Vacuum glass and noise: why 'vacuum' is not a synonym for silence

There is a logic that seems perfect, almost obvious. Sound is a wave that needs a medium — air, water, wall — to travel. In a vacuum, where there is nothing, sound simply does not propagate. It is the principle behind that classic line from science-fiction films: "in space, no one can hear you scream".

That is why, when the social-media algorithm crosses your path with a technology called vacuum glass, the reasoning completes itself in the head of anyone who suffers with noise: if there is a vacuum between the two panes of glass, sound has no way through. It must be the definitive acoustic window, absolute silence bottled up.

It is a smart guess. And, like almost every smart guess about acoustics, it is half right and half wrong — which, in practice, means it can cost you dearly if you buy it for the wrong reason.

The half-truth: where the idea of "vacuum = silence" comes from

Let us be fair to the intuition, because it is not silly. Vacuum glass — known by the acronym VIG, for Vacuum Insulated Glass — really does block part of the noise, and blocks it well. A VIG panel delivers an Rw index in the range of 36 to 39 dB, about 10 dB above a common double glazing. On a logarithmic scale, that is an enormous and clearly audible difference.

In other words: anyone who imagines that VIG "helps against the noise" is not mistaken. The glass is made of two panes of tempered glass, and that mass alone already blocks a good part of the sound. The vacuum between them really does eliminate the airborne path of transmission through the cavity.

The mistake is not in thinking that VIG works. The mistake is in thinking it works against your noise. And this is where the conversation stops being about "does it work or not" and becomes a much more precise question: which type of noise does it work against?

What the vacuum was really invented for: heat

Before answering, it is worth understanding what vacuum glass came to solve — because it was not noise.

The great enemy of thermal insulation is convection: the gas inside the cavity of a double glazing heats up on one side, circulates, and carries heat from outside to inside (or the opposite, in winter). VIG solves this brilliantly: if there is no gas in the cavity, there is nothing to circulate. Heat transfer by convection simply ceases to exist.

The result is spectacular from a thermal point of view. A VIG panel reaches the performance of a triple glazing — with a Ug value around 0.4 W/m²K — in a thickness of a mere 6 to 8 mm, against the more than 20 mm of a traditional double glazing. It is an engineering feat. If your problem is thermal efficiency, vacuum glass is one of the most promising technologies there is.

Notice that none of this is about sound. VIG is, in essence, a thermal invention. Its good acoustic performance is a welcome side effect — not the goal of the design.

Where the vacuum fails: the city's low frequencies

Now the question that matters: against which noise?

Noise is not one single thing. It has frequencies. The song of a bird, a voice, a whistle — these are mid and high frequencies. But the roar of a bus climbing the hill, the exhaust of a motorbike, the jackhammer from the construction next door, the passing truck — that is the low frequency, the bass. And it is precisely that which is the sonic terror of major urban centres.

Against mid and high frequencies, VIG does well. But low frequency is the hardest to block in all of acoustics, and it is exactly where vacuum glass shows its weakness. The reason is physical and direct:

1. Mass. Low frequency is only defeated by mass and by pane asymmetry. VIG, by definition, is thin and light — the opposite of what the bass demands. The advantage that makes it a thermal hero (little thickness) is its acoustic limitation.

2. The pillars. To stop atmospheric pressure from crushing the two panes against each other, the spacing is held open by a grid of micro-pillars of steel or titanium, a fraction of a millimetre in diameter, spread every 30 to 50 mm. These pillars are invisible to the naked eye — but they physically touch both panes at the same time. This creates a small bridge through which vibration can cross as a solid, bypassing the vacuum. The effect is modest, the manufacturers themselves acknowledge, but it exists — and it wipes out exactly the theoretical advantage of "absolute silence" that attracted the buyer.

Here is the honest conclusion: a VIG panel and a good asymmetric acoustic laminated glass may even show similar Rw numbers on paper. But the laminate wins decisively exactly where the city hurts: in the bass. In the end, both block the whistle; only one of them silences the bus.

The vacuum's other bills

Beyond the low-frequency question, VIG carries trade-offs of its own, typical of a technology still maturing — and it is fair to lay them on the table without drama:

• The sealing of the vacuum. Keeping a stable vacuum for decades, against the constant implosive pressure of the atmosphere, is a sealing-engineering challenge that is still being mastered.
• The pillars as thermal bridges. The same pillars that conduct a little vibration also conduct a little heat — small, pointwise thermal bridges that (slightly) scratch the near-perfect thermal performance.
• The size. Thermal-stress limits keep VIG in relatively modest dimensions today — which collides head-on with the monumental, made-to-measure spans of a high-end project.

None of this condemns vacuum glass. Each is a specification decision — the difference between choosing glass by fashion and choosing it by the real problem.

So what actually buys silence?

If your goal is to silence the city, the levers are exactly the ones this series has already taught, and none of them is the vacuum:

• An asymmetric acoustic laminated glass, with the acoustic PVB core that damps the vibration of the bass.
• Inside a well-sealed system, with uniform closing and calculated mass in the frame.
• Read by the metric that does not lie: the Rw index.

Vacuum glass is a brilliant answer — to a different question. It solves heat with an elegance few technologies achieve. But silence against the deep roar of the avenue is won with mass, asymmetry and sealing.

Aken's position: choose the weapon by the enemy

At Aken Studio, we do not choose glass by the headline; we choose it by the enemy. Against the urban bass, we specify mass, asymmetry, acoustic PVB and hermetic sealing — the engineering that effectively silences the bus. For heat, we specify proven insulated builds, with thermal-break rupture and warm-edge spacers. And we follow vacuum glass closely — on the thermal front, where it is genuinely extraordinary — as its sealing and its size limits mature.

Vacuum glass is not the wrong glass. It is the right glass for another problem. And knowing what your problem is — heat or noise, and which noise — is what separates a sound investment from an expensive disappointment.