Bass traps and diffusers

[RoadrunnerOZ]

OK, I guess .....but that sounds like 705 from the spec sheets I found/posted:

704: 4.2 pcf (67 kg/m3)
705: 6.0 pcf (96 kg/m3)
707: 7.0 pcf (112 kg/m3)

Bri

Yeah - you’re right - I meant the 705 (as I don’t know if the 707 is rigid)

 

[totoxraymond]

All my rockwool is wrapped in celofane/ plastic film so no fibres will get airborne and won’t smell.

You mean you got your rockwool airtight?

My understanding is that pourous absorbers need the pourous material to NOT be in an airtight container. That is why it is often said that you must be able to breath through the fabric you choose as cover.

But maybe i'm mistaken.

Thomas

 

[Brian Roth]

Yeah - you’re right - I meant the 705 (as I don’t know if the 707 is rigid)

The higher the number, the more rigid....and it's tough for me to even find anyone here in the USA who has anything in stock besides 703. shrug...

Bri

 

[RoadrunnerOZ]

All my rockwool is wrapped in celofane/ plastic film so no fibres will get airborne and won’t smell.

The only problem with cello-wrapping is it reduces the airflow and thus the damping effectiveness through the spun fibre by having a single skin - especially if it’s tight. The beauty of the board is that all the fibres are resin bonded and don’t shed but allow air passage which interacts with the fibres turning sound energy into heat (except for a little shedding at cut edges which is why I glue them). Unfortunately blanket collapses in a vertical setting, even when it’s wired in place or glued - even if compressed. Good for ceilings though as it lies flat. I’ve been designing and building studios since 1977 and have seen the results of time on acoustic materials - (also most cellophane will break down in 3 to 4 years - especially the newer biodegradable stuff). I had to do some alterations to a studio year before last and the original builder had used Rockwool blanket inside the walls - it had been wired and glued to one surface but due to constant vibration causing it to collapse, the top 1/4 of each wall chamber was empty.

 

[RoadrunnerOZ]

You mean you got your rockwool airtight?

My understanding is that pourous absorbers need the pourous material to NOT be in an airtight container. That is why it is often said that you must be able to breath through the fabric you choose as cover.

But maybe i'm mistaken.

Thomas

Skinning with something like plastic will kill the top and high mid absorption - as you go down in frequency it has less detrimental effect. It can also buzz if loose or tight. Proper broadband absorption relies on the material used being installed as supplied - minus the wrapper.

 

[RoadrunnerOZ]

The higher the number, the more rigid....and it's tough for me to even find anyone here in the USA who has anything in stock besides 703. shrug...

Bri

Ok - wasn’t sure from the spec sheet about that.
There’s probably other brands of compressed fibreglass board in the US. It’s easy to get here. I’ve noticed that if you go to the “acoustic specialist “ companies you pay an arm and a leg, but going direct to the manufacturers and looking for local suppliers which are just insulation material or building material suppliers the prices are pretty reasonable. We also have acoustic hangers for ceilings and spring/rubber floor joist posts for floating floors available at a lot of hardware outlets.
Most hotels, office buildings and apartments use these types of materials here. There’s even paint that can be used that doesn’t clog the fibre gaps for surface finishing and some brands come with pre-coloured or textured finish but they start to get up in price.

 

[Spencerleehorton]

Well Jesco said to wrap them in plastic bags and the very thin plastic film is much thinner and he said it would have little to no effect on LF.

 

[Spencerleehorton]

I got a question, would it be better to have all 12 panels at listening height?
For the corners I’m stacking two panels but everywhere else it would seem better to have them all at listening height?

 

[Spencerleehorton]

Also Jesco said to not go too dense with the fibre that’s why I’ve gone for 30kg m3 as he recommends on his course.

 

[Brian Roth]

Indeed the price goes through the roof for "high end" acoustic products. The clever acoustic designers from decades ago figured out stock Owens products....intended for mundane insulation applications...also had useful properties to do acoustical control. The earliest Owens spec sheets were all about thermal properties. Later data sheets began to mention acoustic control.

In those decades ago, acoustic designers weren't always worried about recording studio acoustics, they had huge enclosed concrete sports buildings that has a RT-60 of 245 years (G!) without some sort of absorption on the walls/ceilings. Fortunately they discovered available, off-the shelf "insulation" products to tame those LARGE building acoustics. Not fancy-dancy $1000 per square inch scams (containing special rare earth crystals!) and the like being sold to the audiophools these days!

Bri

 

[RoadrunnerOZ]

Well Jesco said to wrap them in plastic bags and the very thin plastic film is much thinner and he said it would have little to no effect on LF.

True on LF but as I mentioned above you lose the benefit of all the high absorption. Ok for bass traps but for room levelling and getting rid of standing waves at higher frequencies for drums or for control room monitoring you should really have the fibre open - behind breatheable cloth I’ve found the best option.

I got a question, would it be better to have all 12 panels at listening height?
For the corners I’m stacking two panels but everywhere else it would seem better to have them all at listening height?

If you have at least one opposing surface covered the other can be bare to stop standing waves, same with corners diagonally opposite - so you can stagger your panels - Lo,Hi,Lo, Hi left side Hi, Lo, Hi, Lo right side for example - same front rear - this is for the drum room.
The control room needs to be symmetrical L/R.
I’ve made floor traps by making a raised dais at the rear of the control room with the couch on it - the dais is ported at the front and rear, same each side, and has folded continuous chambers lined with compressed fibreglass - these chamber and fold lengths tuned to the problem frequencies in the room.

Also Jesco said to not go too dense with the fibre that’s why I’ve gone for 30kg m3 as he recommends on his course.

The higher the density the more absorption at LF - you can choose by the thickness of the used panel ie. if not enough absorption add another thickness of fibre board.
You don’t want to kill the room.
When I’m setting up a room after the in-wall isolation is done the surface treatment is done by force propping glass boards against the walls after a sweep analysis is done in the room and also looking at the room modes for that size of room to see where the boards should go, then doing another check - adding more boards or taking them away.
Handy calculator:
https://amcoustics.com/tools/amrocOnce determined then permanently mounting the boards.
For problem rooms I have built Helmholtz absorbers which are like your panels but have a facing board with ports drilled across the face, sealed back and sides - the size of each hole, depth of chamber and panel dimensions govern the absorption frequency. These are tuned for a specific frequency and are not broadband.
https://www.acoustic.ua/forms/calculator5.en.html

 

[RoadrunnerOZ]

Indeed the price goes through the roof for "high end" acoustic products. The clever acoustic designers from decades ago figured out stock Owens products....intended for mundane insulation applications...also had useful properties to do acoustical control. The earliest Owens spec sheets were all about thermal properties. Later data sheets began to mention acoustic control.

In those decades ago, acoustic designers weren't always worried about recording studio acoustics, they had huge enclosed concrete sports buildings that has a RT-60 of 245 years (G!) without some sort of absorption on the walls/ceilings. Fortunately they discovered available, off-the shelf "insulation" products to tame those LARGE building acoustics. Not fancy-dancy $1000 per square inch scams (containing special rare earth crystals!) and the like being sold to the audiophools these days!

Bri

When I started in the late ‘70s there was only low density Rockwool, fibreglass or wool insulation and also lead vinyl (now it’s barium). Wall cavities had the Rockwool bagged in felt or cotton if you were smart so the glass or rock fibres didn’t get into mics, speakers and audio sockets or people’s eyes and lungs. Then particle board and plasterboard with timber framing (no metal framing then) for walls and ceilings. Floating floors or drum booth floors were sometimes concrete slabs poured on polystyrene with spaced rubber blocks.
I saw so called “studios” with egg cartons on the walls (I wonder who ate all the eggs?)

 

[Spencerleehorton]

A friend has offered me 3 x 8x4’ Helmholtz panels which could work for the drum room?

 

[RoadrunnerOZ]

A friend has offered me 3 x 8x4’ Helmholtz panels which could work for the drum room?

Do you know what they’re tuned to? If not, use the calculator above if they’re slats or the one below if they’re round holes- but you need to know the internal depth and also hole diameter, hole panel thickness:
http://www.acousticmodelling.com/helmholtz.phpThe room modes calculator will help determine the problem frequencies in the room
This is for your room size - have a look at the 3D for each frequency to see the problem positions.
https://amcoustics.com/tools/amroc?l=300&w=300&h=220&r60=0.6

 

[RoadrunnerOZ]

This may be a better calculator to use for perforated panel absorber:
http://www.mh-audio.nl/Acoustics/HelmholzPanelResonator.html

 

[Spencerleehorton]

A friend has offered me 3 x 8x4’ Helmholtz panels which could work for the drum room?

This isn’t correct, I’ve checked and they are wide band absorbers with feet on them and they stand long ways!!

 

[JimJhn]

The drum room is more about your personal prefs. I like to make the ceiling non reflective so overhead mics don’t get reflections from ceiling. Wall treatment is totally subjective. Placement of the kit in the room is critical, too. I tend to put the stool near a wall or corner to get the most low-freq help from the boundaries. I also like space couplers in small drum rooms. I’ve been playing with making space DIY couplers With cut PVC pipes. The dimensions are not critical. I use 3” pipe and cut 3” lengths and glue them together and paint the whole thing.

Do you happen to have a photo of what your space couplers look like?

I have been thinking of building something for this purpose, and this sounds like a great idea.

There are so many different plans and approaches out there that it is dizzying.

Thanks!

 

[Spencerleehorton]

Space couplers?

 

[kags]

This isn’t correct, I’ve checked and they are wide band absorbers with feet on them and they stand long ways!!

Then they probably aren’t tuned Helmholtz absorber, whic, by sedition, are not broadband.

 

[kags]

Also Jesco said to not go too dense with the fibre that’s why I’ve gone for 30kg m3 as he recommends on his course.

True. At some point dense insulation becomes reflective for LF. You light Roxul is good to 8” or a bit more, but after that, batts are more useful.