Alternating Placement of Bookshelves as Diffusors

[Obi-Wan zenabI]

Ok, the studio is done, at least phase one...

Construction:
20'x30'X7'2" room,
oak flooring
open stairwell to cinderblock 2-car garage below.
5/8" Drywall over 1/2" sawdusty soundboard stuff

Functions of Room in order of importance:
Rehearsal space
Hi-Fi listening room
Recording Studio

I have a ton of books and several thousand records that must be put up there, and picked up six 3-foot-wide bookshelves to store everything.

QUESTION: I've put the shelves along the long walls in an alternating pattern, with each bookshelf facing blank wall opposite (see attachment). My idea is to reduce bare walls that face eachother to even the response of the room. Cheesy paint representation attached. The brown and black blobs are my big ol' desk, my rhodes suitcase, and my hammond.

Opinions? (before I load the rest of my books and records in...)

Thanks!

Edit: the little squares are my Thiels and my DCM time windows. Not sure where to cram in my antique B&Ws. (those are speakers for my CDs and records) Also, they are centered in the room in real life, and placed outside of nodes as per RoomModeCalc (not sure if they should be in the nodes or out after reading some threads here ) Listening seating is against the far short wall. Nearfields will go on my desk.

 

[Ethan Winer]

I wouldn't expect much help from a few bookshelves. In a room like that you'll probably do better with either absorption or real diffusors. But probably absorption. Another problem I see is the non-symmetrical placement, which is also not a good idea. Especially in the front of the room, from your ears forward, things should be fully symmetrical.

--Ethan

 

[Obi-Wan zenabI]

Ethan,

Thanks for the advice.

It is quite a lot of shelving... three thousand LP records and an English teacher's collection of books-- 18-plus linear feet, 136 square feet of books and such altogether.

At any rate, I 'm beginning to think you're right about it doing more harm to stereo imaging than help in spreading the diffusion around.

But still... everyone on here seems to dismiss bookshelves, but with each row of books amounting to a randomized skyline shape, and with a varying "slot" of space above each row of books, I can't see how they would not do the same job (to lesser degrees, to be sure) as some "metrofusor" and a hemholtz resonator.

I think it will come down to practicality of placement. I think i can fit more instruments/amps/gear in if I slide the shelves all together down towards my listening seating.

 

[Ethan Winer]

everyone on here seems to dismiss bookshelves, but with each row of books amounting to a randomized skyline shape, and with a varying "slot" of space above each row of books, I can't see how they would not do the same job (to lesser degrees, to be sure) as some "metrofusor" and a hemholtz resonator.

A real diffusor is not random, but follows a mathematical sequence. This is not to say random isn't better than a flat wall - it probably is. But it's not really diffusion either.

--Ethan

 

[RICK FITZPATRICK]

No one disputes that a rear wall of random wells formed between books can diffuse AND absorb .....somewhat. And that is the crux. Somewhat. From my understanding though, random distrubution of phase grating type well faces as in a book shelf full of books, actually produces reflections similar to specular reflection of a flat wall. The reason commercial phase grating diffusing units work so good is the well widths and depths are calculated using number theory sequences(quadratic residue/prime root etc.) that maximises the distructive interference produced when wavefront reflections lag by 1/2 wavelengths/ 1 1/2 wavelenths/ 2 1/2 wavelengths etc. And the lowest frequency that can be diffused is governed by the actual physical dimensions of the unit. Although I'm certainly no expert so read this for the scientific background.
http://www.acousticalsolutions.com/education/pdfs/Diffusion_Critical_Listening_Rooms.pdf

 

[gullfo]

wonder what happens if you stack the books in approximately the same ratios as a QRD diffuser? you could calculate the QRD 13 or 19 diffuser and arrange books by relative width and depth... then if anyone asks how you sort your library you can tell them "by quadratic residue sequence"

 

[RICK FITZPATRICK]

then if anyone asks how you sort your library you can tell them "by quadratic residue sequence"

You'll need a DEEP bookcase to offset books with these type well depths. AND the book thickness's will have a bearing, maybe using two or three to get the right well widths. I hope you know I was only trying to illustrate the concept, not to say books could not do the job if implimented correctly. But in reality, random arrangements do little for true diffusion. And even if you DO achieve a similance of a diffuse sound field, understand 2 things. Phase grating devices are ALSO 1/4 wavelength SILENCERS Not to mention your room dimensions and absorption in the room will determine the decay rates of different frequencies, which has a bearing on the so called "diffuse" sound field. Even experts admit that measuring diffusion, especially in a small room, is a very difficult if not impossible task. Not only that, but the room dimensions govern the lowest frequency you could possibly diffuse, if even possible. At least, thats my understanding.

 

[gullfo]

I noticed Ethan Winer now has a new diffuser/absorber unit on his realtraps.com web site...

Ethan - when looking at "typical" plans for a QRD diffuser, the well walls extend all the way to the front. in the pictures on your site, it doesn't look like the diffusers have well walls. how does your design compare to the typical diffuser design?

i was thinking if you did the QRD calculations and then used pin stripe tape to layout the design on each bookshelf (pin stripe tape is thin and would be discrete...) then stacked/arranged the books to fit...

agreed the depth and width of each "well" relates to the lower and upper frequencies affected. however if you stick with a QRD with 7 wells per period, then your effective depth is twice that of using 11,13, or 19.

 

[RICK FITZPATRICK]

Yea, thats cool.

 

[beezelbubba]

Just throw 'em any ol' place!
Doesn't matter!

 

[RICK FITZPATRICK]

Doesn't matter!

From the perspective of your cesspool, I would imagine it doesn't.

 

[Ethan Winer]

Glenn,

> in the pictures on your site, it doesn't look like the diffusers have well walls. <

Sure they do!

I'm taking better / newer photos tonight of the final production models, and they'll be on our site soon. Hopefully the appearance will then be a little clearer.

--Ethan

 

[RICK FITZPATRICK]

Sure they do

What are they made of Ethan?

 

[gullfo]

Glenn,

> in the pictures on your site, it doesn't look like the diffusers have well walls. <

Sure they do!

I'm taking better / newer photos tonight of the final production models, and they'll be on our site soon. Hopefully the appearance will then be a little clearer.

--Ethan

thanks! from the photos it looked like you made a new type of diffuser and I was curious if somehow building them without wells did something more interesting or better... on second visit if i look at the top i see them... it was that straight on shot that made it look that way...

 

[Ethan Winer]

What are they made of Ethan?

Metal, chip board, rigid fiberglass, three kinds of plastic, and fabric - but not necessarily in that order.

--Ethan

 

[Obi-Wan zenabI]

What I wound up doing...

It was a nice idea, but...

The alternating bookshelves with various 1970's electric pianos stuck in between really cramped the room up. I want easy load in and movement in the room.

I wound up sliding all the shelves down (up in my lame pic) to the far end away from my mixing desk. I will build up some 703 absorbers and move 'em around until I get the room tamed a bit, then maybe play around with some of the foam stuff to get any initial reflection points that the fiberglass seems to be missing.

Am I right in making the room more "dead" behind the mixing desk and keeping more reflective surface in front?

Also,

to those watching this thread, I had an idea for a diffusor made out of varying lengths and diameters of pvc pipe, all glued to a board (a circular one would look way cool...) painted nicely, with maybe a puff of fiberglass pushed down into the end.

When I first started getting into this, someone's website described the Roman amphitheaters with their jars placed around as diffusors... it was in some description of a slot resonator.

I really want to try this, but I don't know if my ears are experienced enough to really report back on my success/failure.

Joe

 

[gullfo]

having your "diffuser" bookcases farther away from the mix desk is better. generally you want a room to retain enough energy to sound good but not overly live where the bass modes, indirect reflections and echos make things mushy or indistinct. if you can get proper angles to the walls and just enough absoption to keep the direct sound true and temper the lower frequency ranges, you will probably have a decent room. using the foam at first reflection points can work but typically having a 2" rigid fiber absorber spaced a couple inches off the wall (at the reflection point on either side of your mix position) should be effective. also put a cloud overhead (similar to side absorbers) and maybe some carpet under the desk (if not already there...)

and to answer your question - i prefer the front end to be live and the backend dead - so if you can get the reflections minimized using judicious placement of absorbers you'll have a nice lively front and if the room is long enough and has diffusion and some more proper placement to make the back less lively, you should have a good balance.

 

[Obi-Wan zenabI]

gullfo--

great-- that's just the kinds of stuff I'm planning on adding. In fact, I dropped by SEI (or was it SPI??) in Stratford, CT on my way home from work today. (how nice is it to have a source for condensed f'glass right on your commute??? )

I was planning on coming home with a bundle of the stuff, but stopped because I didn't know if the 3#/cubic ft weight was right, as it seemed to have worse bass reduction coefficients than the less dense stuff.

I will have to poke around in some of the other threads before I settle on which weight to get. Then there's the facing issue... hmm. Time to research.

Also, they were very nice at the shop in Stratford. I always expect gruffness from folks at those kind of places if I'm not a contractor with a huge order....

Cheers, Joe

 

[Obi-Wan zenabI]

Also, it looks like I'll be working out a seprate mixing position and recreational listening position, since the studio's sofa is to be on the back wall very distant from the mixing spot.