Absorption and diffusion of bookshelves

[GuitarRuss]

Something I'm curious about for those of us with quite small rooms is the sound diffusion or absorption qualities of different materials. It has been stated a few times that wood is good for absorption and diffusion - would that mean that a bookshelf full of books would effectively work as a small bass trap and diffuser? (These are just pictures off google)

I'm living in Taiwan right now and bought something very similar to this for about $80 US and it's about 3' by 4'. Should I be using these as cool diffusers since I already have them? Right now these are hanging in my living room.

Here is a professional acoustic diffuser

Wouldn't a bookshelf with some foam in the back of it essentially be the same thing? I can see the depth is varying but would books of different sizes do a similar job?

Right now I'm using a shoe cabinet to put all my cables, stompboxes, and whatnot in - while my bookshelf is in the livingroom. Should I be doing the opposite seeing as because of the doors it will reflect more?

A lot of this professional stuff is really expensive and when space is at a premium in your room... maybe I can have my cake and eat it too, what do you think? Does anyone else have any cool ideas for how to combine functionality and acoustics at a really low budget?

[Jason Jones]

GuitarRuss,

Bookshelves full of books do provide some absorption and diffusion.....but it tends to be very uneven...so you may have very high absorption or diffusion at one frequency and none at another frequency very close. This will contribute to make the frequency response worse than without it. It will also contribute to uneven reverberation times.

It makes MUCH more sense to use absorbers if the budget is tight. If your room is big enough you could use a diy poly diffuser.

Jason

[GuitarRuss]

Thanks for the response Jason. I will be moving from Taiwan in another year, so the idea of spending a lot of money on bass traps doesn't make sense because they will be expensive to ship back home.

I see you are involved in professional acoustics which means that you are very knowledgeable so I believe what you are saying. However, I also wonder what are the actual chances it will make my room worse? While it could screw up my room, couldn't anything else from desks to cabinets to consoles? If I put some foam in the back, behind the books then it shouldn't mess with my reverb times, should it? Also I can vary the books, big, small, big, medium, etc. then wouldn't it be similar to small blocks of wood in those diffusers. Of course, no pro-studio would even need to think about these kinds of things, but with real estate and rental prices where they are, I doubt I will have a big studio room when I get back to Canada either, and my stuff must go somewhere. I was taking a look at a book about Feng Shui (Chinese art of arrangement) and they had a picture of an office with bad Feng Shui, then a picture of the office remodeled and it did look much better, but I noticed all the filing cabinets and the copy machines were now gone in the after picture. Sometimes the acoustician's answers to these questions can be like the Feng Shui master's. I now have two ECM 8000 test microphones so I guess I will just have to learn how to test the acoustics and do before and after tests.

Also, what do you think about the Chinese wood screens as diffusers? I could put them in front of foam to reflect sound out in a scattered way. Where I am now, they are far cheaper than buying a professionally made acoustic diffuser and far more beautiful and worthy of shipping back to Canada. Many of them have hardly any straight angles like these...

[Ethan Winer]

Russ,

Skip the Feng Shui voodoo and aim for either real diffusors based on science, having a known pattern that is sufficiently deep. Or use absorption.

--Ethan

[GuitarRuss]

Ethan, I think you missed my point which I wrote above, which was about using stuff I already have in my house because I will be moving soon. Now foam is cheap enough that I don't mind wasting the money leaving it behind. I'm not trying to Feng Shui my studio, in fact, my example was about a Feng Shui master who improves the aesthetic by making the office non-functional (which happens over here a lot). However, a little art can really help the vibe of a studio and if it happens to improve the acoustics then that's great.

Now you mention depth being important in diffusion, so then it's not just having a reflective surface that has many different angles then. While I know some types of diffusers like skylines are all about varied depth, some other ones I've seen around didn't look very deep... I also like to make decisions based on science, so I while wouldn't imagine my Chinese screens would provide optimal diffusion, it was more a question of whether they would improve things by adding some diffusion. Is your answer that they are suboptimal, or useless for that function?

[Ethan Winer]

Russ,

Originally Posted by GuitarRuss

I'm not trying to Feng Shui my studio

Okay, and I agree appearance and vibe matter too.

Now you mention depth being important in diffusion, so then it's not just having a reflective surface that has many different angles then.

Yes, exactly.

While I know some types of diffusers like skylines are all about varied depth, some other ones I've seen around didn't look very deep

Right, and those are the ones to avoid. Also, assuming a proper diffusor design, it's not the depth of each portion but the depth at the deepest point. That determines the lowest frequency the diffusor is effective to. Diffusors only one inch deep are not useful at all.

One of the problems with this thread is that so far you haven't told us the room dimensions or shown photos etc. So any advice we can give is based mostly on guessing.

--Ethan

[GuitarRuss]

Originally Posted by Ethan Winer

Russ,



Okay, and I agree appearance and vibe matter too.



Yes, exactly.



Right, and those are the ones to avoid. Also, assuming a proper diffusor design, it's not the depth of each portion but the depth at the deepest point. That determines the lowest frequency the diffusor is effective to. Diffusors only one inch deep are not useful at all.

One of the problems with this thread is that so far you haven't told us the room dimensions or shown photos etc. So any advice we can give is based mostly on guessing.

--Ethan

Ethan,

Thanks for the information about diffusion depth, it's always great to learn more, and that information will come into play when I'm shopping for, or building diffusers once I have a permanent studio. I have a one room mixing and recording room that is 12' by 8' and 10' tall with wood floor. Two of the ceiling corners cut in to accommodate pipes. It has concrete walls, and a large window on one side. There are a few irregular corners, and surprisingly, the room has quite a nice sound for such a small room.

When I clap my hands there is no flutter echo and the natural reverb is quite pleasing given the room's dimensions and all the reflective surfaces. Of course, when you start layering, the room sound builds up too much unless you mic really close. I do mostly acoustic stuff here so the sources aren't so loud. Also, I have to double check everything on headphones to make sure it sounds good without the room bias, which slows things down. There's a company here that manufactures different densities of acoustic foam, so I'm going to check that out soon and add that to tame the room sound. I was looking for other temporary measures because I don't want a dead room and I know foam doesn't trap bass or add diffusion.

Thanks again for the info, your posts are quite informative and I appreciate that you offer so much information without charge - I've just started to read your acoustics faq.

[Jason Jones]

Originally Posted by GuitarRuss

However, I also wonder what are the actual chances it will make my room worse? While it could screw up my room, couldn't anything else from desks to cabinets to consoles? If I put some foam in the back, behind the books then it shouldn't mess with my reverb times, should it? Also I can vary the books, big, small, big, medium, etc. then wouldn't it be similar to small blocks of wood in those diffusers.

Also, what do you think about the Chinese wood screens as diffusers? I could put them in front of foam to reflect sound out in a scattered way. Where I am now, they are far cheaper than buying a professionally made acoustic diffuser and far more beautiful and worthy of shipping back to Canada. Many of them have hardly any straight angles like these...

The chances that a bookshelf will be an acoustic problem are really 100%. Designing a diffuser is SO much more complicated than throwing in some random depths.

Would you buy an absorber that had specs like this:

4 Khz 0.2
2 Khz 0.4
1 Khz 1.0
500 Khz 0.2
250 Khz 0.7
125 hz 0.2

This absorber will decrease your reverberation time across the board, but very unevenly. Compared to having nothing on your walls it will sound more tolerable. It would be a fine acoustical addition to a living space especially when you have a couple of these plus couches and curtains that have different absorption qualities.

So, in a pinch if you really have no alternatives a bookshelf is better than a completely bare wall. But, it will skew what you hear.

I certainly can be an impossible perfectionist sometimes.....but couldn't you find some mineral wool or rigid fiberglass over there and wrap it in fabric. That is still pretty cheap and I would happily bless that idea (Just in case, No I don't take myself THAT seriously ).

As to the Chinese wood screen: I am not usually much into Asian art, but that really is beautiful. I can see why you would want it on the wall. Do keep it on the wall, but don't kid yourself about it's acoustic properties. Put over an absorber it might help some around 3 Khz or 4 Khz IF you already have a room that is too dead; but, that's not really your problem.

Summary:

1. Pick up some mineral wool or rigid fiberglass. If you can find it local and cover it yourself it will be cheap and acoustically very good.
2. The bookshelf is better than nothing. You can use it if you can't do #1 but it would be a delusion to think that it was more than a D grade (A-F scale) diffuser.

Jason

[GuitarRuss]

Thanks Jason for answering my questions. A friend of mine has a connection to material to build bass traps. I guess I could build them and then sell them when I leave, most people don't like to build them so they might want to buy mine. With the ideas above I was thinking of half-measures, but it sounds like they aren't even close to that so I'll try something else. Acoustics, like any science, takes a while to acquire a basic knowledge in. Thanks for your time.

[Bob Olhsson]

I've experienced bookshelves working really well but only when they cover a large percentage of the surface area and you take the time to move things around until it sounds good.

[jwl]

Understand that bookshelves are not diffusors. There are several designs for them, each of which must be very precise. If even one "well" of the diffusor is not at the correct depth, then the diffusor loses its effectiveness.

The key point is that a diffusor will scatter reflections evenly in all directions for its effective plane(s).

That said, bookshelves can do a nice job of breaking up some reflections, and books might give a small amount of absorption.

[nDmusic]

I actually think a wall of bookshelves on the rear wall works very well as an 'anti-reflection' strategy for the lowender. If you're really plotting the path of the second/third reflections, then you've gone beyond project studio IMHO. If however, you simply want a non-reflective surface behind you, then bookshelves will get you there. It's not coming straight back at you (for the most part) and this will be a huge improvement. Randomly diffusing and absorbing frequencies on the rear wall (assuming sufficient coverage) is really good coupled with good bass trapping in the corners and a highly (broadband) absorptive surface in front of you. Of course, a wall of books and nice looking bookshelves are likely to cost much more than either broadband panels or pro diffusion products. But if you already have them and more importantly, if you are compelled by a very special member of your household to keep them in your 'studio', then this is a great use for them. ER treatment is also essential to treat first reflections.

Just my personal observations coupled with others I know. Please also remember when speaking with a vendor that they have an interest in selling you their products. I have no doubt they believe in their products and that their products offer a superior solution, but to get to a high quality mixing/critical listening environment, there are other 'tricks' that will get you sounding good without forcing you to spend on products more appropriate for the pro studio.

my 2 cents...

nDmusic
Algorhythmic Productions

[nDmusic]

oh, and don't forget to trust your ears above all else. If you can mix easily and quickly in the room and your mixes translate and you enjoy mixing/listening in the room, then mission accomplished.

nDmusic
Algorhythmic Productions

[GuitarRuss]

Thanks for the advice nDmusic and Bob Ohlsson. Now that I've started moving stuff around and placing foam, I've found it really isn't very subtle at all. I've been surprised at how much the sound improves or gets worse with the placement of different pieces in the room. I will use my ears to get the best out of what I have available.

[theo aronson]

glad I found this thread. I was about to buy a pair of these shelves to put in on the back walls of my control room:

Spine Wall Shelf | west elm

I loved the idea because I need more storage space for books, records, etc...so I figured these would kill two birds with one stone. I thought wrong.
My biggest issue right now is that I'm trying to find something that is multi-functional. I'm trying to avoid covering valuable wall space that could be used for additional storage/shelving with diffusers that help the sound but don't help when it comes to giving me additional storage.

My control room is about 16ft L x 14ft W x 8.5ft H. The front half of the room has an angled ceiling that has absorption built into it.

PROBLEM: I have a weird hi end flutter/flange type thing going on that I can hear in certain parts of the room when I clap. It's really bright and almost sounds tin-like. My ears were directed right away to the metal on the track lighting. Almost sounded like the lights were resonating, but I don't think that was the issue. I picked up 4 T-fusors and threw them on the ceiling tonight and they definitely helped, but didn't fix the issue. Feel like I'll have to buy another couple sets of four t-fusors to actually solve this problem and improve the rooms over all sound. Maybe I should look into some sort of mix cloud that absorbs rather than trying to install diffusors? I feel like there is already plenty of absorption going on in the room.

I attached a few pics to hopefully help explain the situation. The one with the white walls is the room with the previous tenants gear in it before I signed the lease. The picture with blue walls is the newly painted room.

Any advice anyone has would be much appreciated.

Back of room where I'm considering adding some diffusion (on the wall between the black corner bass traps and the large rectangular absorption panel):


Side view of room where you can see half the room/ceiling is treated and angled down and the other half is normal (I do not have any ceiling treatment up yet like the previous tenant did in this photo):

[Glenn Kuras]

A few things you could do. If you want to have book shelves then put them on the side walls behind where you sit. I would rather you did not but that would be the safest place.
As far as the rest of the room, you can use diffusion or absorption to help with flutter echo (slap).

[theo aronson]

Thanks so much for the quick reply, Glenn. What would you ideally like to see on those walls? Should I mount two of those t-fusors (T'Fusor Sound Diffusor - Acoustic sound diffusion products from Auralex Acoustics.) on each side instead of on the ceiling? I bought 4 of them, but can always order more...they seemed inexpensive and had good reviews. I'm open to other suggestions though.

I've also been considering some sort of "mix cloud" for the front portion of the ceiling that is currently naked (where the diffuser traps used to be in the second photo.

Any recommendation on mix clouds? I was looking at the Real Traps RFZ panels and also considering making my own out of UltraTouch R19 (UltraTouch R-19 24.25"(63sf) - Natural Built Home (naturalbuilthome.com)), which is what I used in my drum booth. Anyone have any links to good DIY mix clouds? Tips on making sure you hang clouds and diffusor squares in a straight line? I love doing these simple projects myself but as a first timer it's tough for me to get my lines straight when hanging multiple things on the ceiling.