ESS approach in small/medium room

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ESS approach in small/medium room

Postby detlof » Sat Feb 21, 2004 3:02 pm

I am about to plan for acoustic treatment in my new, unfinished room. Since I will use it as both a recording room and as a mixing and editing room, I want it to be fairly live sounding. I read about the ESS approach in Sound on sound and here: http://www.electroacoustics.co.uk/article/essroom.htm and thought this might be an approach for my room. Room size will probably be 7 m x 3,75 m x 2,5 m. (23´x12,5´x8,2´). Some questions arise:

1. Is this too small a room to do anything like this?

2. Would polys work for this application, or would one have to use Schroeder diffusors?

3. What would happen if one used polys all over instead of making back wall absorptive?

4. Would this approach benefit the room as a recording space? (Ac guitar, double bass, drums, brass, piano, vocals, elec guitar, speech etc)

5. Could this approach benefit the room as a mixing space? Would it be much inferior than to have absorption at the early reflection points?

My idea (totally uncalculated) was to make polys of different sizes and let them cover most of the walls + mount 120 cm wide (4´) floor to ceiling corner bass traps in the front end corners. Let me stress again that this is not calculated in any way, just an idea. I know I will have to calculate on room size, modes, rt60, total absorption of materials bass traps and polys, and above all listen to and measure the room. (did I get it all in there?) An alternative to the all poly approach could be all polys but with Schroeder diffusors at the early reflection points.

Please share your thoughts with me.

regards
Jonas
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Postby Scott R. Foster » Sat Feb 21, 2004 3:12 pm

Jonas:

That's a lot of diffraction gratings to build/buy... but if you got the time/money it sure would look cool [and looking cool is NEVER to be underestimated in value]. An array of 2d diffusers [like the Skyline] would be even cooler.

http://www.customaudiodesigns.co.uk/dif ... kyline.htm

Though something like the Auralex T'Fuser would be much cheaper and with the right paint job might look almost as cool.

FWIW I bet a well thought out array of polys could do the job but the only way to be sure would be to do it and then listen... its your time/money so proceed at your own risk.

Whatever you do, I would suggest you do one room at a time - so what you learn on room 1 can be carried over to room 2... also, if you discover it doesn't work, or aint worth the effort - you are only in for half the pain the ass of having done it.

Good Luck!
SRF
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Postby detlof » Sat Feb 21, 2004 5:09 pm

Hi Scott!
The idea was to make it all polys, to save time and money - they will be much cheaper than making diffraction gratings, though I´m not sure of how effective they are, and wether the ESS aproach relies mainly on the difference in time that arises with diffraction gratings. - Can I achieve that nice and wide diffuse soundfield with polys at the early reflection points?
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Postby Bob » Sat Feb 21, 2004 8:05 pm

Hello:

(When in doubt, I don't know what I'm talking about.)

The first time I saw this ESS page was 2002/08/13. I had forgotten it.

I was thinking about the ESS idea of using difusion at the primary reflection points, as well as around the speakers, and it's effects on stereo imaging. Certainly this results in a live room. And of course real world double-blind tests will tell the tale as to whether it works with human ears and brains.

Most interesting to me was the
Where the primary reflection is from a diffuse surface the reflection will be markedly reduced in level, as the energy is being dispersed in many directions, and so much smaller cancellations will be produced.
However, because the spatial diffusion is accompanied by temporal diffusion, the notches are dramatically damped, to the point of non-existence...The diffusers close to the speakers effectively convert the speakers to large plane sources, which do not suffer from the same constructive and destructive interference effects, removing the biggest obstacle to achieving consistency of frequency response throughout the room.


The rule around here (SF-ABC = SteveFoster ABCs of Room Design) is corner traps, and absorbtion only at the primary reflection points, and optional defusion at other spots especially the rear wall. This results in less absorbtion than LEDE.

ESS recommends damped membrane absorbers, especially on the rear wall. Which seems to me that it makes the ESS design a DELE room, with the significant difference being the difusers close to the hemispherical effects near the speakers (which have their own polar energy plots by frequency).

I started thinking about bi-polar speakers like those at http://www.definitivetech.com, which bounce the sound off the rear walls creating a wider sound field (a delayed plane source), vs the ESS style, vs SF-ABC. I'll skip the bi-polar stuff, and just chat about the last two.

Difusion has 2 effects
1) lowers the amplitude of the first reflected sound, but this effect is position dependant due to the scattering directivity of the difuser (see A/B/C/D of http://www.rpginc.com/research/ndp.htm ) and is proportional to the size of the wells.
2) if the first reflection didn't hit the listener (one of those quiet spaces between the loud-wide scattering peaks in the A/B/C/D), then the subsequent reflections tend to cancel each other out (as I read ESS). For steady sine waves it's obvious. Musical notes tend to change 5 every second. So assuming (doubly big assumption) it takes 10 difuse reflections before that wave bounces into itself and superpositions to zero, at 1130 ft/s / 10 / 5 is 22 ft. So any room larger than that will take too long to have this effect. Voices are even faster than 5 changes a second, so almost any room size won't have this effect.

That leads me back to SF-ABC vs ESS.
The freqency response of a difuser is about 4 octives (65hz to 1khz, 130hz to 2khz, 261hz to 4khz, 500hz to 8khz). Skylines are good from 565hz to over 4khz.
A 4" thick absorber mounted 4" from the wall works from 100hz to 16khz at almost an absobtion coeficient of 1.0 throughout. So that's a wider frequency range. Both effects #1 and #2 above are irrelivent, because there is no polar plot for absorbtion reflections (there aren't any), nor any superposition of subsequenct reflections (there aren't any).

With SF-ABC there would be other reflections similar to #2 for all the untreated or difusively treated surfaces, except they're all at lower volumes due to the increased distance the wave has to travel, and delayed longer in time. But if I read ESS right and they cancel each other out, then the difference in the amount of treated wall surface should indicate how significant this is between SF-ABC and ESS. ESS has about 10% more of the wall treated with difusion. I doubt that makes much of a difference.

So what do you think? Have I missed the boat ?
Regards
Bob Golds
"The only thing we regret in life is the love we failed to give."
"Be a rapturist -- the backward of a terrorist. Commit random acts of senseless kindness, whenever possible" - Jake Stonebender
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Postby Scott R. Foster » Sun Feb 22, 2004 12:08 pm

detlof wrote:Hi Scott!
The idea was to make it all polys, to save time and money - they will be much cheaper than making diffraction gratings, though I´m not sure of how effective they are, and wether the ESS aproach relies mainly on the difference in time that arises with diffraction gratings. - Can I achieve that nice and wide diffuse soundfield with polys at the early reflection points?


Yes indeed polys are cheaper easier to build.

It is hard to say what the quantitative differences would be in the diffusive action of diffraction gratings versus polys for your purpose. AFAIK there is still no generally accepted metric for diffusiveness - much less published data for various devices enabling one to compare apples to apples.

That said, one thing is for sure, and that is that all gratings have lobes of ineffectiveness [parts of the band where they exhibit no diffusion at all]. Polys OTOH - for a given unit dimension - probably have a narrower overall band of effectiveness - but without the lobes. I think you'd be investing in a "try and see" proposition to use polys for this application - but I bet it would work nonetheless - and as you point out, be much easier to build. That's just a guess so proceed at your own risk.
SRF
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Postby Howler » Mon Feb 23, 2004 11:08 am

>The rule around here (SF-ABC = SteveFoster ABCs of Room Design) is corner traps, and >absorbtion only at the primary reflection points, and optional defusion at other spots >especially the rear wall. This results in less absorbtion than LEDE.

"ummmmm....." "I am standing here beside myself"

Dazed and confused in Alabama
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Postby Bob » Mon Feb 23, 2004 6:58 pm

Howler / Steve Foster:

Sorry if I misquoted you.

When I wrote 'around here' I was thinking of a note by Eric somewhere that said something like
if people come to yahoo.acoustics first they' build corner traps
if they came to RO before 2002 then they build hemlmoltz resonators, and slat resonators after
if they came to ... first they build panel traps

(unfortunately I didn't save that one).

Here's what you and others actually wrote (It looked so useful I turned it into a text file)
Steve Foster's ABCs of Room Design:
So my ABC approach to room treatment for the DIY'er stands: 1)keep all
absorption broad band to the very end - treat specific frequencies only if
you can find no way around it; 2) start in the corners, floor to ceiling,
panels as wide and as deep as you dare - catch em all big and small; 3)treat
the front of the room for early reflections with absorption / front
wall-ceiling shaping / adjusting mix-speaker position / voodoo dolls]; 4)
defeat flutter [either absorbers, or diffusion] keeping in mind that if you
have a flat ceiling, the floor to ceiling flutter is by far the largest area
of parallel flat surfaces and therefore probably needs the most attention;
5) Add broadband absorption to hit your desired RT60 [wall panels / clouds /
ceiling grid].

Ya - good ole ceiling grid might be just the ticket to match your needs in
3, 4 or 5 above, but use it only if it fits the recipe... smart to remind
folks it's out there... but I wouldn't start with it and try to work my way
back to the overall solution. I'd say start with the corners and remember
that grid is a cheap and effective tool in trying to piece a solution
together for your room - keep in mind that if polys are used for wall
flutter [vs. wall mounted absorption panels] then treating whole ceiling is
a great way to go - it just about takes that giant floor to ceiling thingy
out of the equation entirely - you can almost forget 3d and start thinking
in 2d [plan view].


Jeff adds
"At least 20% to 35%
coverage of walls and ceiling with good acoustical treatment fairly evenly
distributed will go a long way in a small room. For mixing areas, treating
the early reflection points first is key. After that, so on and so forth
into bass and diffusion and the rest as appropriate."


Scott wrote:
"the reverberation characteristics of virgin mahogany
paneling, lumbered, milled, installed and then hand
rubbed with extra virgin olive oil by a virgin Druid
Priestess would not necessarily sound any better than
wall coverings made of pressed dog poop installed by
drunken sailors."

I would suggest varying the sheathing on opposite sides... perhaps two 1/2"
over one 5/8th layers on one side and then two 5/8th's on the opposite side.
Use double framed - or double studded walls, and if you use wood studs add
RC to one side.

Read the USG links for wall construction methods - USG makes an acoustic
caulk that is readily available in the US - backer rod is a big help - big
caulk guns that take the big tubes save money.

Any sturdy door system will work when doubled [you can add mass to doors
easily by adding a panel to one or both faces of the door [though you might
need to secure the hinges better] - if you add mass to both doors,
differentiate the mass], the main thing to look for IMO is good seals.

I have used pre-hung, steel clad, exterior doors with magnetic seals with
good results - be sure to caulk the units in all the way around [I set mine
upside down and filled the threshold plates on mine with caulk before
installation - drywall mud would work also I suppose].
Regards
Bob Golds
"The only thing we regret in life is the love we failed to give."
"Be a rapturist -- the backward of a terrorist. Commit random acts of senseless kindness, whenever possible" - Jake Stonebender
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Postby detlof » Mon Feb 23, 2004 9:02 pm

LOL!!!!!!
"the reverberation characteristics of virgin mahogany
paneling, lumbered, milled, installed and then hand
rubbed with extra virgin olive oil by a virgin Druid
Priestess would not necessarily sound any better than
wall coverings made of pressed dog poop installed by
drunken sailors."


And then some prefer the aroma of olive oil and virgins while some prefer the smell of dog poo, rum breath and transpiration.... BTW the drunken sailors should both be more diffuse and absorptive, so maybe they´re to prefer after all.

That's just a guess so proceed at your own risk.


Scott, from now on I will hold you personally responsible for all acoustical anomalies in my studio!

;-)
Jonas
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Postby Dan Nelson » Tue Mar 02, 2004 6:45 am

Bob wrote:Howler / Steve Foster:

Sorry if I misquoted you.

When I wrote 'around here' I was thinking of a note by Eric somewhere that said something like
if people come to yahoo.acoustics first they' build corner traps
if they came to RO before 2002 then they build hemlmoltz resonators, and slat resonators after
if they came to ... first they build panel traps

(unfortunately I didn't save that one).



hmm I build none of the above, well a few corner membrane traps once, but the room was large and concrete and it only took two 4' by 8' absorbers to take care of the problem

Dan
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Postby Eric.Desart » Tue Mar 02, 2004 8:25 am

Bob wrote:When I wrote 'around here' I was thinking of a note by Eric somewhere that said something like
if people come to yahoo.acoustics first they' build corner traps
if they came to RO before 2002 then they build hemlmoltz resonators, and slat resonators after
if they came to ... first they build panel traps

(unfortunately I didn't save that one).



Hi Bob,

Wrote that one as a joke!
Basically to tell that there are several ways to obtain a goal.

More correct:
People accidentally finding this (former Yahoo) group first, end up with corner traps.
People finding RO before ca 1 year back, ended up with paneltraps.
Now they also end up with minitraps or corner absorption. This isn't accidental.
People finding John Sayers group first, ended up with Slat type Helmholtz resonators.

The idea used at John Sayers is in fact somewhat comparable what we do here, but by using broadband Helmholtz slat type absorption they integrate absorption and mid/high reflection/diffraction/scattering (to certain degree).
That's what's obtained here by the polys. But polys cover a broader frequency range (size) but less surface.
Personally I like the idea of corner absorption combined with polys. It's simple and effective.

But's it's Scott's ABC (if you mean FAQ). Scott is the brain, combining all this basic loose topic knowledge in a readable logical FAQ. Or I probably am missing something (my head is cheese with holes).

Best regards.
Eric
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Postby Paul Woodlock » Fri Mar 05, 2004 4:03 am

Eric.Desart wrote:(my head is cheese with holes).

Best regards.
Eric


now that's not very good for isolation is it? Caulk them up, your waking the neighbours :)


Paul
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Postby Scott R. Foster » Fri Mar 05, 2004 11:42 am

Hmmm chesse. A slice of Eric's head anyone?

Ooop cat got it.
SRF
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Postby noxix » Tue Mar 09, 2004 5:32 am

I've been interested in the ess design concept for a while. Wish I could hear one. As noted above, it's interesting that its basically a dele room.

Ok, so how about setting up a room with surround speakers, but if you face one way and only activate 2 speakers, you have ESS, but if you face the other way and only activate 2 speakers, you have a LEDE?
===

And as always, with many thanks to the Unnamed Ventricle
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