if same cost, would you choose mineral wool or 703?

[LSP]

I was just about to order from SPI, 2 boxes of 2" 8 lb. mineral wool, when I found a supplier reasonably close by, who has an equivalent to 703. He states that it comes in 4x8 sheets, 2" thick, faced, and is 3 lb. density.

All of my research has led me to the conclusion that both will absorb low end equally well, which is why I'm purchasing them, for bass traps.

So here's my dilemma; the 2 boxes of mineral wool will cost me $120.28 shipped to my door. To achieve the same amount of rigid fiberglass, I would need to purchase 3 of the 8x10 sheets from the supplier, which would also cost 120 bucks.

Now bear in mind that the 703 equivalent is faced, which means that for my bass traps, after cutting them up into 12 2x4 pieces, I will have to peel off (if that's even possible) the facing of 6 of them (since I only need facing on one side, for 4" traps). I was already prepared to add probably some 3 or 4 mil plastic sheathing over the mineral wool, which is probably less than a pain in the ass than removing frk. I will also have to drive around an hour or so, round trip to pick up the fiberglass.

So, given the same cost,(minus the drive time and gas of course) would you guys go for the fiberglass, or the mineral wool?

Thanks for your opinions

[SAC]

As you have constrained the problem, there are negligible differences. So what else could make a difference?

Some have issues with one material over another. Personally, if reasonable best practices and due diligence is utilized, I think the issue is moot. But then, if one is honest, much of what masquerades as acoustics is actually an issue more accurately treated by a psychologist rather than an acoustician.

Dependent upon the particular application, you may need to remove or apply a facing as appropriate. Perhaps you have an affinity or avoidance for one of the operations. For me its 6 of one, 1/2 dozen of the other.

Maybe you will find it worthwhile to establish a relationship with a supplier. Maybe you will never speak with them again. Again, issues beyond the scope of simple material advantages. Only you can answer that.

Shipping of a product long distances may result in additional dust being generated if semi-rigid panels encounter rough handling and crushing (dependent in large part upon packaging). That may or may not be a real issue. But at least with local pickup you can evaluate exactly what you are getting prior to taking possession. Personally, I tend to find that preferable as it moves one more variable under your control. As you have defined the question, this is the only substantial issue that I can see that necessarily exists here.

But, other than factors that only you can answer, you have now reduced the material choice itself to effectively choosing between colors or flavors of ice cream.

Perhaps, contingent upon the additional associated variables, you can just pick one.

[DanDan]

From bobgolds.com

RXL 80 2" (51mm) 8.0 pcf (128 kg/m3)
0.43 0.78 0.90 0.97 0.97 1.00 0.90
703, plain 2" (51mm) on wall 3.0 pcf (48 kg/m3)
0.17 0.86 1.14 1.07 1.02 0.98 1.00

It seems that the 8pcf should do a better job at LF.
It should also be stiffer, possibly enough to not need framing.

Take a look at that site. Products of similar density from different manufacturers can have quite varied absorption figures.
I would try to get names and specs on your 'Mineral Wool' and the '703 equivalent'

DD

[LSP]

Both you and SAC bring up some valid points I hadn't considered.

Since my time is so limited, the removal of the frk (with it's seemingly huge pain in the ass factor) has lead me to another possibility. I could pick up enough of the 703 equivalent to use for the first 2", and then order some of the cheaper 8 lb. mineral wool for the second layer.

I can't see anything wrong with combining the two materials, but that is definitely not my area of expertise. Is there anything wrong with that plan?

Also, in regards to the validity of the "generic" 703. Does't it make sense that as long as I can see in writing that the rigid fiberglass is 3lb. density, wouldn't that indeed be the same as the 703, or are there other variables I'm not aware of?

Thanks again guys

[DanDan]

I can only repeat my recommendation that you get hold of actual absorption figures. They are more informative than a simple density figure.
Bob Golds site has many common products.
Removing the foil is not difficult IMHO.
I am not sure what would happen in that FRK/Fibre/Wool sandwich.
I could guess that it would be fine. However that's a lot of crazy impedance changes. That in close combination with the damped membrane/FRK.
I don't think we really know how that membrane idea works.
I would play safe. See how 703 FRK does here.
Acoustics Forum • View topic - Corner Absorption Comparision test
DD

[PaulP]

I believe the 8 pcf is slightly better by itself, ie in thin quantities, but if you're
going to be using more than one thickness together then a lighter density
would be better.

Apparently reflections occur at the boundary between two layers of different
densities so you don't want to mix and match.

Also Toole recommends (as do several members here) that absorption panels
for early reflections be at least 4" thick so that all frequencies are absorbed
and not just the upper frequencies which could unbalance the room's response.

Paul P

[LSP]

Originally Posted by DanDan

I can only repeat my recommendation that you get hold of actual absorption figures. They are more informative than a simple density figure.
Bob Golds site has many common products.
Removing the foil is not difficult IMHO.
I am not sure what would happen in that FRK/Fibre/Wool sandwich.
I could guess that it would be fine. However that's a lot of crazy impedance changes. That in close combination with the damped membrane/FRK.
I don't think we really know how that membrane idea works.
I would play safe. See how 703 FRK does here.
Acoustics Forum • View topic - Corner Absorption Comparision test
DD

Interesting graph. Having never viewed such graphs; are the higher numeric curves representing the total amount of absorption, or the actual frequency in db's that are present with the bass trap in place? In other words, are the Lenrds performing better, or the corner absorbers?

Also, the main reason, in my case, for wanting the frk fronts, is because my small room is already to dead, and I'd like to reflect the higher frequencies, and after much research on here, it seems that most agree this is the most effective method. In addition, many of the "experts" are saying that frk on the front facing the room actually improves the low end absorption as well.

So, as usual, I believe I'm in another one my paralysis of analysis modes! lol

[LSP]

Originally Posted by PaulP

I believe the 8 pcf is slightly better by itself, ie in thin quantities, but if you're
going to be using more than one thickness together then a lighter density
would be better.

Apparently reflections occur at the boundary between two layers of different
densities so you don't want to mix and match.

Also Toole recommends (as do several members here) that absorption panels
for early reflections be at least 4" thick so that all frequencies are absorbed
and not just the upper frequencies which could unbalance the room's response.

Paul P

Agreed,.. no mixing an matching, just to be safe.

When you state "in thin layers", what exactly do you mean. I'm going to be constructing some 4" thick bass traps, that will straddle the corners. From my research, it seems that I should also place a reflective material over the front panel as well, particularly since my room is already too dead.

[DanDan]

Those graphs are indications of performing power. You will need to look up Sabins etc. if you really want to know. However it may suffice to say that bigger numbers mean more absorption. Note well though, the corner absorber is much much smaller than the other two. It is 24 inchs wide, the other two are 34 inches wide. The bigger two are in fact enormous. If you extrapolate a little it seems like the corner absorber may well be outperforming the others. It certainly does this in terms of bang per buck. The 703 involved has FRK on the front, and this greatly increases the LF absorption.
DD

[LSP]

Originally Posted by DanDan

Those graphs are indications of performing power. You will need to look up Sabins etc. if you really want to know. However it may suffice to say that bigger numbers mean more absorption. Note well though, the corner absorber is much much smaller than the other two. It is 24 inchs wide, the other two are 34 inches wide. The bigger two are in fact enormous. If you extrapolate a little it seems like the corner absorber may well be outperforming the others. It certainly does this in terms of bang per buck. The 703 involved has FRK on the front, and this greatly increases the LF absorption.
DD

Thanks.

[SAC]

No need to be a victim of analysis paralysis!

The NRC values are simply very (overly) simplistic guidelines that ignore a greet many other aspects of a materials absorbent behavior.

They are useful simply as a very quick and dirty comparative guide to materials.

But one should also be aware that what they omit in the form of practical information actually overshadows what they do provide.

Just to run off on a very small aspect as an example... Regardless of densities, the density rating (and the NRC value) does not necessarily provide a 1:1 indication of porosity or gas flow resistance. One material with identical density ratings might be comprised of large fibers spaced further apart as opposed to many smaller fibers more evenly spaced - or for that matter, those small fibers could be rather randomly arranged so that there are local areas of higher concentrations of fibers and local regions that are more sparsely populated, but which over a much larger averaged area provide similar densities! In other words, the gross mass and density ratings do not account for the local distribution of the mass within the localized area. The fact is, you don't know from the information provided!

Likewise, the degree to which not only the surface of the material becomes reflective at various source incident angles as well as the similar effect of ANY covering (especially closely woven cloth!) will render the surface reflective to a great deal of energy as the angle of incidence decreases (0<angle<90). And none of the basic data (NRC, etc) provides insight into this fundamental issue.

So don't sweat the small stuff. Density is fine to use, as are the NRC values. But use them as a general guideline and realize that MANY other significant variables are at play.

And if you want to address them, a few very practical tools (most notably the ETC response) are available that will provide you with quick real time feedback regarding the practical effects of the variable as you apply the various treatments - allowing you to modify or use adjunct treatment as necessary. This measurement will provide a quick measurement of the 'amount' of energy being reflected from a panel and/or surface and also provide additional information regarding the nature of the absorbed and reflected sound power spectrum. Thus providing you with a 'status check' of the energy remaining allowing you to determine both of said energy needs to be addressed, and if so, providing you with sufficient information to determine the optimal method for mitigating the circumstance with respect to the total room acoustical response model.

There is a reason that the advances in acoustical measurements have not only dramatically driven the discipline forward over the past 40 years but assumed a preeminent role in acoustic analysis and design. They quickly provide quantized snapshots of extremely complex multi-variant behavior that is easily reduced to simple behavior that can be modified with only a basic understanding of many of the component variables.

Oh, and by adding a scrim to the front of a porous material and effectively altering its acoustical impedance is an exceptionally simple concept. Now, calculating the effect is not so simple as the model is complex and requires the quantization of many factors that are quite simply, a pain to do! And unnecessary as we can simply measure it and see the real behavior (as opposed to simplified/idealized calculated prediction).

So, bottom-line, pick one that has reasonable NRC figures and relax.

If you want to delve further into the mysterious world of what is really happening at a level heretofore unavailable, I heartily encourage you to do so! The price of entry is minimal and the learning curve is NOT as complex as many who do not do it will tell you!

[PaulP]

Originally Posted by LSP

When you state "in thin layers", what exactly do you mean. I'm going to be constructing some 4" thick bass traps, that will straddle the corners.

In general the thicker the absorber the lighter insulation you should use.
So 8pcf is good if your absorber is 1" thick and 3pcf or less is good if it's
8" thick or more. Thin absorbers benefit from having an air gap between
them and the wall or ceiling. The result is that you can have a high density
thin panel spaced from the wall and it will be similar to a lighter thicker
panel placed closer to the wall.

The more dense insulation is the more expensive it is, because there's
more of it. It's up to you to figure out which path you want to follow.

Paul P

[DanDan]

There is a general understanding that say over 4 inches is tending towards thick. 8pcf Mineral or 6pcf Glass works well at these depths.
As the thickness increases, it becomes more important to adjust, use less dense material. Andre frequently recommends Roxul Safe n Sound, 2.5pcf if I remember correctly.
As PaulP said thin dense panels benefit from an airgap. Thick less dense traps also benefit from an airgap.
DD

[IxtabStudios]

With only 4" of rock wool you can't really absorb under 860Hz...

[DanDan]

From Bob Gold's site here are the absorption coefficients of 705 FRK, four inches thick, mounted directly on the wall, no airgap.
There is very considerable absorption below 860Hz.
This can be increased greatly by mounting with an airgap.

125 250 500 1K 2K 4K
0.65 0.52 0.42 0.36 0.49 0.31

DD

[Glenn Kuras]

From all the lab testing I have done my rule of thumb is up to 6" use 8 pound. For thicker then that then you can start to decrease the density. In fact even at 6" you can, but better safe then sorry.

[avare]

Originally Posted by Glenn Kuras

From all the lab testing I have done my rule of thumb is up to 6" use 8 pound.

I am not asking you to divulge propietary data. Inspection of data from OC shows 4" of 703 has greater absorption than 705 at 125 Hz. I have never seen test data showing better low end absorption at 4" by glass materials used in a pure porous absorber application denser than 703. For that matter lighter either.

Of course Ethan's famous corner tests will come to mind. It a a while to figure what was probably occuring. The 705 panel was dense enough and at a sufficient distance from the apex to also act in a diaphramatic mode also.

Clarification is appreciated.

Andre

[Glenn Kuras]

Originally Posted by avare

I am not asking you to divulge propietary data. Inspection of data from OC shows 4" of 703 has greater absorption than 705 at 125 Hz. I have never seen test data showing better low end absorption at 4" by glass materials used in a pure porous absorber application denser than 703. For that matter lighter either.

Of course Ethan's famous corner tests will come to mind. It a a while to figure what was probably occuring. The 705 panel was dense enough and at a sufficient distance from the apex to also act in a diaphramatic mode also.

Clarification is appreciated.

Andre

I am going off our data compared to others that have tested with 3 pound and 6 pound.

[avare]

Originally Posted by Glenn Kuras

I am going off our data compared to others that have tested with 3 pound and 6 pound.

Thanks.

Andre

[DanDan]

Looking over the density/absorption figures at bobgolds.com I note a peak in LF efficiency amongst some of the Rock products at 3-4 pcf also.

Not exactly on topic but since we are all here, I thought this might be of interest.
There is a test which shows that 705 with FRK facing away from the backing surface has better LF performance than facing in. Also of course it also bounces out some HF. However, I note that in both cases this is a 4 inch panel with a 4 inch airgap. So.... the in the upper facing case, the membrane is 8 inches from the backing surface. Perhaps this alone is the reason for the improved LF.
This is why I see little or no reason to remove FRK from RFZ or Cloud panels.
With any sort of airgap I reckon the membrane is useful at the back, to give a little modal control.
I am of course open to other understandings of what may be actually happening in any of these situations.
DD

[Glenn Kuras]

Originally Posted by DanDan

Looking over the density/absorption figures at bobgolds.com I note a peak in LF efficiency amongst some of the Rock products at 3-4 pcf also.

Not exactly on topic but since we are all here, I thought this might be of interest.
There is a test which shows that 705 with FRK facing away from the backing surface has better LF performance than facing in. Also of course it also bounces out some HF. However, I note that in both cases this is a 4 inch panel with a 4 inch airgap. So.... the in the upper facing case, the membrane is 8 inches from the backing surface. Perhaps this alone is the reason for the improved LF.
This is why I see little or no reason to remove FRK from RFZ or Cloud panels.
With any sort of airgap I reckon the membrane is useful at the back, to give a little modal control.
I am of course open to other understandings of what may be actually happening in any of these situations.
DD

You know you keep barking about this () and I have concluded I am flying to Chicago where you and I will test it in the lab. lol lol lol. Hell if nothing else we can hang out in the city!

[DanDan]

OK, Chicago here I come.
I do seem to focus on some curiosities. However to some effect I believe.
That single/dual speaker drive thing for instance.
I may be reinventing wheels but some things do get clarified or verified.
It would be brilliant to see Lab tests of this. The current advice consensus seem to be to remove FRK from the back of panels. Why? Only bass can hit it back there, usefully I would have thought. If it is useful in front a couple of inches seems unlikely to matter to LF.
My own test seemed to indicate an added LF absortpion with the back FRK on, if you look carefully at some frequency areas, However if I was honest, it is pretty inconclusive. Luckily I don't suffer from honesty .
I would love to see at test of FRK bonded to the front of a Superchunk. Also Space Couplers in front of a SuperChunk.
Ruff Ruff.....

DD