built in correction, a Trinnov will be doing things it shouldn’t like trying to correct reflections in the room so it will only be making things worse. Yes, there could be some room and preference EQ but the speakers should have that built in (pretty trivial if the processing in them is doing phase correction). A Trinnov would be a very expensive box just for a simple EQ and in every case I’ve come across, all of the phase correcting processing it tries to do wasn’t disabled. If your speakers have phase correction a Trinnov won’t make things any better than a simple EQ. You already have the magic it brings.