Soundproofing attempt! Enclosure for a noisy dust extractor

[OscarG]

im a bit late to this thread, been an interesting read... i have done a far bit of sound treatment in my life, i have built 3 recording /rehersal studios in the past 10 years.

what i was going to say when i saw your first attempt is what Bob was saying re the lining, make it loose, make it completely random... essentially with sound treatment you have 3 tools to fight how the sound travels....

mass (thick dense walls to block & shield)
absorption (soft layers to muffle)
random surface treatment via baffles (odd shapes to break up the waves)

the first attempt was certainly missing the latter, so randomizing the inside with loose material would as Bob said would be the way to go.

im slightly confused as to how you have made it worse with your latest attempt, if anything i would have expected it to be about the same... however you do seem to be going for consistency on your work & that goes against you in sound treatment, the air & sound will just roll over it.

i would have placed my baffles at varying spacing (keeping in mind not to restrict airflow but allow areas that let it pool before moving on & i would have also suck off cuts & random shapes to them before i then lined them with a material & foam, but the messier & more inconstant the better.

this is exactly how we build ventilation ducts for studios where we needed reasonable sound proofing but still want fresh air.

Thanks for your post!

I'm due to pick these up tonight...

I was thinking I could cut them down and fit them inside cabinet. Do you think these would work or would I be better off getting that spikey acoustic foam type stuff?

 

[MikeK]

I'm also coming to this dance late, but I think you might be chasing unicorns by trying to build a sound enclosure for your vacuum that is not much larger than your vacuum. I test a lot of rooms for work to make sure the sound doesn't go where it's not supposed to go, and mass is definitely your friend when trying to block sound.

I never saw much success with acoustic foam as a sound absorbing material, but it does well for reducing resonance and reflection. From my experience, most foam and fabric materials are transparent to sound. For a quick treatment of walls, we used mass loaded vinyl sheets or MDF panels glued directly to the surface with acoustic sealant.

I notice you don't have any gasket material on the joints where the panel meets the enclosure. Sound flanking can be difficult to correct, and not having a good rubber gasket to seal the gaps makes it easier for the sound to pass. This could be the source of some of the whistling you hear. Doors and panels are especially difficult, but good astragal seals help.

Another point to consider is the exhaust port, where size, shape, and path are everything. A Z-duct is good at reducing the sound amplitude by absorbing the energy at each change in direction. However, the ducting must be appropriately sized so it is not restricting the airflow and contributing to the sound. Your vacuum is pulling in air at a high pressure, but your exhaust port must be much larger in order to allow the exiting air to leave at a lower pressure. Using a smaller than required port size for the exhaust will contribute greatly to the apparent sound. Increasing the area of the exhaust port will lower the velocity of air while attempting to retain the same volume of air passing through the system.

 

[sunnybob]

sound frequencies are all around at the same time. if the base note is loud it will overpower the treble notes. remove the base and suddenly the treble is very annoying.
i dont think you made it worse, i think you altered it and you now hear different things that have been there all the time but just covered up. Its just like a detective story, you have to hunt one clue at a time. Thats the part I actually enjoy.
I never used any form of measuring on mine. Its was loud and annoying, i built a cabinet, its now a lot quieter and no longer annoying, I have no idea of decibels involved, but the job is done.

One extra thought, are you sure your intake is not blocked? harsh increase in noise and hot motor suggests to me that it is.

keep us informed.

 

[Brandlin]

The logarithmic scale of decibels and the inverse square law that dictates the wave energy as a function of distance combine to make any measurement with a meter very sensitive. Add into this mix the inaccuracies in a cheap meter/phone app and differences in air pressure and temperature and you are in a position where your meter reading comparisons are going to be next to meaningless.

Sound measurement is a VERY sophisticated science. not helped by the fact that the human ear and brain is actually total carp at judging volume. Trying to resolve this down to a single Db number is futile and counter productive.

I strongly doubt you made it worse. What happened is the material you added removed a lot of the lower frequency and you can now hear the higher frequency notes that were already there.

I agree with what giant beat has said. In general terms your work is far too regular. You need to break up the waves by being random. There is nothing wrong with the cheap materials you are using and I strongly doubt you will see any improvement in spending money on commercial foams.

The last thing you want is a square box that encourages regular reflections of waves. And even though you have made a long 'baffle tunnel' you made it a regular size with 90 degree corners, you need to break up ANY regularity as much as possible. You also need enough space around the vac to allow air movement and deflect, break up and absorb it, a bigger box means you can get more irregularity in there.

A smaller issue is that you might want to insulate the box from the surface it sits on. One option would be to suspend it on short bungy chords under your bench. Though i doubt this is a significant contributor.

 

[OscarG]

Thanks for input, will take the time to read everyone's comments.

My head's buzzing at the moment, thought I'd quicky make this. Do you think the design on the right would be better?

I'm wondering if currently I'm wasting the lower half of the box and the air is exhausted before it's "tamed" if that makes sense?

I'm thinking in the 2nd design there's more of an enclosed wall around that noisy motor and the exhausted air will be forced to travel further and hopefully lose some intensity before it enters that baffle box.

 

[sunnybob]

I'm not all fancy pants drawings like you (lol) so I have very quickly sketched out my system.
One point, because the thing is fully enclosed inside the box, I removed the top motor cover to allow air to move more freely. There was a foam cover over the motor as a very poor attempt at sound deadening, that went as well.

 

[OscarG]

sound frequencies are all around at the same time. if the base note is loud it will overpower the treble notes. remove the base and suddenly the treble is very annoying.

ah! So the green blanket (now known as the stupid green blanket) might have acted like a graphics equalizer, turning down the bass so I notice the treble more!?

That actually makes sense and provides an answer as to why it seems "whinier" now!

 

[sunnybob]

Speaking as a hi-fi audiophile from the 60's....and paraphrasing the original quote....
By george, He's got it.
=D> =D> =D>

 

[OscarG]

The logarithmic scale of decibels and the inverse square law that dictates the wave energy as a function of distance combine to make any measurement with a meter very sensitive. Add into this mix the inaccuracies in a cheap meter/phone app and differences in air pressure and temperature and you are in a position where your meter reading comparisons are going to be next to meaningless.

Sound measurement is a VERY sophisticated science. not helped by the fact that the human ear and brain is actually total carp at judging volume. Trying to resolve this down to a single Db number is futile and counter productive.

I strongly doubt you made it worse. What happened is the material you added removed a lot of the lower frequency and you can now hear the higher frequency notes that were already there.

I agree with what giant beat has said. In general terms your work is far too regular. You need to break up the waves by being random. There is nothing wrong with the cheap materials you are using and I strongly doubt you will see any improvement in spending money on commercial foams.

The last thing you want is a square box that encourages regular reflections of waves. And even though you have made a long 'baffle tunnel' you made it a regular size with 90 degree corners, you need to break up ANY regularity as much as possible. You also need enough space around the vac to allow air movement and deflect, break up and absorb it, a bigger box means you can get more irregularity in there.

A smaller issue is that you might want to insulate the box from the surface it sits on. One option would be to suspend it on short bungy chords under your bench. Though i doubt this is a significant contributor.

Thanks for post!

Maybe I should just ignore the towels/foam and just use MDF as thick as possible, make the walls 36mm thick.

To combat the regularity, do you think something like this would work?

Inside walls of a (much bigger) box, with glued/screwed on bits of MDF random shaped nonsense.

I've learned so much from this thread and you guys, thanks so much!

 

[sunnybob]

I think youre ready for the big time now,
go surf for an "anechoic chamber"

:shock: :shock: =D> =D> =D> =D> =D>

 

[OscarG]

I think youre ready for the big time now,
go surf for an "anechoic chamber"

:shock: :shock: =D> =D> =D> =D> =D>

Holy moly!

Got my work cut out!

I have to say and I know this terms seems to be dirty with regards to sound reduction, but doesn't it seem a little ahem..."regular", repeated patterns? Doesn't seem that random?!

Do you think If I buy a load of Stealth Bomber models and glue them to inside of box it'll work?

 

[sunnybob]

I thought you might like that. :twisted: :roll:

Its all about the angle of the dangle. If you can reflect EVERY frequency before it reaches your ears, you have absolute silence.

Sound waves is even more complicated than tropical fish keeping (but only just)
Dont give up the fight. 8) 8) 8)

 

[OscarG]

ha... just been reading about how the Stealth Bomber works, seems it the same principle, all odd angles and curved surfaces so nothing gets reflected back to the radar.

 

[Lazurus]

Blimey this all seems a lot of work and expense chasing a holy grail. How about a weatherproof box outside the workshop feeding the inlet through the wall, cheap and easy fix?

 

[Brandlin]

Maybe I should just ignore the towels/foam and just use MDF as thick as possible, make the walls 36mm thick.

To combat the regularity, do you think something like this would work?

Extra mass helps. But if you ONLY use increased mass to damp then you need LOTS of it. Going to 36mm MDF may help, but its a lot more expensive than putting in additional wadding to absorb sound.

I would:

1. Stick to 18mm MDF but make the box bigger to give greater airflow, allow for more dampening material inside.
2. dont mount the vac in the dead centre and make the inside of the box have varying corner angles (mitre off three corners say) so you try to reduce any way you can get a standing wave.
3. build a 'Z' baffle as you have but make each tunnel section a different dimension and don't make every turn 90 degrees.
4. Roughly cover the insides with the kinds of material you already have done but bunch them up randomly.
5.Insulate the Vac from the box on soft rubber feet or hung on bungees. Use thick rubber seals on any openings like doors.
6. Accept you simply wont make it silent and ANY improvement is great.

 

[OscarG]

Thanks Brandlin, I'll try that.

I went on a bit of an anechoic chamber and diy sound baffle youtube journey last night. Interesting, apparently staying in an enechoic chamber too long can make you go a bit loopy!

They had some people making DIY sound absorption baffles using Rockwool sound insulation. Seen I could get some for £25 from Wickes, do you think that would work better than towels for this dust extraction silencer application?

I discovered people talking about reverb rooms and how none of the walls are parallel to stop standing waves. That worried me a little as I thought the effects of a reverb room are what I'm trying to avoid? Sorry if I've misunderstood that.