John Sayers' Recording Studio Design Forum Archive

http://cgi.ebay.com/ws/eBayISAPI.dll?Vi ... 82563&rd=1

I am trying to decide whether or not to buy some of this stuff, but I am afraid it won't be worth a ....!!! Has anyone had any experience with this? Does it compare to Auralex stuff?

Thanks,

Rob

That company isn't selling the same stuff as Auralex from all reports I've heard; little is mentioned about fire retardant, their "specs" appear to be cut and paste from auralex' site, and sculpted foam only makes it easier for the company to charge more for less; the newer Auralex offerings include solid, full thickness foam with higher absorbent ratings as a result.

Unless you're not into DIY at all, you could build your own treatments using rockwool for less than half that price per square foot, and actually get your room to sound good. With foam, it's not that easy to balance out a room because the absorption isn't as good or as wide-band... Steve

knightfly wrote:That company isn't selling the same stuff as Auralex from all reports I've heard; little is mentioned about fire retardant, their "specs" appear to be cut and paste from auralex' site, and sculpted foam only makes it easier for the company to charge more for less; the newer Auralex offerings include solid, full thickness foam with higher absorbent ratings as a result.

Unless you're not into DIY at all, you could build your own treatments using rockwool for less than half that price per square foot, and actually get your room to sound good. With foam, it's not that easy to balance out a room because the absorption isn't as good or as wide-band... Steve

I have been building traps with 703like fibergalss (4" thick). For mid-highs I am not sure what to do...

Thanks,
Rob

Agreed. You can build better panels for less money with 703 or rockwool and they're a known quantity in terms of absorbtion over the frequency spectrum.

Rob, your panels should do everything foam will and absorb better at lower frequencies; in most cases, this is a GOOD thing because the thicker material does more to absorb lower mids, leaving the room sound more even in reverb time/frequency response... Steve

Even the Auralex stuff is not that good. We did a test in a room with nothing and then with the Auralex corner foam stuff. Hardly any difference at all. Did the same test with our product and it was night and day. Not trying to sell ours but what ever you do, DO NOT PUT FOAM UP.

Glenn

Rob,

To answer your original inquiry, I can tell you definitively that the eBay stuff you came across is inferior to similar products that we make. Their "test data" will appear to tell you otherwise. But they cannot seem to back those numbers up with anything concrete.

Of course, I represent Auralex, so feel free to insert the appropriate number of salt grains.

Addressing the more general aspect of your inquiry, please note that Glenn's experience is only one of many. There are multiple possible solutions to any given problem or set of problems. Foam apparently did not work well for Glenn. That is not to say it is right or wrong for your application. If you would like specific help on the selection of proper materials, consider providing Steve and Thomas with more specific information about your problem. They are very good at helping you develop solutions that are specifically tailored to your needs.

Rob,

Not to start any kind of war here, but could you explain why when Ethen tested your product in a IBM sound lab that they found the bass trap of yours to only have a NRC at 125Hz of .60 and you guys put some kind of number like 1.25 at 125Hz down?
http://www.realtraps.com/data.htm
Here is the link for you to look over.

Glenn,

I assume your inquiry was directed at me and not Rob? If so, it's WAY off-topic.

But I'll humor you:

First, the "NRC" is the average absorption of four octave bands (250, 500, 1000 and 2000 Hz) rounded to the nearest 0.05. The absorption coefficient is the correct name of the frequency-dependent quantity to which you are referring.

Second, there are many answers to your question. Hopefully, the information in the full LENRD test report (PDF) will help you out. You should notice that there is some preamble to the report addressing concerns that are probably related to yours. There is also a separate study of LENRD behavior conducted by a third party at the end of the document.

While you're at it, I would encourage you to review the following links as well:

http://www.auralex.com/auralex_acoustic ... s.asp?Q=10
http://www.auralex.com/literature/acoustology_504.pdf

I just re-edited the latter link earlier today. It contained a lot of competitor-unfriendly verbiage that didn't really serve any specific purpose.

Finally, I think if you are truly interested in learning about this particular issue, it would serve you best to disregard any potentially misleading information from anyone with an axe to grind. Seek your answers not from Ethan or me, but from independent experts. I try to remain objective and product-generic on these types of forums. In fact, this is one of the few forums where open discussion of specific products is encouraged by the forum owner. Even so, I would always urge folks to learn from experts such as Steve and Thomas and John here (and many others elsewhere) that are not affiliated with any corporation. Their advice will always serve you best, especially if you are wary of being misled by the likes of us greedy manufacturers.

Glenn,

Not to add fuel to the fire, but I would like point out one more thing:

Here's a good, objective way to compare Ethan's results to ours:

• What we tested in 1996 amounted to 32 LENRDs.* The raw number of sabins (abbreviated "Sab" = units of absorption - like feet are units of length) measured at 125 Hz was 75.97. Divide this by the number of units tested and you get 75.97/32 = 2.37 Sab/LENRD.

• Ethan's published number for LENRDs at 125 Hz (from the second table down on your link) is 9.47 sabins per 4' unit. Since LENRDs are 2' units, 9.47/2 = 4.74 Sab/LENRD.

So what Ethan is showing is actually a higher value than what we measured. This is not "playing with the numbers." This is simply straightforward absorption. The purest way to compare the results.

*The report says 48, but they were 16" units. Forty-eight 16" units = thirty-two 24" units. The final and current LENRD is a 24" unit.

Jeff,

Wow I felt like you sent me out of class to read a freaken book!!!
Thanks for all the info, but I was more talking about the first graph not the second. After reading what you gave me I do see how testing can be skewed, but if two products are tested the way the manufacture recommends mounting, is that not a good number? If it is a good number then I think it is easy to see why corner foam is not a good product to use to bass trap.
Ok if you got a few places that the high end is driving you crazy then, yes putting few pieces of foam up is not bad. Which does kind of bring us back to the question at the start, "is that stuff on ebay just as good". I have no problem with Auralex, you folks have done a lot to get people to think about acoustics and how important they are, but how is your product different from the "Other" foam company? If I have 2 pieces of foam with the same density then how can one be better? I have used the Auralex stuff and the other stuff and have really not heard any difference. I am sure you will say there is, but is it a huge difference?
BTW, what is up with is "Axe to grind" stuff?

Thanks,
Glenn

If I have 2 pieces of foam with the same density then how can one be better?

You have thrown quite a few thigns in theis thread trying to learn about absorption. I'll give a bit to help with this point.

Foams of the same densitycan vary in

strand length
strand width
raw material density
material hardness
(unreported) skinning in processing
varying density in a block due to process system
varying density in a block due poor process/raw material control.

I hope this short list helps.

Adnre

myfipie wrote: but how is your product different from the "Other" foam company? If I have 2 pieces of foam with the same density then how can one be better?

That's like saying - "a Yugo is a car - and a Mercedes is a car - so how can one be better if they have the same size tires?"

Why don't we begin here with a simple examination of the 2 products.

1st off - it appears you think they are the same - which means you haven't looked at the product data from the manufacturers - just at the foam.

According to the documentation provided by the manufacturers they are 2 completely different materials - with different properties........... so from my perspective a better question would be - if you have 2 materials with completely different chemical compositions - how can they be the same?

2nd......... I wonder exactly how you determined that they were the same density? WHat scale did you use to meansure them? When was it last calibrated - and how large a sample base did you take your tests from?

Sincerely,

Rod

myfipie wrote: I have used the Auralex stuff and the other stuff and have really not heard any difference.

That's why we test in labs and don't let people "listen" to determine what reality is - you can't measure anything with a pair of ears...... \


Psychologically you can fool yourself into hearing anything you want - hell my boss does that all the time.............

Sincerely,

Rod

Glenn,

The two foams in question are not the same. From an acoustical standpoint, Ethan actually beat me to the punch and proved it. Just look at the difference that was measured between the LENRDs and the other "corner foam" units. (Ethan's 2nd graph on the page you linked below.) And since they advertise their products as being the same as ours, yet from an acoustical standpoint they are clearly not, well, what do you think?

(BTW, the densities are not the same either. Certain samples of ours compared to certain samples of theirs could push a 2:1 difference in density, respectively.)

{Edit: Paragraph deleted in light of the numbers in question not actually being about Auralex products. See next post.}

If you would like to know exactly how much sound LENRDs are going to absorb in your application, you will have to put them in your room and find out. That may sound crass, but the reverb chamber method is simply not desiged to measure the absorptive effect of these sorts of devices as they are applied to small rooms. They will absorb sound in the range down to 80-100 Hz, just like we've always said. Whether they're the best solution for your specific application is exactly why we employ so many acoustical experts. To help folks figure out what is going to work.

Finally, I used the "axe to grind" figure of speech because it could be perceived that someone like myself or Ethan might have other, non-altruistic motives in presenting our information to the public since we each have products to sell. Sorry, did I misuse the term?