There is more bad soundproofing advice on the internet than almost any other home topic. People glue foam to a wall to block a neighbor (it can't), buy a "soundproof" curtain expecting silence (it won't), and add one more layer of drywall expecting a miracle (the physics says otherwise). The frustrating part is that acoustics is not mysterious. The behaviour of sound in a room, and through a wall, is described by equations that have been settled for a century.
So we built three calculators around those equations. They are free, there is nothing to sign up for, and each one shows you the exact formula it used — with your numbers plugged in — so you can check our work. Use them to predict three different things before you spend money:
- How echoey your room is (and how much absorption will fix it) — the Sabine equation.
- How much quieter a treatment will actually feel — the loudness rule.
- How much sound a wall, door, or barrier can block from its weight alone — the mass law.
A quick reminder that runs through all three: absorbing sound and blocking sound are different jobs. Soft, fluffy things (panels, curtains, carpet) absorb — they cut echo inside a room. Heavy, sealed things (mass, dense layers) block — they stop sound passing through to the other side. The first calculator is about absorption; the second and third are about blocking. If that distinction is new to you, start with our guide to absorbing versus blocking sound.
1. The Room Echo Calculator (reverberation time)
When a room sounds boomy, hollow, or "live" — when voices echo and music turns to mush — what you are hearing is reverberation: sound bouncing off hard surfaces and taking a long time to die away. The standard measure is RT60, the time in seconds for a sound to fade by 60 decibels (to about a thousandth of its energy). A bare, hard room can ring for two seconds or more. A comfortable living room sits closer to half a second.
Reverberation time was first quantified by Wallace Clement Sabine at Harvard in the 1890s, and his equation is still the one acousticians reach for:
RT60 = 0.161 × V / A
- V is the room's volume in cubic metres.
- A is the room's total absorption in sabins — found by multiplying each surface's area by its absorption coefficient and adding them all up.
- 0.161 is a constant in metric units (it becomes 0.049 if you work in feet). It comes from the speed of sound and the 60-decibel decay target.
The lesson hidden in that fraction is simple: reverberation time goes down as absorption goes up. Double the absorption in a room and you roughly halve the echo. That is the entire reason acoustic panels work — they pile sabins into the bottom of that equation.
Reverberation Time (RT60)
RT60 = 0.161 × V ÷ A = 0.161 × 50.0 ÷ 7.3 = 1.11 s
How to use it. Enter your room's length, width, and height, then pick the dominant material for the floor, walls, and ceiling. Set roughly how furnished the room is (a sofa and a rug absorb a surprising amount), and then add acoustic panels one at a time to watch the reverberation time drop. The readout shows your RT60, the room's volume, and the total absorption, with a target band of 0.3 to 0.6 seconds — the range most people find comfortable for an apartment living or listening room. Above about one second, the room will sound noticeably echoey.
Two things usually surprise people. First, bare rooms are far worse than they expect — a room with hard floors, painted drywall, and no furniture can post an RT60 over two seconds. Second, it takes more absorption than you think to fix it. One foam square does almost nothing; you are trying to move a number that scales with the whole room's volume. A few full-size NRC 1.0 panels, a thick rug, and heavy curtains together will move it a lot.
One honest caveat: the Sabine equation assumes sound spreads evenly through the room, and it loses accuracy in spaces that are already very dead or oddly shaped. Treat the result as a well-founded estimate, not a lab measurement.
2. The Noise Reduction Calculator (how much quieter?)
This is the calculator that settles the most arguments, because it corrects the single most common misunderstanding in soundproofing: the difference between decibels and loudness.
Decibels are a logarithmic measure of sound energy. Loudness is how loud something seems to your ears. They are not the same, and the gap between them is huge:
- Cutting the sound energy in half lowers the level by only 3 dB — a change you can barely notice.
- To make something seem half as loud, you have to lower the level by about 10 dB — which actually removes 90% of the energy.
That second relationship is the one that matters when you are deciding whether a treatment is worth it. The rule, drawn from decades of psychoacoustic research, is that perceived loudness roughly halves for every 10-decibel drop:
Perceived loudness = 2 ^ (−ΔdB / 10)
So a 10 dB reduction feels half as loud (a 50% improvement). A 20 dB reduction feels a quarter as loud. A 30 dB reduction feels about an eighth as loud. The improvements stack up fast, which is good news: you do not need to block all of a noise to make a room feel peaceful — you need to knock 15 to 25 dB off it.
How Much Quieter Will It Get?
Loudness = 2^(−ΔdB ÷ 10) = 2^(−20 ÷ 10) = 0.250 → about 75% quieter · Received = 70 − 20 = 50 dB
How to use it. Set the slider to how loud the noise is now — there are reference points along the way (a normal conversation is about 60 dB, a TV around 70, city traffic near 80). Then pick the treatment you are considering, or drag the fine-tune slider to any reduction you like. The tool shows two numbers: the sound that still gets through in decibels, and how much quieter that feels as a percentage, along with a plain-language verdict.
The treatment presets use STC values, the standard single-number rating for how well a wall or door blocks airborne sound. As a rough guide, an STC rating behaves like a decibel reduction for speech and television. The interpretation acousticians use:
- STC 25 — normal speech is easily understood through the wall.
- STC 30 — loud speech understood; normal speech is heard but not understood.
- STC 35 — loud speech is audible but not intelligible.
- STC 40 — loud speech is a faint murmur.
- STC 45 — the onset of real privacy; loud speech is heard but not understood.
- STC 50 — loud speech is not heard at all.
The big caveat — and the tool says so too — is bass. STC is measured for speech-range frequencies, so it tells you very little about a subwoofer, a bass guitar, or the thump of footsteps overhead. Low frequencies leak through far more than an STC number suggests, which is why you can still feel a party's bass line through an otherwise solid wall. For low-frequency and impact noise from neighbors, expect less than the calculator's headline figure.
3. The Mass Law Calculator (will adding mass help?)
The first rule of blocking sound is the oldest one: mass. A heavy, limp barrier is harder for sound to vibrate, so less energy makes it to the other side. Physicists describe a single, solid panel with the mass law, and it is worth knowing because it tells you exactly how much a heavier door or an extra layer of drywall will buy you.
TL = 20 × log₁₀(m × f) − 47
- TL is transmission loss in decibels — how much the barrier knocks down the sound.
- m is the barrier's surface mass: its weight per square metre, in kg/m².
- f is the frequency of the sound, in hertz.
- 47 is the field-incidence constant for a real, randomly-arriving sound field.
Two rules of thumb fall straight out of that formula, and both are baked into the calculator:
- Double the mass, gain about 6 dB. Twice as heavy is meaningfully — but not dramatically — better. This is why "just add mass" has diminishing returns, and why stacking endless drywall is a losing game.
- Every octave up, gain about 6 dB. Mass blocks high frequencies far more easily than low ones. Bass is hard to stop — exactly what the noise calculator warned about.
Will Adding Mass Block It?
TL = 20·log₁₀(m × f) − 47 = 20·log₁₀(10.7 × 500) − 47 = 27.6 dB
How to use it. Build up a barrier by adding layers — sheets of drywall, mass-loaded vinyl, plywood, glass — and the tool sums their surface mass and reports the transmission loss at the frequency you choose. The little spectrum chart shows that 6 dB-per-octave slope at a glance: tall bars on the right (treble blocked well), short bars on the left (bass leaks through). Switch the frequency to 125 Hz to see how little even a heavy wall does against deep bass.
This is where mass-loaded vinyl earns its place in a renter's toolkit: it adds real kilograms per square metre to a thin hollow-core door without any construction — exactly the surface mass this calculator rewards. A heavy sound blanket is cheaper by the square foot, but be clear-eyed about it: at barely a kilogram per square metre it adds only a little mass, so it tames echo far more than it blocks.
Two important caveats live inside this one. First, the mass law describes a single, solid layer. The best-performing walls don't just pile on mass — they decouple, using an air gap or resilient channels so the two sides can't vibrate together. A decoupled wall outperforms what the mass law predicts, so treat the calculator's number as the floor for a simple barrier, not the ceiling for a clever one. Second, a single-frequency transmission loss is only a rough proxy for STC, which is a curve fit across many frequencies. Use the mass-law number to compare options and understand why mass matters — not as a precise STC rating.
The fine print: how accurate are these?
Every formula here is a textbook standard, and we tested each calculator against worked examples computed by hand before publishing. But a few honest limits apply to all three:
- They are estimates, not measurements. Real rooms have leaks, flanking paths, and odd geometry that no simple equation captures. A 1% air gap can turn a 40 dB wall into a 30 dB wall — which is why sealing gaps almost always beats adding material.
- Perceived loudness is personal and depends on frequency; the "10 dB sounds half as loud" rule is a well-established convention, not an exact law.
- STC and single-frequency numbers understate the bass problem. If your noise is low and rhythmic, expect less than the headline figure.
Used with those limits in mind, the calculators will keep you from the two most expensive mistakes in soundproofing: buying absorption when you needed mass, and expecting a small change to deliver a big result. If you want the full playbook, start with genius ways to silence noisy neighbors, seal your door and window, and mask whatever survives with earplugs or a white noise machine.
FAQ
What is a good RT60 for a room?
For a home living room, listening room, or office, an RT60 of roughly 0.3 to 0.6 seconds feels balanced — speech is clear and music isn't muddy. Below about 0.3 seconds a room starts to feel unnaturally "dead"; above one second it sounds echoey. Larger spaces and concert halls are deliberately longer.
Why does my room need so many acoustic panels?
Because reverberation depends on the whole room's volume, and one small panel adds only a sabin or two of absorption against it. The Sabine equation scales with volume, so a big, hard room genuinely needs several square metres of absorption — a few full-size panels plus a rug and curtains — to drop into the comfortable range.
Does doubling the drywall double the soundproofing?
No. The mass law says doubling the mass adds only about 6 dB of transmission loss — a real improvement, but far from double the blocking and nowhere near double the perceived quiet. Decoupling the wall (an air gap or resilient channels) usually buys more than another layer of mass.
Is STC the same as decibels blocked?
Roughly, for speech — but not literally. An STC 45 wall does not block exactly 45 dB at every frequency. It is a single number fitted to a curve across the speech range (125–4000 Hz), and it overstates how much bass a wall stops. For low-frequency noise, the real-world reduction is less than the STC number.
Why does bass get through everything?
Both the mass law and STC show why: barriers block roughly 6 dB less for every octave you go down in frequency, and STC barely measures the lowest frequencies at all. Long bass wavelengths vibrate a wall easily, so stopping them takes far more mass, decoupling, and sealing than stopping speech does.
Sources and method
These tools use established acoustics, not house formulas. Reverberation time uses the Sabine equation (RT60 = 0.161·V/A). Transmission loss uses the field-incidence mass law (TL = 20·log₁₀(m·f) − 47). Perceived loudness uses the standard psychoacoustic relationship that a 10 dB change corresponds to a doubling or halving of loudness (loudness ∝ 2^(ΔL/10)), and the STC interpretation follows the widely cited Berendt/HUD descriptions. Absorption coefficients and material surface masses are representative mid-frequency values from standard architectural-acoustics references. Every result on this page is computed live in your browser from the same formulas printed above.
A mineral-wool, wood-framed panel rated NRC 1.0 — the maximum. Each 2 ft × 4 ft panel adds about 8 sabins of absorption, which is the unit the Room Echo calculator counts in. Made in the USA.
Drop the panel count into the RT60 tool and watch the reverberation time fall. Two or three of these transform a hard, ringing room.
*Price shown on Amazon and subject to change.
Mass-loaded vinyl is the renter's way to add the surface mass the Mass Law calculator rewards. Rated STC 20, it both blocks and absorbs, and it hangs over a door or wall without construction.
Add an "MLV layer" in the Mass calculator and you can see why it works — it stacks real kilograms per square metre onto a thin door.
*Price shown on Amazon and subject to change.
A heavy, washable moving-style blanket (NRC 0.35) with 18 grommets — by the square foot the cheapest way to hang a layer over a door or doorway. It's an absorber that tames echo and takes the edge off noise, and it adds only a little mass, so lean on it for the Room Echo tool, not for blocking.
It is huge and genuinely heavy for a blanket. Hung over a door it kills echo and softens what comes through — a cheap way to hear what absorption does before you spend on mass.
*Price shown on Amazon and subject to change.
| Pick | Product | Link | |
|---|---|---|---|
| Best for Echo | ATS Acoustics — ATS Acoustics Panel 24 x 48 x 2 in (NRC 1.0) | $79.95 | Check → |
| Best for Mass | Audimute — Audimute isolé Sound Barrier + Absorber (MLV, STC 20) | $149.00 | Check → |
| Budget Absorber | US Cargo Control — US Cargo Control Sound Dampening Blanket (96 x 80 in) | $76.48 | Check → |
Lillie Metayer
Lillie Metayer is the founder of a local program that helps apartment-dwellers take action against noise pollution. Involved in environmental activism since high school, Lillie is passionate about raising awareness of the harms of noise exposure and helping people reduce noise in their communities. In her free time, Lillie enjoys playing the violin and spending time outdoors.
