Wood workshop ... and a baby

[RolandC01]

Hi All,
I have an acoustic problem that I hope I can get some assistance from this forum. I build classical guitars as a hobby. I am currently converting an partially underground basement into a workshop. Reason being that with a large percentage of it being underground, the sound should be less disturbing to my neighbours. The problem is that the entrance to the basement is about 3meters away from one of my neighbours and they have a new born baby. I fear that the noisy machinery will be too loud for the little one and as such I'd want to minimise what gets to them.

Brief explanation, of the basement:
It is about 6m X 6m, basically the size of a double garage. The area is split in two (by a single brick wall ) into 3m x 6 meter areas. The back wall (3m end) is completely underground. All outer walls are double brick walls. The entrance to the basesment has one door and each single garage area has one window.

I have bought 20m X 1.2 m X 25mm of acoustisorb which is a "sound insulator". The thing is Im not exactly sure what would be the best thing to do with it. I cannot completely block off the window as it is the only ventalation into the room. I was thinking that maybe I just attach the stuff to the walls or should I make lots of those trap panels and stick them in all the corners? Maybe make a big panel and put it infront of the window? Or use it like a curtain accross the entire length of the windows wall.

The machinery that i am using are : table saw ( probably the loudest ) followed by the vacuum cleaner, jig saw, band saw and electric drill. I built a box for the vacuum cleaner and put some 50mm foam on the inide and that made a huge difference.. Im guessing, but I'd think that most of the sound is in the mid to higher frequency range , so the sound insulator stuff will help?

Im not too concerned about how it will look as it is a workshop. Its made of polyester so it does not need to be covered.

Thanking you in advacnce for your assistance and appologies for the crude drawing.

Many thanks, Roland

[xSpace]

Hi Roland, great to meet someone of your ability.

I'm going to give my opinions, maybe some of the others will get you closer with their abilities as well.

I use tools like you mention and the mids and highs...the highs are ingrained in my ears...are the initial problem. The continuing problem is that when you place these pieces of equipment into an enclosed environment the build up can produce a low frequency build up.

Since the window is the really only offending part as far as we know then you have to think about that. At my shop we have a dust extraction unit that reads 91dB from about 3 feet away from the mouth...so the external is louder then the inside of the shop...damn the bad luck right?

Closing the window off with a comparable wall thickness should be taken under consideration, but that would require you to develop a system to get conditioned air in and out while dealing with the ability of the equipment to damage this system.

What are the options of building a chute that attaches to this window that basically redirects the flow out of this window upward? Bare in mind, whatever was offending to your neighbors, once this chute is installed, may now become an offending sound directly into your home.

It could be designed in such a way as to funnel out the window and go towards the corner and back up the other way, away from the neighbors house.

What's your thinking on that?

Brien

[xSpace]

Well, I missed door entry part.

What kind of door is there now? Solid?

[RolandC01]

Hi Brien,

Many thanks for your prompt response. I can definitely look at the option of creating some sort of ducted air into the place. The redirected funnel should also not pose too much of a problem.

What should be done with the sound absorber ( acoustisorb )? Is it better to put directly onto the walls or should I make a few panels and mount a small distance from the walls? 20m of this stuff if a fare length and I really want to use it to its maximum capability.

The door is a solid maranti door. The ceiling is a concrete slab, the floor is also concrete. The walls have been newly plastered, primed and painted, while the floors have also been freshly painted. With the place empty, if I wistle, the place echos for a good 1.8 seconds.

Many thanks,Roland

[xSpace]

What is that on the drawing that is in between your workshop and the neighbors house? Is that a fence of some sort? If so, how tall and what is it made of...brick I am thinking?

You want to inspect the seals on the door and make certain they are not leaking. A solid Mahogany door is good but with poor seals the highs can still penetrate the area.

I'll get back to you on the acoustic fabric, but if one of the folks that has a better idea wants to chime in...be my guest

[RolandC01]

Hi,
The wall refered to in your previous question is a precast concrete wall about 3cm thick. Its 1.4 meter high.

In the interum ive been doing allot of reading about acoustics and I think that I may be heading in the right direction. I read an amazing article on Ethan Winer website. It made me realise that I need to have some idea of what sort of frequencies Im dealing with. So I did a search on the net and came across a study that was done on table saws and frequencies they generated and how to minimise them (http://www.me.mtu.edu/courses/meem4704/ ... le_saw.pdf). Long story short, a table saw generate hi db frequencies between 2500-8000hz. (They said putting acoustic foam into the saw housing has the greatest effect on decrease the sound. Also something Im going to do.)

So from Ethans site the optimal position of a broad band absorber away from the wall would be between 10mm for 8khz and 34mm for 2500khz. So if I double up on the acoustic absorber and mount it at 10mm from the wall I should be covered for the entire range. Together with this info and some of the wonderful tuts on building acoustic panels on this forum, I'll be able to get a few made up and installed this weekend.

Please comment if Im heading in the right direction.

Many thanks,Roland

[xSpace]

Yes you are headed in the right direction. A decrease in 5dB in the offending part of the frequency as the chart on your linked page shows is an improvement.

So that is a start. Absorption at high frequencies is the easy part, it's the buildup inside an enclosed environment and the issues with parallel surfaces.

You have 20 meters of acoustical fabric to build panels out of and you know from another site that making an air space has the potential to be helpful.

http://www.spec-net.com.au/tontine/acoustic/acous2.htm
AcoustiSorb 1 has the following sound absorption coefficients when tested to AS1045 by the Reverberation method:

Frequencies 125 250 500 1000 2000 NRC
Plain 25mm 0.12 0.39 0.65 0.76 0.83 0.65

Those are the numbers on the product you have. It is unclear to me if this is an un-faced material as something with a facing will produce different results when spaced from the hard boundary. If the facing is hard enough it can actually reinforce the frequency.

In any event if it is un-faced it will benefit you to space it out, even if this spacing will aim more at the lower frequencies not the highs you have interest in.


I did some calculations on what I would do with this material.

I would cut the pieces 1.24m long. This should give you 16 pieces. The idea is to break up the parallel surfaces so in order to do this you would start at one corner of your long wall length and place one of the panels there, vertically, basically centered up from floor to ceiling. With your 2 meter ceiling height this will result in approx. .38m from the floor and from the ceiling.

Measure 1.2m away from the edge of that panel and place another panel. Continue this process until you hit the other corner. Then turn around 180 degrees and step to the opposite wall. Install a panel directly in the corner at .38m from the floor. Measure from the edge of that panel 1.2m and install the next panel.

When you are completed you should have a hard surface(your walls) with a soft surface directly across from it where your panel should be on the opposite wall. This process will require 5 of the 16 panels you have.

On the short walls, install the panel at the corners. This should take 2 panels per wall and will use 4 total of the 16 panels you had leaving you with 7 panels.

At least 5 of these panels should be placed directly on the overhead ceiling, edge to edge, which will take the hard reflective nature out of the ceiling. I would pay specific attention to make certain if an adjustment was needed to get the panel directly over the equipment that you do this accordingly.

Of the last two panels I would take at >least< one but maybe both of them and build a stand off bracket over the window. Then I would place the panels on the brackets. This may reduce your direct lighting but it will not stop the flow of air and will reduce the sound energy that is trying to get out of this window.

edit: This may be the only case where I would say that carpet, if it were not flammable, would be a good idea due to the high frequency issues.

[RolandC01]

Hi Brien,
Thank you so much for this detailed explanation. I understand 100%. I will get working on this as soon as possible.
Cheers,Roland