[Beowulf] [OT] acoustic engineers around?

Prentice Bisbal prentice.bisbal at rutgers.edu
Tue Mar 22 11:58:34 PDT 2016

I was on vacation (stay-cation, actually) last week, so I'm just seeing 
this now. I was really into all of this acoustic magic when I was in HS 
and college, and even took "The Physics of Sound" as a tech. elective in 
engineering school. And a few years ago, I started playing bass, which 
renewed my interest in this sort of thing. Those are my credentials, 
which hardly make me an expert, but here is my two cents:

1. Raising your subwoofer off the floor by way of an elastomeric 
suspension should help reduce the couple with the floor, but it will 
also reduce the base response. Most subwoofer are designed to go on the 
floor, which means they were probably designed with floor coupling 
taking into consideration. When I put one of my bass amps up on an amp 
stand, A lot of the bottom end disappears. You probably want to use a 
product specifically for decoupling speakers from floors like these:

Auralex SubDude:   http://www.auralex.com/product/subdude-ht/
Auralex Gramma:  http://www.auralex.com/product/gramma/

These two products are from the same company, but I'm sure there are 
plenty of others out there.

In the book "Stuff! Good Bass Players Should Know" by Glenn Letsch 
the author claims that Sorbothane is great for isolating tube (valve if 
your British) amps from the bass amps they are resting on, you might 
want to investigate that for isolating your subwoofer, too:


2. It's important to differentiate between materials that prevent 
acoustic reflections, and those that absorb acoustic energy. They're not 
always the same. Not every material that reduces reflections will 
necessary stop transmission. Acoustic ceiling tiles absorb reflections, 
but I don't think they do much to stop transmission through them, 
especially of the lower frequencies.

For absorbing bass frequencies, and preventing reflections,  it seems 
that the best material out there (certainly on a cost basis) is mineral 
wool (aka rock wool) . After years of being absent from the US 
marketplace, rock wool is making a comeback, and Roxul sells a version 
called Safe 'n' Sound that is very dense specifically for fireproofing 
and soundproofing. Not sure if it or something similar is available in 
your part of the world, but I'm glad it's available here. I'm going to 
use it in renovations I'm making to my house so I can play my bass at 
all hours without disturbing my neighbors.

I've been doing a lot of research on rock wool recently, and it 
apparently has been the go-to material for soundproofing music studios 
for years, even when it wasn't available to the general public here in 
the states.


If you google 'rock wool' or 'mineral wool' and "bass trap"s, you should 
find a lot of interesting 'how-tos' It seems the best solution is to put 
triangular bass traps in the corners.

If you want to absorb bass in certain directions, you can also use rock 
wool and some standard lumber to create 'gobos' to block the sound from 
going in certain areas:



I've read some how-tos on this, and the authors who used Safe 'n' Sound 
claim it makes a significant differences across the entire audio spectrum.

You could also by rock wool boards (denser, harder rock wool), put 
acoustically transparent fabric over them, and just hang them on your 
walls, so they look like wall decorations, but I think the board form is 
much more expensive and harder to come by, at least here in the states 
it is.


I hope that information gives you a start.

If you plan on doing renovations, you might want to look at Homosote, 
which would attach to the studs before you attach the drywall, but I'm 
sure that's beyond your current scope.


You could also put dense vinyl  sheeting up against the studs before the 
drywall, but ,again, that's probably beyond your current scope.


On 03/14/2016 02:36 PM, C Bergström wrote:
> This is the smartest list I subscribe to - I'm not sure if anyone has
> the knowledge/time, but I'm trying to solve a general problem.
> ------------
> Moving condos and new location is *very* noise sensitive. I feel
> fairly confident I can spam absorbent material as needed to reduce the
> db from high frequency sound going out the door, but bass is going to
> be more of a challenge.
> My crazy ideas
> #1 Raise the subs 1-1.5 meter off the ground and decouple them from the floor
> #2 Put some highly dense material directly under the subs.
> #3 low pass filter so only dealing with 80Hz and not even more
> problematic lower frequencies
> I'm a little fuzzy on the details of if subwoofers typically produce a
> directional sound and or if it depends on the box.
> "bass traps" appear to be more marketing hype than actually
> functionally useful for my case.
> (lowering the volume to the subs and adding "buttkickers" is an
> option, but that's more for fun and less about sound quality/general
> problem)
> ----------
> My walls are at least 150mm thick concrete fwiw.
> Thanks
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