Absorption or Diffusion?

[tkingen]

Hello all,

I have a small room...11' x 11.3' x 8' high. It must perform as control room, live room for acoustic guitar, and studio/instrument storage. It has a carpeted floor, sprayed "cottage cheese" textured ceiling, and a 6' closet to house various instrument cases, boxes, etc. There are also a couple of small wood dressers for mic and cable storage, a desk for the computer and monitors, and a small wood case that houses a couple of preamps, delta1010 breakout box, and headphone distribution amp.

The bass frequencies have been tamed to an acceptable state (to my ears, anyway) with bass traps. Now, it's time to consider the mids and highs. I'm wondering if, in a room this size, is absorption more important than diffusion? Or a combination of the two? How should the front and back walls be treated? If I'm tracking, the 11.3' measurement would be the front and back walls, if mixing the 11' would be the front and back walls.

Also, my chair is currently sitting on a carpet protector, and there seems to be some phasing issues happening when recording acoustic guitar. I'm thinking it's probably due to the reflections between the ceiling and carpet protector. That would be an easy fix by removing that flat sheet of plastic, but then, of course it exposes a carpeted floor. I know that typically it is best to have an absortive ceiling and a reflective floor, but pulling up the carpet is not an option. So, maybe absortive floor and a reflective or diffused ceiling?

Apologies for all the questions. I'm trying to make the best of what I have and this forum seems to be the best for getting advice from knowledgable people!

Best Regards,
Terry

 

[Ethan Winer]

Terry,

Diffusion is great, but you have two things fighting against that working for you. One problem is your room is small so diffusors may be too close to you to be fully effective. The other problem is good diffusors cost a lot of money. The cheap ones I've heard all sounded terrible - worse even than a bare wall.

--Ethan

 

[tkingen]

Ethan,

Thanks for your answer. I suspected that would probably be the case with cheap diffusors. I'm going to focus on absorption, with the knowledge that this small, cramped room is never going to sound like a professional recording facility.
Ethan, thanks for the information that you provide on your website. That really helped me out in taming the bass buildup in the room. Even though I didn't purchase any of your products, someday I will!

Respectfully,
Terry

 

[fitZ2]

Hello Terry. I wrote this last night BEFORE Ethan posted, so bear with me.

Absorption or diffusion huh? Your room is almost square, and good thing it is NOT a cube. Square rooms are terrible to treat, although not impossible. Just difficult to balance acoustically because of modal distribution. Absorption is your friend in this space(as is most). The size is the determining factor for diffusion. This is really too small for any practical application of diffusers. Diffusion in small rooms is a subject of special study by quite a few acousticians and a few universities, as diffusion is not completely understood, although there are differences of opinion in the practical size of rooms at which diffusion occurs and I am certainly no expert. I did ask this question directly on a Physics forum, from which I recieved two different answers from two different acousticians, both of which were in conflict to the other The most I could make of it was, Absorption can CREATE diffusion in a small room, when used in small patches distributed throughout the room. However, one did say that below the modal response of the room, there is no support for diffusion, which is determined by the 3 dimensions of the room. These determine the lowest wavelengths that can be diffused, and physical objects, to have any diffusion affect on sound, must be relative in size to the wavelength of interest. At least. that is my understanding.
Now here is a rare one. In the book by Alton Everest called the Master Handbook of Acoustics, there is a section on diffusion, and a section on the current practical application of diffusers of that time period. This is when quadratic residue and prime number principles were being introduced in commercial diffuser products in the 80's. In these pictures, I saw a few instances of SMALL rooms lined with these types of diffusers. When I asked my questions on the Physics forum, I specifically referred to the pages with these pictures, and asked if diffusers really worked in small rooms as shown.
This is what I was told. A well known acoustician from europe, said when he opened this book, he could hardly believe this was a book on acoustics , AND did NOT consider the use of diffusers as shown in the book "classically theoretical" and implied that he emphatically denied thier usefullness in that context. However, the next reply, also from another well known acoustician, said, "No doubt they DO work in small rooms.........", but then went on to explain the modal response/room dimension/diffusion connection. The only thing I can add, is John Sayers said on this very forum, that(in so many words. not a quote)....they do NOT work, and he has seen many studios that have had to tear out these diffusers to make room for installation of updated designs.... Sooooooooo....I began to search the net for information regarding SMALL ROOM DIFFUSION. From what I found, I have decided, that for all practical purposes, all the products advertised as "diffusers" DESIGNED for small rooms........(and this is only my opinion, as I have YET TO SEE PROOF THEY WORK) ARE SNAKE OIL in fancy packaging. Positive proof by test, is something very new, and within the last couple of years, and from my understanding, has been demonstrated at AES(Acoustical Engineering Society) conventions, but I do not follow up on current scientific discovery in this regard anymore. Who knows?


Well, thats the best I can offer. Maybe someone else can give you better advice.

fitZ

 

[tkingen]

fitZ2,

Thanks for sharing your research and taking the time to type it! I knew that this small room was going to be a problem, and indeed it was/is. It didn't take long to realize that broadband absorption was going to be the most effective way to treat it.
Once the bass traps were in place they were tested by recording a rosewood Martin dreadnaught. With proper mic placement the bass frequencies no longer boomed, but there were still flutter echoes causing phasing problems in the mid frequencies. So, I used 2" and 3" acoustic foam panels at strategic places on the walls and ceiling. I know that foam is not the best way to go, but it was acquired at a good price that made it worthwhile for the sake of experimentation.
So, besides the corner bass traps, there is carpet on the floor and foam patterns on all four walls and ceiling. Guess what? It's pretty good! Certainly the best recordings that I have personally ever made at home ;~) The tracks aren't reverberant sounding (of course), but I have a couple of fairly good reverb plugins that give a good illusion of space when used judicially. So, absorption was a good way to go.
Once my wife and I purchase a larger house we will definitely buy traps from Ethan to help achieve more professional results. But, until then, I am going to enjoy this little cubicle of a recording studio and keep on recording!

Thanks again,
Terry