For professional audio engineers, loudspeaker designers, and music lovers, the performance of a speaker system hinges not only on the quality of the components but also on how those speakers physically interact with their supporting surface. This seemingly simple boundary condition can greatly impact the sonic characteristics, including clarity, definition, and soundstage. Speaker decoupling, how a speaker is connected or isolated from the surface it rests on, can mean the difference between a pristine audio experience and one that’s compromised by unwanted resonance and vibration. In this article, we’ll explore the key factors that affect speaker decoupling and examine the common approaches including spikes and isolation products.
Three Critical Factors in Speaker Placement
When placing speakers in any environment, three main physical factors must be considered to optimize sound quality:
- Speakers may excite their supporting structure.
- Structure-borne noise may be conducted throughout the listening space and into adjacent areas.
- Energy from the speaker strikes the supporting surface and is conducted back into the speaker enclosure.
1. Excitation of the Supporting Structure
One of the primary concerns when placing speakers on a surface is the potential for them to excite the structure beneath them. When a speaker emits sound, the reactive force from the driver’s motion causes vibrations to be transferred to the supporting surface. This can lead to rattling, buzzing, or resonant vibrations that negatively impact sound quality.
We’ve all experienced how placing even a mobile phone on a hard surface amplifies sound and introduces harsh overtones. The same principle applies to loudspeakers: Energy from the speaker causes the surface to vibrate, leading to unintended noise and distortion, particularly if the surface is not designed to handle such forces.
2. Structure-Borne Noise
A solid surface might seem like an ideal platform for speakers, but it also comes with its own set of challenges. Energy transferred from the speaker to the supporting surface can propagate through the structure and create structure-borne noise that distorts the listening environment. This noise can affect other equipment, disrupt the acoustic balance of the room, or even be conducted into adjacent spaces.
Additionally, because sound waves travel faster through solid materials than through air, as illustrated in Figure 1, structure-borne noise may reach the listener before the acoustic sound, introducing timing discrepancies and muddling the overall sound. This effect can also allow vibrations from other sources (e.g., other speakers, subwoofers) to enter the speaker, further degrading performance.
3. Energy Reflected Back into the Speaker
When vibrations travel from the speaker into the supporting surface, they don’t just dissipate. They are also conducted back into the speaker cabinet, similar to hitting a section of pipe bolted to a concrete wall: the energy travels down the pipe, hits the wall, and then an inverse wave is conducted back along the pipe. This back-and-forth energy exchange is conducted back into the speaker enclosure, resulting in smeared sound, less articulate bass, and reduced clarity. Any artefacts that are common in both channels are perceived to be in the middle and result in a collapsed and two-dimensional phantom image. Managing internal reflections is essential to preserving clarity, precision, and spatial definition. The artefacts are timing variations re-entering the speaker enclosure and are not revealed during sweep frequency testing in the anechoic chamber.
Contemporary Alternatives to Control and Mitigate Vibration
The industry has found several ways to combat all the aforementioned effects with varying degrees of success. Let’s look at these, summarized in the categories of spikes, footers, and isolation.
Spikes and Footers
Spikes are a common accessory and are often included with new floor-standing speakers. They can be screwed into the underside of the speakers with the principal goal of firmly anchoring the speaker and opposing any movement, in accordance with Newton’s Third Law of Motion. As the speaker cone moves forward to produce sound, the speaker enclosure naturally wants to move backward. Spikes help minimize this reciprocal motion to ensure a more accurate propagation of energy.
Additionally, spikes reduce the contact surface between the speaker and the supporting surface. For example, a modest-sized floor-standing speaker may exert a pressure of around 0.5 pounds per square inch (psi) on the floor. By using spikes, this pressure can be increased dramatically, potentially reaching 5,000psi depending on the spike’s contact point radius. However, spikes do not create a one-way path for energy flow, despite often being described metaphorically as acting like a diode. A spike doesn’t create a P-N Junction and energy is still conducted in both directions as they represent a hard mechanical connection with the supporting surface.
Mechanical footers are another alternative, often crafted from materials such as stainless steel or exotic metals. These footers may include internal bearing surfaces made of metals, glass, or ceramic balls, with their construction and the combination of materials intended to manage energy transfer between the speaker and the supporting surface. However, like spikes, they are still mechanical connections that will conduct energy in both directions, making them only partially effective in managing the energy between the speaker and the supporting surface.
Isolation
On the other hand, isolation products are designed to decouple the speaker from the surface using materials like foam, rubber, sorbothane, or damping compounds. These products absorb vibrations and prevent energy transfer to the supporting surface. However, they often face challenges, such as frequency-specific performance, where their effectiveness is limited to certain frequency ranges for a given weight load.
Additionally, over-isolating a speaker can result in unwanted motion, especially in low frequencies, which can smear transients and reduce bass accuracy. Another drawback is that some isolation materials degrade over time, reducing their effectiveness and potentially leaving residues.
Another Alternative
IsoAcoustics has developed a patented solution that overcomes the limitations of both spikes and traditional isolators. Their technology combines isolation with controlled energy management, maximizing acoustic performance without the issues inherent in other approaches. IsoAcoustics products provide true isolation without creating a rigid energy path between the speaker and the surface. They use resilient elastomers that absorb and dissipate vibrations. Additionally, this design manages movement in both the lateral and vertical planes, stabilizing the speaker while minimizing energy transfer.
IsoAcoustics products are engineered to respond effectively across a broad frequency range, ensuring consistent sound performance, with tight bass, clear transients, and accurate imaging. Their internal structure resists lateral and circular oscillations, preventing the rocking motions that can occur with traditional isolators. This results in a stable and accurate sound reproduction. Furthermore, IsoAcoustics products are adaptable to various surfaces, from hard floors to thick carpets, providing reliable performance in different environments.
IsoAcoustics products, including the GAIA series, are tested at the National Research Council (NRC) in Ottawa using both the anechoic chamber and a laser vibrometer. The anechoic chamber tests revealed a variance of less than 0.3dB across separate trials runs, demonstrating consistent output across the entire audio spectrum, regardless of whether the speakers were mounted with IsoAcoustics products or conventional spikes. There is no loss in bass response at lower frequencies or any added coloration of sound, which speaks to the transparency of IsoAcoustics isolators in preserving the original audio characteristics.
For more specific vibration analysis, the GAIA products are tested using a laser vibrometer. In this setup, speakers are mounted on a test rig with GAIA isolators and spikes, and the testing apparatus allows for a quick switch between the two. This setup also allows for a third scenario, where bungee cords are attached to suspend the speaker, breaking the connection to the floor and providing a baseline where the speaker no longer transmits vibrations through the surface (Photo 1). The speaker height is maintained to within 0.25” throughout all three scenarios.
When the same sweep frequencies are applied to the speaker, the results demonstrate how vibrations are conducted back into the speaker when conventional spikes are used.
In Figure 2, the purple line on the graph represents these vibrations being conducted back into the speaker, leading to a smearing of the sound and interfering with the speaker’s ability to reproduce sound accurately. The distortion caused by these vibrations can degrade sound quality, leading to a lack of clarity and openness.
In contrast, the green line represents the speaker’s performance when mounted on GAIA isolators. The GAIA isolators significantly reduce the transfer of vibrations back into the speaker, and result in improved sound clarity, openness, and overall definition. The testing shows that the GAIA isolators perform similarly to the suspension scenario with bungee cords (blue line) in minimizing vibrations, though the latter suffers from poor sound quality due to the instability of the freely swinging speaker.
Ultimately, the GAIA isolators mitigate the detrimental effects of vibrations, allowing the speaker to deliver more accurate sound with better clarity and openness, without sacrificing bass response or adding coloration.
Conclusion
For professional audio engineers, loudspeaker designers, and music lovers, understanding and managing speaker decoupling is essential for optimizing sound quality. While spikes and isolation products each offer partial solutions, both come with inherent limitations. IsoAcoustics’ patented technology overcomes these challenges by offering true isolation, controlled energy management, and consistent acoustic performance across all frequencies.
By minimizing resonance, reducing structure-borne noise, and preventing energy from conducted back into the speaker enclosure, IsoAcoustics delivers a clearer, more detailed and immersive listening experience — allowing your speakers to perform at their best in any environment. VC
This article was originally published in Voice Coil, January 2025
