background noise

Boiler1 · Post by **Boiler1** » Wed Apr 13, 2005 3:50 am

I'm about to rent space near a railroad track and a loud corner.

I used a radio shack sound level meter outdoors at street level and have peaks above 100db. Background is more or less constantly above 85db. Primary causes are train whistles (very few per day) and more constantly cement trucks slowing down to navigate the sharp corner outside and then re-accelerating with low rumbling deisel engines. Trains are not too bad since they are electric commuter trains and move very slowly as they approach the nearby station.

If wall construction can get me, say, 65 db of isolation, but background is 100db, does that mean I'll still hear net 40db?

On a related (wall costruction) topic, I see repeated calls for two leaf wall systems, which I understand so long as the air space is, say, 1 foot or less. I have been toying with an airlock (say, 6ft x 4ft) outside of my contol room. If the control room wall is double leaf and the opposite wall of the air lock is double leaf, then it seems I have 4 leaves. That seems to be sub-optimal. From a sound proofing perspective, is it better to have unfinished walls in the airlock? I probably won't do that for cosmetic reasons, but I'm wondering. If, for cosmetic reasons, I do finish off the inside, is it best to do it with, say, 1 layer of 1/2" gypsum, in order to promote flex? Another way of asking: is there a distance between walls at which they stop acting like one system and become, in effect, 2 soundproof walls, and if so, will I get better soundproofing by employing two of them?

knightfly · Post by **knightfly** » Wed Apr 13, 2005 5:42 am

First part; here's a link to better understanding of human hearing -

http://www.madshrimps.be/gotofaqlink.php?linkid=2307

if your screen resolution's at 1024 x 768, hit the Page Down key about 7 times til you get to the Equal Loudness contours graph; note that (lowest, dotted line graph) at 1000 hZ, if a sound is barely audible, then at 40 hZ the sound would need to be 50 dB to still be BARELY AUDIBLE.

Just above the Equal Loudness graphs, there is an explanation/graph of A weighting vs. C weighting; the RS sound meter can do both, and you didn't mention which you used in your measurements. If it was set on C weighting, your noise would have seemed much louder since low frequencies would have been given much more "weight" in the reading.

Another good link -

http://www.norsonic.com/web_pages/correlation.html

On your second question - double leaf effects can continue out to as much as 20-30 feet; there is no SET distance beyond which this just "switches", it's more gradual.

From a practical standpoint (not going crazy from excessive calculations, that is) it's more applicable to normal wall constructions, with air gaps up to a foot or two; beyond that, it's mainly good to know there will be SOME weakness caused by the multiple leaf effect; I've finally come to grips with this, and have decided (in the interest of sanity, mainly MINE) to go with this -

If I were to build a sound lock smaller than about 6 feet on a side, I would first decide whether sound leakage with ONE door open was important or not - IOW, will the sound lock be used WHILE music/noise is going on??

If that would be the case, then I would build all surrounding barriers around the sound lock using DOUBLE leaf construction, and I would add at least one more layer than I thought I might need in each case, to (at least partially) compensate for the multi-leaf losses at low frequencies. Doing this would make it so the lock could be opened at any time, with little or no PERCEIVABLE effect on isolation; in fact, iso might even IMPROVE with one of the doors open in some cases

If, however, the lock would NEVER be used while noise needed to be stopped, then I would re-analize the design so that DOUBLE leaf construction were used throughout, with NO EXTRA leaves anywhere. (Meaning that, with all doors closed, there is a mass-air-mass barrier between inside world and outside world.)

This would give the best attenuation for any given amount of materials used in construction, BUT would severely WEAKEN the isolation if either door of the lock were opened during tracking/mixing.

Ya pays yer money and ya takes yer choice, so to speak... Steve

Boiler1 · Post by **Boiler1** » Thu Apr 14, 2005 4:40 am

Thanks, for the reply. I get what you said about double leaves in an airlock; still considering which way to go.

As to the overall sound levels and whether to rent this place at all, here is some more detail. Yes, I did use the C scale. In fact, today I went back and got inside the building to measure. results are way beter indoors. Background is around 55 db using the C scale; it's below the meter's capabilities on the A scale. Looking at the links you provided, I'm not sure which scale is more important. Are you saying that I should ignore the C scale readings since I cant hear much down there? That would be welcome news since the sounds I'm most concerned about are deisel engine reverberations and slow moving trains.

If so, given that good mics can pick up sound at low freqs and some mics plot out quite flat, do we all end up printing lots of Low freq info that we dont use? If so, does it waste alot of system resources, etc. Sort of an existential question.

More importantly, do you think I can get this place fairly quiet? It's built like a tank with cement floors 2ft thick and a seemingly similar cement roof. All new walls will be new, with at least 2x5/8" sheetrock on all leaves and air spaces between leaves. Also, the ample windows will soon be redone with modern double glazed, over which I will sheet rock. I can even live with a little bleed into the mixing room, but I'll need a perfectly quiet vocal booth. Does it sound manageable?

Many thanks.

Wireline · Post by **Wireline** » Thu Apr 14, 2005 5:00 am

I hate to be such a pessimist about this, but:

My studio is 1/2 mile from the tracks...while whistles are problematic (!!!) the biggest factor I have to deal with is the subsonic and sonic rumbles caused by 250 tons of steel running at 65 MPH...You can work around some of these issues, but the fact remains no matter how much treatment you do, its still you vs. 250 tons of fast moving train...

If I had ANY option right now, I'd move the studio in a heartbeat...

Boiler1 · Post by **Boiler1** » Thu Apr 14, 2005 5:14 am

Interstingly, I'll be about 50 yards from the tracks, but I'm maybe 500 yards from a station at which virtually all trains must stop, so no body ever barrels through. Top speeeds are probaby 10-15 mph, albeit that can cause lots of low freq noise as the loco tries pushing the train. On the good side, there are no freight trains on this line; only commuter and amtrack passengers. 80% are electric, though deisels do come thru often enough. You may still be right to be pessimistic. What get you most? claks? whistes? How ofen are takes blown? How often can you move something in protools? Which rooms are affected? Live, control, booth, all? Appreciate your sharing.

Wireline · Post by **Wireline** » Thu Apr 14, 2005 5:54 am

Boiler1 wrote:Interstingly, I'll be about 50 yards from the tracks, but I'm maybe 500 yards from a station at which virtually all trains must stop, so no body ever barrels through. Top speeeds are probaby 10-15 mph, albeit that can cause lots of low freq noise as the loco tries pushing the train. On the good side, there are no freight trains on this line; only commuter and amtrack passengers. 80% are electric, though deisels do come thru often enough. You may still be right to be pessimistic. What get you most? claks? whistes? How ofen are takes blown? How often can you move something in protools? Which rooms are affected? Live, control, booth, all? Appreciate your sharing.

Perhaps you are better off because of the slow moving trains...

We have no passenger service, just freight....long haul jobs with up to 5 locomotives...The clickity clacks are pretty well shut out of the studio, and the whistles are quiet enough (usually) to deal with...I have used some noise filtering in Samplitude (I guess PT has something similar) to reduce/eliminate the things that do manage to get through...

One thing that was very helpful was getting a grasp on train schedules...as they seem to run pretty much on time, I'll call a break or record strictly DI's instruments until its quiet again....had a few takes ruined early on, but hey...who hasn't?

The thing that really PISSES me off: When we purchased our property (home in front, dedicated studio buildings in back) the train speed limit was 25 through town...nary a peep outta them...then the City and Southern Pacific cut a deal to up the limit to 65...Since then, several businesses have had to relocate because of the noise and traffic congestion caused by a 1.5 mile train...and if memory serves, we've had over a dozen people killed and scores injured at poor crossings, non functioning warning gates and lights, etc...took the railroad a couple of years to get all those things fixed...

But back to topic: I am under the impression there is no acoustic problem that cannot be solved with money - its up to you to decide if the cost/benefit ratio is acceptable...We've done a lot of things to help reduce the problems, but only (AFAIK) tearing it all down and building the thing outta 3 ft cement with redundant airlocks and floating floors will completely solve the problem...

We are always on the look out for a new place to set up the studio...

knightfly · Post by **knightfly** » Thu Apr 14, 2005 5:57 am

Is the space you're looking at on a slab on grade, or an upper floor?

Can you make changes, and if so what's your budget?

Is there any other place available that's a couple miles further from the tracks, and NOT under an airport flight path?

The A scale is closer to human hearing, so better used for neighbor/cops measurements; the C scale is flatter, so more like what you'll get "on tape".

Your main concern should be LF TL; fix that, and everything else will disappear; hence my questions above.

Anything that doesn't contribute to the mix should be thrown away; i.e, there's no use for 40 hZ train rumble in an acoustic guitar or flute track, so if engaging a low cut filter will kill anything like that you should do it. If you have 24 tracks in a mix, and each track has 40 hZ rumble, and only two tracks have any USEFUL info down there, then all others should be cut. Otherwise, you'll make a CD about "rumble"

(Just my existential opinion based on experience)

One cheap and dirty way to find out how much of this will matter - make a recording in the room when a train's going by, making sure to ALSO check the sound level (C weighted this time) on your sound level meter - play it back in the room, adjust levels til the sound meter says the same - now, cut the level by 30 dB (when there's NO train running), and see if you can hear it or it's objectionable - if not, you can build inward enough to kill it. If it's still too loud, check your bank account, because the cost just went up a bit. If cutting the level by 40 dB STILL isn't quiet enough, find a different location... Steve

Boiler1 · Post by **Boiler1** » Thu Apr 14, 2005 9:38 pm

This is on a second floor. The trains are actually built way up on an embankment (higher than my ceiling) , which must be man made; this may be why they're not as loud as I would have thouhgt (that and the slow speed); I think they would be louder if coupled to ledge rock, but who knows?

The second floor construction is very solid (at least 24" thick cement supported by steel); can definitely handle the weight of a buildout. I can make changes as necessary, but need to remember I'll probably have to clean up my mess after the lease (so use-specific).

Bank account...not so sure. I have budgeted only $15K for a control room of roughly 24' x 16' (including the airlock we discussed); this cost assumes the building owner buys my materials (wood studes, gypbd and insulation) at cost and gives me his crew at $120/day for each man. I have not been intending to do a floating floor at first, but could add more $ if that's needed.

I like to track in the control room when working alone (80%) , so I'm starting with this room and a booth ( the airlock with all doors closed at first). The rest of the buildout could take a couple of years depending how the 3rd party biz ramps.

I continue to look at other spaces, but nothing is available right now. The rent is also cheap here, so it gives me a little more to work with in terms of an operating budget that makes breakeven (and profits) earlier.

I really like the recording idea; need to see how I can get in there for that.
I would think I could do the play back at home if I got the db back to recording volume. The point of cutting by 30 db is to simulate the buildout? I'm listening to see if I can hear the train at all? No filters engaged, right? If I hear the train having cut the overall leve by 40db, that indicates I wont be able to get the walls to cut enough? Am I understanding the goals of the test correctly?

Thanks

Boiler1 · Post by **Boiler1** » Sat Apr 16, 2005 7:05 am

I'm scheuled to do a quick recording on Monday. Just want to ensure I understand the proposed test. Any thoughts on my last post?

knightfly · Post by **knightfly** » Sat Apr 16, 2005 5:56 pm

Sorry, heavy schedule lately; yes, that's the idea; make sure when you record the train noise inside the room, that you make notes of the ACTUAL SPL (I would use C weighting, slow) - then, you should be able to play it back anywhere quiet thru full-range speakers, crank the volume until you get the same SPL, then drop the level by steps until you no longer hear the noise. However many dB you had to drop the level (from where it was during recording) is the LEAST amount of TL you would need to improve the space, and likely at very low frequencies, before it would be inaudible.

You can verify the frequency range that's causing the most problem with spectral analysis if your software allows - otherwise, it's fairly safe to assume it's in the 30-50 hZ range in most cases for trains.

Keep in mind that, at about 50 hZ, the human ear's threshold of hearing is around 50-55 dBA - so if your meter shows less than that (and you can't hear it) it's a good thing... Steve

Boiler1 · Post by **Boiler1** » Thu Apr 21, 2005 12:28 am

Well, I think I'm in luck, but want to check my methodology with you to make sure. I did recordings in the space (Neuman TLM 193 and an ADAT). Recorded acoustic guitar to use as my reference volume; I was averaging 75db on the RS meter using C weighting and slow.

Came home. Recorded the ADAT track onto Protools. Cranked the Protools track through NS-10s to get back to 75 db. Master volume fader on Pro-tools was at zero db. To get the 30 db reduction, I reduced the master fader by 30db. Couldn't hear anything.

To double check, I recorded the ProTools track to a CD. Took that to a room with surround sound (to check with a subwoofer). Again cranked the volume so the guitar track was at 75 db on the meter. The surround amp showed -12db. From there, I reduced the volume on the amp to -42 db. Again the sound was gone, even with the sub cranked above flat.

So, assuming I can build a wall system that will elimate at least 30 db, I should be home free. Any errors you see in the above methodology?

The tricky thing is can you really trust the db on a surround amp and on the front panel of a Digi 002 to be real db (or at least close)? Is reducing by 30 db the same when you start at zero db as it is when you start at neg12 db?

knightfly · Post by **knightfly** » Thu Apr 21, 2005 3:38 am

I don't see any glaring holes in your methods;

The tricky thing is can you really trust the db on a surround amp and on the front panel of a Digi 002 to be real db (or at least close)? Is reducing by 30 db the same when you start at zero db as it is when you start at neg12 db?

Probably not exact, but close enough; thing is, construction/design isn't any MORE accurate, so if you "overkill" by several dB (shoot for 40 dB @ 60 hZ, for example) then you will be MUCH more likely to succeed... Steve

Boiler1 · Post by **Boiler1** » Thu Apr 21, 2005 11:52 am

Sorry: I may have sent you a private reply; had clicked on the link in a notification email. Meant to reply here.....

Just had a thought (dangerous)...

I plan to build a room within a room for my control room. The exterior wall is an existing cement block wall up to, say, 4 ft, at which point a large set of old, single pane windows begins; they run up to 9 ft, and then the block runs to the ceiling. The windows will soon be replaced with double pane windows. My plan is to let the landlord upgrade the windows, then cover them with at least two layers of 5/8" gypsum on 2x4 studs (I was thinking of building slightly in front of the wall to create a gap, and then fiill the gap with fibregalss insulation). Technically, that gives me three leaves: the glass and block wall, the covering wall, and the wall I would build facing the inside of the control room.

Is therre a better way to seal up the windows to make the covering wall and the glass and block wall function more like one leaf?

Also, if I build the way I was planning, I would have the following (going from control room toward exterior): gysum, studs, 1ft airgap (filled), gysum again, studs, smaller airgap, then window/cement block exterior wall. In other words, for each leaf, the studs would be on the same side (the outside) of the gypsum. I know you prefer to have gyp, stud, air, stud, gyp. Should I worry about this? Perhpaps I could put the board right up against the windows and block, and put the studs inside, but it would seem much easier to build if I put the studs up first and applied gypsum on the inside. Hopefully, you can follow that.

What would you recommend?

knightfly · Post by **knightfly** » Fri Apr 22, 2005 2:49 am

What would you recommend?

A sketch or two; I'm even shorter on available "net time" than usual, and sketches bypass most of the "interpretation" involved trying to understand constructions based on verbal descriptions... Steve

Boiler1 · Post by **Boiler1** » Fri Apr 22, 2005 9:06 am

I'll try to attach something.