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#1647880 - 04/24/04 08:25 PM Auralex Question
cominginsecond
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Obviously, it's important to absorb much or most of the high and mid reflections in small rooms. However, another truism is that rooms that have absorbed too many of these reflections sound dead and lifeless. Also (and bear with me here, I'm building up to my question) I've heard that Auralex foam is less absorbant than Owens-Corning 703 (this is the reason that many people prefer the 703 to the Auralex).

Given these three premises, isn't it quite possible that the Auralex foam is a happy medium between coating your walls in 703 (which could lead to a "dead" room), and simply doing nothing (which lends itself to an abundance of really bad reflections)? If not, what am I not understanding?
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#1647881 - 04/24/04 08:57 PM Re: Auralex Question
Bill@Welcome Home Studios
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"...If not, what am I not understanding? "

a couple of things.

"...it's important to absorb much or most of the high and mid reflections in small rooms."

Thats one.

" I've heard that Auralex foam is less absorbant than Owens-Corning 703 ..."

Thats two.

Lets start with number two... Foams and fiberglas absorb differently across the audible spectrum. Check the specs, and you will see what I mean. The compressed fiberglas products absorb more evenly across their entire effective range, while the foams drop off in effectiveness, thereby providing uneven treatment. If you want less absorbtion, use less absorbing material. Don't use inferior material that absorbs unevenly.

As for number one, we are trying to end up with a room that responds evenly to all audible frequencies. If it takes absorbtion to acheve this, then that is what we want to do. But to only absorb the highs and mids would be a disaster acoustically. That is why we use 'bass traps'.

So think about trying to even out the room response, not about trying to deaden the room.

People use foams because they see them as a quick fix, because they think that it looks cool, because they are uneducated about acoustics.

Bill
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"...it's easier than hitting the kids, and almost as much fun..."

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#1647882 - 04/24/04 09:46 PM Re: Auralex Question
cominginsecond
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Quote:
Originally posted by bpark@prorec.com:
If it takes absorbtion to acheve this, then that is what we want to do. But to only absorb the highs and mids would be a disaster acoustically. That is why we use 'bass traps'.
I didn't imply that one should absorb only the highs and mids, only that, from what I understand, in small rooms, most of the high and mid reflections need to be absorbed because they're almost always really bad. Sorry if I wasn't clear enough in my original question.

Quote:
Originally posted by bpark@prorec.com:
So think about trying to even out the room response, not about trying to deaden the room.
I know that one aim is to even out the room response, but the phrase "even out the room response" doesn't seem to address room reflections (i.e. awful sounding reverberation). If I understand it correctly, the two issues (evening frequency response and minimizing undesirable reflections) are related, but still separate. You could have an even freqency response but still have bad reflections (on one end of the spectrum) or a dead room (on the other end of the spectrum), right? What am I missing here?

I apologize if I am covering basics that everyone else on this forum already knows.
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#1647883 - 04/25/04 05:29 AM Re: Auralex Question
Andre Vare
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Registered: 03/13/04
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You already received a good response from Bill. He summed up the use of foam quite well with

Quote:
People use foams because they see them as a quick fix, because they think that it looks cool, because they are uneducated about acoustics.
you wrote:

Quote:
If not, what am I not understanding?
Just about everything

Quote:
Obviously, it's important to absorb much or most of the high and mid reflections in small rooms.
It is not obvious to the acoustically uneducated (to use Bill's word) that it is important to control early reflections at ALL frequencies, in ALL sizes of rooms. The technical criteria that is becoming standard is that reflections within 15 ms of the initial sound be at least 10 dB lower than the initial sound. I addition to achieving this by absorbing sound at reflective surfaces from which the early sound comes, the surfaces can also be splayed or be treated with diffusers. John Storyk uses this concept in rooms that are too small for direct time delay in treating the back walls with diffusers. Going a step further, the ESS design concept treats all surfaces which may create early reflections with diffusers.

Quote:
However, another truism is that rooms that have absorbed too many of these reflections sound dead and lifeless.
This is mostly true. What is ironic from an acoustic viewpoint is that there is a way to get quite amazingly good listening acoustics in small rooms by using the non-environment design concept. This would be effective down to around 100 Hz or so keeping within the size restrictions. If the studio owner could afford the space and funds to go non-environment, then they could afford a larger room to use conventional treatment. Despite the non-environment room being relatively straightforward, in the design sense, the cost can be considerable, plus there is the "saleability" of it to customers who would dismiss their studio just hearing (as in communication) about the room's design.

You did not define how small, small is in your post. Rooms as small as 1200ft^3 can be treated to be quite acceptable using conventional techniques.

Quote:
Also (and bear with me here, I'm building up to my question) I've heard that Auralex foam is less absorbent than Owens-Corning 703 (this is the reason that many people prefer the 703 to the Auralex).
Did you read my thread "Why I have a headache?" WHICH Auralex foam products are you referring to? I checked my Auralex master table and stopped counting after 20 foam products.

Bill already wrote why people use foam type products so much. If you look at the absorption of the 4" wedge, which their thickest wedge product, the absorption drops below 0.9 at 250 Hz. They have a 1" product that drops below 0.9 at 1600 Hz! Not even any effective reflection control at midrange. 703 at the same thickness it drops at 125 Hz, a full octave lower. Aralex sells a 4 pcf mineral wool absorber which drops off at 100 Hz!

Quote:
Given these three premises, isn't it quite possible that the Auralex foam is a happy medium between coating your walls in 703 (which could lead to a "dead" room), and simply doing nothing (which lends itself to an abundance of really bad reflections)?
No. They are products appropriate for some applications, but not the way they are used most of the time.

In your response to Bill you wrote:
Quote:
I know that one aim is to even out the room response, but the phrase "even out the room response" doesn't seem to address room reflections (i.e. awful sounding reverberation).
Now you are changing the topic. Read Ethan's FAQ and his article from this month's Electronic Musician. Both are on his website. Early reflections being controlled by carefully located panels of absorption. Low end absorption being controlled by full range absorbers. Undesirable reflections and echoes being controlled by diffusion. The desired reverb time being defined as the square root of the room volume divided by the reference volume times the reference reverb time.

Have a look at the topic "empty room from scratch" as an example of all these factors being used in designing the acoustic treatment for a 1250 ft^3 room. The various links will give you much of the information more detailed than mentioned.
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#1647884 - 04/25/04 11:21 AM Re: Auralex Question
Ethan Winer Moderator
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Registered: 06/12/00
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CIS,

> what am I not understanding? <

Bill and Andre explained it all really well, so I'll add just two reasons rooms need substantial absorption at low frequencies.

1. We all know that obvious midrange echoes and ambience damage clarity and imaging, and the same thing happens at low frequencies. Below a few hundred Hz it's not so much true reverb as "modal ringing" that makes bass notes sustain longer than they should. So without effective bass trapping bass instruments sound muddy, and it's difficult to distinguish individual notes.

2. Just as important to tame is the severely skewed low frequency response that occurs in all rooms. If you look at my Acoustics Vibes article from the Feb 2004 issue of EQ magazine, now on my web site, you'll see how truly awful the low end response is in all rooms.

--Ethan
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www.realtraps.com
The acoustic treatment experts

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#1647885 - 04/25/04 01:24 PM Re: Auralex Question
cominginsecond
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Registered: 04/19/04
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Thank you Ethan.

Andre, while you are very knowledgeable, and I did glean some useful information from your post, I found it to be a little condescending. I have read the FAQ, and I have read Ethan's EM article, and I still had these questions, and for you to say that I don't understand anything isn't helpful in the least.

Also, I wanted to just make sure that the issues of evening out room response was a separate issue from controlling reflections, and I have received confirmation that they are, in a roundabout way. Bill seemed to conflate the two when he said "So think about trying to even out the room response, not about trying to deaden the room".
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#1647886 - 04/25/04 08:20 PM Re: Auralex Question
Godspeed,YouBlackEmperor.
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Registered: 11/07/01
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In truth, if you have moderate bass absorption, say, just across the corners, and things are linear at the mix position and youre not sitting in a cancellation or between a node, youre ok. (As long as you ignore clients requests for more bottom as they may be sitting in a spot where theres nothing from 110-140Hz ).
I dont think youre going to kill major room problems and get even response below 400Hz with bass trapping as is generally touted here. Can you control bass reflections and get the bass sounding tight? Yes. Can you get even response across a room? No.
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#1647887 - 04/26/04 04:20 PM Re: Auralex Question
Ethan Winer Moderator
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Blackie,

> I dont think youre going to kill major room problems and get even response below 400Hz with bass trapping as is generally touted here. <

Bass trapping is the only solution I know of. If you have a better suggestion I'd love to hear it! But you are correct than nothing can ever make a room truly flat, especially the small rooms many people use these days for mixing.

I see it this way: An untreated small room has a frequency response that varies by about 30-40 dB across the low end. Acoustic treatment and bass traps can get that down to a 15-20 dB span. A 15-20 dB improvement is enough to go from "This totally blows" to "Wow, I can actually hear what I'm doing!"

And that's really all we're trying to accomplish here.

--Ethan
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www.realtraps.com
The acoustic treatment experts

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