Wall Treatment

  • Thread starter Thread starter John Sayers
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John Sayers

John Sayers

Solar Power!!
I've been reading a lot of pages on wall treatment discussion and it's good to see that people are starting to understand the absorption coefficients and their relation to frequency response. As you've now recognised the rigid fibreglass is much more effective than the regular acoustic foams.

If you look at the formula for the RT60 (Reverberation Time) of a room it goes like this:

RT60 = k(V/Sa)

k is a constant that equals 0.161 when the units of measurement are expressed in meters and 0.049 when units are expressed in feet.
Sa is the total surface absorption of a room expressed in sabins. It is a sum of all the surface areas in the room multiplied by their respective absorption coefficients. The absorption coefficients express the absorption factor of materials at given frequencies.
V is the volume of the room.

The Sa figure is very important to the outcome. In other words how much treatment you actually have on the surface area of the room.

A 10' x 10' x 10' room has a total surface area of 600 sq ft (4 x walls, ceiling and floor) so if we apply 24, 1' x 1' foam panels we have only changed 24 sq ft of the surface area or 4%. Treating one whole wall will only effect 16% of the surface area.

My point is that you really need to treat whole walls to really change the RT60 of a room to any effective degree.

cheers
John
 
I am thinking of doing something simlilar to the panels you made for Amirel's studio. I am still a little unsure of the design...
 
version2

The design is simple. You create a sealed box and place timber slats across the front with gaps between the slats.

There is a Helmholtz Calculator to tune it to a frequency or you can vary the parameters (slot width, slat width, slat thickness,depth from wall) and create a broadband absorber. The slats in Amirels studio vary the slot width and the slats also vary in width. In the controlroom the depth from the wall also varies.

Take a look at the slot resonators in Joe Egans beautiful studio

Notice that the slat widths are different and if you look at the plan on the first page you will see that they are at an angle to the wall behind thus varying the depth from the wall. So it is a broadband low-mid absorber. The slats also act as diffusers at their edges.

Hope this helps :)

cheers
John
 
Very nice. Thanks for the input John. This is right up my alley. I will get some pics for the site soon. Thanks again.
 
John,

I have lots of listening experience, but not much recording experience, and my knowledge and experience with room treatments has been limited almost exclusively to speaker placement. You were kind enough to explain to me earlier what "rigid fiberglass" is and why it is so useful, and how it opens up treatments that are both aesthetically pleasing and reasonably priced.

I'm in the position of not even knowing the categories of my ignorance, so I'll have to walk around the issue until it sounds something like a question.

Over the years, I've found that my stereo equipment sounded better or worse -- to a remarkable degree -- according to the room it was in. Yet, not a single room conformed to any standard, and at times the best-sounding violated the most "principles" of placement. Ironically, I don't think my system ever sounded better than it did in the living room of a tiny apartment we had for six years when we were first married, with the speakers seemingly far too close together, symmetrically aligned to the sweet spot but with one stuck under a triangular landing for the staircase, and a television between them (because there was no place else to put it).

Today we own a larger house, yet just to get acceptable sound, I have my speakers probably three feet off the back wall and at least five feet out into the room from the sides (the TV is still between them, but back a few inches, not protruding). I've placed the sofa eight feet in front of the floor-standing speakers, and in the center seat the sound is quite good, although I'm obviously using them at that point as very large nearfield monitors.

The left wall is glass, usually covered with wooden large-slat Venetian blinds. Ditto behind the speakers. The right wall is sheetrock and fireplace even with the sofa with a pellet stove insert. Perhaps problematic is that the room is peaked in the middle -- front-to-back -- but where the room "ends," there is a hard triangle of sheetrock as it transitions into the lower ceilings in the kitchen and dining area, both of which are open to the living room.

On the right side of the room, the addition of the dining area behind adds enough space for the sound to stretch its legs a bit, but the kitchen area truncates this somewhat on the left. There is another space / sunroom that is open off to the left -- all of this behind the sofa, which with the speakers and TV defines the living room and listening area.

OK, so I can't cover my windows with fiberglass (we like the view), the wooden blinds would seem to make acceptable semi-hard diffusers, leaving just the ceiling and triangle, the two rear corners, the relatively small areas above or below the windows, and the right wall (that has the fireplace) open to any sort of treatment.

What do I do? Is there any methodical way to begin dealing with a complexly shaped room that is essentially too short front-to-back to allow full wave propagation (if I'm even expressing that correctly)? I know from the experience of hearing the same system now in at least three different rooms that the room interaction is responsible for perhaps as much as 50% of the perceived sound quality -- there is nothing subtle about it!

I'd very much like to "get my stereo back," and I suspect room treatment may be the only way to do so. The problem is that I don't have any idea where to begin.

I apologize in advance for anything I've said that may sound incredibly stupid to those of you who know more about this topic.

With kind regards,

Mark H.
 
No I fully understand what you are saying Mark H.

i think there is a big difference between what I call a hifi speaker system and a working monitoring system. The first is for listening to music on the second is for making music on.

The common thing you have is the mix of the music on the CDs you play. The rooms may vary but the mixes still sound cool. That's because they were probably mixed on working speakers as opposed to listening speakers I you get my drift. You are using these mixes as your determinant when assessing your rooms and speakers. The people who did the mixes can't do that as they are creating the original so their speakers must be dead accurate.

cheers
john
 
Hi John,

Thank you for your response. I'm sorry I was unable to phrase the question better. I'm more interested in room treatment from the recording aspect, but to learn about what it does and how it works, I thought it might be better if I started with something I have more experience with, which is listening.

While learning about the effects of room treatment for recording, it also occured to me that I could better sell the concept of wall treatment to my spouse if I started with something we both could benefit from as well (better sounding music in our living room).

My sorry experience as a recordist is limited to uncontrolled venues (such local auditoriums and concert halls, people's homes, lectures and teachings, etc.), so I would like to set up a small studio in my home for mixing, dubbing and some voice-over work to begin with. Do you think treating the living room / listening room first would be a waste of time and money?

You have my permission to be completely blunt with me. I'm just a middle-aged former brass player and singer who long ago realized my meager talents in music were better put towards listening and helping others, and recently that interest has expanded into recording. My collection of about 1400 classical CDs were all acquired at the rate of two per week over a period of 15 years, by giving up other priorities. I've bought most of my equipment used, and I don't care a whit about the latest fads in "high-end audio."

I very much appreciate your guidance and opinions.

Best wishes,

Mark H.
 
Mark - I'd definitely look at treating your listening room aka living room. I'd suspect that having done that you will notice that it actually has becomne a better recording room as well. :)

cheers
JOhn
 
Hi John,

As I check out more of the information on this forum, I'm beginning to understand how many of my questions are already answered here. You shouldn't be shy about pointing people to your incredible website, John! I'm embarrassed that I wasn't aware of it. It's the perfect place to start understanding all this. Thank you so much!

So I'll be in the woodshed reading and will get back to you when I have some specific, informed questions.

Thanks for your patience and help, as always,

Mark H.
 
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