First runs

There is good news right off the bat. Even with no bottom support, 2 inch foam is a good deal quieter than 1 inch. I first tested with loose track, checking to see if the track position had any effect on the sound. I found that after I got to be within 5" of the edge, the readings fell off slightly, losing 3 dB right at the edge. I'm not sure if that is because there is a benefit to supporting the track directly or because the mic was half looking at the floor. Here are my first tests, with caulk still a bit wet.

The rightmost track is caulked directly to the foam. Track caulked to 1 inch gave a whopping 74 dB with no bottom treatment. Track directly on 2 inch foam is 68 dB, a very significant 6 dB improvement. The track is floating on the caulk rather than pushed down hard, but I discovered as I disassembled my earlier caulking job that there was always a thin layer of caulk between ties and foam.

Track 2 (counting from right in this view) is a no-name roadbed made of ground cork and rubber. It is caulked to the foam and the track is caulked above. Performance is no better than directly caulked track, 68 dB.

Track 3 (second from left) adds a layer of dense material to the sandwich, under the roadbed. This is pastelboard, which consists of 1/8" high density fiberboard with a layer of clay baked onto the top. (It is perfect for modeling concrete.) It cuts the level some, but not enough to be worth the effort (this stuff is hard to cut.) 66 dB.

The last track is roadbed on camper tape. This is a soft foam (memory foam?) with adhesive on one side. This is the best reading of the set at 63 dB. Since that is the lowest value I've seen on anything other than Sonex I suspect camper tape completely isolates the track from the foam.

Tomorrow I will chase down some other roadbed materials and try a few more combinations.

pqe

"Gold Standard" test?

Dear PQ,

Did you ever do the "flextrack placed (not glued) straight on top of a thick bath-towel" gold standard test a la the Kalmbach "Trackwork special" booklet?

Happy Modelling,
Aim to Improve,
Prof Klyzlr

Gold Standard

Prof- Yes, I did, but with 4" Sonex.

edit on 10/18 for those without the prof's audio experience.

Sonex is an acoustic wall treatment that absorbs better than 80% of the sound that lands on it. By laying track on it I could measure the direct sound of the loco, which turned out to be 58dB SPL at 6". If I put the loco on a reflective but non-resonant surface the reading goes up to 63dB SPL. That is the baseline to these tests- If the reading from a loco on roadbed on foam gets down to 63 dB, my job is done.

pqe

Plans to add ballast?

PQE - great stuff - please keep at it.  I'll relate my experience in this noisy arena.

I built freemo modules - and light is the ultimate goal as modules need to travel - so 2" foam is common.  I did not like the drum aspects of foam that you are investigating as I set up my modules downstairs to run switching when not at a meet.  So after much research, I settled on building hollow/spaced spline roadbed using pine ripped to 1/8" * 3/4.  Two center splines followed by spacers and a single outside spline on each side (glued with yellow wood glue).  To further deaden noise I glued (with DAP clear) 1/8 * 3/4 splines cut from soundboard (similar to homasote) to the outside wood splines.  This was followed this with 1/2 soundboard roadbed over the entire spline subroadbed (also glued with DAP clear).  I painted the whole sandwich with latex house paint to avoid swelling - shrinkage issues related to changing ambient humidity as the modules travel to different environs.  The modules are 5.5 feet long - side frames are wood truss construction and center supports are similar at about 16" spacing.

I then laid flextrack (fastened with a small band of DAP - clear) and handbuilt Fasttracks turnouts (spiked).  This resulted in a very very quiet set up with noise limited to engine motor and wheel sounds only.  Great!

I then filled the landscape/scenery spaces around the subroadbed with 2" foam ensuring that I had at least 3/32" DAP between the foam and the subroadbed. Still quiet.

I then ballasted and it all went to crap.  Ballast is sifted (to scale) crushed basalt spread among rail ties and outside to form realistic roadbed contours, wetted with wet water followed by 50:50 white glue/water mix. In some areas the ballast did intrude onto the scenery foam.

My conclusion is as mentioned in a post before in your Foam I post  - the ballasting directly connects the rails, where the sound originates, to the surrounding scenery material - and it doesn't matter what the subroadbed is  - the hard connection established between the glue and rails via the ballast negates any deadening effort under the tracks - and the mass of the track is not sufficient at scale to deaden vibrations from engines and wheels.  I did not lose all quieting efforts - the setup is still quieter than track on foam - but it was somewhat disappointing when I ran trains after ballasting.

Please don't stop your tests at the rails/subroadbed only - find the quietest combination - then continue testing as you add ballast.  Thanks.

Frank

Thanks Frank,

I'm away from home and don't have access to my scenery

materials including what finely ground foam I have on hand; I'm wondering if anyone has ever tried using this as a substitute for or additive to kitty litter/sand/finely ground rock as ballast?  If so I'm curious to known what the outcome was and whether anything was needed to improve its appearance.  Seems to me it would have to be more sound-absorbant than what's commonly used for ballast (with an appropriately flexible glue to hold it down).

Soft options

My first trials on this rig demonstrated the value of isolating the track from the foam foundation with a layer of soft tape. After a trip to my (reasonably) LHS, I added soft foam to all tracks.

The treatments are as follows:

• Track 1 (right) One layer of Woodland Scenics Track-Bed, a soft foam.  66 dB SPL
• Track 2 Track-Bed on cork/ rubber composite 64 dB SPL
• Track 3 Cork on pastelboard on camper tape 62 dB SPL
• Track 4 cork on camper tape 64 dB SPL

From the previous test, I know cork alone is no better than track with no roadbed at all, 68 dB.

What this tells me is that the best option is at least two layers of roadbed, one dense and one resilient. An extra layer of high mass can give 2 dB beyond that. Whether 2 dB is worth the extra work of using pastelboard is up to the modeller, but 2 dB is below most people's notice. I think the 4 dB difference between cork alone, and cork on soft foam might be worth the work in sensitive situations.

For a bit of context, a BLM paragon diesel with sound on measures 78 dB at idle. With sound off, it does not measure above the noise floor of most rooms at reasonable speeds (48 dB on step 12). That was on WS track-bed, but at those levels, a dB here or there just doesn't matter. 

Notes:

Those who have been following closely may have noticed that cork on camper tape measured a bit higher today. As I mentioned the caulk was not finished curing, or maybe it is some other factor, but it's not significant. The Bachman loco has more variation than that, and might have been feeling a bit louder today than Friday. All that matters is relative values in the same set of tests.

These tests are not sensitive enough to evaluate differences between different brands of soft tape. I suspect almost any resilient tape will do, but keep a mind to long term stability. I have seen many soft foam products turn to an ugly sticky mess after a few years due to bacterial action. I trust the camper tape and the WS product (as well as the contractor's pipe insulation mentioned on this thread) but I'd stay away from the weatherstripping tapes at the hardware store.

After a break to catch up on other responsibilities, I'll tackle the ballast and glue problem. Please send your suggestions.

pqe

It would be interesting to see if the choice of adhesive has

any effect on the outcomes you see.  I recently tried using a Loctite Spray Adhesive to attach a length of ME flex track to a sheet of the WS Track-Bed for a portable DCC programming track and it seems to be holding quite nicely.  I used blue masking tape to catch the overspray which turned out to be less than I expected.  The nice part of this is that the adhesion is limited to the underside of the ties so they aren't embedded in much that might complicate things as much as the caulk appears to in the photo above.

The caulk is sloppy

" I do know that loose track is quieter than caulked track"

that seems kinda counter to the real thing where firm track is quieter than sloppy track? .......DaveB

Would be curious to know if it's loose vs. caulked or loose

vs. semi-rigid vs. bonded as tight as possible.  It strikes me that track vibrations that are swallowed up by the subroadbed (of whatever materials) are better than those that go on to resonate into the open air.

If price were no object to these trials, http://www.amazon.com/Acoustical-Rubber-Flooring-Underlayment-Padding/dp/B005TUI5CG/ref=pd_sim_sbs_hi_2

Loose track

"It's not very efficient at transferring energy"

So the loose track banging around on the foam might make more noise but transfer less? Is there some sweet point where tacking it down in spots is better than both fully loose or fully glued? ....DaveB

Probably, but it's not a solution

Loose track will most likely be tightened by ballast application. I had to take some time off to rebuild my workspace, but that's done now, so I'll return to these tests tomorrow.

pqe

Foam drummer

I'm looking for a way to test ballast effects without having to build and ballast yards and yards of track. I'm also not entirely comfortable with my test method of letting my 45 tonner accelerate from 0 to step 16 and hitting reverse before it crashes into the bumper. (I do this 10 to 20 times and take the median readings). So, I've been trying to build something with a bit more class. The ideal is something that applies sound to the track at a consistent level and does not move. That way I can build short test sections, which will lead to more tests at less cost. This is my first attempt:

That's a vibrator motor strapped to the chassis by the battery support. Its hard to see, but there is a cheap plastic truck glued to the underside to provide an appropriate force to the track. I can control the motor speed with the black trim pot. It sort of works, but there are two serious flaws: it is predominately one frequency (which changes with the pot setting) and there is a buzz between the truck and track sometimes. I need something that will transduce pink noise into the track. I've ordered a gadget which will arrive Monday. Once I figure out how to get wheels on it, I'll get back to testing.

pqe

Foam Drum II - Ballast/Dap/Sill plate

PQE

 Effect of ballasting on noise level

Interesting research you're doing, big effort.

I use DAP to glue 3/16 "sill plate" foam as subroad-bed onto 2" insulating foam glued to 3/8 plywood benchwork.

Then DAP (outdoor; door and window) again to glue flex-track to sillplate.

Then DAP diluted with 40 to 50% water for ballasting; flows nicely. Ballast remains flexible after curing.

I ballasted one section of track ( about 12 ") with diluted white glue in between DAP diluted track sections.Glued section is solid/rigid; DAPed sections are flexible to touch but looks solid. As train runs onto and then off white glued section of track there is clearly an audible difference - DAP is quieter.

Sill plate foam is a construction sealer used between concrete foundation wall and wood framing sillplate . Almost a minibubble-wrap in 4" wide rolls, several thicknesses available. Cuts with scissors or knife. Paintable but best if roughed up with coarse sandpaper first.

I also use diluted DAP for adding scenic material to layout. Thicker or thinner dilution depending on slope/location/need.

I need to find easy way to create diluted DAP - takes me longer to mix it up than to use it.

Gandydancer

Dear PQ, Sounds like a job

Dear PQ,

Sounds like a job for a basic noise gen
(free downloadable white-noise test files are available,
or most audio editors like Audacity can generate the required noise and even sweep-test files)

connected to a simple exciter, such as the Dayton DAEX25 from Parts-Express
http://www.parts-express.com/pe/showdetl.cfm?partnumber=300-375

or their smaller brother, the DAEX13
http://www.parts-express.com/pe/showdetl.cfm?partnumber=300-379

It can be as simple as wiring a 3.5mm minijack to the exciter, and running a (relatively light weight) cable to the PC soundcard. You already have the mic and analysis gear to "calibrate" the resulting "noise-inducer" for end-to-end testing...

Happy Modelling,
Aim to Improve,
Prof Klyzlr

PS I really would reccomend using the Audio Editor as the "test tone generator", as it would allow you to sweep thru the induced frequencies, and really nail down "what material is resonating at what frequency"...
(Have your Notch-Filter/Parametric-EQ at the ready... )

Hi Prof

Ballast

Bruce, you read my mind.

skip the WS Foam

Go to Home Depot and get a roll of Eco Foam underlay. It's the same kind of foam as the WS roadbed but thicker and cheaper. You'll have enough to cover your entire layout for $50 Rick.

I'm still wondering if there are shades of ground foam available

that would be suitable for use as ballast.  Some of the WS and AMSI finely ground foams don't look that bad from a textural standpoint (to my eyes anyway but then with age...) but color choice is less than would be desired.  Scenic Express carries a lot of stuff, including rubber ballast for larger scales (I've emailed them to find out if they have anything for S scale and below) which they claim reduces noise.

Foam Drummer Mk II

Parts arrived and I put together a new test rig:

This one is electronically powered with a direct transducer-- that's a speaker without a cone. You just stick it on a flat surface to vibrate anything at audio rates. It's riding on a basswood foundation with three solidly mounted wheels. Three, because I discovered with the Mark I that it's hard to get four wheels to touch trak solidly without buzzing, unless the wheels are sprung, which throws an extra variable into the mix. Here's the full system in action:

The device on the lower left is a signal generator that can produce noise or tones at various frequencies. The meter is visible to the right of the microphone.

This has many advantages over my previous test setup:

• My Bachman 45 tonner was a bit inconsistent in sound output
• This system lets me perform more tests, such as individual frequency measurements
• I can test short sections of track, saving materials and time
• My previous test method could be considered loco abuse

I've already run a set of tests on the four tracks shown, which I'll put in the next post.

pqe

Soft options revisited

I've run more tests on the track laid on foam in various combinations:

This time I used the mark II drummer, so I've acquired more data, and some puzzles. The SPL data for the tracks were

• Track 1 (right) WS Track-bed  69 dB SPL
• Track 2 Track-bed on cork  70 dB SPL
• Track 3 cork on heavy board on camper foam 64 dB SPL
• Track 4 cork on camper foam  68 dB SPL

Now, with the exception of track 3, these differences are pretty minor. The puzzle is how can the two layer sandwich of Woodland Scenic Track-bed on cork be noisier than Track-bed alone? The answer comes from looking at the spectrum of the noise coming off the foam. I'm using Pink noise as the signal, so I am putting all frequencies into the track at once. (This is quite different from what my 45 tonner does.) Here is the spectrum of track 1:

And here is track 2

The two layer sandwich passes less energy in the 1 khz to 8 khz range but more in the sub 100 hz range. These add up to nearly the same overall value, but they will sound different, especially from a distance. For quiet sounds, the ear is most sensitive in the 1 khz to 4 khz range. So track 3 sounds quieter, even though it can measure more energy. To complete the set, here are the spectra for track 3 and 4

Track 3 is much less energetic in the critical band, with very little showing from 500 hz to 2 khz, and less overall.

Track 4 is similar to track 2, with less energy overall but not so much dip in the critical range.

How doe this all relate to how things sound? For one thin, pink noise is not a good model of loco sounds, which are mostly low frequency.  If I want to sort this once an d for all, I'm going to have to find out what the actual spectrum of a loco is. Tomorrow.

pqe