Speaker Placement Vs. Acoustic Treatment....if you get one, do you need the other?

[GabeHerman@gmail]

I've been working in a fairly small control room and have been reading up on Acoustics and Speaker Calibration.

My question:

I'm realizing that the EQ response of my room changes dramatically when I move around the space. This really gets frustrating when I have clients with me who aren't experiencing what I am due to where they are sitting behind me. When you already have set up your monitors in the ideal monitoring position and you are still getting these results, how do you go about calculating what materials to use where?

I understand that absorption behind the monitors is good as it keeps sound from bouncing back into the listening position, and I know that diffusion is good on the back wall as it compensates for standing waves and such. I've also read that some absorption is good immediately to the sides of the monitor position to help with early reflections and flutter. But I also know that these treatments have to be measured to be completely effective. How do you go about determining how much of these treatments to use, and where?

Thank you for the support and any first hand info/experiences, including online and printed resources would be appreciated! I'll be posting some photos soon to help you understand the room size and components...

[Scoobz]

Hi Gabe,

How big is your room?

Yes you're thinking correctly about your room, the idea is to cut down on your room's influence on what's coming out of your speakers.
In order of things to do

General advice is to have the speakers setup symmetrically along the short wall (so the speakers point the length of the room) an equal distance from the walls either side. You should also place them in an equilateral triangle (eg the distance they are from each other should equal the distance to your ears, this should be somewhere in the region of 0.8>2m for nearfields)
A good starting point is to sit 38% of the room's length from the front wall (the end you have your speakers)

Treat your 'RFZ' reflection free zone, this is normally done with a mirror and a friend. You sit in the listening position and your friend runs the mirror across walls, ceiling, desk etc. If you can see the speaker in the mirror you want to put something in that spot.
Usually this is some form of insulation, about 2" thick (although thicker is better) rigid fibreglass or rockwool (mineral fibre). You also want to space this away from the wall (again usually the thickness of the material you are using) as this will extend the absorption to the lower frequencies.

Next is bass trapping, when low frequency waves (which are long) bounce off a wall and collide with the waves still coming from the speaker this causes a cancellation, null or dip. This is the SBIR you are talking about behind the monitors, so you want something thick and spaced from the wall back there. Bass 'hangs out' in the corners of the room, the standard way of dealing with this is to put thick, dense insulation across the vertical corners (a panel about 4 foot wide floor to ceiling, andat least 4" straddling the corner)
(The ceiling/wall corners and floor/wall corners also need to be addressed if you still have response problems)

Depending on the size of your room you will need either diffusion (scattering) or absorption on the back wall

There's other options, like superchunks but for now those things I suggested should be a great benefit.

You're making 8 panels, 1 for each vertical corner, 1 behind the speakers, and one for each side and 1 for the ceiling (RFZ)

My advice is to get some measurement software (room eq wizard is free, ETF or R+D is payware) and a cheap measurement mic (the behringer ecm8000 is fine for this purpose) so you can see what improvements you've made and what still needs to be addressed

Let us know how you get on

[Scoobz]

If you have money burning a hole in your pocket, Gik acoustics and Real traps give proven results, if not get yourself over to one of the other sub forums and start reading up broadband traps.

They're basically panels made of insulation with an open weave fabric covering them, sometimes in wooden frames, sometimes simply the rockwool/703 just covered in a fabric 'bag'

Good luck!

[Ethan Winer]

Originally Posted by GabeHerman@gmail

When you already have set up your monitors in the ideal monitoring position and you are still getting these results, how do you go about calculating what materials to use where?

It's simpler than you think. Here's the short answer, which will get you 99 percent of the way there. All rooms need:

* Broadband (not tuned) bass traps straddling as many corners as you can manage, including the wall-ceiling corners. More bass traps on the rear wall behind helps even further. You simply cannot have too much bass trapping. Real bass trapping, that is - thin foam and thin fiberglass don't work to a low enough frequency.

* Mid/high frequency absorption at the first reflection points on the side walls and ceiling.

* Some additional amount of mid/high absorption and/or diffusion on any large areas of bare parallel surfaces, such as opposing walls or the ceiling if the floor is reflective. Diffusion on the rear wall behind you is also useful in larger rooms.

I understand that absorption behind the monitors is good as it keeps sound from bouncing back into the listening position, and I know that diffusion is good on the back wall as it compensates for standing waves and such.

Actually, both of those are wrong. Your speakers point away from that wall, and diffusion works at frequencies much higher than those generally considered to create standing waves. More here:

Front Wall Absorption

I've also read that some absorption is good immediately to the sides of the monitor position to help with early reflections and flutter. But I also know that these treatments have to be measured to be completely effective. How do you go about determining how much of these treatments to use, and where?

See these two articles:

How to set up a room
Early Reflections

--Ethan

[GabeHerman@gmail]

This is all really helpful, but I am also confused about something else...

Is it that there's an abnormally large amount of Bass present in the corners that radiates to the rest of the room, or is it that there's an absence of High Frequencies?

My control room dimensions are:

13 ft long x 9 ft wide x 8 ft high

I'm installing some new furniture today, so I'll attach some photos tomorrow.


I have already hung a 4" thick bass trap suspended from the ceiling with a 3" gap between the wall and the panel. It is wrapped in fabric and is filled with Owens Corning 708 rigid insulation. There are auralex wedge panels in the corners behind the monitors. The back wall has no treatment, though there are some cubbies I use for storing mic cases and hanging audio cables. There is a small couch on the back wall.

One problem I'm going to have to deal with is that the door is located over my left shoulder in the corner making it impossible to fill with insulation.

More photos might help make sense of the issue.

I'm also wondering if given the smaller dimensions of my room I might just try to make the whole thing dead?

[Ethan Winer]

Originally Posted by GabeHerman@gmail

I'm also wondering if given the smaller dimensions of my room I might just try to make the whole thing dead?

Not necessary to make it totally dead, but you need a lot more than one bass trap! If it were my room there'd be at least 12 bass traps if not more. Seriously. I'd also worry more about reflections from the wall behind you than the wall you face when listening.

--Ethan

[GabeHerman@gmail]

Ethan and Scoobz:

Thanks so much for your advice. I've been reading a lot from your website and from previous threads you've posted and I'm really learning a lot.

I dont have pictures yet, cause I'm still trying to figure out how to do it without posting the pics to the web first.

In the meantime, I have gotten a cheap dbx reference mic and "shot" my room using some admittedly inappropriate software (PAZ Freaq by Waves). I've noticed the following things:

1. my room is not as bad as I thought it was (at least though the PAZ lens) but I am experiencing a bump at around 118Hz, and a dip at around 348Hz.

2. I'm hearing some VERY obvious comb-filtering when I sit down or stand up from the listening position. I assume this is because I have yet to treat my RFZ around the listening position first and possibly this is enhanced by the fact that I have no treatment on my ceiling at all yet. Am I correct in assuming that this will all go away when I do treat this area? This also is true when I play pink noise and walk from the front to the back of my room. I am certain that I can fix this with bass traps in the corners and wall/ceiling areas.

3. I wish I had a pic to post of this, but the window to my live room is approximately 4' x 8' (wide dimension) and the left facing edge protrudes into the RFZ a little bit. (maybe a foot or more). Should I treat the other side as if there was a window on the opposite side? (to maintain stereo imaging) Or is it worth considering some 1D QRD diffusion on the opposite side from the window to mimic the reflective properties of the glass? Maybe I'm over-thinking it?

4. I am an amateur carpenter/cabinetmaker and am quite comfortable building something like a QRD diffuser, but I'm wondering if this is something I'll need to be thinking about on the back wall since I'm 8'4" from the back of my head at the listening position to the face of the back wall. Any opinions on this would be most helpful.

I am really appreciative of all of your advice and Ethan, I'm really impressed by your videos on diffusion and resonance...I know this isn't the right thread, but Kudos!
jummp

[Ethan Winer]

Originally Posted by GabeHerman@gmail

2. I'm hearing some VERY obvious comb-filtering when I sit down or stand up from the listening position. I assume this is because I have yet to treat my RFZ around the listening position

Yes.

Should I treat the other side as if there was a window on the opposite side?

Symmetry is very important. If you have a window where a panel needs to go, put the panel on a stand. Or hang it from the ceiling using long wires.

am quite comfortable building something like a QRD diffuser

In a room 4 by 8 feet I'd forget diffusion and use only absorption.

--Ethan

[GabeHerman@gmail]

Quote:
Should I treat the other side as if there was a window on the opposite side?
Symmetry is very important. If you have a window where a panel needs to go, put the panel on a stand. Or hang it from the ceiling using long wires.

But I use this Window to see into my tracking space. I cannot block it with a panel. I hear what you are saying about symmetry. Perhaps I should then not treat the opposite wall at all?

Quote:
am quite comfortable building something like a QRD diffuser
In a room 4 by 8 feet I'd forget diffusion and use only absorption.

As I had posted before, My room is 9ft wide, 13ft deep and 8ft high. My head is positioned 38% back in the room and that leaves about 8 feet from the back of my head to the rear wall. Does this still mean no Diffusion?

[Ethan Winer]

Originally Posted by GabeHerman@gmail

But I use this Window to see into my tracking space. I cannot block it with a panel. I hear what you are saying about symmetry. Perhaps I should then not treat the opposite wall at all?

Maybe I misunderstood. Where is the window in relation to you? In front? Off to one side?

that leaves about 8 feet from the back of my head to the rear wall. Does this still mean no Diffusion?

In that case you could benefit from diffusion behind you. I saw 4x8 feet and thought "the guy's mixing in a closet."

--Ethan

[Scoobz]

Hey Gabe,

Given that you have already made traps and have carpentry skills I'd just get making movable panels and start experimenting.

Also with a room your size you're going to want some proper traps on the back wall but like I said after speaker placement the first thing to look at is your RFZ. You won't believe the difference it will make to your imaging.

Ditch Paz, it's not as accurate as you think, get the 30day demo of Smaart.

Your peaks and dips are due to room modes and SBIR, panel/s behind the speakers 1st after corners. Then get some insulation in the floor/wall corners, it's dead space anyway so fill it up.

You need a ceiling 'cloud', some Gobos (movable panels on stands) for the sides (RFZ) and don't forget the front wall behind speakers and rear wall.

I think in a room that size you're better off not bothering with reflection control.

When you're making the corner traps make sure you can take the face off easily so you can try a limp mass membrane (to add some top end back into the room if you find it too dead) this is not applicable to the RFZ.

Now get some pictures up man!

[GabeHerman@gmail]

Hahaha....No, not a closet. More of your average, small bedroom.

I have been busy the last couple of days in my woodshop building several wooden frames out of Poplar (no nails, just glue) for my RFZ. I will post the pics when they are done. So far they are looking beautiful. I have built 6 of them already ranging in size from 5' x 2.5' to 4'x2'. The materials list has only got me up to just under $200.

I'm sorry I have been slack on the pics. That's my bad. I've been in the shop, and my i-phone doesnt have a wide enough lens to get the whole Gestalt of the room anyway. I did spend a couple of minutes this morning doing up a rough schematic showing the arial view of the basic layout as well as where some key components of the room's architecture are located. See the attachment for this diagram.

Follow-up question about bass trapping and insulation; I have a bunch of O.C. 708 2" thick rigid fiberglass insulation panels. If I double up their thickness, will this be adequate for bass trapping? Or should I be looking at rock wool in thicker pads?

Thanks for the heads up about the software Scoobz. I'll check it out on Monday.

More pics to come! Thanks a million for all your help!

[Ethan Winer]

Yes, double them up to four inches thick for bass traps.

--Ethan

[Glenn Kuras]

Just to add you can also cut the 703 to 17x17x24 inch triangles and stack them floor to ceiling in the corners. This will work VERY well also. Close to twice the absorption at 50hz over a 4" 703 straddling the corner.

Glenn