Bag End E-Trap

[MidnightSensi]

The SPL meter may still say 100db. Might say more, might say less. Depends on where you are and if 50 happens to be a modal issue. The big thing is how LONG it reads higher.

If I play 50Hz at 100db and it takes 3 seconds to decay to 40db, that's a problem. Then, if I add some bass control and now it only takes 1 second to decay to 40db, that's much better (in a residential sized room) but still not good enough.

As for taking sabines and dividing by the area, that's how the measurements are made to go into a coefficient. That's why you can have a number bigger than 1.

For instance, the Monster is 7.5" thick and the sides are exposed. So, that's 8 sq ft each PLUS 7.5"x24"x2 PLUS 7.5"x48"x2. However, when the standard (and the labs) calculate, they only take into account the square footage of the face (8 sq ft) even though there is more than 50% more area exposed and absorbing sound. And, in reality, that's what it will really do in your room.

Sabines is actually a more accurate way to look at things as it looks at a relative difference between an empty room and a room with a proper sample size in it.

Not a perfect standard but at least everybody does it the same.

Bryan

As I was typing you were answering my questions!

Your point about the time makes sense, because, that's really the issue. The magnitude of sound can be reduced with EQ, whereas the ringing/time-smearing can't.

Are Sabins a measurement of meters or ft? Because if we want to make them into coefficients we need the same units....so Sabins must either be m^2 or ft^2....

The reason I ask is: I'm thinking if I want to get an idea of how many panels it would take to dampen my room, I could use the equation backwards and figure out how many Sabins of reduction I want at a given frequency and then use that to find the surface area I need of a specific panel....and therefore figure out how many I would need to buy and what products would make the most sense.

Real Traps says it is ft^2, but, everywhere else I see says m^2.

 

[bpape]

Actually, the triangles reduce overall effectiveness since the average thickness is less and the thinnest point is VERY thin compared to the 'specified' thickness. Look at 2" wedge foam some time - the thinnest portion will be well under 1/2". Very little of the area is actually even close to 2". Companies try to sell it as 'diffusion' but it's not. You can't absorb and diffuse from the same surface.

I should have been more clear on the surface area thing. It's the area of the sample. A 2'x4'x 2" wedge foam panel has the same area for the forumula as a 2'x4'x7.5" panel with no surface irregularities. There is also a specification to have a a minimum amount of square footage.

You can try to predict all you want but it won't always come out. For example, let's say that we put them all on the side walls with a space between them. That will be a different result than if we stacked them all side by side on the rear wall. It would be different in decay time (different amounts of edge exposed) and also in how it would potentially change frequency response since in one case you're dealing with early reflections and in the other you're more positioned to deal with length related bass issues.

Also, understand that no room is perfect. To make the formulas work perfectly, the room has to be perfectly square in all 3 dimension, there can be nothing in the room, and the room must be perfectly rigid. Change any of those and the formulas will get you close (sometimes) and miss other things completly.

Bryan

 

[MidnightSensi]

Actually, the triangles reduce overall effectiveness since the average thickness is less and the thinnest point is VERY thin compared to the 'specified' thickness. Look at 2" wedge foam some time - the thinnest portion will be well under 1/2". Very little of the area is actually even close to 2". Companies try to sell it as 'diffusion' but it's not. You can't absorb and diffuse from the same surface.

I should have been more clear on the surface area thing. It's the area of the sample. A 2'x4'x 2" wedge foam panel has the same area for the forumula as a 2'x4'x7.5" panel with no surface irregularities. There is also a specification to have a a minimum amount of square footage.

You can try to predict all you want but it won't always come out. For example, let's say that we put them all on the side walls with a space between them. That will be a different result than if we stacked them all side by side on the rear wall. It would be different in decay time (different amounts of edge exposed) and also in how it would potentially change frequency response since in one case you're dealing with early reflections and in the other you're more positioned to deal with length related bass issues.

Also, understand that no room is perfect. To make the formulas work perfectly, the room has to be perfectly square in all 3 dimension, there can be nothing in the room, and the room must be perfectly rigid. Change any of those and the formulas will get you close (sometimes) and miss other things completly.

Bryan

Well, If I don't use some kind of math, how can I predict if I need two panels or fifty? Or, ultimately, if ETraps are more effective or a traditional bass trap for my subbass? Or, on a wholistic level, how many of each different type of panel I would need for my room. A room made of stone and glass would be different than my carpet and draped room to treat... My room is semi-abnormal because it is reinforced concerete and has two Danley CS-30s powered by a Crest CD2000. The room is more of a pressure tube than a home theater... so I have to imagine I require more bass traps than a typical room.

When I get into the office tomorrow I'll post some updated pictures of my room, you mind taking a look and seeing where I would start?

 

[bpape]

No problem.

As for Sabines, it's kinda both

From Acoustic Engineering Journal:

****************************

1 square meter of 100 % absorbing material has an absorption of 1 square meter of open window. In honor of W.C. Sabine, the unit of absorption is also named sabin or metric sabin. However, these units are used not very often. One sabin is the absorption of one square foot of open window, and one metric sabin is the absorption of one square meter of open window.

****************************

As long as you keep your units consistent (Room volume and area of absorption both in either feet or meters) you're OK. Time is obviously constant for both.

As for how many you'll need, that's only a portion of the problem. It's also where it's needed. Again, if you put all the panels together, your ending decay will be different than if they're all spread out. You'll also need to figure everything in the room - carpet, people, surfaces, construction (walls absorb), air, glass, doors, furniture, etc. Then you'll know in theory what the room should be like. You can then easily test your starting point by actually measuring the room with something like Room EQ Wizard and see how the decay times balance in reality to what you calculated.

Bryan

 

[MidnightSensi]

The wide angle lense kind of skews things. The screen is 106" 16:9, for a reference. The rear seatback is 3 feet from the rear wall....you sit about 5ft from the rear wall with all the padding and so forth.

Areas I have thought about treatments:

-I want to convert the side of my rack so that it is an acoustic foam. Something like a GIK 242 or some other 2" thick panel that I could easily mount on that. It actually serves to balance the room, since that corner is open, so with some treatment that rack I think is in a good spot.

-Under the screen and behind the mains, I want to do some sort of bass traps that have a pretty wide band. I don't want to go overboard though, so just the basics. I was thinking maybe three, one centered under the screen (which would cover up those outlets, which is a bonus) and one behind either speaker to the left and right of the screen.

-In the left rear corner, behind that darker chair, I have a square area that basically goes unseen. This is where I could put a low bass trap and have it go unnoticed. The right rear corner has a closet door, so not much I can do there.

-Perhaps over the speaker brackets I could hang some and make them flush mount like rmk did.

Whatever I do, I want it to look clean. The less I see the panels the better. Although my room is obviously dedicated, I don't want to just toss a bunch of panels in there blindly. I want to start with just a few and work my way up so I can hear the differences it makes.

I was thinking of this:
Order two GIK tri-traps, they are 4ft tall and 2ft wide. Put one in that right rear corner and the other in the front left, by the rack.

Although I may look for a United States manufacturer, because between the exchange rate and shipping, a place in the UK might not be the place to buy stuff from.

 

[nibhaz]

Although I may look for a United States manufacturer, because between the exchange rate and shipping, a place in the UK might not be the place to buy stuff from.

Are you sure you are looking at the right website? GIK has a European website and US website.

 

[MidnightSensi]

Are you sure you are looking at the right website? GIK has a European website and US website.

Yeah, it looks like a set of Tri-Taps is 258USD, plus shipping...which makes it 281 to my address. That's not too bad. I might spring for a set just to try it...

I wonder if they have any Audioholics member deals or something. Especially ones with member galleries that take pictures often.

 

[MidnightSensi]

A nice Christmas surprise....

My friend that is redoing his studio dropped off a bunch of thick acoustic foam for me today. I'll snap pictures later, but, it basically looks about 8" thick, it has three different layers of 'stuff' .... He gave me a fair amount, so, I might put some black grill cloth I have here at the shop and do some DIY acoustic panels this weekend. Before I even bother I'm just going to set the foam in my listening room and try it out, see if it helps...

He also gave me some flat heavier stuff, that looks more like Dynamat (but its black and not dynamat). It's very heavy. Might be good for lining my rack.

 

[jostenmeat]

I would be skeptical of foam being able to effectively absorb 50hz, or other bass frequencies, unless it was some one-of-a-kind-super-duper foam.

I know, it's free, might as well try. But, you also seem to want to find the most streamlined looks in your attempts to tame the one problem frequency in your otherwise "flattest room you've ever had". With that in mind, I'd look for the most effective materials first of all.

Take the above with salt, what the hell do I know . . .

 

[bpape]

Agreed. The foam likely won't do it but hey, it's free.

Looking at the pics, I'd say that directly beside your speakers will also need treatment due to the close proximity to the side walls.

Bryan

 

[nibhaz]

A nice Christmas surprise....

My friend that is redoing his studio dropped off a bunch of thick acoustic foam for me today. I'll snap pictures later, but, it basically looks about 8" thick, it has three different layers of 'stuff' .... He gave me a fair amount, so, I might put some black grill cloth I have here at the shop and do some DIY acoustic panels this weekend. Before I even bother I'm just going to set the foam in my listening room and try it out, see if it helps...

He also gave me some flat heavier stuff, that looks more like Dynamat (but its black and not dynamat). It's very heavy. Might be good for lining my rack.

I’ll echo Jostenmeat and bpape, and postulate that the foam will be ineffective in the bass region.

If it is of sufficient quality, it should be suitable for HF absorption at the 1st reflection points, so you should definitely be able to get some use out of this free material. Since you have a dedicated room, with complete control, I would consider mounting some of this foam on the ceiling at the early reflection points if it doesn’t interfere with your PJ.


The black heavy stuff is most likely mass loaded vinyl (MLV). That might once have been part of a limp mass membrane, or was used in an effort to achieve better sound isolation. I’m not sure what use you may find for this material. How many sq/ft did you get, and what is the thickness?

What do you have in that closet in the back of the room? How deep is it? Do you need it for storage?

 

[Savant]

I’ll echo Jostenmeat and bpape, and postulate that the foam will be ineffective in the bass region.

Foam that's 8-inch thick will control low frequency problems. How much relative to fiberglass (FG) of the same thickness is the real issue. Foam of similar density to "703" or "705" FG would provide roughly the same performance at low frequencies, assuming equal thickness. But foam usually isn't available at such densities. Thus, typical acoustical foam will not perform quite as well at low frequencies as the same thickness of FG. If the 8-inch acoustical foam is sculpted (as opposed to solid), it will have an even lower relative performance at low frequencies than the same thickness of 703 or 705. As an example, 2-inch sculpted ("wedge") foam has about 60% of the absorption of 2-inch (solid) 703/705 at 125 Hz. (Source.)