STC Rating Explained: What It Means and Why It Matters

An STC rating (Sound Transmission Class) is a single number, usually between 20 and 80, that measures how well a wall, door, floor, or window blocks airborne sound such as speech, TV, and conversation. The higher the STC rating, the less sound passes through. Most U.S. building codes require a minimum STC rating of 50 for walls between apartments. However, the STC rating only measures mid-to-high frequency airborne noise. It does not measure bass, footsteps, or how a wall will actually perform once it is built.

That paragraph answers the question most people search for. Everything below it is for anyone who needs to do something with that number, whether that means buying the right interior door, specifying the right wall assembly, or explaining to a client why an STC rating of 50 does not mean silence. If you would rather skip straight to a professional opinion on your own space, DeWalls' soundproofing services cover everything from a single noisy room to a full commercial build-out across North Texas.

Understanding the STC Rating: What It Actually Measures

An STC rating measures how much a building partition, such as a wall, ceiling, floor, door, or window, reduces airborne sound as it passes from one side to the other. The test focuses on the 125 Hz to 4,000 Hz frequency range, which is roughly the band where human speech lives. That range was not chosen at random. It exists to answer one practical question: if someone talks in the next room, how much of that conversation will you actually hear?

The STC rating itself comes from ASTM International's E413 standard, which explains how raw sound transmission loss data, collected in a lab under ASTM E90, is converted into the single number you see on a spec sheet. A hollow-core door might carry an STC rating of 32. A party wall in a new Texas apartment complex might be built to hit an STC rating of 50. A recording studio wall might be built to reach an STC rating of 65 or higher.

How the STC Rating Is Actually Tested

Here is the process in the order it actually happens in a lab, since almost no consumer-facing article walks through it:

1.  Two reverberation rooms are built side by side, separated only by the test wall, door, or window.

2.  A loudspeaker in the source room plays sound across sixteen one-third-octave frequency bands between 125 Hz and 4,000 Hz.

3.  Microphones in the receiving room measure how much of that sound made it through at each frequency.

4.  The difference between the two measurements, at each frequency, produces a transmission loss curve.

5.  That curve is compared against a standard reference contour defined in ASTM E413, and the single STC number is the value where the curve fits that contour most closely.

Here are the key facts worth remembering about how an STC rating works: 

• It is not a decibel measurement. It is a classification number derived by fitting a wall's transmission loss curve, tested across sixteen frequency bands, against a standard reference contour.

• It is a comparison tool. An STC rating lets you place a hollow-core door, a solid-core door, and a fully soundproofed wall assembly on the same scale.

• Two walls with the same STC rating can still sound slightly different in real life, because they can reach that number through different combinations of mass, frequency response, and construction.

For most homeowners and property managers, the practical takeaway is simple: the STC rating tells you, at a glance, which product will do a better job of keeping sound where it belongs.

Why the STC Rating Isn't a Straight-Line Scale

Here is something most articles skip entirely, and it is the single most useful thing to understand before spending money on soundproofing: an STC rating does not behave like a percentage.

Because sound is measured on a logarithmic scale, moving from an STC rating of 30 to 40 does not feel like the same jump as moving from 50 to 60, even though both are "10 points." As a general rule in acoustic engineering, a 10-decibel reduction in sound is perceived by the human ear as roughly half as loud, not simply "10% quieter." STC point differences follow this same logarithmic relationship in practice.

This explains two things that trip people up constantly: 

1. Upgrading a wall from a code-minimum STC rating of 50 to 55 can feel almost pointless, while going from 50 to 60 feels like an entirely different room.

2. A contractor quoting "five more points" is not offering 5% more soundproofing. Depending on the starting point, that jump could be barely noticeable or genuinely dramatic.

If there is one number worth remembering from this entire guide, it is this: a 10-point increase in STC rating corresponds to sound being perceived as roughly half as loud. That single fact reframes almost every decision covered below.

Everyday Sounds and Decibel Levels: Putting the STC Rating in Context

Numbers on a spec sheet only mean so much on their own. It helps to know what the sounds an STC rating is actually trying to stop feel like in decibels, since that is the scale the STC test is built on.

Sound Source	Approximate Decibel Level	How It Feels
Whisper	30 dB	Barely audible
Quiet conversation	50 dB	Comfortable background level
Normal conversation	60 dB	Easily understood at close range
Vacuum cleaner	70 dB	Noticeably intrusive
Busy city traffic	80–85 dB	Disruptive over time
Motorcycle at close range	95 dB	Uncomfortably loud
Rock concert or power tools	110–120 dB	Potentially harmful with prolonged exposure

 These figures are the kind commonly cited by organizations such as OSHA and the CDC when discussing hearing safety, and they help explain why the STC rating scale was built around the 125 Hz to 4,000 Hz range in the first place. Normal conversation, the sound most people actually want blocked, sits squarely in that band.

A few practical takeaways:

• Every 10 dB increase feels roughly twice as loud, which is exactly the same logarithmic relationship covered in the previous section.

• An STC 50 wall reduces a 60 dB conversation to somewhere around 10 to 15 dB on the other side, which is why loud speech becomes a faint murmur rather than disappearing completely.

• Low-frequency sources like traffic and bass are perceived differently than the mid-range speech frequencies STC was built to measure, which is exactly the gap covered later in this guide.

The STC Rating Scale: What Each Range Actually Sounds Like

The table below translates the STC rating scale into what you would actually experience standing on the other side of the wall.

STC Rating	What You Will Hear	Typical Example
20–25	Normal speech heard and understood clearly.	Open doorway, single pane of glass.
30–35	Loud speech is audible; normal speech is understood.	Standard hollow-core interior door.
35–40	Loud speech is audible, but words are hard to make out.	Typical uninsulated interior wall.
45–50	Loud speech is reduced to a murmur and rarely understood.	Code-minimum apartment demising wall.
50–55	Normal conversation stays private; loud sounds are faintly heard.	Above-code multifamily wall, hotel room wall.
60–65	Most sound, including loud music, is barely audible.	Home theater, executive conference room.
65+	Near-total isolation.	Recording studio, broadcast booth.

Two details in this table matter more than the numbers themselves.

1. An STC rating of 50 does not mean 50 percent of sound is blocked. There is no percentage built into the number at all. It is a relative classification, not a fraction.

2. Real assemblies can beat these ranges by a wide margin. Independent testing on certain fire-rated wall assemblies used in multifamily construction has reached an STC rating of 62, well past the code floor, simply by combining the right materials instead of relying on mass alone

If you are unsure which STC rating your own home or office currently sits at, a professional soundproofing assessment can identify the gap between what your walls are doing today and what your project actually needs.

STC Ratings by Common Wall, Door, Window, and Floor Assemblies

Most people shopping for soundproofing are not comparing abstract ranges; they are comparing an actual door, an actual wall, or an actual window against what they already have. The table below lays out commonly reported STC ranges for real, frequently used assemblies, based on published manufacturer and industry testing.

Walls 

Assembly	Typical STC Rating
Single 2x4 stud wall, no insulation, drywall both sides	33–35
Same wall with batt insulation added	38–39
Single stud wall, insulated, with resilient channel	46–50
Double layer of 5/8-inch drywall, insulated	50–53
Staggered-stud wall, insulated	50–55
Double-stud wall (separate top and bottom plates), insulated	55–63
Double-stud wall with mass-loaded vinyl and resilient channel	63+

Doors

Assembly	Typical STC Rating
Hollow-core interior door	20–25
Solid-core wood door, no seals	30–35
Solid-core door with acoustic seals and threshold	35–39
Purpose-built acoustic door assembly	45–50+

Windows

Assembly	Typical STC Rating
Single-pane window	20–25
Standard double-glazed window	28–33
Laminated acoustic glazing	40–44
Industry-average STC-rated replacement window	Roughly 38

Floors and Ceilings

Assembly	Typical STC Rating
Bare wood joist floor, no ceiling below	30–35
Standard floor-ceiling assembly with carpet	45–50
Concrete slab with resilient flooring	50–55+

A few things worth noticing in these tables:

• The jump from a hollow-core to a solid-core door is one of the single cheapest STC upgrades available for a homeowner, often adding close to 10 points for a modest cost difference.

• Windows are frequently the weakest point in an otherwise solid wall. A wall rated at STC 50 next to a standard double-glazed window rated at STC 30 will perform closer to the window's rating overall, because sound takes the path of least resistance.

• Ranges vary by manufacturer and testing lab, so these numbers are a planning reference, not a substitute for checking the specific product's tested rating sheet.

Why the STC Rating Matters (And Why the Code Minimum Is a Floor, Not a Target)

An STC rating shows up in three very different conversations, and the "right" number changes depending on which one you are having.

1. Privacy and Everyday Comfort

If you are renting an apartment, running a home office next to a nursery, or trying to hold a confidential conversation in a conference room, the STC rating tells you whether you will be overheard, or whether you will be doing the overhearing. Homes across fast-growing suburban markets, including much of the Dallas-Fort Worth area, are frequently built to the bare code minimum, which is one reason newer neighborhoods still feel surprisingly noisy between units and why residential soundproofing upgrades remain such a common request from homeowners.

Common everyday privacy concerns tied directly to STC rating include:

• Overhearing a neighbor's TV or conversation through a shared apartment wall.

• A home office that lets phone calls bleed into the rest of the house.

• A nursery or bedroom that is too exposed to living room or kitchen noise.

• Shared-wall townhomes where music or a home gym is audible next door.

2. Building Code Compliance

In the United States, the International Building Code addresses sound transmission directly in Section 1206. It sets a minimum STC rating of 50 when tested in a lab, or a Field STC of 45 when tested on the completed building, and the same threshold appears in the International Residential Code for walls and floor-ceiling assemblies separating dwelling units. Texas adopts the IBC and IRC as its base building code, with local amendments varying by city. That five-point gap between the lab number and the field number is not a rounding error. It is the code itself acknowledging that real construction rarely matches lab conditions exactly.

Situations where this code minimum typically applies include:

• New multifamily construction, including apartments, condos, and townhomes.

• Hotel and short-term rental construction.

• Walls separating a residential unit from a public corridor, stairwell, or parking structure.

3. Specialized Design Requirements

Hospitals, classrooms, courtrooms, and recording studios all have their own reasons to push well past code minimums:

• Hospitals need higher STC ratings for patient confidentiality.

• Classrooms need a target STC rating to protect speech intelligibility.

• Recording studios and podcast rooms need an STC rating of 65 or higher, since anything close to code minimum would make the space unusable.

• Executive offices and conference rooms typically target 50 to 55 to protect confidential conversations.

STC Rating Requirements Around the World

If you are only reading U.S. sources, you are missing part of the picture, because STC itself is largely a North American metric. Other countries measure the same problem with related, but different, numbers.

Country	Governing Code	Minimum Requirement	Metric Used
United States	IBC Section 1206 / IRC	STC 50 (lab) / FSTC 45 (field)	STC, per ASTM E413
Canada	National Building Code	STC 50 historically; since the 2015 edition, an Apparent STC (ASTC) of at least 47	ASTC (accounts for flanking noise)
United Kingdom	Approved Document E	DnT,w + Ctr of at least 45 dB for separating walls in new-build flats	DnT,w (on-site, ISO-based)
Australia	National Construction Code, Part F5/F7	Rw + Ctr of at least 50 for walls between separate units	Rw (lab, per AS/NZS ISO 717.1)

Two points are worth calling out here, because almost nobody explains them clearly.

1. The UK and Australian numbers are not literally "STC." They are built on the ISO 717 family of standards rather than ASTM E413. The numbers land in a similar range, but treating a UK Rw of 45 as identical to a US STC of 45 is a common but technically inaccurate shortcut.

2. Canada changed its approach in 2015. Instead of requiring an STC rating of 50 on the isolated wall assembly alone, the National Building Code moved to Apparent Sound Transmission Class (ASTC), which factors in flanking sound that sneaks around a wall through the floor, ceiling, and adjoining structure. Canada's current benchmark of ASTC 47 is arguably a more honest number than a lab-only STC rating, because it reflects what people in the next unit actually hear.

Signs Your Home or Business Needs a Better STC Rating

You do not need to know the exact number to recognize when a space is underperforming. These are the practical warning signs worth watching for.

Residential signs:

• You can clearly hear TV dialogue or music from an adjoining unit or room.

• Conversations at normal volume in one room can be understood in the next.

• A home office or nursery is exposed to household noise throughout the day.

• Guests or tenants mention noise as a recurring complaint.

  
  

Commercial and office signs:

• Confidential conversations in a conference room can be heard in the hallway or adjacent office.

• Open-plan layouts make it difficult to take calls without disrupting nearby coworkers.

• Clients notice echo or noise bleed during meetings, which can come across as unprofessional.

Industrial and mechanical signs:

• Equipment noise travels well beyond the intended work area.

• Nearby offices or neighboring businesses have raised noise complaints.

• Vibration from machinery is noticeable in adjoining rooms, which is a separate but related problem to airborne STC performance.

If any of these sound familiar, the fix is rarely "start over." In most cases, targeted upgrades to an existing wall, door, or window close most of the gap. A free noise assessment is usually the fastest way to find out which upgrade will actually move the needle for your specific space, whether that is a residential property or a commercial one.

The Blind Spots: What the STC Rating Doesn't Tell You

An STC rating is useful precisely because it is simple, a single number you can compare across products. That simplicity comes at a cost, and the cost shows up in three specific gaps.

1. It ignores everything below 125 Hz. Bass-heavy music, HVAC rumble, subwoofers, traffic noise, and heavy machinery all live at frequencies the STC rating does not test. A wall can carry an impressive STC rating of 55 and still let a neighbor's bass line through almost untouched, because low frequencies travel through mass and structure in ways this test simply does not measure.

2. It does not measure impact noise. Footsteps, dragged furniture, and dropped objects transmit through a structure rather than through the air. That is measured by a completely different metric: Impact Insulation Class (IIC). A floor-ceiling assembly can carry an excellent STC rating and still transmit every footstep from the unit above, which is exactly why codes like the IBC require both an STC minimum and a separate IIC minimum for floor assemblies.

3. Lab numbers and field numbers are not the same number. The STC rating is measured in a laboratory under close to ideal conditions, with no flanking paths, no construction gaps, and no penetrations for outlets or plumbing. Field testing, conducted under ASTM E336, measures the same wall after it has actually been built, and it almost always comes in a few points lower. This is exactly why the IBC allows a Field STC of 45 to satisfy a lab-rated STC 50 requirement.

 

How the STC Rating Compares to Other Acoustic Metrics

Because the STC rating gets quoted constantly but explained rarely, it is easy to lose track of which metric answers which question.

Metric	What It Measures	Where You Will See It
STC	Airborne sound (speech, TV, music) through walls, doors, partitions.	Wall assemblies, doors, interior partitions.
IIC	Impact or structure-borne sound (footsteps, dropped items).	Floor-ceiling assemblies.
OITC	Airborne sound including low-frequency noise like traffic and aircraft.	Exterior walls, windows near roads or flight paths.
NRC	How much sound a surface absorbs inside a room (echo control).	Ceiling tiles, acoustic panels, not isolation between rooms.
Rw / DnT,w	The ISO-based international equivalent of the STC rating.	Product specs and building codes in the UK, EU, and Australia.

If you are specifying a window for a house near a busy Texas highway, the STC rating alone can be misleading. The OITC rating is more relevant, since it accounts for the low-frequency traffic rumble that STC ignores entirely. If your problem is an upstairs neighbor's footsteps, no amount of STC improvement on the ceiling below will help. That is strictly an IIC problem, and it usually calls for acoustic treatment applied at the floor level rather than the wall. Vibration-driven noise from mechanical equipment is a related but separate challenge, typically addressed through vibration and industrial acoustics work rather than a simple STC upgrade.

Common STC Rating Myths, Debunked

A few beliefs about the STC rating show up constantly in online forums and even in some product marketing. Each one is worth correcting directly.

1. "Doubling the STC rating doubles the soundproofing." This is not how the scale works. Because the STC rating tracks a logarithmic relationship, moving from 30 to 60 is not simply "twice as good." It is a much larger real-world improvement than the doubled number suggests, precisely because of the perceived-loudness math covered earlier.

2. "A high STC rating means a room is soundproof." Even a wall with an STC rating of 65 will let deep bass, heavy footfall, and vibration through, because none of those are measured by the STC test. A high STC rating means "excellent at blocking speech and mid-range airborne sound," not "completely silent."

3. "The manufacturer's STC rating is exactly what I will get once it's installed." Manufacturers report lab numbers. Installed performance depends on framing, sealing, flanking paths, and workmanship, which is exactly why field testing under ASTM E336 exists as a separate, and usually lower, measurement.

4. "More mass always means a higher STC rating." Mass helps, but it plateaus. Two layers of the same drywall stacked directly against each other, without any separation, barely outperform one thicker layer, because both layers vibrate together as though they were one solid mass. Real gains beyond that point come from decoupling the layers, not from adding more of the same material.

5. "Only new construction can achieve a high STC rating." Existing walls, doors, and windows can be retrofitted with mass-loaded vinyl, additional drywall layers, or acoustic seals without a full teardown, often closing most of the gap to a target STC rating at a fraction of new-construction cost.

6. "Every room in a home needs the same STC rating." A hallway closet and a home theater have very different noise goals. Matching the STC rating to the actual use of the room, rather than chasing the highest possible number everywhere, is usually the more cost-effective approach.

How to Improve Your STC Rating

There are three physical principles behind every effective soundproofing project, and almost every technique on the market is a variation on one of them.

1. Add mass. Denser, heavier materials are harder for sound waves to push through. Upgrading from half-inch to five-eighths-inch drywall, or adding a layer of mass-loaded vinyl, are two of the most common ways to raise an STC rating without rebuilding a wall from scratch.

2. Decouple the structure. Sound travels efficiently through anything rigidly connected, including studs, framing, and shared surfaces. Staggered-stud or double-stud framing, resilient channels, and isolation clips all work by breaking that rigid connection so vibration cannot travel straight through the wall.

3. Seal every gap. An unsealed electrical outlet, an unsealed baseboard gap, or an unsealed door threshold can undo a large percentage of a wall's rated STC performance, because sound always takes the path of least resistance. Acoustic caulk and putty pads around penetrations close these leaks.

None of these techniques perform as well in isolation as they do combined. Layering a soundproofing membrane between drywall sheets and installing resilient channels on the same wall can lift the overall STC rating by 10 points or more, a bigger jump than either technique would produce alone.

What It Actually Costs to Raise Your STC Rating

Technique	Typical STC Gain	Relative Cost	Best For
Upgrade drywall thickness (½" to ⅝")	1–3 points	Low	Budget-conscious minor improvements.
Add a mass-loaded vinyl layer	3–6 points	Low to Medium	Retrofits without opening the wall.
Install resilient channels	5–10 points	Medium	New construction or full remodels.
Add a second, decoupled layer of drywall	5–8 points	Medium	Existing walls being finished or refinished.
Full staggered or double-stud rebuild	10–20+ points	High	New builds, studios, dedicated media rooms.
Seal existing gaps and penetrations only	2–5 points	Very Low	Quick wins on an otherwise finished wall.

Sealing gaps, the cheapest item on this list, can still be worth several STC points on its own. It is usually the first thing worth checking before spending money on anything else, since a well-built wall with an unsealed outlet box can underperform a mediocre wall that is properly sealed. A licensed acoustic contractor can usually spot these gaps in a single walkthrough.

DIY Versus Professional Installation

Factor	DIY Approach	Professional Installation
Typical STC gain	2–8 points	8–20+ points
Access to lab-tested assemblies	Limited	Full access to tested, documented systems
Risk of missed flanking paths	Higher	Lower, since gaps are diagnosed first
Verification	Smartphone decibel comparison only	Field testing available under ASTM E336
Best suited for	Sealing gaps, adding a rug, weatherstripping a door	Wall rebuilds, studios, code-required assemblies

Verifying That It Actually Worked

Lab data is a starting point, not a guarantee. Field testing under ASTM E336 measures actual sound isolation after installation, confirming that the materials, sealing, and workmanship delivered something close to what was promised on paper. For anything beyond a small DIY project, whether that is a multifamily building, a commercial tenant improvement, or a home studio build across North Texas, bringing in a specialist early and budgeting for post-construction testing avoids disputes and expensive rework later.

 

STC Rating and Property Value: Why It's Not Just About Comfort

Sound isolation is often treated as a comfort issue, but it has a measurable effect on how a property performs financially, especially in competitive rental and resale markets.

• Multifamily properties with above-code STC ratings tend to see fewer noise-related complaints and lower tenant turnover, since noise is consistently one of the top reasons renters cite for not renewing a lease.

• Home buyers increasingly ask about shared-wall noise in townhomes and condos, making a documented STC rating a genuine selling point rather than a technical footnote.

• Commercial tenants value acoustic privacy in conference rooms and executive offices, and it can influence which office space a growing business chooses to lease.

• Home theaters, media rooms, and music spaces built to a higher STC rating are frequently highlighted in real estate listings as a premium feature, not just a technical spec.

For landlords and property managers weighing the cost of an upgrade, the math often comes down to comparing the one-time cost of commercial soundproofing improvements against the ongoing cost of vacancy and turnover driven by noise complaints.

A Simple Way to Sanity-Check Sound Isolation Yourself

You cannot get a certified STC rating without lab equipment and a trained technician. However, if you are simply trying to decide whether a soundproofing upgrade is working, a smartphone decibel meter app can offer a useful, though uncertified, comparison. Here is a practical way to run the test:

1. Play music or talk at a consistent volume on one side of the wall or door.

2. Measure the decibel level on the other side before making any changes.

3. Make your soundproofing upgrade, whether that is sealing a gap or adding a layer of drywall.

4. Measure the decibel level again, in the same spot, at the same volume.

You will not get a real STC rating out of this exercise. Smartphone microphones are not calibrated for lab-grade testing, and a single decibel reading cannot replace the sixteen-frequency-band analysis behind an actual STC rating. Even so, this before-and-after comparison tells you whether a change made a measurable difference, which is genuinely useful for anyone weighing a DIY project against hiring a professional.

Choosing the Right STC Rating for Your Space

Instead of guessing, match your situation to the table below.

Your Situation	Main Noise Concern	Recommended STC Rating
Apartment or condo shared wall	Neighbor conversation, TV	50–55
Home office or nursery	Calls, conversation, household noise	45–50
Home theater or media room	Music, movie soundtracks	60+
Bedroom facing a busy street	Traffic noise	Prioritize OITC over STC
Podcast studio or recording space	Everything, including background hum	65+
Open-plan office in a commercial building	Speech privacy between meetings	45–55
Standard interior door replacement	General household privacy	35–40 minimum

If your noise problem is traffic, aircraft, or anything low-frequency coming from outside, do not shop by the STC rating alone. Check the OITC rating on windows and exterior doors instead, since that number is built specifically to measure the frequencies traffic and aircraft noise occupy. For industrial facilities and warehouses across Texas dealing with equipment noise, the same rule applies: industrial noise control usually requires OITC and vibration data alongside the STC rating, not the STC rating alone.

Quick summary before you shop or hire: 

• Match the STC rating to the room's actual purpose, not the highest number available.

• Check OITC separately for anything facing outside noise, especially traffic or aircraft.

• Budget for sealing and installation quality, not just the material's lab rating.

• When in doubt, ask for the tested assembly's full data sheet, not just the headline STC number.

Questions to Ask Before Hiring an Acoustic Contractor

Not every soundproofing contractor works the same way, and the difference shows up in results. Before signing a contract, it is worth asking:

• Can you show completed projects similar to mine? A contractor's portfolio should include work in comparable spaces, whether residential, commercial, or industrial.

• Do you offer field testing after installation? Verifying the finished STC rating under ASTM E336 confirms the work actually performs as promised.

• What warranty backs the installation? Materials and workmanship warranties both matter, since a high-STC assembly installed poorly will underperform its rating.

• How long has your team been in this specific trade? Acoustic contracting is a specialized skill separate from general construction, and experience shows in how flanking paths and gaps are handled.

• Can you walk me through your recommended assembly and why? A contractor who can explain the reasoning, not just the price, is more likely to deliver the result you actually need.

DeWalls' about page and FAQ page answer most of these questions directly, and are a reasonable model for what to look for from any acoustic contractor, regardless of who you eventually hire.

 

Serving Homes and Businesses Across North Texas

STC rating requirements do not change much from one Texas city to the next, since most municipalities in the region adopt the same base IBC and IRC provisions. What does change is the age and construction style of the local housing stock, which affects how much work is needed to hit a target STC rating. Older homes in established neighborhoods around Dallas often need different upgrades than newer construction in Irving or fast-growing suburbs like Addison, where soundproofing projects frequently focus on shared walls in newer multifamily developments. Homeowners and businesses throughout Dallas County and the surrounding Metroplex face largely the same underlying acoustic challenges, just at different starting points depending on when and how a building was constructed.

 

STC Rating FAQs

What is a good STC rating?

An STC rating of 50 is the building-code minimum for apartment and condo walls. An STC rating of 55 to 60 is considered good for hotels and upscale multifamily buildings, while 65 and above is reserved for studios and theaters.

What is a good STC rating for a bedroom or apartment wall?

Most homes are comfortable with an STC rating of 45 to 50. If the wall faces noisy neighbors or a busy street, aim for 55 or higher.

Does the STC rating measure bass or low-frequency sound?

No. The STC rating focuses on the 125 Hz to 4,000 Hz speech range. Low-frequency sound, such as bass or traffic rumble, needs additional mass and damping, and is better tracked by the OITC rating.

Is the STC rating the same in the field as in the lab?

Not usually. Lab-rated STC numbers assume ideal conditions. Field-tested STC, measured under ASTM E336, is typically 3 to 5 points lower because of flanking paths and construction gaps.

What is the difference between STC and IIC?

STC measures airborne sound, such as voices and music, passing through a wall. IIC measures impact sound, such as footsteps, passing through a floor-ceiling assembly. A floor can score well on one and poorly on the other.

What is the difference between STC and NRC?

STC measures how much sound a wall blocks between two rooms. NRC measures how much sound a surface absorbs inside a single room, which controls echo rather than isolation.

Is a lower STC rating better than a higher one?

No. A higher STC rating always indicates better sound isolation. A lower number means more sound passes through the material.

What STC rating do I need for a home theater?

Most home theaters perform well at an STC rating of 60 or higher, since this keeps movie soundtracks and bass-heavy audio from disturbing the rest of the house.

Can I improve my STC rating without major renovation?

Yes. Sealing gaps, adding mass-loaded vinyl, and upgrading a door's seals can meaningfully raise an STC rating without opening the wall, though larger gains typically require adding or decoupling layers.

The Bottom Line on STC Ratings

An STC rating is a genuinely useful shortcut, a single number that lets you compare a door, a wall, and a window on the same scale. It was never designed to tell the whole story. It says nothing about bass, nothing about footsteps, and it is measured under lab conditions that real construction rarely matches exactly. Used well, the STC rating is a starting point for a conversation about what you are actually trying to block, not the final word on how quiet a room will be.

Key takeaways worth carrying forward:

• The STC rating measures airborne sound only, primarily in the speech frequency range.

• A 10-point increase feels roughly twice as significant as the number itself suggests, due to the logarithmic scale.

• Code minimums are a floor, not a target, especially for anyone chasing genuine privacy rather than bare compliance.

• Sealing gaps is often the cheapest, fastest improvement available, before any material upgrade is even considered.

If you are specifying a wall, door, or window for a real project in North Texas, the questions worth asking are simple: what kind of noise is the actual problem, what STC rating does your local code or situation genuinely require, and are you even checking the right metric. Sometimes the answer is not a higher STC rating at all. It is a completely different metric. For a project-specific recommendation, the team at DeWalls Acoustic Specialties reviews these numbers against real Texas construction every week and can point you toward the right assembly before you spend a dollar on materials.