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C flux 3 dust extractor sound isolation.
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Hi there guys,?
I'm building a cupboard for my c flux 3 dust extractor to keep the noise down. I'm looking for suggestions on how to keep the noise down while having a return air back into my work shed. I'm was thinking of baffle system - see my sketch attached. I'm also worried if I don't get it right, it will amplify the bass sound acting like a complex baffles in a subwoofer speaker design. - C flux has quite a deep sound.
Anyone have any idea for return air?
Attached are a few images - note- I have not finished boxing in the space ( boxing around beam and up to brick wall etc. I will seal everything
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The extraction will go through the brick wall into the 6" PVC(can just see it in the pic.)
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Chris.   ?
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I've never tried to silence a dust collector, but I have a lot of experience building silencing enclosures for generators.? The problem is similar, as both scenarios require maintaining good airflow.
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There are two main approaches that can be taken:
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1) build a baffled return path, requiring the air to make one or more sharp turns before escaping back to the shop
2) install a return air duct, and buy off-the-shelf duct silencers
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I'll address both approaches.? But first, in both scenarios, you want to start by thinking about the quality of the enclosure itself, to minimize directly transmitted noise.? I see that Laguna rates that dust collector at 88 DB.? I'm noise sensitive, and so I'd definitely want to damp that down.? The two principles for minimizing directly transmitted noise are adding mass to the wall (i.e multiple layers of drywall or plywood), and decoupling the inner and outer surface of the wall with interior air gaps.? Search for "STC wall assembly", and you'll find lots of examples of how people approach building walls to minimize sound transmission for inspiration.? One thing that will turn up in those searches in the use of viscoelastic damping compounds (Green Glue is the most commonly mentioned), and I'd advise not using such a thing in this particular application.
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For the case of a baffled return path: making the sound bounce around before it escapes back to the workshop can be effective, but the gold standard for damped return paths is to put a sound absorbing material on the interior surfaces of the baffle.? For your dust collector, I'd advise 4" wedge (or triangle) acoustic foam, with the valleys of the foam oriented across the path of air flow, forcing the sound to move across a rough surface.? If the valleys are aligned in the direction of airflow, they'll be less effective.? .? Lots of vendors sell equivalent foam, so you can shop around for the best price.? You might consider building a big enough baffle that foam could be added, see how it performs, and then only buy the foam if you think you want better sound damping than you're getting without it.? Once complete u-turn is a minimum for good results in a baffle, but two u-turns in better.
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For the case of a return air duct: figure out the highest CFM you expect your dust collector to draw, and size a return duct large enough so that the airspeed doesn't exceed 8m/s (or 1575 FPM).? You can do that with a single return duct, or multiple.? You then buy an off-the-shelf duct silencer, which is basically just a giant car exhaust muffler.? .? Again, lots of companies sell these, so you can shop around.? The downside of this approach is that the ducting itself can allow a lot of direct sound transmission, which is easier to avoid when building a baffle.? Also, return air ducting may require duct fans, else you can add too much back pressure on the dust collector and retard it's performance.
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Were it me, I'd probably pursue the baffle approach.? But in either case, if you have the time to experiment, you can start small, and scale up your approach only to the extent that early experiments don't produce sufficiently good results.
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-Michael Wolf
Lake Tahoe, CA
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The noise is primarily from the motor and the exhaust return. If you make a dedicated sound box? to surround?the motor?but still allows airflow, you may attenuate over half the problem easily and cheaply. We have accomplished that with shop scrap and upholstery foam in prior iterations.
The other half of the problem is the exhaust. I have used duct silencers, they definitely work but are pricey and sometimes difficult to fit in tight layouts. I'd suggest instead making a baffle box specifically to knock that down also.
You could?fix acoustic foam, but it becomes a liability for cleaning and it's a lot of area. I might suggest hanging up heavy moving blankets curtain-style in staggered formation for baffling,?bonus that they are easy to work around and clean when needed. We have also used upholstery foam similarly but it is much more expensive.
There is nothing you can do to make a practical cyclone dust system quiet, you can only make it less noisy. I have a 5hp cylcone?hanging off the roof 6 ft from the CNC control station with a silencer and it is possibly?10dB quieter than without but still requires raising your voice for conversations. With active noise cancelling PPE, the best money spent, you forget all about it and sometimes forget to turn it off.
On Wed, Jan 15, 2025 at 2:06?AM Michael Wolf via <missingeggacct= [email protected]> wrote: I've never tried to silence a dust collector, but I have a lot of experience building silencing enclosures for generators.? The problem is similar, as both scenarios require maintaining good airflow.
?
There are two main approaches that can be taken:
?
1) build a baffled return path, requiring the air to make one or more sharp turns before escaping back to the shop
2) install a return air duct, and buy off-the-shelf duct silencers
?
I'll address both approaches.? But first, in both scenarios, you want to start by thinking about the quality of the enclosure itself, to minimize directly transmitted noise.? I see that Laguna rates that dust collector at 88 DB.? I'm noise sensitive, and so I'd definitely want to damp that down.? The two principles for minimizing directly transmitted noise are adding mass to the wall (i.e multiple layers of drywall or plywood), and decoupling the inner and outer surface of the wall with interior air gaps.? Search for "STC wall assembly", and you'll find lots of examples of how people approach building walls to minimize sound transmission for inspiration.? One thing that will turn up in those searches in the use of viscoelastic damping compounds (Green Glue is the most commonly mentioned), and I'd advise not using such a thing in this particular application.
?
For the case of a baffled return path: making the sound bounce around before it escapes back to the workshop can be effective, but the gold standard for damped return paths is to put a sound absorbing material on the interior surfaces of the baffle.? For your dust collector, I'd advise 4" wedge (or triangle) acoustic foam, with the valleys of the foam oriented across the path of air flow, forcing the sound to move across a rough surface.? If the valleys are aligned in the direction of airflow, they'll be less effective.? .? Lots of vendors sell equivalent foam, so you can shop around for the best price.? You might consider building a big enough baffle that foam could be added, see how it performs, and then only buy the foam if you think you want better sound damping than you're getting without it.? Once complete u-turn is a minimum for good results in a baffle, but two u-turns in better.
?
For the case of a return air duct: figure out the highest CFM you expect your dust collector to draw, and size a return duct large enough so that the airspeed doesn't exceed 8m/s (or 1575 FPM).? You can do that with a single return duct, or multiple.? You then buy an off-the-shelf duct silencer, which is basically just a giant car exhaust muffler.? .? Again, lots of companies sell these, so you can shop around.? The downside of this approach is that the ducting itself can allow a lot of direct sound transmission, which is easier to avoid when building a baffle.? Also, return air ducting may require duct fans, else you can add too much back pressure on the dust collector and retard it's performance.
?
Were it me, I'd probably pursue the baffle approach.? But in either case, if you have the time to experiment, you can start small, and scale up your approach only to the extent that early experiments don't produce sufficiently good results.
?
-Michael Wolf
Lake Tahoe, CA
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-- Brett Wissel Saint Louis Restoration 1831 S Kingshighway Blvd (at Shaw Blvd) St Louis, MO 63110 314.772.2167 brett@...
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The sound waves are going to bounce around the hard surfaces.and then bounce through your baffles.
You should have a sound absorption product on your walls. You have a narrow space to work in so I would suggest trying acoustic ceiling tiles glued to the wall and ceiling surfaces. Pick a type that has a better sound absorption rating. I believe most ceiling tiles are Class A fire rated. I can’t say that they will dramatically reduce sound but every little bit helps. They are also a relatively low cost solution.
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Michael Wolf talks about a larger mass wall with multiple layers of drywall and plywood decoupling.?? You have a brick wall between the dust collector and the shop.? The sound is NOT going to be able to cut through this brick wall.?? However, the section above the brick wall looks to have something like a 1/4" thick sheething.?? This area does need to be handle if you want to prevent sound from coming through that.? You can do multiple decoupling layers here or just build some custom fitted acoustic panels.?? I would also put an amount of acoustic panels inside this small closet area to cut down the amount of mid/high frequency sound generated by the collector motor/cyclone.? This will only help things.
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As far as the "return air to shop" goes, you do NOT need to worry about creating a subwoofer like port/baffle.? This ported subwoofer effect only occurs when air is pushed into a sealed container (i.e. the subwoofer cabinet).? The sealed area acts like a spring which pushes the air back out.? This constant reversal of air direction/pressure creates that low subwoofer resonance.?? In your scenario, the are would only be moving in one direction (i.e. constant push back into the shop), so it would not create that natural port resonance.?
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However, Michael is right when he is stating that the return duct should be lined with sound absorbing material.? However, 4" wedge/triangle foam is not going to be the most optimum solution.?? Sure, it works, but it's about as effective a 2" solid foam and the jagged edges will cause air restriction.?? Air flows easier across a smooth surface and not as good across a rough/jagged surface (unless your duct is so huge that it doesn't matter).? I would say 3" foam is best.? However, dense fiber panels are actually better than foam for absorbing acoustic energy.
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Brett's suggestion on curtains can work.? However, this is still not as acoustically absorbant as dense fiber panels.
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Here is a link to DIY acoustic supplies if you are interested in making some:
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-Aaron
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To the original poster, it might be more practical to buy a quieter dust collector.
The RL200 is around 70db I think. ?
I was able to have conversations next to the RL200 while it was running. ?
Joe
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On Jan 15, 2025, at 8:56?AM, aaron.gatzke via groups.io <aaron.gatzke@...> wrote:
The sound waves are going to bounce around the hard surfaces.and then bounce through your baffles.
You should have a sound absorption product on your walls. You have a narrow space to work in so I would suggest trying acoustic ceiling tiles glued to the wall and ceiling surfaces. Pick a type that has a better sound absorption rating. I believe most ceiling tiles are Class A fire rated. I can’t say that they will dramatically reduce sound but every little bit helps. They are also a relatively low cost solution.
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What about RockWool insulation as a sound absorbing material.? I've seen a few videos where this characterisic of the insulation is mentioned. Dave Davies
To the original poster, it might be more practical to buy a quieter dust collector.
The RL200 is around 70db I think. ?
I was able to have conversations next to the RL200 while it was running. ?
Joe
On Jan 15, 2025, at 8:56?AM, aaron.gatzke via <aaron.gatzke= [email protected]> wrote:
The sound waves are going to bounce around the hard surfaces.and then bounce through your baffles.
You should have a sound absorption product on your walls. You have a narrow space to work in so I would suggest trying acoustic ceiling tiles glued to the wall and ceiling surfaces. Pick a type that has a better sound absorption rating. I believe most ceiling tiles are Class A fire rated. I can’t say that they will dramatically reduce sound but every little bit helps. They are also a relatively low cost solution.
-- Dave & Marie Davies
318-219-7868
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Here is a link to a video of the sound level of the RL200
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On Jan 15, 2025, at 9:39?AM, Joe Doherty <joeinno@...> wrote:
To the original poster, it might be more practical to buy a quieter dust collector.
The RL200 is around 70db I think. ?
I was able to have conversations next to the RL200 while it was running. ?
Joe
<IMG_0188.jpeg>
On Jan 15, 2025, at 8:56?AM, aaron.gatzke via groups.io <aaron.gatzke@...> wrote:
The sound waves are going to bounce around the hard surfaces.and then bounce through your baffles.
You should have a sound absorption product on your walls. You have a narrow space to work in so I would suggest trying acoustic ceiling tiles glued to the wall and ceiling surfaces. Pick a type that has a better sound absorption rating. I believe most ceiling tiles are Class A fire rated. I can’t say that they will dramatically reduce sound but every little bit helps. They are also a relatively low cost solution.
David,
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Take a look at this chart:
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Roxul has several options.?
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The AFB stuff is very flexible but it basically crumble in your hand.? Harder to work with because it makes a mess when you cut it and needs fabric wrap and support.? Acoustically it does okay.
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The Rockboard 60 is okay, but there are other options that are better.
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Rockboard 80 is good if you are limited to a 2" thickness and need the best low frequency absorption.? However mid/high frequencies are not absorbed as well as other materials.
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The downside of Rockboard is that it will sag over time if not supports.?? It's also heavier.
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I generally recommend Owens 703 because it's very light and has good mid/high frequency absorption.? It's also easy to cut and work with.? It doesn't sag and it's fire resistant.?
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Cotton is very good acoustically, but not fire resistant.
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Each of the materials works best in a particular scenario.?? It just depends on what your needs are.
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-Aaron
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Good to know a baffle is the way to go. A minimum of 2 u turns. I have some 50mm acoustisorb 3 dense material. I have a 1200x 2400mm sheet.?
I was going to do a staggered studed wall to isolate the inner and outer faces of the cupboard, but it becomes complex when coming to the door and baffle outlet to make that work. Seems redundant if I'm not isolating the door as well ( 2x doors). I have used 1 outer and 1 inner sheet of 19mm chipboard.
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Question I have is if the c flux 3 has an 8" inlet, what should the minimum opening be in the tightest part of the u turn baffle be so I don't choke the dust extractor? What would be the minimum size where I wouldn't need a fan to assist the airflow? 8" inlet = 180 x 180mm square opening. It's going to be hard to do a trial and error thing here, so I would like to play it safe and go on the larger side for the baffle throat as I can always make it smaller by reducing the opening. What would be the minimum size?
Thanks Chris.
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Hi Chris,
You have the correct cross-section of 8” pipe (180 mm^2). If you know the maximum air speed in your system, you can linearly reduce it (by increasing baffle cross section) to achieve ~1500 FPM recommended by Michael.
For example,?Recommend air speed for carrying wood chips is 4000 FPM (give or take some).?Assuming?4500 FPM as a maximum possible air speed in your system, you can make the cross section 3X of the 8” pipe to reduce speed to 1500 FPM. Obviously, if there is sound dampening material applied to the baffle walls that would be in addition to the clear air path of 3X. Making it bigger is not going to hurt. If you are going to place an air filter in this path then the cross section will need to be increased accordingly.
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On Jan 15, 2025, at 4:54?PM, Chris via groups.io <Hope752@...> wrote: ? Good to know a baffle is the way to go. A minimum of 2 u turns. I have some 50mm acoustisorb 3 dense material. I have a 1200x 2400mm sheet.?
I was going to do a staggered studed wall to isolate the inner and outer faces of the cupboard, but it becomes complex when coming to the door and baffle outlet to make that work. Seems redundant if I'm not isolating the door as well ( 2x doors). I have used 1 outer and 1 inner sheet of 19mm chipboard.
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Question I have is if the c flux 3 has an 8" inlet, what should the minimum opening be in the tightest part of the u turn baffle be so I don't choke the dust extractor? What would be the minimum size where I wouldn't need a fan to assist the airflow? 8" inlet = 180 x 180mm square opening. It's going to be hard to do a trial and error thing here, so I would like to play it safe and go on the larger side for the baffle throat as I can always make it smaller by reducing the opening. What would be the minimum size?
Thanks Chris.
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Thanks Imran,
So just so I understand, making the cross section of the baffle throat 180 x 540mm shouldn't restrict my suction power. Obviously allow for sound material. If you were doing the same task, would you make it any bigger just in case? Maybe 180 x 600? And adjust the vent size if necessary.
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Wondering if I should increase the baffle mouth opening after the first u turn, then again bring it down to size. Maybe it would work like a muffler?
Chris.
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Hi Chris,
I don’t know enough about this to be much help. I wanted to educate myself as I read the thread and wanted to know the relationship between air velocity and x-section area and it turned out to be pretty simple.
When I suggested going a bit bigger, it was from the point of view that the x-section can always be reduced but harder to increase. Maybe Aaron or Michael will chime in to provide better guidance.?
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On Jan 15, 2025, at 11:19?PM, Chris via groups.io <Hope752@...> wrote: ? Thanks Imran,
So just so I understand, making the cross section of the baffle throat 180 x 540mm shouldn't restrict my suction power. Obviously allow for sound material. If you were doing the same task, would you make it any bigger just in case? Maybe 180 x 600? And adjust the vent size if necessary.
?
Wondering if I should increase the baffle mouth opening after the first u turn, then again bring it down to size. Maybe it would work like a muffler?
Chris.
?
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Don't forget to allow for dust build up and clean out, just in case.
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On Wed, Jan 15, 2025 at 10:22 AM, David Davies wrote:
What about RockWool insulation as a sound absorbing material.
Rockwool works okay as a material to put into a wall cavity to "deaden" the cavity and minimize transmission through the wall.? For dampening reflected noise, it's certainly better than a hard surface, but it's far inferior to almost any product that's specifically designed for dampening reflected noise.
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-Michael Wolf
Tahoe City, CA
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On Wed, Jan 15, 2025 at 10:41 AM, Aaron Inami wrote:
Take a look at this chart:
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For those unfamiliar with acoustics: a high Noise Reduction Coefficient (NRC) is better than a low one.
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As a noise-sensitive person, if I'm buying anything for damping reflected noise, I'd be looking for a material tested in compliance with one of the recognized standards (AS1045 is common) and look for the highest possible NRC that doesn't break the bank.? But there are circumstances where larger quantities of lower rated absorption delivers a better ultimate result.
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-Michael Wolf
Tahoe City, CA
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On Wed, Jan 15, 2025 at 02:41 PM, imranindiana wrote:
You have the correct cross-section of 8” pipe (180 mm^2). If you know the maximum air speed in your system, you can linearly reduce it (by increasing baffle cross section) to achieve ~1500 FPM recommended by Michael.
The 1500 FPM recommendation (actually 8 m/s) comes from European standards for maximum airspeed in return air ducts.? It's too high of a number for baffles.? Mostly because baffles tend to be implemented where there's a chamber that allows the air to more or less come to a halt, and then you have very poor aerodynamics leading into the path of the baffle.? As such, 1500 FPM through the baffle probably imposes more back pressure than you'd want on the typical dust collector.? High pressure dust collectors like an Oneida High Vacuum collector or a Hocking Polytechnic Vacumobil MD 160 might not mind the extra back pressure.? For baffles, I'd stick with HVAC ducting air-speed limits, which I believe are about 600 FPM (as per ACCA manual D).? But of course a baffle is essentially a really crappy HVAC duct, so 300 FPM would be even better.
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Note that this implies a baffle with a cross section of several square feet, depending upon the CFM you think your collector is moving.? That flies in the face of people's instincts for baffles, where they want a small cross section because they fear letting more sound escape with a large cross section.? But the effectiveness of a baffle is all about forcing the sound waves to bounce off the sides of the baffle multiple times, combined with a good sound attenuating liner to the baffle, and large baffles work very well when done correctly.
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-Michael Wolf
Tahoe City, CA
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On Wed, Jan 15, 2025 at 08:19 PM, Chris wrote:
Wondering if I should increase the baffle mouth opening after the first u turn, then again bring it down to size. Maybe it would work like a muffler?
I would advise against that.? I've never actually tried it.? But I think it would increase the back pressure of the baffle without making any notable increase in the sound muffling.? If you look at how mufflers are built (or duct silencers), they work on a different principle.
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-Michael Wolf
Tahoe City, CA
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On Wed, Jan 15, 2025 at 11:19 PM, imranindiana wrote:
When I suggested going a bit bigger, it was from the point of view that the x-section can always be reduced but harder to increase.
Cross section of the baffle is all about how much back pressure it imposes on what you're trying to muffle.? It doesn't really have anything to do with how effectively the sound is muffled.? The speed of sound is roughly 67,500 FPM, much more than the ~4000 FPM of a dust collector duct, or a baffle that's probably well under 1000 FPM.? So regardless of the FPM of air through the baffle, the sound is going to bounce around inside the baffle and be muffled.? A longer baffle pathway will make the sound bounce around more, and which will increase the muffling, and more effective sound deadening material will increase the muffling from each bounce, but neither has much to do with the cross section.
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If the airspeed was high enough, you'd get some air speed noise (e.g. the "woosh" that you hear from some HVAC systems), although in a workshop environment you probably wouldn't care.
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-Michael Wolf
Tahoe City, CA
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On Wed, Jan 15, 2025 at 01:54 PM, Chris wrote:
so I would like to play it safe and go on the larger side for the baffle throat as I can always make it smaller by reducing the opening
In terms of sound muffling performance, there's almost no reason that you'd benefit from later making the baffle cross section smaller.? The only time that pays off is when the cross section is large in relationship to the baffle length, and so sound is able to pass through the baffle without bouncing around much.
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Also, keep in mind that I'm giving advice aimed at making really big reductions in the sound level of the dust collector.? But you shouldn't lose sight of the other noise sources in a typical workshop, and there's no point in pushing the sound level of the dust collector beneath the "noise floor" created by other sources of sound.? Particularly if you have a dust collector that's automatically switched on/off when you turn tools on/off, you just need to make the collector quieter than the tools you're running.? Laguna rates this collector at 88 dB.? If you're only triggering it when you're operating a tool that produces 70 dB noise, than a 20 dB reduction in dust collector noise will probably make you happy.? I'm glossing over the details of different noise levels at different frequencies.? But even considering that, you'll probably be pretty satisfied with even a 30 dB reduction.
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To give an example, I first started building "hush boxes" for generators to quiet down camping trips I take with a big group of friends (Burning Man).? A single wall hushbox constructed of 3/4" ply with an internal lining of 4" wedge acoustic foam perpendicular to the exhaust airflow and a 90 degree bend in the exhaust path is enough to make a muffled Honda generator quiet enough that people are happy to sleep next to it in a tent (i.e. no additional sound isolation) without complaint.
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-Michael Wolf
Tahoe City, CA
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imran
Jonathan Smith