Tips
The Importance of the Flooring in Your Listening Space
So much is written about room acoustics that you would think it holds THE key to great sound. And yes, while the room's acoustics are important, many living spaces provide an acceptable amount of absorption and diffusion to keep the room well away from the “racquetball court” category. The degree of acoustic control within the listening space is a somewhat personal call. Some people like the sound and feel of a more lively space, and some want a very controlled studio-like setting. What is not considered or discussed often enough is the floor. I don’t mean the discussion about “Should I put an area rug in front of my speakers?” I mean the floor itself. As with most of my thoughts regarding what to do with an audio system, this discussion falls under the category of trying not to cause problems that are totally avoidable if only someone mentioned it to you. These ideas are for you if you are looking for ideas on improving your listening space. Unless your sound room has acoustics similar to the above racquetball court, the floor should be one of your first areas to consider when considering improving your listening space. There are several significant reasons for this.
The floor, like the walls and ceiling, is another surface that the speakers interact with. It is the closest and most consistent plane to the speakers, and the speakers are in direct contact with it. More importantly, it is the foundation of the system. Without talking about the nature or structural integrity of the substrate (what’s below the floor), which is very important, I wanted to mention more doable and less costly concepts. In this case, the actual flooring your speakers make contact with.
The material that covers the substrate or structure on the floor can be considered an enabler or a disabler. This means that the type of flooring you choose can either enhance or hinder the performance of your speakers, a concept that is often overlooked but crucial to understand.
How can your flooring be a disabler?
Let’s examine a carpeted floor. It will put two layers of spongy material between the speakers and the substrate. Regardless of how heavy the speaker is, these two spongy layers will destabilize the speaker, allowing the cabinet to move when playing music. This will do two things: 1. Create a tail-wagging-the-dog scenario, where primarily the bass driver’s pistonic movement will become compromised when the structure it is moving against is not utterly stable. 2. Because we are playing back a stereo signal, the left and right speakers will play both common and discrete music signals. Each speaker will be displaced independently from the other, causing any common left and right music signal to no longer play as one. One obvious example to think about here is the bass impact being compromised. The delicate timing of discrete left or right signals related to the other channel will no longer be in phase with that channel. Think here about a potentially beautifully big and quiet soundstage that never reaches its potential or maybe the natural decay of a flute on the left side of the orchestra that never makes it over to the right side of the stage, covering up the naturalness of the recorded space. With common or discrete signals, the carpeted flooring scenario has disabled the system’s potential and, consequently, your investment’s value.
The Speaker Isolation Question
I'm going to get my thoughts about this out there now so there is no ambiguity. Decoupling the speaker from the floor has become a popular idea; isolating the speaker from the floor and the system benefits. In practice, a decoupled speaker has lateral-plane compliance, meaning the reaction forces generated by the drivers during playback displace the cabinet. That displacement is dynamic, continuous, signal-dependent, and different for each speaker. A decoupled speaker is mechanically stable only when it isn't being a speaker, when it's just still mass. The moment (pardon the pun) it becomes a speaker, the premise fails. Rigid coupling to a solid floor wins, and it isn't close.
How to make your floor an enabler - the good kind...
Stiff flooring that interfaces the speaker to the substrate provides the stability to hold the speaker firmly in place while playing music. A rock-solid structure for a driver motor mechanism to function within will improve the driver's efficiency and clean piston motion. Transient behavior and “slam” will be greatly improved over a compliant flooring type. This stability will also mean that the speaker will remain stable in space and not change position relative to the other speaker, maintaining whatever alignment has been determined through the setup process. During the setup process, this type of stability can provide a considerably cleaner music signal for the setup person to work with. Finer and more precise driver relationships can be developed with a cleaner music signal, leading to a more complete and thrilling version of what an audio system can produce.
What type of stiff flooring is good to choose?
Because I advocate using height-adjustable feet on the speaker, stiff flooring should be considered for a number of reasons. These feet are typically spikes but can also be rounded pad-type feet that disperse energy over a wider surface area. Sometimes, the spikes are extremely pointy and sharp; sometimes, they are slightly rounded or ball-ended. In all cases, the flooring should be mechanically compatible with the feet on your speakers.
If you have or are choosing a tile floor, here are a few things to be mindful of. The flatter the tile and the smaller the grout line, the better for speaker setup. It’s easier to position the speaker during the setup process without worrying if the speaker constantly changes attitude with every movement on the floor. Ultimately, finding uniform pressure of the feet on the floor with a flatter tile is also faster and easier. Tell the tile setter that the speakers will put a lot of energy into the floor so that a marginally bonded tile can lose its bond or pop over time. A popped tile can significantly reduce energy transfer into the substrate, but that energy still has to go somewhere. It can either hang out where it can be stored, moving on greener pastures in its own sweet time, or reflect back to where it came from. Spikes and most all footers are not really energy storage devices, so what that energy does will be very situational. Still, one thing is certain: a popped tile will create an increased impedance path for energy to travel, which is not good. When a tile loses its bond, it makes a hollow sound (like a low popping sound) when you knock on it with your knuckle. You'll know if the tile’s bond is solid because it will sound dead with the same knock. You’ll have to figure out how to tell your tile setter to ensure he sets the tiles well. They can get a little touchy when you tell them to do the job, ummmm, correctly…
If you choose a wood floor, I’d suggest an engineered hardwood over a solid one. Solid hardwood is not very moisture resistant, so it swells with changing humidity levels, which WILL (!) mess with a precision speaker setup. Yes, you heard that correctly. An even mildly swelling floor will impact the speaker setup. An engineered floor is made from layers of material and your choice of wood on top, so it has many layers of glue to help stabilize the floor’s “positional integrity.” God, as my witness, I never thought I’d be writing those words, but here we are!
One of the best flooring choices I have encountered is bamboo. Technically a grass, bamboo is constructed of stiff strands surrounded by a softer cellular material. This structure is, in principle, analogous to constrained layer damping; the stiff strands transfer mechanical energy efficiently, and where that energy encounters the softer material, some of it converts to thermal energy. We cannot destroy energy; we can only store it, transmit it, or convert it. Bamboo does the last of these unusually well.
If you happen to be applying flooring type to a concrete substrate, there is a next-level technique worth considering if you are building or renovating a dedicated listening space. If permitted by your local building code, cutting completely through the concrete slab to create an isolated island under the speaker positions, with the finish flooring becoming part of that island, mechanically decouples the speakers from the rest of the slab. The practical benefit is that vibrational energy from the speakers has a significantly harder time traveling through the concrete to the equipment rack and components. All components are sensitive to vibration, some alarmingly so. The cut will require a small gap between the island and the surrounding floor, perhaps a quarter inch, which is a minor aesthetic consideration in what is otherwise a clean and permanent solution.
Interfacing the interface! If your speakers have big rounded pads, like a Rockport Lyra, there’s not much to be concerned with regarding the foot touching the floor, regardless of what floor you have. But if the speakers have spikes, even fairly “dull” ones, there should be an interface or footer between the spike and the floor. Spikes on tile can easily slide around during playback and dig into a softer material on some stone floors. Spikes WILL dig into any wood or bamboo floor, especially over time. This will, of course, damage the floor. It will also throw off the precision speaker setup as the spikes pound into the floor at varying degrees while music plays. It would be best to find an appropriate interface for your particular spike to the footer. How pointy is the spike, and is there a nice seat in the footer for the spike to become stable? For example, a rounded indentation in the footer is not a good solution for a spike. Try to use a footer made from a very hard material, such as Titanium as it will pass energy pretty cleanly. I am positive there is also an ideal shape for a footer that would direct energy in a particular direction, but that’s out of my league. A small low-mass titanium footer with a well shaped seat would be a great solution. There are a lot of footers for spikes on the market, and the perfect interface will, of course, be situational.
After the speaker setup is completed and the adjustable feet, whatever those may be, are finalized and tightened down, you can put a small amount of silicone around the perimeter of the footer to hold it firmly in place. We do not want to glue the footer down with silicone under it, compromising the interface, but only to hold it in place around the outside.