Soundproofing & acoustic · Brisbane & SE Queensland
Soundproofing & acoustic insulation, Brisbane.
Sound is rated by STC, not R-value. Pumped-in cellulose fills the cavity and covers the joists with no gaps, so for the same thickness it’s noticeably better than batts at airborne noise like traffic, planes and voices.
I’m Peter Johnson. I’ve sound-insulated media rooms, units and flight-path homes for 40 years, and I’ll be honest with you about what it can stop and what it can’t, because sound is subjective and I won’t promise you a number I can’t measure.
Full cavity, no gaps
where sound batts leave them
The metric most companies get wrong
Sound is measured in STC, not R-value.
R-value rates resistance to heat. Sound is rated by STC (Sound Transmission Class) and the two have nothing to do with each other. Pumped-in cellulose quietens airborne noise because it adds mass and fills the cavity completely with no gaps; a cut-to-fit batt always leaves some.
Here’s the thing that should make you suspicious of a “sound batt” pitch: the batt companies don’t even rate their sound batts with an STC rating. They still quote you an R-value, which is the wrong metric for sound entirely. If the sales rep is pointing at an R-number to sell you on noise reduction, they’re answering a question you never asked. Acoustic performance comes from mass and a fully-filled cavity, and that is exactly where a pumped-in product wins over one that’s cut to fit.
I won’t print a hard multiplier like “three times the sound rating” on this page, because I can’t measure your build-up from here and an honest acoustic figure needs an Rw/STC test under the Australian standard. What I can tell you straight is the direction: for the same thickness, dense-packed cellulose is noticeably better than batts at airborne noise. For the full technical case on why full contact beats cut-to-fit, see why I only recommend cellulose.
Watch: cellulose vs fibreglass for sound
A side-by-side soundproofing demonstration from the US Cellulose Insulation Manufacturers Association (CIMA), the same reason full-contact cellulose beats a cut-to-fit batt for airborne noise.
Clean white polyester batts fitted into an internal wall cavity for sound control, full contact, no gaps left for sound to slip through.
Airborne noise is the job
What sound insulation actually stops, and what it doesn't.
Bulk insulation works on airborne noise. It's not a magic wall. Here's the honest split, the same way I'd explain it standing in your hallway.
It genuinely helps with
- Outside traffic noise from a busy road
- Overhead plane noise if you're under a flight path
- Voices, TV and radios travelling between rooms or floors
- The everyday airborne noise between units, duplexes and granny flats
- The high-pitched, scuffing part of footstep noise (partly)
It won’t fix
- The bass thump of footsteps. That travels through the timber joists and comes out of the ceiling below like a drum. The only real fix is a rubber-isolated ceiling installed after we insulate, and that gets costly.
- Anything where the cavity stays full of gaps. Sound is just as gap-sensitive as heat. The building-science rule of thumb is that even small gaps wreck the result (Choice Magazine puts the thermal loss at around 30% for just 1% gaps), so downlights and exhaust fans punched through a ceiling can wipe out the benefit before you start.
- A guaranteed decibel figure. Sound is subjective and depends on the whole build-up; any honest number needs a sound engineer’s report before and after.
The honest headline: insulation is a tool for airborne noise, not structure-borne thump. If a company promises to “soundproof” your home with a few batts and a fixed number, walk away. The same gaps that bleed your heat bleed your sound, which is exactly why a seamless pumped-in job out-performs a cut-to-fit one.
The question I get asked most
“There's a tenant downstairs. Can you insulate between my floors, and how much noise will it stop?”
This is the classic between-floor question: kids upstairs, a tenant or a media room below. Here's the full, honest seven-point answer, in my own words.
“Results from sound insulation can not be guaranteed as the nature of sound transference is very difficult to stop, and any results are subjective without a full sound engineer’s report before and after insulating your floor.”
The short version: we pump it in through 80mm holes from below, it knocks down the high-pitched airborne noise, it won’t stop the bass thump of footsteps, and downlights will ruin it unless they come out first.
- 1
Yes, we pump it in from below through 80mm holes
The first thing to say is that your ceiling of downstairs can be insulated by pumping cellulose fibre insulation into the between floor cavity from below. We need to cut rows of 80mm holes across the floor about 1.5 m from the wall and every 450mm apart. Then we can move across the room about 3 meters and cut another row of holes the same. For example on a room 8m wide and 6m long we would need about 3 rows of 12 holes in the ceiling to insulate it.
- 2
The holes cost about $10–20 each to patch, and that's on you
Our quote does not include the repairs costs of the holes and depending on the plasterer you use it would cost about $10-20 dollars a hole for the repair and painting. I'd rather tell you that up front than surprise you with it after the job. The patching is a job for a competent plasterer, not something we leave you guessing about.
- 3
It won't stop the bass thump of footsteps
How much noise this will stop is a very subjective thing, I have insulated many floors over the years and regardless of what the sales people say, it is very hard to stop the bass noise of footsteps as the sound travels through the timber joists and comes out on the ceiling plaster like a drum. The only way to help stop this bass noise is to have a rubber isolated ceiling installed after we insulate it but this could be very costly.
- 4
It WILL knock down the high-pitched airborne noise
The kinds of noise any in floor insulation will stop is the high pitch type of sounds, Talking, Radios, even the scratching from the vacuum but the foot steps thumping will mostly not be affected. There may be some perceived difference in the footstep noise but only to the extent of the high pitch or scuffing part of the step.
- 5
Downlights ruin it. Get them out first
We would not recommend insulating the floor if you have any downlights or exhaust fans in the lower ceiling, these will need to be gaped around and with sound insulation just 1% gaps will reduce any benefit by 50%. If you have downlights then I would recommend removing them before we insulate the between floor area or you will ruin any chance of getting a result. If you do have your downlights removed, leave the holes there until we finish our job as we may be able to use some of them for the pumping of insulation.
- 6
Pumped-in fills the cavity where sound batts leave gaps
Although Cellulose Fibre is by far the best sound insulation for the same depth of product and because it is pumped in it is far more likely to fill the floor space completely with no gaps (unlike sound batts which suffer from gaps during installation and mice burrowing through them over time).
- 7
I can't guarantee a result without a sound engineer's report
Results from sound insulation can not be guaranteed as the nature of sound transference is very difficult to stop and any results are subjective without a full sound engineers report before and after insulating your floor. That's the honest answer. Anyone who promises you a fixed decibel drop without measuring it first is selling you something.
The same gap discipline applies to walls. If you’re quietening a wall during a build or a reno, see wall & wet-spray cellulose insulation.
Rooms we sound-insulate
Media rooms, units and flight-path homes.
Over 40 years I've quietened all sorts. These are the jobs where airborne sound insulation earns its keep.
Media rooms & home theatres
A dense-packed cavity around a media room keeps the movie in the room and the kids' noise out of it. We pump cellulose into the surrounding walls and the floor above so the airborne sound (dialogue, music, TV) has far less chance to travel through to the rest of the house.
Flight-path & main-road homes
If you're under a flight path or on a busy road, full-contact cellulose in the ceiling and western walls cuts the steady drone of traffic and the overhead plane noise. We've done it for homes where the planes were the whole reason they called. It's airborne noise, which is exactly what bulk insulation works on.
Units, duplexes & granny flats
Shared-wall living means hearing the neighbours. Pumping cellulose into an existing wall cavity adds mass and fills the gaps that let voices and TV through. It won't turn a unit into a recording studio, but for everyday airborne noise between dwellings it makes a real difference.
Internal walls: bedrooms, offices, bathrooms
Wet-spray or pump-in cellulose in internal wall cavities during a build or a reno quietens the everyday noise between rooms: a home office you can take a call in, a bedroom away from the lounge, a bathroom you don't hear through the wall.
One thing that makes us different on these jobs: a proper pump-in needs a real rig and trained installers, so the cavity actually gets filled completely. A company that only sends a man out with sound batts in a ute will leave the very gaps that wreck the result, and sound is every bit as gap-sensitive as heat. If you want the technical reasons full contact beats cut-to-fit, read why cellulose.
From our jobs, not a stock demo
Watch: real soundproofing jobs.
The explainer up top is a US lab demo. These are our own jobs — between-floor pump-ins, a flight-path home, and walls packed with cellulose for sound.
Filmed on real jobs over the years — our methods, safety standards and products have moved on since. Subscribe to the channel for more.
Honest answers
Soundproofing: the questions I get asked most.
What's the difference between an STC rating and an R-value?+
They measure two completely different things. R-value measures resistance to heat; STC (Sound Transmission Class) measures how well a build-up stops airborne sound. The catch is that the batt companies don't even rate their sound batts with an STC. They still quote R-value, which is the wrong metric for sound. So if a sales rep is selling you a 'sound batt' and pointing at an R-number, they're answering a question you didn't ask. Sound performance comes from mass and a completely filled cavity with no gaps, which is exactly why pumped-in cellulose tends to do better than a cut-to-fit batt for the same thickness.
Is cellulose better than batts for soundproofing?+
For the same thickness, dense-packed cellulose is noticeably better than batts at airborne noise, but the reason matters more than the headline. Cellulose is pumped in, so it fills the whole cavity and covers over the joists with no gaps; a sound batt has to be cut to fit and always leaves some gaps, and the building-science rule of thumb is that even small gaps wreck the result (Choice Magazine puts thermal performance loss at around 30% for just 1% gaps; sound is just as sensitive). I won't quote you a specific decibel figure or a multiplier, because acoustic results depend on your whole ceiling or floor build-up and are subjective without a sound engineer's report. The direction is clear; the exact number needs a measured test.
Will insulation stop the noise of footsteps from upstairs?+
Mostly no, and I'll be straight about it. The bass thump of footsteps travels through the timber joists and comes out of the ceiling plaster below like a drum. Bulk insulation in the cavity does very little to that. You might notice a small difference in the high-pitched scuffing part of a step, but the heavy thud will mostly still come through. The only real fix for footstep noise is a rubber-isolated ceiling installed after we insulate, and that can get very costly. What insulation genuinely helps with is airborne noise: voices, radios, TV.
How much noise will between-floor insulation stop?+
It's a very subjective thing. After insulating many floors over the years, the honest answer is that it knocks down the high-pitched airborne sounds (talking, radios, even the scratch of a vacuum), but the footstep thumping mostly comes through regardless. Results from sound insulation can not be guaranteed, because sound transference is very hard to stop and any result is subjective without a full sound engineer's report before and after. We pump it in through 80mm holes from below; the hole patching (about $10–20 per hole) is a plasterer's job and isn't in our quote.
Why do downlights ruin sound insulation?+
Because every downlight and exhaust fan is a hole the insulation has to be gapped around, and as a rule of thumb even small gaps wreck the result. Choice Magazine puts the thermal performance loss at around 30% for just 1% gaps, and sound is just as gap-sensitive. A few downlights scattered through a ceiling can wipe out the result before you start. If you're serious about quietening a between-floor space, I'd recommend removing the downlights before we insulate, and if you do, leave the holes open until we finish, because we can often use some of them to pump the cellulose in.
Can you soundproof a room that's already built?+
Often, yes. For a wall cavity we can drill a row of 80mm holes and pump cellulose in from one side, then you get the holes patched. For a between-floor space we pump up through the floor or down through the ceiling. We've done media rooms, flight-path homes and units this way. It's most effective for airborne noise; if it's heavy structural or footstep noise you're chasing, the cavity fill alone won't be the whole answer, and I'll tell you that before you spend the money.
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Get a quote for a quality sound insulation installed properly today. Fill in our simple online form and you’ll have a detailed quote within 48 hours for most houses. I’ll tell you honestly what it can stop and what it can’t, no fixed decibel promises, no overselling. Servicing Brisbane & SE QLD.
Peter Johnson
Owner / installer · Comfort Zone Insulation Team® · Since 1986
In the trade and want to install it yourself? We make cellulose in Tiaro and run exclusive territories, franchise with the family.