square room woes!!!

Posted: Tue Mar 04, 2003 11:42 am

Alright,
I know the subject of mixing room set-up has been beaten to death, but I
really need some words of wisdom. I have a newly constructed 11' X 11'
room in my basement that I just built to record and mix in. I have been told
by many and have read numerous posts that trying to mix in square room is
tantamount to pissing in the wind. However, it's all I have to work with...My
question is...Can a room this size be treated to be usable? I know it will
never be optimal, and that there will always be a challenge with bass
frequency accuracy. I am putting 4" thick rock wool panels (2' X 4') at various points on the side walls (gave up on trying to find 703 / 705 board), above the console/speakers, diffusers in the rear of the room and a pretty much live front of the room. Some words of encouragement please, the thought of my new dynaudio BM6a's being worthless in this space depresses the hell out of me. Thanks.

Posted: Tue Mar 04, 2003 12:42 pm

Hey Rob,

Yes, a room that shape is pretty bad, and the only thing worse is if your ceiling is also 11 feet high! But it is definitely possible to make the room quite usable, if not ideal.

The most important thing you'll need is bass traps. What causes low frequency problems in any room is reflections off the walls, floor, and ceiling. So the more you can reduce the reflections, the flatter the room will be at the low end.

> I am putting 4" thick rock wool panels (2' X 4') at various points on the side walls <

Are these panels semi-rigid? If so, they're equivalent to fiberglass. Four inches is great, and if you space them off the wall so there's a four-inch air gap between the panels and the wall, they'll help even more.

You can also build wood panel bass traps using the plans linked on my Articles page:

www.ethanwiner.com/articles.html

Those plans show how build serious bass traps that will absorb low frequencies even more than very thick fiberglass or rock wool.

Finally, if the panels you have are indeed rigid, you can place some across the room corners for even more effective low frequency absorption. This photo is from the Acoustics FAQ I plan to post here very soon:

<img src="http://www.ethanwiner.com/corner-trap.gif" alt=" - " />

This picture shows the corner viewed from above, looking down from the ceiling.

If you can hang in there another day or two for my new FAQ article, a lot more of these issues are explained in great detail.

--Ethan

Posted: Tue Mar 04, 2003 8:59 pm

Thanks a bunch Ethan. You are indeed a master, and very re-assuring. I appreciate it, and look forward to your future updates.

Posted: Tue Mar 11, 2003 10:15 am

Rob,

You think 11'-0 x 11'-0 is horrible just because it's square? Not so fast!

I love debunking myths, and the myth of the square room is surely one of the most entrenched. So here we go.

Modal distribution is of course one of the most important criteria for good bass in any small room, but there is no law that says you must have 3 different fundamental modes, or any fixed number for that matter. I know this goes against everything you may have read before, but bear with me here.
Since you're dealing with a rectangular space and thinking in 3 dimensions, and know that 2 of your modes will have identical frequencies, the real question is what is the other frequency , or put another way, what is the ceiling height? Is it by chance somewhere around 8 ft.? If it's 8 ft. exactly then you're looking at 121 sq. ft. of opposing surfaces at 70.6Hz, and 176 sq. ft. of opposing surfaces at 51.4Hz. Musically speaking, these two frequencies are exactly an augmented 4th away from each other (just intonation), and that's a very good thing. If you have only two modal frequencies to work with, it doesn't get any better than that. Well, an equal tempered aug. 4th would be slightly better, and for that you'd need 8'-3". In other words, the two keys associated with 51.4Hz and 70.6 Hz (essentially "Ab" and "D") are exactly opposite each other on the Circle of 5ths (or musical clock), so that in the first two octaves or so where it really matters, the modal frequencies are by definition evenly spaced. This stuff is real easy to see if you do your modal calculations at the piano, which can be seen as a beautifully laid out logarithmic modal chart.

Now I'm not saying I would design a room from scratch this way, but my point is that in the low octaves, a devil's tone * between modal frequencies is not all that bad. And no-one has been able to show me how two sets of opposing surfaces is all that different from one set of the same square footage. And 121 sq. ft. compared to 176 sq. ft. is not all that bad--a 60/40 split.

There is the fact that 51Hz is a little high for your lowest modal frequency. But good bass trapping can lower that somewhat. And hey, lots of gospel music is in the key of "Ab".

An interesting aside is that "Ab" and "D" also just happen to be the two axes of mirror image symmetry on the piano.

OK, I know I've just gone way out on a limb, but I like it out here. Bring on the chainsaws. But you'd better have 'em gassed up.

--Wes

* I forgot what I was gonna say down here--something about the devil being in the details...

Posted: Wed Mar 12, 2003 9:15 am

Wes,

> You think 11'-0 x 11'-0 is horrible just because it's square? Not so fast! <

I'll bet you $100 that I like to debunk myths even more than you do! Smile

Hey, I've been saying all along that too much is made of room modes by people who have no ability to change them anyway.

> Musically speaking, these two frequencies are exactly an augmented 4th away from each other <

I assume/hope your point is not the musical relationship, but the fact that the modes fall halfway between each other, right?

--Ethan

Posted: Wed Mar 12, 2003 10:51 am

Ethan,

Quote:

I assume/hope your point is not the musical relationship, but the fact that the modes fall halfway between each other, right?

Exactly. Halfway between the octave is as even as it gets with only two fundamentals. The reason I like to talk about acoustics in musical terms is to make it more accessable to musicians, and to help people realize they can hear this stuff.

Of course I'm often guilty of utterances like "the cube root of 2", but I try and pause to say "you know, a major 3rd". I know everybody wants to talk in layman's terms, and math does make lots of folks edgy, but I figure if they can't get a handle on a concept like "major 3rd", they're in the wrong business.

Hey, thanks for deleting that mess my computer spewed out last night.

--Wes

Posted: Wed Mar 12, 2003 1:16 pm

Wes,
I enjoy your bringing acoustics into musical terms, it keeps me focused on what this is all about.
But I'm a little confused by your saying that the piano keyboard has 2 axes of mirror image symmetry. I can see one axis, but don't understand where the second axis is.
Thanks,
Scott

Posted: Wed Mar 12, 2003 4:26 pm

Scott,

Quote:

the piano keyboard has 2 axes of mirror image symmetry. I can see one axis, but don't understand where the second axis is.

Look at the the pattern of black and white keys, and notice that if you choose "D" as the center, the pattern to the right of "D" going up is an exact mirror image of the pattern to the left of "D", going down. The same thing works with "Ab" (A flat). It's no accident that these two notes are exactly six 1/2 steps apart (or 1/2 an octave), but rather an inevitable manifestation of the laws of symmetry. Here are some more interesting observations concerning the piano keyboard:

There is only one way to divide 12 things (notes) into two groups (black and white) so that by the pattern and the pattern alone, each note has a distinct visual identity, and that's how the piano is laid out. You won't confuse an "Ab" with any other note because it's the middle one in the group of three black ones, for instance. Try it for yourself and see--there's no other pattern that works. It has to be five and seven, in that particular sequence (2 blacks, 3 blacks, etc).</li>
The ratio of five to seven is 1:1.4, a well known and highly recommended modal ratio. It's also, in musical frequency terms, the interval of an augmented 4th (just intonation), or the distance between the two axes of symmetry of the piano, "D" and "Ab".</li>
The ratio of seven to twelve is the nearest possible approximation of the Golden Ratio division of the number 12. It's also, in frequency terms, the interval of a major 6th, which is one of the musical manifestations of the Golden Ratio. The Golden ratio itself (1.618), and many of it's close approximations along the Fibonacci series, make excellent modal ratios. Many people are familiar with the ratio 1.6 from the Alton Everest books.</li>
Also, if you take a piece of gridded graph paper, and plot 12 units over, and 7 units down, then draw the hypotenuse, that's a 30 degree angle--the angle your speakers should be tilted in if you have an equilateral listening triangle .</li>
The relationship of five to twelve has been raising eyebrows for centuries. The Circle of 5ths (or 4ths rather--same thing looked at the other way) consists of twelve keys, each five 1/2 steps apart. By a strange coincidence, our clock consists of twelve hours, each five "minutes" apart, visually speaking. A geodesic dome (think of a soccer ball) has twelve nodes; each node is a five sided pentagon, and each is located a Golden Ratio distance from five other nodes, compared to it's five nearest neighboring nodes. Plato and Buckminster Fuller both figured this one out, over two thousand years apart. And the sign of the Pythagorean Brotherhood was the pentagon inside the circle, a sort of visual icon symbolizing this principle. Pythagoras was a pretty jammin' musician, as well.</li>

Well that's all for today. Did that clear things up a bit?

--Wes

P.S. This stuff really does apply to acoustics. I promise...

Posted: Wed Mar 12, 2003 10:52 pm

Dude....That was some of the goofiest, most wacked-out stuff I've read in a long time.

5's, 7's and 12's.

I think my brain just melted.

Peace,

James

Posted: Wed Mar 12, 2003 11:19 pm

Keep 'm coming Wes!
Great, man, I've been digging through all these numbers of roommodes, difusors etc. and it's coming together.

I have the studio construction on a budget from Everest, which really got me going. What books would you suggest as a "must-read". I'm really interested in understanding the principals of acoustics, not just read to plans of existing studios.....

Greetings,
Dirk

Posted: Thu Mar 13, 2003 12:11 pm

Dirk,

Quote:

I'm really interested in understanding the principals of acoustics, not just read to plans of existing studios.....

Here are two for starters:

"On the Sensations of Tone" by Hermann Helmholtz

" The Acoustical Foundations of Music" by John Backus

I strongly urge you not to swallow this stuff whole, especially the music theory part of it. Although these guys may have impeccable credentials in the world of science, J.S.Bach they ain't, as far as I know. But it'll sure get you thinking.

One of the true geniuses of the twentieth century in my estimation was a composer by the name of Harry Partch, who may have understood the art/science of music, ratios and harmonics more deeply than anyone in human history. (How's that for a sweeping statement with emergency escape hatch?) Unfortunately, or fortunately, depending on how you look at it, his understanding of the physics of music was so profound that it caused him to abandon the standard 12-tone scale altogether, being unable to put up with the compromises inherant in the 12-tone equal-tempered system that we all know and love.( Thirds and sixths are always out of tune by 14 cents. ) And so he struck out on his own and developed a system of non-tempered music based upon, among other things, a 41-tone scale (41 different steps just to get up or down one octave!), and invented a whole orchestra's worth of new instruments for which to score his music.

Harry Partch's book is entitled "Genesis of a Music". Although not about acoustics per se, I consider it a "must read" for any musician who simply would like to have their mind blown.

--Wes

Oh yeah, 41 equals 5+7+5+7+5+7+5, but that's probably just a coincidence...

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