6" 705 frk vs 6" 703 frk which is better???

[Weasel9992]

Originally Posted by avare

Succinctly,
Andre

Nice.

Frank

[Ethan Winer]

Originally Posted by Glenn Kuras

So if you test the 2 in your factory and there is no difference at a certain frequency in the test graph from nothing in the room then we can conclude nether did anything?

That's a great point, but it's explained clearly in my Alternative Test Methods article. Testing in a small room can assess absorption at only that room's mode frequencies. But the same is true for a lab test when you measure below the lab's certified range. The main difference is that in a small room with ETF or REW, you can see where the modes are. In a lab test it's all mushed together and third-octave averaged. So there's actually more guessing needed to interpret lab tests. Again, I'm talking only about very low frequencies, below where the lab is certified.

Explaining this to professional acousticians is the entire reason I wrote that article! Obviously Sound & Vibration magazine agreed because they published it.

Or if it only helped by 2 db, at a certain frequency, then that is what you will get in EVERY room? I have seen 8 traps help in one room 15 db and in another room (different size) 5 db at the same frequency.

Well, that's a totally different issue. Lab tests won't tell you how many dB peaks and nulls will be improved either for a given room. The point of these tests - indeed any such tests - is to assess only absorption versus frequency. How much a given room is improved depends on placement and other factors. But if 705 tests better than 703 at 60 Hz in one small room, it will be better at that frequency in all other rooms too. That's the real point.

--Ethan

[Glenn Kuras]

I can agree with all your points, but I still think there has to be a better way to test commercial products to give advice to customers. It is kind of hard to say with a straight face to someone that spent thousands of dollars on products by just showing them a "home test".
I think we are all on the same page though.

[ejsongs]

hey glenn and ethan,

i may be over simplifying this but wouldn't the obvious solution here be to test at ethan's place, ibm and ral using the exact same method(s) and then comparing the results.

i gather this might be expensive but then you would know...wouldn't you?

ej

[Glenn Kuras]

Actually you would want to test IBM and River Bank as one test which would tell you how much absorption a certain product has. Edit. There have been tests called round robins that test several labs with the same product to see how well they do. BTW Riverbank is proud that they came out right in the middle meaning they are not showing LOW numbers or high numbers.
Testing in a room tells you how well that product works in that given room. Understand what I mean?

[Ethan Winer]

Originally Posted by Glenn Kuras

I can agree with all your points, but I still think there has to be a better way to test commercial products to give advice to customers.

But that's not what I've been discussing. As I explained way back in Post #7 above, I'm looking only for comparative data, not absolute sabins of absorption. The point is not to test commercial products for publication, but to compare the relative difference between 703 and 705, or filling a corner versus straddling with a panel. I could have sworn I stated that very clearly!

--Ethan

[Glenn Kuras]

But that's not what I've been discussing. As I explained way back in Post #7 above

Yes but by post 9 you kind of starting talking about labs themselves. I do agree that you can test 2 different products in a room to see which product is BEST for that room.

I think I also stated that I see no problem with your density report. In fact I was the one that brought it up!

[Weasel9992]

Originally Posted by Ethan Winer

But that's not what I've been discussing. As I explained way back in Post #7 above, I'm looking only for comparative data, not absolute sabins of absorption. The point is not to test commercial products for publication, but to compare the relative difference between 703 and 705, or filling a corner versus straddling with a panel. I could have sworn I stated that very clearly!

...and a lab would be an ideal place to do that.

Frank

[Ethan Winer]

I stand by my statements about the limitations of labs. Eventually Frank and I will agree on this - one way or the other! - by email.

[ejsongs]

Originally Posted by Glenn Kuras

Yes but by post 9 you kind of starting talking about labs themselves. I do agree that you can test 2 different products in a room to see which product is BEST for that room.
!

i am getting a bit confused here. if this is true then the same would apply for a lab or any lab or room for that matter of fact. simply because each lab is a room.

so if that is the case since all rooms are different then it seems as if none of the data anyone post is reliable in that who knows how well a product or either of your products will work in my room.

am i missing something?

[Weasel9992]

Originally Posted by ejsongs

i am getting a bit confused here. if this is true then the same would apply for a lab or any lab or room for that matter of fact. simply because each lab is a room.

What I'm asserting is that laboratory conditions are wholly different than a 12'x16'x8' domestic room. The lab environment is designed specifically for the purposes of testing, and the tests are conducted by skilled technicians. What I'm saying is that lab results can and should be relied on in terms of broadly applicable results and one can use for the purposes of generalized extrapolation. In other words, lab results are generally applicable; the results you get in your room from your testing is applicable only in that room or in a room just like it.

Frank

[Glenn Kuras]

Also the lab is going to give you sabins which is then used (by someone like us) to calculate how much absorption you will need for your room.

[Abel]

Originally Posted by Weasel9992

What I'm asserting is that laboratory conditions are wholly different than a 12'x16'x8' domestic room. The lab environment is designed specifically for the purposes of testing, and the tests are conducted by skilled technicians. What I'm saying is that lab results can and should be relied on in terms of broadly applicable results and one can use for the purposes of generalized extrapolation. In other words, lab results are generally applicable; the results you get in your room from your testing is applicable only in that room or in a room just like it.

Frank

I agree completely. The quote from Scorpius (post #20) suggests that both literature, simulation and measurements DO NOT support Ethan's results.

[Ethan Winer]

Originally Posted by Abel

The quote from Scorpius (post #20) suggests that both literature, simulation and measurements DO NOT support Ethan's results.

Yes, and that's the whole problem. You must have missed the first few rounds of this, which goes back three or four years now. I have to run out for an appointment in literally five minutes, so I'll hit the high points and elaborate more tomorrow.

* The difference in absorption between 701 and 703 and 705 depends on the thickness. With thinner materials the OC data for their 700 series shows 705 as best. In Scorpion's tables 703 is better, then 701 is better. So which do you choose?

* None of that data shows what happens when a membrane is attached to the face, as is common practice now, and believe me that changes things.

* That data is for Type A and E400 mounting which is not how bass traps are usually placed, straddling a corner.

* That data is subject to the same run-to-run variations as all other lab tests. If what Frank said earlier about +/- 6 percent variations is correct, that potentially hides small absorption differences such as appear in the OC data.

Edit: Here are some additional points for why the data published by Owens-Corning is not necessarily valid for determining whether 705 or 703 is better for bass traps:

* As rigid fiberglass is made denser it starts to behave as a diaphragm all by itself. If any improvement happens below 125 Hz it will not show in a standard lab test.

* Related to the above, standard data is incomplete because it goes no lower than 125 Hz. Since a bass trap mounted across a corner has a peak absorption well below 125 Hz, it's clear that octave data down to only 125 Hz is inadequate.

* The Owens-Corning data is also inconsistent. If we consider rigid fiberglass as having linear absorption due solely to gasflow resistance, then the data from Owens-Corning makes no sense. For example, why is two inch thick 705 eight times more absorbent at 125 Hz than one inch thick? And why is two inch thick 701 only a little better at 125 Hz than one inch thick? This shows that more is going on than plain gasflow resistance.

* The OC data is given only at octave intervals, so only very coarse trends can be seen. It would be much more revealing to see this data at 3rd or even 12th octaves.

--Ethan

[Abel]

Originally Posted by Ethan Winer

* None of that data shows what happens when a membrane is attached to the face

what do you mean by that? are you talking about FRK?

[AwwDeOhh]

What i'm interested in, and this conversation sparked my memory (thanks!):

What would be the benifit or detriment of using BOTH 705 and 703 in the SAME trap (say 4" trap....2" of each)

Example: Having a 2" 705 panel, then a 2" 703 panel on top of it in the same trap. I assume this would give a different result than just 4" of one or the other... but in what way?

What if you switched the layers around... 703 in back, 705 on top?

Even crazier... using 1" panels in a 4" trap and alternating them 703-705-703-705. Or even throwing in a 701 in the mix!!!

Am i giving anyone headache yet? No blurry vision i hope!!

[Glenn Kuras]

Am i giving anyone headache yet?

Yes
No way to know unless you test it in the lab. I don't think you would see major difference between the 703 and 705 mixing it up. Hard to really say though.

what do you mean by that? are you talking about FRK?

Yes

[bpape]

I'm going to jump in here for just a minute.

While I agree that in a small room, with REW, one can get COMPARATIVE data, it doesn't help me any as a designer to give absolute data.

It's kind of the same thing as using a cheap mic to measure a room. It's OK for comparing how your frequency response changes when you move seating or speakers around - but it won't give you accurate results as to your actual response. It just tells you were the major problems are and if they're getting better or worse.

As a room designer, it's important to me to know what a product will do in absolute terms. It doesn't have to be exact, but it needs to be reasonably close to accurate. When I design a room, I need to know how each square foot of material will absorb/reflect. When we look at those things, we pretty much ignore anything but the first digit after the decimal point and consider the rest error. So a product that shows .58 at 125Hz vs one that shows .51 at 125Hz are treated basically the same. It's within the error. BUT, I know it's .5ish vs .7ish.

Hope that makes sense instead of just fanning flames.

Bryan

[Glenn Kuras]

Bryan,

Those are great points. Could you give the guys on here a example of how you would give advice on a room using lab numbers? Just a general thing to show. I think most people do not understand the true reason for the numbers and how you would come up with a recommendation of treatment.

[bpape]

When you look at a room, you look at several things:

- Size of room
- Usage for room
- Surfaces and materials in the room.

Every surface and item has it's own characteristics in terms of absorbtion coefficients. Generally, we look at it on a per square foot basis except for things like people where it's used as a factor per person.

Once you know the size and usage, you can come up with a target decay time curve. You then lay in the square footage of all of the walls, ceiling, floor, furniture, people, etc. and see where you stand in an untreated state.

That lets you know what is still needed to bring things in line to the target. ie - how many square feet at what frequency band. Then the trick is to put those things in the proper places in the room to deal with things like modal issues, reflections, SBIR, etc.

Bryan

[Ethan Winer]

Originally Posted by bpape

While I agree that in a small room, with REW, one can get COMPARATIVE data, it doesn't help me any as a designer to give absolute data.

Of course, but the whole point of this thread has been about comparative data between 703 and 705. This is what the OP asked about, and this is what I addressed. I already stated that at least twice now.

The two main things I'd like to test are the comparative difference between 703 and 705, and the comparative difference between a corner that's filled versus one with panels straddling. People ask about this all the time, but nobody really knows for sure because no DIY'ers are willing to drop a grand on a lab test to find out. My Density Report is a first effort at getting to the bottom of this, and one of these years I hope to test it again with twice as much material to get a more definitive difference between sample types. I also hope to test filled versus straddling some day. But it's not going to happen in a lab unless we run a Gearslutz fundraiser and everyone kicks in $100.

--Ethan

[Ethan Winer]

Originally Posted by Abel

are you talking about FRK?

Yes, that, or the type of plastic membranes used on my company's products. As promised, I just added more points to my Post #44 above.

--Ethan

[Glenn Kuras]

I also hope to test filled versus straddling some day. But it's not going to happen in a lab unless we run a Gearslutz fundraiser and everyone kicks in $100.

I have told you many times that I would be more then happy to kick in for testing. But if you want to know how good it is to fill the corner you can look at our Tri Trap numbers which will get you close.

[Glenn Kuras]

Of course, but the whole point of this thread has been about comparative data between 703 and 705. This is what the OP asked about, and this is what I addressed. I already stated that at least twice now.

I think Bryan was trying to back you up.

[Ethan Winer]

Originally Posted by Glenn Kuras

I have told you many times that I would be more then happy to kick in for testing. But if you want to know how good it is to fill the corner you can look at our Tri Trap numbers which will get you close.

I know, but as I've also said many times I believe a small room test will give a more conclusive answer. Yep, I actually believe that.

--Ethan

[Glenn Kuras]

Originally Posted by Ethan Winer

I know, but as I've also said many times I believe a small room test will give a more conclusive answer. Yep, I actually believe that.

--Ethan

Fair enough. Glad we have Franks room report to back up our numbers.