Advice needed on reducing external rumble entering studio.

[Travelreview]

This is my first posting on the construction site (A superb Resource!) although I have read hundreds of previous threads and all the stickys.

I am now scouring my city to locate an available rental space of approx. 1500 sq. ft in which to locate a small audio/video recording and post production studio.

In our city, the vast majority of affordable raw space is located either in large converted factories (Not ideal, since there are neighbouring industrial and residental tenants upstairs, downstairs, to the left and to the right), or are unfortuantely situated very close to freight train rails.

In any case, after 6 weeks of searching, I came across a good potential location, but it has a different problem to contend with.

The space is housed in the corner 1/3rd of the shipping area of a former factory, (a 1 storey cement block structure with a shared cement slab floor, no basement, and a 21' high cement slab ceiling). It also has an adjacent 2 floor office area, currently seperated from the proposed studio with simple LOW STC single stud single leave walls.

The problem is that directly across the street is a bus repair depot, and during weekend evenings, several busses park just 6 feet away from the front cement block wall where the live room of the studio will be, and these busses leave their deisel engines on for hours, thus creating very audible LF rumble.

The problem is made worse by the fact that the studio wall which faces these busses has a 12'H x 10'w cutaway where a low STC garage door has been fitted behind many years ago. Almost none of the rumble vibrates the cement floor, but it really bleeds through the wall!.

Obviously I realize that we will have to seal up that cutaway section with a HIGH STC wall, but I am unsure if we can realistically remove most of the rumble even if we build a staggared double stud double layer STC 56 insulated wall (or perhaps a filled cement block wall of about STC 50??) to tightly fit and seal off the garage door and it's cut-away in the cement wall.

I don't expect miracles, and I have a limited budget for this project, so I can only afford to spend about $1250 USD in materials to deal with trying to seal that problem wall and treat it. If the problem is too difficult and expensive to deal with, I will forget about this location and continue hunting for another space.

The question is...
Will simply walling up the garage door and sealing it off with a properly constructed wall of STC 50 to 56 drastically reduce the LF rumble, or will additional and more costly soundproofing be needed to cut the rumbling bleed-through from those nearby deisel engines???

- RON

[Travelreview]

For some reason the attachments did not link to my posting, so I'll try attaching them again.

I have included a floorplan of the raw space as it is now, and another with a draft plan of how I hope to rebuild the space for studio usage....

-RON

[AVare]

Will simply walling up the garage door and sealing it off with a properly constructed wall of STC 50 to 56 drastically reduce the LF rumble, or will additional and more costly soundproofing be needed to cut the rumbling bleed-through from those nearby deisel engines???

Stop thinking STC and start thinking Transmission Loss (TL). STC gives little indication of low frequency attenuation.

From what you have descirbed, the chepest is to reproduce the current wall construction. Will it be enough? We don't know, as we only your post indicating that the rumble is coming from the opening.

IS 1250$ US enough? I don't know. I don't even know where you are grographically, to estimate construction costs, much less if you are going to do the labour yourself or pay for it etc.

[Travelreview]

Thanks AVare,

I'm up in CANADA.

All labour to be done by us!

The aforementioned $1250 USD is our budget for building materials needed to solve that specific rumble/wall issue, as another $6500 USD (plus our labour) will be budgeted for other acoustic treatments and the CR/ISO construction.

The only obvious source of the majority of rumble is the garage door area, but it is all but impossible for us to determine if additional rumble leakage is coming from other sources, but of course it is quite possible!.

Perhaps a double framed insulated wall or dual (insulated) cement block wall is what we are thinking of sealing that opening with (and we will most likely not add the exit door there, as is incireectly shown in the floorplan).

I have not found any charts with god TL ratings for these types of walls (Although plenty of STC charts exist), and have seen no specs or charts on their affects on LF below 125 hz or so, so we still have no idea if this will indeed significantly reduce the rumble from entering. Any thoughts???

- RON

[AVare]

I thought I had replied, but it did not show up.

I have not found any charts with god TL ratings for these types of walls (Although plenty of STC charts exist), and have seen no specs or charts on their affects on LF below 125 hz or so, so we still have no idea if this will indeed significantly reduce the rumble from entering. Any thoughts???

Start in this this Forum with the topic "Under 100 Hz Isolation Performance"

http://www.johnlsayers.com/phpBB2/viewt ... highlight=

351 wall types tested in the first NRC document down to 50 Hz. The second NRC document focuses on concrete block walls.

We have no data on the rumbling, or the rest of the wall, except what you have told us. We can not tell if it is enough for you or not.

[knightfly]

If you use a computer and software to record, you could gather more info on your problem frequencies by using a good (20-20k) condenser mic and recording some of the bus noise, then analyzing it for frequency content (fft module, or just spectrum analyzer, depending on your software) – that way, you'd know what frequency component you need to isolate the most and could design the wall accordingly – you would want your mass-air-mass resonance of your wall to be lower than the bus crap by several hZ, and (as Andre pointed out) a wall with good low frequency TL – these two pretty much go hand in hand, so one should equal the other...

To find out just how much of the noise is actually coming through the wall vs how much of the problem is your floor, I would go to your local auto parts store and buy a mechanic's stethoscope – these cost anywhere from $6 to $15 USD or so, and look like a doctor's stethoscope except instead of the round "cup" that fits on your chest (or wherever you're using the stethoscope to listen) these have a long, thin probe that's typically about 1/8" thick and 10-12 inches long, and are normally used to pinpoint bad bearings, leaking valves, etc, on engines – In your case, you would wait til the bus noise is happening and (carefully) place the tip of the probe against your wall, then the roll-up door, then the floor – this won't give a scientific quantity to the noise, but it WILL tell you if your floor is going to be part of the problem – I'm betting that anything that low frequency will be coming through nearly EVERYWHERE, and if so you'd need to do a fully floating floor and "room-in-a-room" setup to kill it – if that's the case, you'd be looking at quite a bit more $$$ and would probably want to keep looking.

The good news is, you probably already have most of what it takes to check on this, with the possible exception of the stethoscope – and $15 or so is cheap to find out what you need to know.

If you were REALLY desperate, and use Samplitude (as I do) you could place a mic against the roll-up door, and record that along with your music – then, using the noise reduction algorithm in Samplitude you could simply "subtract" the noise from your recordings – in all seriousness, even though I've had excellent results in cleaning up problem recordings for people, I would NOT recommend this as a normal way of working, it was mainly just kidding around... Steve

[Travelreview]

Thanks for the helpful advice Knightfly,

I will take all your advice and purchase the stethoscope as well as try to do a proper Spectrum Analysis of the rumble using the flatest microphone I have (a Schoeps CM6 with MK41 capsule).

I'll post the results in a few days and see if you think the rumble problem is worth trying to solve, or if I should pass on this problem space and find an alternative location for the studio...

RON

[Travelreview]

Here are the current SPL measurements taken with B&K SPL meter and a B&K 1/2" measurement mic. All these db readings are in C scale (flat) with +/- 3db accuracy. These are the first such measurements I have ever made, so please forgive me if I neglected to add other needed results or details.

Remember that all walls are currently hollow painted cinder block (except the 2 floor single stud sheetrock partion wall between the live room and 2 levels of our adjacent offices), and the floor/ceiling are both cement slab.

Perhaps this info will allow someone out there to help me determine the types of high TL wall configurations necessary for me to build and seal up the studio section's wall areas facing the bus parking area.

I am hoping to get the studio's live room interior SPL down from it's current 66db (when a bus is parked nearby with engines blazing) to something approaching 26 db or lower, with a materials budget of about $1500 USD (plus our labour). The rest of our budget will be needed to build and treat the CR and iso areas which will be in the rear of the studio.

I assume we will need the most TL (and highest STC) in the 10'w x 12'h cut-away in front of the current sheetmetal garage door.

The second most TL may be needed in the office doorway area (perhaps by adding a second soild core fire-door with good acoustic caulking??).

And the third most TL may be needed to beef up the wall area of the studio which is adjacent to the left of the garage door. This large wall section once contained a 12''w x 12'h loading dock, which was non-acoustically sealed up years ago with what I assume to be fibreglass thermal insulation and a basic single stud sheetrock wall.

I am trying to decided if I should use concrete blocks (filled or unfilled) or double framed steel stud (no RC) walls with dual layers of 5/8" sheetrock, and 4" Roxul.

Finally, I was wondering if I could considering building the CR outer walls out of cement blocks, as opposed to the dual leave sheetrock designs seen here often. The floors are solid 8" cement and I don't think they will have any problems carrying the extra tons of load. ANY THOUGHTS???

RON

[knightfly]

I'm impressed - there's a lot of info there, especially for a "newbie" - I'm not seeing as much attenuation between 6" from the bus and outside the door as you would if the door wasn't there, likely because of reflections off the door increasing the apparent sound level - if you still have the equipment available, you should take some readings at the far end of the building as well, just for reference.

Before you can make any decisions, you'll still need to check with the mechanic's stethoscope (contact is important, it increases the differentiation between sources better) - this will tell you more about where inside the building the noise is emanating from (a lot of it will be that door) - Also, you'll get more low frequency noise when a bus is leaving - motor under load, changing frequencies, road rumble) -

Another thing - in order to design a really effective barrier, you still need to know what frequencies are prevalent - that way, you can avoid (like the plague) any combinations that have weaknesses at those particular frequencies. For this, you'll need some kind of recording software that allows spectrum analysis of sorts - you didn't mention if you already have that. There are several plug-ins and a few full programs that let you do this - One I use is Samplitude - With it, you can see exactly what frequency components are involved (and their relative levels) so you know exactly what you're fighting against. I'm not familiar enough with the other offerings out there (cubase, nuendo, sonar, PT, etc - ) to know if they can help, but Waves offer plugs that do this as do a few others.

Once you have this information, it's much easier to make decisions on wall construction based on the prevalent noise (things like NOT choosing a wall spacing that has the same mass-air-mass resonance as your noise )

Sound locks with serious door seal kits are most likely going to be necessary, at least at the bus end of the building - You're probably looking at materials costs of at least $500 per door, or maybe $1200 per double door sound lock - otherwise, trying to design walls, etc, with more than about 40-45 dB STC is an excercise in futility.

If you still can, take some measurements at the far end of the building using the same settings (grab new ones at the bus and outside door for comparison) and let me know what you have available for spectrum analysis... Steve

(Oh yeah, stethoscope...)

Also, is it an option to ditch the big door and block it up? Had to ask... Steve

[AVare]

Great work you did, and all I can do is agree with what Steve wrote.

A major consideration. Is the wall between the office corridor and the studio room the construction as the rest of the office walls?

If it is, assuming that for the moment the major source of the noise is coming through the loading dock doorway, once you have corrected that, you will probably then have the major source of rumble being from the office door through the office hallway walls.

Good luck, once again, nice data collection.

Andre

[Travelreview]

Thanks AVare and Knightfly, I appreciate the encouragement!.

I'll attempt to answer a few questions (and raise a few thus far unmentioned issues).....

I still have the B&K SPL measurement gear and I will use it again in a couple of days so as to measure the entire interior studio space and office areas every 3 feet throughout the building. I am still looking for a local source for the mechanic's stethoscope and will post the results of those tests soon.

In terms of AVare's question about the wall construction of the corridor between the office and the studio room, it is made of the same simple low STC single stud single frame sheetrock walls with 2" of pink household thermal insulation that the entire 2 floor office area is constructed with. I am sure this corridor and it's ceiling may need to be rebuilt and fortified with additional sheetrock layers on each side and better insulation material (perhaps 4" Roxul or similiar). If necessary I can pull this segment of the wall and ceiling down, and build a new double frame wall with 2 masses and an insulated air space as per John's site.

As far as the garage door itself is concearned, the building's owner has informed me that we must return the building (at the end of the lease) in the same or better condition as when I rented it, and it must have all the same features as it now has, thus permananetly removing the garage door and it's rails are not an ideal option at this stage. I was hoping to build a +/- 10" thick high TL/STC exterior wall to seal up the current cut-away area, and cover the studio side of the garage door with OC 703 and/or Roxul to reduce any sympathetic vibrations it may generate.

I am in the process of trying to load Steinberg WaveLab and ETF Acoustisoft (demo) to use for the Spectral Analysis. Since I don't have electricity in the building, and my laptop does not have a mic preamp, instead of on-the-spot computerized RTA Spectrum Analysis, I will instead record the rumble and engine noise at various points in the space with the B&K and/or Schoeps mic hooked up to a portable minidisc & high end DV camera, and put these recordings through the software at my office to get the Spectral Analysis results at various locations both inside and outside the building when a bus is operating nearby. I will also bribe a bus driver to rev up the engine and make a few passes up and down the block at various velocities so as to see what different frequencies are present under varying conditions. I'll post these results once they are compiled.

As far as the office door itself is concearned, currently it is a poorly sealed and very corroded fire-door which I will replace with a new exterior solid core fire-door (and perhaps add a second similiar door) and seal it using the best seals and acoustic caulking we can afford (I suspect the $295 studio acoustic door seals may have to be added at a later date due to our budget!).

One issue I did not mention will add a bit of further complexity to this situation. This space is just the end corner of a larger 4500 sq. ft structure which is soon to be subdivided, and there are currently massive 8' x 10' archways cut into the cement block walls between my garage bay and the 2 similiar sized adjacent vacant garage bays to the left (which each have another awful sheetmetal garage door.) The arches in the seperatation walls will be filled with painted cement block that is identical to the existing cement block wall material, but at this point the arches seem to allow a fairly large amount of additional rumble to pass through (from the adjacent garage bay doors) and reverberate throughout the structure and then bounce through the arches and pass into the section of the building that we hope to rent. This is perhaps the main reason why the SPL does not drop as much as expected in some sectors of the studio.

Anyway, I'll get the software up and running soon, and expect to make another series of measurements for both SPL and Spectral Analysis this week, and will post them here for your advice and consideration.

Once again thanks for all your help...

- RON

[Travelreview]

Thanks yet again Knightfly and AVare.

Posted are gif versions of the RTA results that you have asked me to provide in order to have your further assistance in determining if this space is usable as a studio site, or if these rumble and high SPL issues make this too big of a project for a novice such as myself to contend with!

The first 3 graphs are with 1 BUS WITH ENGINE ON, garage door closed.

The last 3 graphs are with 1 BUS WITH ENGINE OFF, garage door closed.

The weakest TL links in this all concrete structure will certainly be the cutaway where the low STC garage door now covers (I am sure this 10" deep cutaway will need to be sealed up with a high TL wall!), and the adjacent area to the left where a similiar sized loading dock has been sealed up some years ago using simple single wood stud wall poorly insulated with pink fiberglass and covered by single ply 5/8" gyprock.

Hopefully these results can help you to better assist me in determining the exact types of walls and the specs for the needed construction materials which will be best suited to block as much of the nearby bus engine noice as possible.

These measurements were all taken using a shock mounted ultra flat respose Dr. Schoeps Collette CMC5 microphone with a Schoeps MK-41 cardiod capsule pointed at the noise source from various distances, as recorded in mono at 16bit/48khz digital rate. These results were then captured via 1394 link to Protools and processed through Waves spectral analysis software using "peak hold" function over 5 second intervals within each sample.

Once again I am new to all this, so please let me know if additional samples or other information would be necessary to help determine what types of wall construction would be needed to bring down the interior noise floor to an acceptable level. I have ordered the Mechanic's Stethoscope as suggested by Knighfly, and it should arrive in a few days, so those results are pending.

I have also redesigned the floorplan to keep all open mics as far away from the noise source as will be possible. New SPL readings have also been included.

Any and all assistance would be greatlyu appreciated as I have just 10 days to decide if I sign a lease for 1-3 years on this potential studio location.

Thanks for all your help and patience, I am learning a great deal from all of you out there, and I am very appreciative of this superb online resource.

RON
Montreal

[Travelreview]

Just wanted to add a NEW chart of the current structure, with the correct SPL readings taken with B&K spl meter and a 1/2" B&K mic.

Please note that the wall on the extreme left has three 10' x 8' cutaways in it, which will be sealed with similiar cinder block by the building's owner.

The partition walls dividing the studio from the already existing two level office suite on the right side (which we will use for Video editing suites and storage) is made of simple single stud frames covered with 2" OC pink fibreglass and 5/8" sheetrock , and will most likely need to be either rebuilt or beefed up!>

Ron

[knightfly]

Got your PM, and am borderline on suggesting you pass on this place under your particular circumstances - first, with no experienced help you will make mistakes that will cost you time and materials to fix - second, from your noise graphs you will need a minimum of around 40 dB TL at 50 hZ to adequately kill the bus crap - while this is definitely doable, it seems like a waste of money to have to block up that doorway only to remove it in a few years - If you do sand filled block, then put a gypsum inner wall, you can get more than enough isolation (with no mistakes) to kill the noise.

However, concrete block construction is nowhere near as easy as it looks - the blocks fit together just fine when they are being stacked without mortar between them - when you start "buttering" them and trying to get them to STILL stack straight, it's another story. Experience here is very valuable. Building normal stud walls is easier for beginners NOT to goof up.

One possible option is to negotiate a deal with the owner to ALSO block in the front door while the others are being done, with the understanding that you will be responsible to open it back up at lease end - that way, experienced masons will be doing the work and you can just add an inner frame and wallboard to top it off.

To kill those lower frequencies, you'll need a fairly wide air gap to get the mass-air-mass resonance lower than the noise - probably around 8 inches, depending on the outer mass - less if that is sand-filled block - using sand-filled block, a 150mm air/insulation gap and two layers of 15mm gypsum on studs would net you around 38 dB TL at 50 hZ, with an STC (for higher frequencies) of around 65 dB. I don't have actual figures on this, it would probably be better - you might even be able to get those results without the sand filling, I'm not sure.

Until you find a stethoscope, you won't know whether floated floors are mandatory or not - the slab could be responsible for a fair amount of the noise penetration too, although that door seems like the most likely suspect -

My gut feel is that this is pretty much a "coin toss" at this point - if you can scrape up either more money or a construction-experienced friend it would tip the scales more in favor -

I'm not sure just how much help I'll have time to give in this either, it seems like I keep getting further behind on necessary functions around here - I don't want to get your hopes up that I'll be able to guide you as much as you may need, or as quickly - That's about the best I can do as far as your decision-making goes, sorry... Steve

[Travelreview]

Thanks Knightfly,

I will make a decision about that specific studio location next week.

You suggestion about us offering to pay the building owner's contractor do the installation of the sand filled brick exterior wall to cover the garage door is pure genius!. I have contacted them already and they appear eager to take on the task for around $1375 USD (including materials!), which seems like a reasonable deal to me. We will build the adjacent wooden stud sheetrock walls with Roxul filled air space ourselves.

A few other questions may pop up in the future, so I'll post them here on a new thread and see what you and the other experienced forum users have to suggest.

Thanks again for all your assistance, and for moderating this superb online resource for insight into practical studio design and construction...

Ron
Montreal