[McTwins]

Allen,

I would like to see some room graphs of before and after from you. Here is a before and after room set up Frank did with bass traps.
Please post yours
http://www.gikacoustics.com/news_030709.html
I will say that if you take something like our D1 and place fiberglass behind it that would be a great solution also. But to just diffuse 40hz?

Needless to say just for fun here is a link to calculate diffusors
http://www.digitalaudiorock.com/cgi-bin/qrd.cgi
Have fun

Hi
I was looking at the measurment in GIK's web site, Room Report. The modal ringing at 40-45Hz and 70-80Hz in the CSD hasen't change before and after. I am supriced that after so many broadband absorbtion in the room coulden't fix the problem.  If I would be a costumer I woulden't be satisfied.
I would like to see Reverberation time T30 in that specifically measurement, it would be interesting to see.
The only thing that could fix the modal ringing is with a Helmholtz resonators tune to both of the freq required.
That's why I have abandoned the absorbtion with fiberglass or mineralwool on low freq.
GIK has allredy proven to me that it dosen't work under 100 Hz.
Thanks
 

[Big Red Machine]

I own and use RealTraps, GIK traps and SRL diffusers.  All of them do what they are suppose to do and well.  My diffusers are of 9.5" depth which I understand is tuned to 1K Hz and up for diffusion.  Most people's rooms would not be big enough to put large and deep diffusers like Allan proposes to deal with 40Hz null.  This is why I use absorption for bass and front (behind speakers) and diffusion for back and sides.  I do believe that deeper diffusers will diffuse lower.  SRL diffusers, which came out before GIK and RealTraps, do work very well but I have to admit that I did not get them to deal with anything below 100Hz issues.  I do think the size and depth of them should diffuse lower frequencies than the ones Real Traps or GIK offers.

I've been kicking around the project of building a few QRD diffusors and the research I have done so far indicates that a rather substantial diffusor of approx 4' x 4' x 1' deep can get you down to approx 480 hz depending on the prime number and subsequent width of the 'slots'.

My questions is whether I would add any absorption behind that diffusor or is that not practical?

[woodsyi]

My thinking is that one uses diffusers to keep your room lively without smearing the sound.  I think absorption in the same place as diffusion would only deaden your room without adding any more clarity.  I did use absorption on the early reflection points before and it works about as well as diffusion for this purpose except that you lose a little bit of twinkle in the highs.  The back wall QRD diffuser (4' x 6' x 9.5") makes a big difference in eliminating the standing waves in the mid/upper frequencies and really locks in the soundstage depth.  Overall, diffusion definitely keeps the room livelier and keeps that twinkle in your highs.   For deep bass though, the fiberglass traps (4" panels and stuffed batting above the ceiling tiles) smooth them out.  Using 4 subs (2 firing forward and 2 firing backwards out of phase) also help smooth things out at the bottom.  A good bass to me is one that I don't notice unless I lose it.  But without it, the highs can sound shrilly.  It's amazing how much more treble I can enjoy when bass is firm and tight.  With good bass -- which does not draw undue attention to itself -- and good diffusion, I really can enjoys the tingling treble that decays just right.  I missed some of that air when only absorption was used for mid/high frequencies.  YMMV depending on your room make up and size. 

[Ethan Winer]

GIK has allredy proven to me that it dosen't work under 100 Hz.

I can't speak for those graphs, and the graph labels are illegible anyway. But I can tell you for certain that porous style bass traps such as GIK and RealTraps sells can reduce ringing below 100 Hz. How much the ringing is reduced depends on how many traps you have, how large they are, and how carefully they're placed.

--Ethan

[bpape]

GIK has allredy proven to me that it dosen't work under 100 Hz.

I can't speak for those graphs, and the graph labels are illegible anyway. But I can tell you for certain that porous style bass traps such as GIK and RealTraps sells can reduce ringing below 100 Hz. How much the ringing is reduced depends on how many traps you have, how large they are, and how carefully they're placed.

--Ethan

Agreed.  244's won't get 40Hz much.  Tri Traps and Monsters will reach that low - though not with a 1.0 coefficient.  Placement can be critial, and unfortunately in many real world rooms, potentially not possible to do things in the optimal places.

Bryan

[Vinyl-Addict]

GIK has allredy proven to me that it dosen't work under 100 Hz.

I can't speak for those graphs, and the graph labels are illegible anyway. But I can tell you for certain that porous style bass traps such as GIK and RealTraps sells can reduce ringing below 100 Hz. How much the ringing is reduced depends on how many traps you have, how large they are, and how carefully they're placed.

--Ethan

Ethan, How do you determine the optimum placement of bass traps? Lets' assume the roomsize is 13 x 16 feet with an 8 foot ceiling. Where would you place traps in that room to treat it effectively....effectively being the key word?

[MaxCast]

I always see diffusion placed vertically.  Can they be placed horizontally?

[Big Red Machine]

I always see diffusion placed vertically.  Can they be placed horizontally?

I've seen them mixed in some photos but I am guessing that since sound travels so multi-directionally it might not matter.

[Ethan Winer]

Ethan, How do you determine the optimum placement of bass traps?

Generally, the best place to put bass traps is wherever bass accumulates in the room. This depends mainly on the size and shape of the room, where the speakers are placed, and of course frequency. Since different frequencies wind up in different places, my usual "shotgun" approach is to treat as many corners as possible, plus some or all of the rear wall. This article explains a good way to find the best places when you have only a few traps:

Pink noise aids placing bass traps

Lets' assume the roomsize is 13 x 16 feet with an 8 foot ceiling. Where would you place traps in that room to treat it effectively....effectively being the key word?

Again, it depends a lot on where the speakers are. But you can never go wrong with corners, and I generally start in the front wall-wall corners. Remember that rectangle rooms have 12 corners, not only four. My living room has traps in 11 of the 12 corners.

--Ethan

[Ethan Winer]

I always see diffusion placed vertically.  Can they be placed horizontally?

It depends in the type of diffusor. Well-type QRD diffusors are usually arranged with the wells vertical, to scatter sound left and right rather than up and down. With a 2D skyline type it doesn't matter (of course).

--Ethan

[planet10]

You have 2 subs. That is the minimum needed to take advantages of the techniques Floyd Toole describes in his new book to get flat bass in room.

dave

[srlaudio]

Hey Woodsyi,

   
The 1000 hz spec is the "target" frequency.  This is in the center of it's range musically, so it goes much lower in reality.  I had a long discussion with the owner of the only lab in the country to test diffusors, and he informed me that large diffusers DO trap bass.  It has to do with the width of the panel and an area of science known as fluid dynamics.  As soon as he publishes papers regarding this, I will post them here.  Meanwhile, I am having a ton of fun with my crazy big diffusers.

[TRADERXFAN]

What does your owner friend say about lack of well dividers on QRD's?  Is that something he recommends?

Thanks

Tony

[srlaudio]

"Well dividers" were not a part of diffuser design.  "Fins" which were in the channels themselves were in the original designs, but were scrapped after real world testing.  "Well dividers" are seen in some diffusers, but must be a nod to manufacturing ease, as opposed to real world performance.  One thing that has been agreed upon is that higher prime number (one of the variables in the equation) designs sound better.  Higher prime numbers generate wider diffusers.  That is what I have observed in my experiments.  A single large diffuser always sounds better than multiple small diffusers placed side by side.  As a matter of fact, it is known that placing multiple 2D diffusers side by side starts to generate lobing, which exactly what you do not want.  Yes, it is more work, and harder to transport, but it is worth the effort to use the largest panels that will fit in your space to achieve the acoustics that you desire in your listening room.

[srlaudio]

I always see diffusion placed vertically.  Can they be placed horizontally?

In larger rooms, 2D diffusers can be "arrayed" to give a broader vertical dispersion.  This involves placing a unit with channels going horizontally rather than vertically on top of one with vertical channels.