A moulder in Thailand bought a 37 kW single shaft shredder for a room inside their building. Nice machine. Two weeks later the neighbours on the other side of the wall filed a complaint, and the site manager called me asking about a “quiet motor.”
I asked him to stand next to the machine and tell me what he was hearing. He came back with a good answer: “It’s not the motor. It’s the material banging around in the hopper and hitting the floor.”
He had just diagnosed his own problem, and it was not the one he thought he had.
La réponse en bref
On a plastic shredder, the loudest sound is usually not the motor. It is the material. Plastic bouncing inside the steel hopper, chips falling into the discharge, and the rotor slamming into hollow parts — those three make most of the noise. The motor and gearbox are a steady hum underneath.
On dust, the same logic runs the other way: the shredding chamber is not your main dust source. The discharge point is. Every drop of shreds into a bin, box or conveyor releases a puff of fines. If you only fix one thing, fix the discharge.
That is why an acoustic enclosure around the motor does almost nothing, and why a lid on the hopper does a lot.
What a shredder actually sounds like
Numbers first, because “loud” means nothing in a quote.
| Condition | Typical level at 1 m | What dominates |
|---|---|---|
| Running empty, no material | 70–80 dB(A) | Motor, gearbox, idling rotor |
| Running empty, with idler blades | 75–85 dB(A) | Blade tips passing the fixed knives |
| Feeding film or soft sheet | 80–88 dB(A) | Hopper resonance, film slap |
| Feeding hollow parts (drums, crates) | 92–105 dB(A) | Impact — parts bursting inside the chamber |
| Feeding thick-wall or hard scrap | 90–100 dB(A) | Heavy impact, plus structural vibration through the frame |
| Crusher stage immediately after | 88–98 dB(A) | Continuous cutting, adds to the shredder |
Read the spread. The same machine can sit at 78 dB(A) one minute and spike past 100 dB(A) the next, purely based on what you drop in. That is why a single “noise level” figure in a brochure tells you very little, and why I always ask what material a customer is running before answering any noise question.
A single shaft shredder is quiet on film and brutal on hollow parts. The machine did not change. The material did.
Hollow parts are the worst case and everyone underestimates them. A sealed drum going into a shredding chamber is not being cut, it is being crushed by a rotor turning at 73 rpm with tens of kilowatts behind it. When it lets go, the whole frame rings. Ten of those a minute is a very different site than ten boxes of film.
Where the noise actually comes from
Position matters more than the source list, because you cannot fix what you cannot locate.
| Sound source | Where it sits | Share of total (hollow parts) | Can you fix it? |
|---|---|---|---|
| Material impact inside hopper | Above the rotor | Large | Yes — hopper lid, rubber lining, feed control |
| Discharge drop | Below the screen | Large | Yes — chute, lined bin, curtain |
| Structural vibration | Frame, floor, feet | Modéré | Yes — pads, anchors, mass |
| Rotor and blades | Chamber | Small to moderate | Some — blade clearance, sharpness |
| Moteur et boîte de vitesses | Behind the rotor | Small | Barely worth it |
| Hydraulic unit | Separate, on S Series | Small (5.5–7.5 kW) | Yes — move it, box it |
This is the table I run through with anyone complaining about noise. The two biggest rows are both material behaviour, and both are fixable without touching the machine. The row everyone wants to fix first — the motor — is near the bottom.
The hydraulic power unit is worth a note because it is a separate box on our S Series machines (5.5 kW up to 7.5 kW). It does not have to sit next to the shredder. Moving it 10 m away or into a small cabinet is one of the cheapest noise wins available, and almost nobody does it.
What actually works, ranked by effect per dollar
I have been on enough sites to know which fixes earn their money. This list is roughly in order of what I would do first.
| Fix | Realistic reduction | Cost | Notes |
|---|---|---|---|
| Control the feed (no hollow parts in bulk) | 5–15 dB(A) | Free | The biggest win and nobody wants to hear it |
| Lid or rubber curtain on the hopper | 5–10 dB(A) | Faible | Stop the chamber being open to the room |
| Line the discharge chute and bin | 5–12 dB(A) | Faible | Also fixes most of the dust |
| Full acoustic enclosure | 15–25 dB(A) | Haut | Only worth it if you must sit under 85 dB(A) |
| Rubber anti-vibration pads under the feet | 2–5 dB(A) | Très faible | Also stops the floor acting as a speaker |
| Rotate or replace blades on time | 2–6 dB(A) | Faible | Dull blades chew instead of cut, and chew is louder |
| Move the hydraulic unit away | 1–4 dB(A) | Faible | Applies to machines with a separate HPU |
| Enclosing the motor only | 0–2 dB(A) | Faible | Almost pointless on its own |
Notice the top three. Feed control, a hopper lid and a lined discharge cost very little and deliver most of the benefit. The full enclosure is the only item on the list that costs real money, and it is the one most people reach for first.
If you are checking whether noise will be a problem before you buy, the installation requirements article covers the siting side — how much floor and what foundation you have to work with, and why the room you put it in decides the noise question more than the machine does.
The compliance line, roughly
I am not going to quote your local regulations — they differ by country and change. But you should know where the lines usually sit, because it shapes what you need to buy.
| Limit | Typical figure | What it means for you |
|---|---|---|
| Hearing protection threshold | 85 dB(A) over 8 hours | Above this, PPE is mandatory in most jurisdictions |
| Exposure action level | 80–85 dB(A) | Risk assessment required, signage usually required |
| Pain / immediate risk | 120+ dB(A) peak | Not reachable on a shredder, but impulse spikes matter |
| Boundary / neighbour limit | 45–65 dB(A) at the property line | This is the one that gets you shut down |
The last row is the one that bites. A machine that is perfectly legal inside your building can still get you a complaint if it runs at night and your boundary is close. That is a siting problem, not a machine problem, and it is why I ask about the neighbours before I ask about the motor.
If you are running hollow parts and sitting near a boundary, budget for an enclosure from the start. Retrofitting one after a complaint is more expensive and you will be doing it in a hurry.
Dust: the same mistake, mirrored
Everything people believe about shredder noise, they believe the opposite about dust. They think the action is inside the chamber. It is not.
| Dust source | How much it matters | Why |
|---|---|---|
| Discharge into bin or conveyor | Highest | Every drop is a free-fall and a puff of fines |
| Screen area and undersize drop | Haut | Fines fall straight through and are airborne immediately |
| Hopper opening | Modéré | Open top means an open dust path to the room |
| Cutting chamber itself | Faible | Mostly enclosed, mostly wet or coarse |
| Transport and pre-shredding | Variable | Baled material sheds dirt before it ever reaches you |
Three factors decide how bad it gets:
- Humidité. Dry scrap is far dustier than washed or damp scrap. PET bottles straight off a storage yard are the worst case.
- Screen hole size. Small hole means more fines, and fines become dust. This is the same trade-off as in the shredder screen size article — a small screen costs you throughput, power and blades, and it also costs you dust.
- Fill height. A discharge dropping 1.5 m into an empty bin throws far more dust than the same discharge dropping 200 mm onto a full one.
That third one is nearly free to fix and most sites never do it. Keep the bin mostly full, or shorten the drop with a chute or a curtain.
Dust control that pays for itself
| Measure | Effect | Cost | Also helps |
|---|---|---|---|
| Enclosed discharge chute | Haut | Faible | Noise |
| Curtain or flap at the drop point | Medium–high | Très faible | Noise |
| Local extraction hood at discharge | Haut | Moyen | Keeps fines off surfaces |
| Dust collection with a filter unit | Haut | Medium–high | Required if you sell regrind |
| Hopper lid or cover | Moyen | Faible | Noise |
| Process damp or washed material | Haut | Process change | Everything |
| Sealed bins instead of open boxes | Moyen | Faible | Housekeeping |
Two things worth saying plainly. First, a dust collector is not just a compliance item — it is a product quality item. Fines sitting on your regrind hurt bulk density and make buyers complain. Second, a collector that is sized wrong is worse than none, because it pulls your fines somewhere and then plugs. Size it for the discharge, not for the room.
There is a wider point here about where fines cost you money, covered in the article sur les coûts d'exploitation — dust is material you paid for and cannot invoice.
Check before the machine arrives
- What material will you run most of the day? Film is a different site from hollow parts. Size the noise plan to the worst material, not the average.
- Who is within 100 m? Neighbours, offices, another tenant. This decides whether you need an enclosure.
- Will it run at night? Night limits are tighter almost everywhere.
- Where does the discharge land, and from how high? Fixing a 1.5 m drop is cheap. Fixing a complaint is not.
- Is your scrap dry? If yes, plan extraction before the machine is delivered, not after.
- Is there a separate hydraulic unit? Then you have a free noise win sitting on the floor.
- Are you on a suspended floor? A mezzanine or steel deck will amplify everything. Pads and anchors matter more than usual.
FAQ
How loud is a plastic shredder?
Empty, a single shaft shredder usually runs 70–80 dB(A) at one metre. With material it depends entirely on what you feed: soft film sits around 80–88 dB(A), while hollow parts like drums and crates push it to 92–105 dB(A).
Is the shredder motor the main noise source?
Usually not. Motor and gearbox noise is a steady hum and sits low in the mix. Material impact in the hopper and the drop at the discharge dominate, especially with hollow or hard scrap.
How do I reduce shredder noise?
Start with feed control, a hopper lid and a lined discharge — those are cheap and deliver most of the reduction. Add anti-vibration pads under the feet. Only consider a full acoustic enclosure if you must stay under 85 dB(A) at the operator position.
Do acoustic enclosures work on shredders?
Yes, typically 15–25 dB(A), but they are the most expensive option and they fight you on access for blade changes and cleaning. Fix the feed and the discharge first, then measure again before you buy one.
Where does the dust come from on a shredder?
Mostly the discharge point, then the screen area. Each drop of shreds into a bin releases fines. The cutting chamber itself is a minor source because it is largely enclosed.
Does screen size affect dust?
Yes. A smaller hole produces more fines, and fines are what becomes airborne dust. If dust is a problem and you are running a small screen, opening the hole up helps on both counts.
Can I run a shredder indoors?
Yes, a lot of our machines do. It needs a lid or curtain on the hopper, a lined or enclosed discharge, and extraction at the drop point. Siting matters as much as the machine — see the installation article for floor and foundation requirements.
Where to go from here
If noise is the reason you are reading this, the single shaft shredder spec guide covers the machine side, and the double shaft article is worth reading if your material is hollow or bulky, because a different rotor changes the noise profile as well as the output.
If dust is your problem and the fines are eating your yield, screen size et machine capacity both feed into the same numbers. And if the shredder is one stage of a bigger line, the line article covers where extraction and enclosures belong in the layout.
SLECOTECH (Streamline Eco Tech) designs and manufactures industrial shredders, granulators, washing lines, and complete plastic recycling systems. The company is based in Yuyao, Zhejiang, China, and exports to more than 30 countries. If you send us the material, the room dimensions and who is next door, we can tell you what noise and dust measures you actually need — and which ones you can skip.
See the single shaft shredder range or talk to us about the SC Series integrated unit if noise and dust are pushing you toward a single enclosed machine.