What is best to use as platform to place subwoofers and speakers on? Aftermarket products promise better sound and less vibration based on different principles and design. Does it work for its intended purpose, or is this another hifi myth. Analysis of the effect on a V110 subwoofer reveals the facts.
Now when the floor-piercing spikes from the 80’s have become a little bit out of fashion, other solutions have emerged for loudspeaker platforms that promise better sound and less noise for the neighbor.
A soft surface isolates the speaker mechanically, so vibrations are not transferred to the floor. This will give better sound because resonances and noise from the floor will disappear and sound transmission through the floor will be reduced – assuming that the floor actually gets less vibration.
This can be investigated and measured.
A V110 has a hard base, with a thin layer of felt underneath. This provides a solid and stable coupling to the surface.
For testing, large soft foam blocks are placed under the V110. This works like a soft decoupling platform, good enough for measurement and testing. It is ugly and dangerously unstable, but that does not matter for this purpose.
Now the standard solid platform can be compared to decoupled platform.
Mobile app measurement
With the Accelerometer mobile app we can measure acceleration and vibration. The mobile phone is placed on the floor, then observe what happens on the screen.
REW is used to make a tone of 20Hz, played at a suitable loud level, 108dB, to create vibration in the floor.
Without decoupling, with solid platform, we now measure around 0.05g peak value vertical acceleration.
With soft decoupling we measure exactly the same.
This is a simple test that anyone can do. The measurement signal can be played back from a 20Hz audio file, and the mobile app is all that is needed to measure. Make sure that the same audio signal is played at the same sound level, and the phone is located exactly in the same location, for comparable observations.
Measurement with more advanced equipment
A more thorough analysis, with better equipment, provides better and more complete information about what is happening.
Measurement of system response for sound pressure in the listening position and vibration in the floor provides detailed information about what happens to both frequency response and in the time domain.
Frequency response and analysis of what happens in the time domain reveals whether there are differences that are audible and may affect sound quality.
The vibration level on the floor directly shows how much sound is transmitted through the floor out of the room. If decoupling reduces the noise level in other rooms, this will be displayed by the vibration level being lower.
Vibration is measured with the v-sensor turned upside down so that the heavy part is free to move. Frequency response and absolute level are not calibrated, it does not matter here when comparing measurements made using the same sensor, just note that the frequency response for vibration does not match the graph.
All measurements were repeated several times, and the analysis is based on the average of several sets of measurements.
When we look at the difference in frequency response measured at the listening position, we see there is no significant difference, only a small measurable deviation around 100Hz:
Vibration shows measurable deviations from around 30Hz and up, but the difference is too small to provide significant noise level reduction in adjacent rooms:
Deviations below 15Hz are due to inaccuracies in the measurement setup.
This shows that decoupling has no effect on the noise level in adjoining rooms.
Then it is interesting to see if sound quality improves. We find out by studying what happens in the time domain.
Decay at listening position shows a measurable difference around 100Hz, and is otherwise identical:
Vibration decay shows greater differences, measurable, but still so small that it does not matter for sound transmission:
Why is it so?
We see that decoupling has no effect at all at low frequencies. And this is expected because it is the acoustic sound energy in the room acting on the surfaces that creates vibration and motion. Vibration transmitted mechanically from the speaker has such a small effect that this is completely overshadowed by the acoustic energy.
- Decoupling and isolating platforms may have a small effect on sound from the upper bass and upwards in frequency.
- The platform must be sufficiently soft so that the resonant frequency is well below the active frequency range – 5Hz for subwoofer, 50Hz for speaker.
- Decoupling of a V110 has so little effect that it is barely measurable, on a wooden floor.
- The platform has no effect on vibrations in the floor at very low frequencies.
- Unfortunately, decoupling does not prevent audio noise down to the neighbor.