SPCR

OMG, the fortress of solitude of my dreams

jaganath wrote:wow....that's fascinating that 99% of the ambient noise is in the sub-200Hz region. would be neat if a measurement could be made at say, 2am in the morning (when there is minimal traffic) to definitely confirm it is noise from cars/traffic flow; but I fully understand after your Herculean labours, midnight vigils are not exactly what the doctor ordered.

Hey I already mentioned, I'm no Hercules!!

Yeah, a check on the freq spectrum in the wee hrs of the morn is next. I suspect it is the traffic noise, as well as any residual noise from the 2 fridges and one freezer in the house. If any of the compressors in those machines are going, it transmits some very low freq vibrations into the frame of the house, which is picked up by the mic. The ACO Pacific mic is absolutely flat, btw, to below 10 Hz... probably not such a good thing for my needs!!

It's been suggested by a helpful SPCR reader (who happens to be in the business of anechoic chamber design) that the concrete slab which lies below the carpet and underlay is a source of low frequency noise "flanking" -- it doesn't come through the walls and acoustic batting but up through the floor. With the very low freq noise from traffic noise 1.5 blocks away, I expect this is the main noise path. It's probably conducted through the ground, the cement slab and into the room. I don't hear it because the noise is still at a fairly low level, and human hearing sensitivity falls away steeply below about 100Hz... but the mic's sensitivity doesn't.

The questions are:

1) Would a floating floor by itself (without floating walls & ceiling) eliminate most of the low freg noise transmission? I hypothesize yes -- if most of the low freq noise is via conduction, it enters the house through the floor, causing up/down movements. Those same vibrations in the walls cannot cause anywhere near the same level of noise as in the floor because it's in a perpendicular plane. It might cause a fair bit of noise in the ceiling tho, as that's parallel to the floor, but how much of the vibration is conducted up to the ceiling? Probably not as much as the floor.
-- and --
2) since all of SPCR's noise measurements are done with A-weighting, and there's no reason to change this, is the elimination of the low freq noise worth pursuing?

If the answer to 1) is yes, then I'd go ahead and install a floating floor. It's not that difficult or expensive, at least not the way I'd go about it. My basic approach:

a. Remove all the wall blue fill & frames,

b. loosely put down a 1.5~2" thick layer of high density foam, or even better -- closed cell foam* -- over the entire floor.

c. lay two overlapping layers of medite board over the entire floor, probably each with 5/8" thickness, and join the two layers using 1" screws. This MDF platform would become the new floating floor -- it would touch nothing except the foam beneath it, and extend to about 1" from the walls. That edge would be covered up by the blue fill which goes up against the walls.

Someone w/ experience or greater knowledge -- perhaps my helpful angel from anecholand -- needs to tell me whether this floating floor is worth doing.

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*Why closed cell foam? It would be recycled from all the packing material in boxes that come with product samples, especially cases. It's very uniform -- the density of all the packing closed cell foam seems to be the same and ~1.5" thickness is very common. I've done a quick and dirty test on how much resilience it has under pressure: A wood board under 1' sq was placed atop a similar amount of the foam, and I stood on it placing my ~165lb weight on it. The compression was about 1/4", and it still felt quite resilient when I bounced my weight on it by flexing my knees up/down quickly. Now, the MDF floor I described above would have a weight of approximately 300 lbs and cover an area of 120 sq ft -- less than 3 lbs per sq foot, compared to the 165 lbs/ft I applied by standing on a sq foot.

The only questions about closed cell foam is whether there's enough here to cover the whole floor, and how effectively it stops mechanical conduction of low freq vibration. I know from extensive experience with trying to stop low freq conduction from HDDs (in the other direction) that open cell foam is much superior to closed cell foam. But this may be due to the relatively higher resilience (softness) of the open cell foam, which is appropriate for the low mass of a HDD. Some experimentation is probably needed to check this.

I see canada as the location. Dead of winter will give way different than summer, I am in the cold and it is quite dramatic. the mention of the fridge noising the frame of the house is the same for me too. winter changes everything regardless of room.
I hope it works out. This place has done alot to help my "little" pc...

Dunno if this is of any help now

http://www.silcom.com/~aludwig/My_Music_Room.htm

One take on the floating floor idea: You don't need to cover the entire floor with the foam. Most commercial floating floor assembles use a system of resilient piers to support the floor structure. The open space around the piers between the floating floor and the subfloor below is typically either left open or filled with no-density insulation. Too much intervening contact between the floating floor and the subfloor, even if it is foam in between, will result in increased transmittance.

If you want I can dig up some examples to work from and send them over.

) Would a floating floor by itself (without floating walls & ceiling) eliminate most of the low freg noise transmission? I hypothesize yes -- if most of the low freq noise is via conduction, it enters the house through the floor, causing up/down movements. Those same vibrations in the walls cannot cause anywhere near the same level of noise as in the floor because it's in a perpendicular plane. It might cause a fair bit of noise in the ceiling tho, as that's parallel to the floor, but how much of the vibration is conducted up to the ceiling? Probably not as much as the floor.
-- and --
2) since all of SPCR's noise measurements are done with A-weighting, and there's no reason to change this, is the elimination of the low freq noise worth pursuing?

If the answer to 1) is yes, then I'd go ahead and install a floating floor. It's not that difficult or expensive, at least not the way I'd go about it. My basic approach:
...

great work on getting this room sound proof, especially for a domestic enviorment. I suspect my own project recording studio has lesser isolation than this

You could do a test to see if the lows are actually structural transmission from the flooe (I believe so) by placing the mic stand on a layer of foam and measuring. I would expect a significant reduction in low freq to a point where you could evaluate the worth floating the floor or not.

Regardless here is a link to my favorite reference site for basic acoustics and recording
http://www.saecollege.de/reference_mate ... stics3.htm

hope this helps.

Seems like the A-weight filtering solves the problem. Now you are headed into Science Project territory - not that there is anything wrong with that.

Here's another potential low freq noise source - your furnace. If it has a gas pilot light, it may set up a low freq resonance inside the furnace - especially if your house is like mine (frame with footings and subfloor).

Looking good, can't wait to see the first review done in that room.

CA_Steve wrote:Seems like the A-weight filtering solves the problem. Now you are headed into Science Project territory - not that there is anything wrong with that.

Your probably right. According to my angel from anechodom, "The isolated floor won’t buy you much. You need mass to block low frequency energy. Think floating concrete slabs." uh, no, that's not doable. So we'll leave the fl as is and use A-weighting as usual.

Here's another potential low freq noise source - your furnace. If it has a gas pilot light, it may set up a low freq resonance inside the furnace - especially if your house is like mine (frame with footings and subfloor).

This does not seem to be an issue. Even right next to the gas furnace, the perceptible noise is very faint and not that low in freq.

One thing. You have to breathe - You will run out of O2 with the door closed in a few hours. Forced air heating ducts would supply fresh air but would be very noisy.

malmal wrote:One thing. You have to breathe - You will run out of O2 with the door closed in a few hours. Forced air heating ducts would supply fresh air but would be very noisy.

The idea is to leave the gear being tested in there with the mic and the operator be outside with the audio PC. No one will ever be in there for hours w/ the door closed... unless they've been very bad.

Right!
Even your breathing would be picked up by the mike.

Because it is going to be a well sealed garage, this leads me to ask...

- How are you moderating the room temp, air quality, and humidity (in rainy season)? Leave the door open in between testing? Room fan? Dehumidifier?

CA_Steve wrote:Because it is going to be a well sealed garage, this leads me to ask...

- How are you moderating the room temp, air quality, and humidity (in rainy season)? Leave the door open in between testing? Room fan? Dehumidifier?

The garage was abandoned -- see the second or third post I made in this thread. This room is smack in the middle of the house. In general, the door will be left open. We'll monitor humidity and temp -- add a heater/fan if necessary.

Yep - missed that.

The sound men I work with at the Orpheum routinely put rubber-backed carpet pads under mic stand bases for symphony or lectures to isolate them from vibration. Ditto for lecterns with mics mounted on them.

Isolating the measurement mic stand in some fashion from the floor might well accomplish as much as you need to reduce floor transmitted low frequency vibration. The same under whatever is supporting the device being measured may also help. Obviously it should not be directly under the device itself, but some isolation for the bench or table holding the device.

DanceMan wrote:The sound men I work with at the Orpheum routinely put rubber-backed carpet pads under mic stand bases for symphony or lectures to isolate them from vibration. Ditto for lecterns[url] with mics mounted on them.

Isolating the measurement mic stand in some fashion from the floor might well accomplish as much as you need to reduce floor transmitted low frequency vibration. The same under whatever is supporting the device being measured may also help. Obviously it should not be directly under the device itself, but some isolation for the bench or table holding the device.

The mic is already mounted in a shock suspension with elastic... something like this:

Here are the ambient room freq spectrum captures at 1am, with the room in the same state as before -- half lined.





I'm getting a sinking feeling about the noise reduction in there. I can hear the low freq noise of cars half a block away. It's faint, but it might be enough to affect noise measurements and readings. I'll have to finish the room -- particularly the door -- and then try some serious bouts of recording and measurements to know for sure.

Too bad those imglinks dont work?

here:

Wibla wrote:Too bad those imglinks dont work?

Oops.... corrected. It was past 1am, I was pretty foggy.

Awesome project Mike! Nice to put a face with the name.

If I was on your side of the world I'd definitely pitch in with some of the grunt work. I'm in the process of remodeling several rooms myself, so I ken how you feel right now. Reminds me on how I'm way over due on sending a donation your way...if only for the swanky SPCR sticker.

Thanks for the kind of work you have done over the years and continue to do and the passion you put into it.

DrCR

Just a thought, but I suspect that computers aren't humming away at 200hz or less? So maybe it's kinda a mute problem to completely isolate the room from those low frequency noise outside.

CraftyChicken wrote:Just a thought, but I suspect that computers aren't humming away at 200hz or less? So maybe it's kinda a mute problem to completely isolate the room from those low frequency noise outside.

No computers inside the room -- except if one is being tested. I doubt any of the PCs in the labs other rooms can be heard or detected even with flat weighting at >0 dB, at any frequency. The loudest one measures about 23 dBA/1m and it's 20' away on the other side of a sealed wall, in a carpeted room. All the PCs in the lab sit atop some foam damping.

I've truly enjoyed the progress of this project, from hearing about the idea and fund raising to the stage it is at now. This website is such a great resource in my efforts to have quite computing. Keep up the good work and keep the photos coming.

With the help of some friends, a solid core door was hung on the door frame today. It's in addition to the inner hollow core door -- that onesswings inward, and the new outer one swings outwards. Turns ou the new door is slightly warped, but nothing too serious. Have to work on getting a latch in place, as well as a stop and sealing all around the door, and to fill the gap at the floor. Right now, without those details, the 2nd door appears to be provide no improvement in sound isolation at all.

It's nice to see more of you than your ear & hand

Mike,

You might could contact GK Acoustics and request some sort of ventilation system.

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Btw, I'd put up drapes between that board and the window so it appears to just be a regular window with drapes in front. A boarded window looks a little off I think.

Is installing weatherstripping on a window/door difficult?

If you've the time/energy, I'd love to see any info on doing that. The birds outside wake up before I do, and they sing

I remember the physics lab optics table was a heavy metal thing on inflatable rubber bushings. It measured in the tons range, if I recall.