There are two ways to cut OC703 to get wedge/corner pieces.

Do people typically do 17x17x24 inches?

Or is the larger format 24x224x34 inches the preferred?

The bigger the better, always. If you can fit the larger size, go for it.

--Ethan

The bigger the better, always. If you can fit the larger size, go for it.

--Ethan

Where do you think the law-of-diminishing returns fits in this situation?

Does double the volume = double the bass control?

According to Floyd Toole these types of traps are a waste of time (the the purpose you're thinking) as it it "sound pressure not particle velocity that is maximum at such locations" i.e. corners, hence stacking OC703 in the corners is not really doing what you want it to do - you need a membrane absorber.

However, he also states that:
"A significant advantage of these resistive absorbers is that they are inherently non-resonant, being similarly effective over a wide bandwidth." So make sure you know why you want to put them there before you actually do it.

Also if you're looking at absorption panels in the room make them 4inches thick as a minimum, otherwise you'll be effectively turning down your high and mid frequencies relative to lower stuff which will really screw up your room.

According to Floyd Toole these types of traps are a waste of time (the the purpose you're thinking) as it it "sound pressure not particle velocity that is maximum at such locations" i.e. corners, hence stacking OC703 in the corners is not really doing what you want it to do - you need a membrane absorber.

However, he also states that:
"A significant advantage of these resistive absorbers is that they are inherently non-resonant, being similarly effective over a wide bandwidth." So make sure you know why you want to put them there before you actually do it.

Also if you're looking at absorption panels in the room make them 4inches thick as a minimum, otherwise you'll be effectively turning down your high and mid frequencies relative to lower stuff which will really screw up your room.


Um.

No offense intended, but:

who are you?

Um.

No offense intended, but:

who are you?

Entirely taken, suit yourself...I don’t know why I bother - there are more than one schools of thought when it comes to this stuff, and I'll take my lessons from someone who back up his thoughts with science, not rhetoric i.e. Toole. Have a look at my post in the master thread a few pages back....actually no, you're cleary not interested.

Entirely taken, suit yourself...I don’t know why I bother - there are more than one schools of thought when it comes to this stuff, and I'll take my lessons from someone who back up his thoughts with science, not rhetoric i.e. Toole. Have a look at my post in the master thread a few pages back....actually no, you're cleary not interested.

Actually I am interested and my question was not rhetorical in nature. It is helpful for me to know where information comes from. It's not a perfect way to determine if someone is giving good information but it is a start.

I find your response above rather informative in itself, to be honest. When Ted, Ethan, Terry, Bryan, Dennis, et al are all challenged here in any manner, they tend to respond by taking the high road. And I respect that.

Now, you seem to be making an argument against current and commonly accepted methodology and I am supposed to accept it with only a flimsy reference to a scholar in the field but no actual data, or context? While I maintain I have no expertise in this subject (and really no interest in being an expert), I can often recognize someone who knows just enough to be dangerous. The aforementioned individuals who work in this field I am sure know of Mr. Toole and take his opinions and data into consideration when making recommendations.

Now, you seem to be making an argument against current and commonly accepted methodology and I am supposed to accept it with only a flimsy reference to a scholar in the field but no actual data, or context?

Floyd's work is actually a combination of hundreds of other tests and papers in one easy to read reference. He's also been in the game longer than most and has seen the "trends" come and go. He's widely acknowledged as an expert in his field and unlike some of the others you've mentioned doesn't sell AT himself......leave that for another day.

I was of a similar mindset to yourself until I got a copy of Sound Reproduction and it opened my eyes. Parts of it are on google books, wet your appetite with that perhaps.

Floyd E Toole was Vice President and Director of R&D at Harman International Industries, and much more..

He is known as A leading industry expert in Acoustics & psychoacoustics, One of if not "THE" industry guru on this stuff...

He has published much of the Harman White papers and his new Book is
Sound Reproduction Loudspeakers & Rooms... Its A must read IMO...

Cheers...

According to Floyd Toole these types of traps are a waste of time

I have huge respect for Floyd, but in this regard he is simply wrong. Not just a little wrong, but totally wrong. And it's simple to prove.

Porous type bass traps can target very low frequencies even when "only" four to six inches thick. My recent video Hearing is Believing (http://www.realtraps.com/video_hearing.htm) shows six-inch traps making a large improvement to below 40 Hz, and they're not even straddling the corners. However, as you'll see in the video there are a lot of traps in the room.

"A significant advantage of these resistive absorbers is that they are inherently non-resonant, being similarly effective over a wide bandwidth."

Yes, and this advantage is so significant that it trumps just about any reason one could come up with for not using porous traps.

--Ethan

Where do you think the law-of-diminishing returns fits in this situation? Does double the volume = double the bass control?

It's not entirely linear, but having more and larger traps flattens the response better than fewer smaller traps, and also reduces modal ringing more. You can't make any room perfectly flat, so my approach is to use as much bass trapping as acceptable and call it a day. Even four 2x4 bass traps will make a big improvement in most rooms, but more is better still.

--Ethan

I hope you don't mind an additional question...

I will be using an acoustically transparent screen and will not have 17 or 24 in which to place corner bass traps. If I place 6' of OC703 along the front wall, will I get at least some bass trapping? Or should I be doing something else.

Also wondering if you have any thoughts on the THX baffle wall idea? Other than bringing the acoustical treatment out to line up with the front speakers, I can't seem to find any specifics.

Thanks
Greg

Six inch thick rigid fiberglass on the front wall definitely helps, and especially near the bottom by the wall-floor corner.

I'm not aware of the THX baffle. Got a link?

--Ethan

Here is a link

http://www.thx.com/cinema/builtTHX/baffle.html

TheBland brought it up in my build thread and since my speakers hang off the wall if I made the front wall acoustic treatment thick enough it would seem to also from this 'baffle wall' THX mentions.

Thanks
Greg

This thread just goes to prove that just because you are an expert does not necessarily mean that you are right.

There are many schools of thought on sound...

From what I've read, the baffle wall has to be custom designed for your specific installation.

CJ

http://www.thx.com/cinema/builtTHX/baffle.html

Ah yes, this is the way monitor speakers are usually installed in million dollar recording studios too. It's great if you have the space and the budget. But having very thick insulation on the front wall helps a lot.

--Ethan

Looking at that drawing it would seem to me that having insulation on the front wall would act as a quasi baffle wall, in that in would control the reflections coming back off the screen. I guess there will be some diffraction effects from the speakers themselves that a true baffle wall would control.

I have huge respect for Floyd, but in this regard he is simply wrong. Not just a little wrong, but totally wrong. And it's simple to prove.

Porous type bass traps can target very low frequencies even when "only" four to six inches thick. My recent video Hearing is Believing (http://www.realtraps.com/video_hearing.htm) shows six-inch traps making a large improvement to below 40 Hz, and they're not even straddling the corners. However, as you'll see in the video there are a lot of traps in the room.



Yes, and this advantage is so significant that it trumps just about any reason one could come up with for not using porous traps.

--Ethan

Hey Ethan ... I have a question then ... Theatre will have 7.1 surround with 4 speakers for side surround ( a pair for each row of seats ), plus a pair on the back wall, in the front of my theatre I can build corner bass traps easily

however at the rear wall of the room in one corner I have the entrance door ( no way to move it ) and on the other side I have about 15" on the side wall to another door to the basement bathroom - as a result I could only make maybe 1 small corner bass trap only on the bathroom side

http://i433.photobucket.com/albums/qq54/ScruffyHT/untitled.jpg


my question is ... could I make the rear wall 6" thick OC703 like in your video with the lower portion as a bass trap and the upper portion empty so that it does not make the room too dead and then cover it all in GOM ?

would there be any benefit to making that wall 4" of OC703 with a 2" air gap behind it ? ( I have read that this air gap can be beneficial )

could I make the rear wall 6" thick OC703 like in your video with the lower portion as a bass trap and the upper portion empty so that it does not make the room too dead and then cover it all in GOM ?

Sure, though I'd probably cover the entire rear wall. Or use diffusors for the upper half, depending on how far behind the back row that wall is.

would there be any benefit to making that wall 4" of OC703 with a 2" air gap behind it ? ( I have read that this air gap can be beneficial )

An air gap is a free way to get similar absorption as thicker material. But it's not better than solid filled. And adding wood frames to create a gap may be more effort than using thicker material.

--Ethan

Sure, though I'd probably cover the entire rear wall. Or use diffusors for the upper half, depending on how far behind the back row that wall is.
--Ethan

Thanks Ethan ... the back row will be ~ 4' from the back wall

what type of diffusors would you use and can I DIY them and still cover with GOM ?

Hi Steve, Sorry Not Ethan but As I pointed out over at the Shack I would not recommend covering QRD diffusors or any type for that matter with fabric due to the unpredictable effect on performance.. The only type of diffusor that may be ok to cover with fabric is The Polys depending on the way there/its implemented...

Cheers....

Well if Polys are the only kind that can be used then how do I figure out how many and what dimensions they need to be ?

the back row will be ~ 4' from the back wall. what type of diffusors would you use and can I DIY them and still cover with GOM?

At four feet I'd use 1-dimensional QRD well type diffusors 3 to 6 inches deep. I'm sure GOM type fabric will be fine, as long as it's fabric in their "acoustically transparent" series.

--Ethan

Hi Steve, as you know I am happy to help you or any one in any way I can with honest unbiased answers...

You asked me if you can cover the QRD based diffusors (like the types I have made) with fabric, If I thought it would work I would be very happy to say so as Diffusors are part of A usefull tool in room treatmens and you could benefit from them in your Awesome large size theatre you are building...

I have never seen nor do I recommend any form of QRD diffusors be covered in any form of fabric covering over the front wells other than an extremely open weave fabric making it pointless from your stand point...

The reason is it "WILL" effect the uniform of diffusion in the hemidisc thus crippling the performance of such a design ....

If covering with Acoustically transparent fabric could be done with little effect to performance I am sure the big manufacturers such as RPG and the like would of found A way, make them more appealing...

As for Polys, Bryan Pape of GIK has them I think and he would be only to happy to help you in any way as you know, I have'nt built them as yet but they are very very basic to make out of thin 2-3mm PLY or MDF.. Also you can fill the cylindrical formed air gap behined them with Fiberglass giving them the ablity to abbsorb the lower freq...

Athough I agree with Ethan that QRD diffusors are better suited for your back wall, BUT placed on the left and right sides due to your 4-6ft from back wall seating distance and Absorbtion in the middle of the rear wall behined the main listening positions....

Hope this helps, Cheers mate....