How to locate, define and deal with mysterious noise / vibration entering your room?

[666666]

I am nearing completion of my new basement drum recording room. It's a "room within room" system, a full "inner" room that sits on the basement floor slab, self-standing, is not attached to the building in any way other than sitting on the slab. The outer walls also sit on the slab but ARE attached to the building. The inner walls are two layers of 5/8" sheetrock and outer walls are 5/8" + 1/2" sheetrock. The room sits in one corner of the basement, about 18" away from the concrete foundation wall on two sides.

So now that all the sheetrock is up, I was inside the new room and noticed a very noticeable 60-cycle hum type sound. I checked the entire building, shut off all appliances, killed all circuit breakers... noise does NOT seem to be coming from within the building.

I then went outside and noticed that the neighboring property has an in-ground pool... and there is a large pump (likely for the pool) only 25 feet away from where my drum room is... and it is AWLAYS running and making that 60-cycle hum type noise. So I suspect that this pump IS the source of the noise I am hearing inside my room.

The noise just seems quite "loud" inside my new ultra "sound-proofed" drum room compared to in other nearby rooms in the building or even when standing outside closer to the actual pump. I am thinking that maybe the pump is flanking, vibrating the soil, vibrating the concrete foundation of my building and causing my actual inner drum room structure to resonate with this 60-cycle hum type sound. (The inner room is bolted tightly to the concrete slab... and at this point cannot be undone... perhaps a mistake but I never would have expected such a problem) But maybe this is NOT correct and perhaps what I'm hearing inside the room is just ambient sound bouncing around.

The problem is, when I'm inside the new drum room, I cannot tell WHERE this 60-cycle noise is coming from, meaning, the sound gets louder or softer depending on where you stand or place your head... cannot locate where the sound is being emitted from, whether the floor or outside wall etc. I'm not sure if what I am hearing is sound flanking / vibrating through the concrete and inner room structure, or if perhaps I am merely hearing ambinet sound that is just coming in through the basement windows, into the basement and then boucing around inside the basement, eventually getting into my room (doors of the room have not been installed yet)... though if it IS ambinet, it is not obvious in other areas.

The noise is not THAT "loud", but it is clearly audible. Because drums have high SPLs, I'm thinking that this 60-cycle noise I am experiencing will not cause me TOO much trouble... doubtful that it will ever find its way into drum mics. But it still bugs me and it COULD possibly find its way into a mic if I had to record some other softer sound source.

So... a question for the "pros"... how would you LOCATE the exact source of a sound like this? Are there special meters that could be used to locate the areas where the sound is most intense, etc? Or maybe a device that measures vibrations through solids?

Next, I would think that it might be a good idea to DEFINE the sound, see just what it is in terms of frequency and otherwise...

And once the sound is located and defined, then I'd think you could start figuring how to counter-act / stop or at least reduce the sound.

So, in sum, how would you locate, define and deal which such a noise issue?

[Ethan Winer]

Originally Posted by 666666

how would you LOCATE the exact source of a sound like this?

I think you already did. Ask your neighbor to turn off the pump as a test and see if the 60 Hz goes away. Ground does indeed conduct sound, so it seems likely the pump is the source.

Also, the reason the level changes in different parts of your room is for the same reason the level changes when bass tones are played through speakers.

--Ethan

[666666]

Originally Posted by Ethan Winer

I think you already did. Ask your neighbor to turn off the pump as a test and see if the 60 Hz goes away. Ground does indeed conduct sound, so it seems likely the pump is the source.

Thanks Ethan!

I'm quite convinced at this point that the noise is indeed from the pool pump. But what I am trying to determine is how exactly that pump noise is getting into the room. Is my concrete slab floor actually vibrating and setting my sheetrock inner room walls resonating? Or is the pump sound entering the basement through the air, through the basement windows, and then bouncing around inside the basement and entering the room through the open door? If I put my ear directly against the concrete foundation wall and also my sheetrock wall, I think I can sense the 60Hz vibration but it's hard to tell... quite faint. But the sound really "sings" when you're just standing inside the room.

Since my inner room is located in the CORNER of the basement, I am wondering if somehow there is some mode issue with bass building up in the concrete corner and then penetrating my sheetrock walls....?

I cannot ask the neighbors to stop using their pool pump... so this is a problem. Even if they allowed me to study and modify the pump somehow (to perhaps try to decouple it from the ground as much as possible), I suspect the pump is mechanically connected to water pipes which run under the soil to the pool, so it may be hard or impossible to lessen the degree of vibration entering the ground from the pump.

I tell ya, stopping "sound" has to be the most difficult quest that exists. I feel I've been struggling with this all my life and still no true success. I thought this time I'd nail it with my very carefully built "room within room" structure, everything done perfectly... had high hopes... and now there's a quite noticeable 60Hz pool pump noise ringing away, probably louder than in any other room in the whole building. It's so frustrating!

I guess I should have made the inner room walls "floating", sitting on top of some type of rubber suspension and NOT bolted to the floor. Though I must question how much of a difference there would have been if the inner room was sitting on rubber as opposed to being bolted down. With all the sheetrock, the room weighs so much that it still would have been very tightly pressed to the slab.

One main reason I DID bolt down the walls is because I designed the wall plates to act as water barriers.... the basement leaks and the wall plates have been fully sealed and bolted to the floor... I already had a big flood recently outside the room and my wall plates kept ALL the water out of the room so it worked great and I'm glad it was built this way. If the walls had been floating on rubber chances are that it would have been hard or impossible to create a 100% reliable water seal. Remember too, wood wall plates (treated 2"X4"s) are never perfectly straight and the concrete slab floor in this case is also far from dead flat... so bolting the plates down allowed me to get everything really snug with almost zero gaps anywhere... and I of course used tons of high quality silicon sealer and adhesive as well just to make sure. A buddy of mine has his basement room walls NOT sealed to the floor... the boiler sprung a leak one time and he came in to find all his gear (guitar pedal boards, speaker cabinets, bass drums, etc) floating in 4" of water... not good... cannot allow such a possibility, sealing the room from potential water leakage was very important to me. (Note, my basement is open on one end so standing water can never build up higher than say an inch... the 2"X4" wall plates are more than enough to keep all water out even if the boiler cracked in half - and yes, my plates wrap around the entire room, even under the door... it's fully "sealed")

But if indeed I determine that the 60Hz pump hum IS entering the room through the concrete slab and then setting the sheetrock walls resonating, I will always be wondering just how much better it would have been IF I had set the entire inner room on rubber strips and NOT bolted it down.

There is an 18" gap between two of the room outer walls and the outer concrete foundation walls.... this is where the corner is. Again, I am wondering if somehow the hum is building up in that corner. Would it make any sense to try to pack that entire 18" wide path around the corner area with batt insulation or rigid insulation? Again, I'll note that the room itself has dual walls and I WILL be using corner bass traps INSIDE the room once it's done... but just wondering if I need "corner bass trapping" outside the room as well...? Walking around the basement (and in this 18" gap etc) is no help in terms of determinng where the 60Hz hum is worst... because you hear it everywhere in varying degrees... it's like a phantom... it follows you everywhere but when you try to pinpoint it, it disappears or becomes greatly reduced... etc.

Or maybe I'll just go out tonight and drive an axe into that pool pump

[Rick Sutton]

Is your room still in a bare wall and floor type of state or is it finished out the way you intend to use it?
Also, what are the dimensions of your room?

Highly reflective rooms (think echo chambers) have the uncanny ability to amplify sounds and if the isolation is especially good in the mid and upper frequencies you'll hear your weakest isolation frequencies (bass) become obvious. Road rumble is a good example of this. Bass traps outside the room are useless. Trapping in the room should bring the room into focus and tame the amplification of the 60hz.
At this point I'd finish the room out with some deep trapping and not worry about it.
Drums will be no problem and if you record softer instruments close micing and a little high pass filtering will kill any problems, but I think that the "hum" will drop dramatically after you change it from an echo chamber into a good sounding recording room.

[666666]

Thanks Rick!

Yes, the room is still in an unfinished state... bare concrete floor and bare sheetrock... and nothing else. The reflections are so bad in there right now that it is hard to even understand someone speaking 5 feet away.

Everything you said makes a great deal of sense and helps explain why I never noticed the pool pump noise in that part of the basement BEFORE the new room went up but yet now really notice it when standing within my new "echo chamber". I was indeed hoping that once traps were added to the inside of the room the pump noise would become way less noticeable... thanks for confirming that speculation, I feel a bit better now and can't wait to finish off the room and get some traps in there.

The dimensions of the room... I'm ashamed to reveal them as I'm sure they are probably about as bad as can be... but I only had so much space to work with and had to do my best... it was not possible to make the room any larger. It's about 11.5' X 17.5' X 7' high... perfect rectangle and flat ceiling. I will of course be using much bass trapping all over the place, I have no desire to "hear" this room at all through the mics, I will be happy with a very direct tight dry intimate drum sound with zero room sound... and I'll deal with "space" by either re-amping the recorded drum program into a larger room and recording that, or just using high quality outboard reverb. Not ideal but better than nothing. I prefer a tight dry drum sound anyway. I plan to run traps in all corners of course, and also run traps on most of the wall area that will be nearest the drums to hopefully fully eliminate close reflections... etc.

I don't have room for traps thicker than 4" on the walls / ceiling so hopefully that's good enough. Given my physical limitations here, what type of trapping material might be recommended? 705 perhaps? Or would 703 be ok? I am guessing I need the most dense stuff since I have such little physical space to work with.

Thanks!

[dcharrison]

Ok, the good news is your neighbor has a pool. Be nice. Don't play your drums at night and maybe he'll let you swim in it!

You are probably correct about the source. The pump is no doubt vibrating on a concrete slab which is vibrating the soil (and perhaps more significantly, the water in the soil). The soil is vibrating your concrete slab which is vibrating your interior space like a tuning fork resting on a guitar box. If you turn on a mic and record the sound, you will probably find that the frequency correlates to the resonant frequency of the room, or some part of the room.

Here's how to fix it. Start wherever your relationship with your neighbor permits.

1. Isolate pump from ground
Get a small concrete air conditioning pad and mount the pump to it. Find a dense foam rubber pad or a series of Sorbothane pads and place them between the small concrete pad and the original slab. Replace rigid pvc connections to the pump with flexible hose. This is how it should have been done in the first place. Your neighbor's house will be quieter and his pump will last longer. Short of digging up all the pipes and wrapping them in foam, this is the best you will be able to do. This two slab technique is also good for air conditioning compressors. The mass of the top slab resists the vibration of the equipment and the sorbothane decouples the remainder from the ground.

2. Fill any empty cavities. If you didn't pack your walls with insulation, do it now. Any empty space will resonate. If this is a damp space, you can't use cellulose or cotton because of mold. Your only other choices are fiberglass and foam. Go with the fiberglass and psck it densely.

3. Glue or staple Soundblock film on wall, floor and ceiling as if you were building a balloon and didn't want the air to get out.

4. Decouple the floor of your booth from the basement floor
Whatever your reasons for bolting it down, you need to float your room over the concrete. The easiest way to do this, now, is to put down sleepers with rubber isolation pads on top of the existing floor and put floor decking on top of that. I believe Auralex sells a product for this. Stop the new floor 1/2" from the walls. Fill the gap at the perimeter of the new floor with foam pipe insulation so that it is flush with the wall. Now your floor is floating, but your walls are not.

5. Attach resilient furring channels to the walls. attach a new layer of sheetrock (preferably the yellow fiberglass wrapped stuff) to this furring, placing the bottom of the sheetrock snugly against the foam edge of the floor.

6. Repeat for ceiling.

7. Play real loud and use web style shock mounts on all your mics. When you are finished, take a swim with your new neighboer.

[Rick Sutton]

Originally Posted by 666666

it was not possible to make the room any larger. It's about 11.5' X 17.5' X 7' high...
I don't have room for traps thicker than 4" on the walls / ceiling so hopefully that's good enough. Given my physical limitations here, what type of trapping material might be recommended? 705 perhaps? Or would 703 be ok? I am guessing I need the most dense stuff since I have such little physical space to work with.

Most of us deal with space restrictions, it comes with the territory.
My drum booth is very small and heavily trapped and I have gotten many great drum tracks in there. Luckily I have non parallel walls and a floating floor but still quite tight.
I use 703 and air traps behind. I'd be inclined to completely kill the ceiling and build traps that triangulate the corners of the room to get around 2 feet of depth.
I would also look into point #2 from dcharrison.
Enjoy your new room!

[666666]

Originally Posted by dcharrison

2. Fill any empty cavities. If you didn't pack your walls with insulation, do it now. Any empty space will resonate. If this is a damp space, you can't use cellulose or cotton because of mold. Your only other choices are fiberglass and foam. Go with the fiberglass and psck it densely.

Guys, I greatly appreciate the info. Thanks!

Regarding point #2....

Here's how my walls are insulated:

I have R-15 batt insulation between my inner wall studs (studs are 2"X3"s on 16" centers)... I wrapped wire around the backside of the studs to keep the insulation pressed tightly against the sheetrock of the inner room and to keep the insulation from potentially falling back toward the outer wall framing. The goal was to not have ANY part of the inner walling touch ANY part of the outer walling... including insulation.

As for my outer walls, I have not added ANY insulation at all.... and that is because there is literaltey not enough space. There is perhaps just barely 3.5" left inside the outer wall cavity to the point where the inner wall insulation ends.... so if I add 3.5" batt insulation in the outer walling, it will touch the insulation of the inner walling. Doing this would make my walls truly "packed" with insulation but would leave me with no air space whatsoever between my inner and outer walls and would also "couple" the inner and outer walls, at least in terms of batt insulation.

So... in this case, what would you guys do? "Pack" the space between the inner and outer walls with insulation (thus technically "coupling" and having zero air space), or leave it the way I have it now which is R-15 pressed tightly into the inner wall and nothing in the outer wall.

The total space between the inner and outer walls is about 7"... so I have 3.5" of insulation and 3.5" or air space right now.... this initially seemed like a good plan. Yes, I realize that my inner and outer walls are quite close together, but I was indeed fighting here, trying to conserve every inch.

Thanks again for all the input!

[dcharrison]

What you've done seems sensible, but don't the studs couple the inner and outer walls? They certainly couple to the slab which is probably the source of the vibration making a new floating inner wall a must.

Another way to kill resonance in a membrane (sheetrock) is to add a viscous mass. There's a very effective product called Dynamat sold through auto stereo stores. (probably not the most effective way to buy it) It is peel-n-stick, and a couple of square inches on an 18" ride cymbal will deaden it completely. People often use small patches of it between sheetrock layers.

With a 7' ceiling, I can see why you wouldn't want to add much height to your floor, Certainly not the 6" that sleepers, insulators and sub floor would add. Sorbothane is an amazing material. Put it in your shoes and it will cure your plantar fasciaitis. Put it between two surfaces, and most vibrations never make it through. It isn't sold widely as an acoustic treatment, but you see it here and there as internal shock mounting in microphones, turntable isolators, and subwoofer isolators. If you are adventurous, you could try buying a few sheets, cutting it into strips and floating a new floor directly over the one that is tied to the slab. If you used interlocking decking (a 4'x4' tongue and groove product readily available at building supply stores) you could staple the sheets to each other at the seam (maybe even squirt in a little wood glue) and they'd probably hold together--especially if you covered them with glue-down carpet. That would only add about 1 1/2" to your floor height and give you a completely floating floor. The Sorbothane people are very helpful and accessible.

This is such a congenial forum. I am surprised that no one suggested the obvious $5 fix: Buy a bag of sackcrete and pour it slowly into the skimmer of your neighbor's pool while the pump is running.

p.s. To get a good look at this noise, make a recording of the empty space and load it into Adobe Audition's editor (you can download the free demo for this). Select View, Spectral Frequency Display. Unlike a wave editor, this displays time on the horizontal axis, frequency on the vertical axis, and amplitude as color intensity. You can zoom in to the low frequency and any continuous noise will appear as a bright horizontal line. The motor on a pool pump typically runs at 3450 rpm, sometimes with a 1725 RPM "power saving" mode. That's probably too high to be soil conducted, but look for multiples. Pumps also produce cavitation noise, a weird phenomenon where the suction pressure of the impeller creates a vacuum which is implosively filled with water. Lord only knows what frequency that is, but you'll be able to see it all in Audition. Take a sample before and after and tell us how you come out.