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Room Acoustics 201 - Part 1
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Having written recently about acoustics....
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...and specifically the Cathedral Sound Acoustic Panels, the floodgates have opened with all sorts of good questions about our approach to room acoustic treatment. We decided it would be worth preparing a primer on our approach both to speaker positioning, and to acoustic treatment, because for high performance audio, these go hand in hand. As we began preparing this piece we realized that it is too much for a single email, so our plan is to send it to you in three parts over the course of three months. At the end we will package it all together for viewing as a whole on our website, and depending on the response may even make print copies available. If you cannot view the images and diagrams please open this email in your browser by going to "File"in your menu and choosing "Open In Browser".
During the release period for this room acoustic writing project, we will have a special 12% discount on ALL acoustic products.
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Part 1: the mid-room approach to speaker placement and fundamental room treatment
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In this Part 1 we will make the case for a mid-room speaker placement approach. In some respects our acoustic treatment approach has things in common with other speaker placement approaches, and even though we will focus primarily on two channel stereo, elements can be applied to other set-up arrangements including home theater.
We will focus primarily on the easiest type of room to work with, which is a "normal" rectangle. We will interject some discussion of non-rectangular rooms, especially in Part 3. Why are rectangular rooms easy? Because this is acoustically the most predictable room type, regardless of the overall size of the room. The large flat surfaces - the walls and ceiling - gather energy, and where they meet, acoustic energy will build and basically horn load back out into the room.
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Mid-Room Speaker Placement
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If we think of the room in terms of where acoustic pressure is greatest (let's call these points "pressure zones") the primary pressure zones will be the corners. Secondary pressure zones are the mid-points of each wall. In our approach we want to acoustically treat and reduce pressure in the primary pressure zones - the corners - and use the secondary pressure zones - each mid-wall - to reinforce the music. So in our approach we will place the speakers at the mid-walls in these secondary pressure zones, and also sit in one of these secondary pressure zones. You can view this in our Diagram #1. This leaves one more mid-wall position unused, and this position, behind and between the speakers, can also be an important location for acoustic treatment. (More on this later.)
This idea of using the secondary pressure zones to reinforce the music system may run contrary to approaches you have considered in the past. Back in the early 1990's our Ultra Systems affiliate was the world wide distributor for Michael Green's RoomTune acoustic products. Michael, and the head of our German distribution partner, Joachim Gerhard, of Audio Physics (and now owner/designer of the new line of speakers called "Sonics",) had come upon this idea as an alternative to the popular "rule of thirds" popularized by Harry Pearson at the absolute sound magazine, or the "live end, dead end" concepts derived from recording studios. The unique power of this mid-room placement concept is that you are working with the room, rather than trying to beat it into submission by throwing massive amounts of damping and diffusion at it. This concept of working with the room acoustically will lead to a much more open and lively concert hall type acoustic, as compared to a dead-ish and dry-ish studio acoustic which would result from the other approaches. For a "you are there" virtual reality sonic recreation of the original musical event, our mid-wall approach has proven far superior in room after room.
This approach has sometimes been called "near field listening" (although this can also have other meanings) because the listener may be closer to the speakers compared to other approaches. Interestingly as you move your speakers closer to the middle of the room, and therefore closer to the listening position, in fact the sound of the speakers will recede further back into the open space behind the speakers and away from the listening position. This may seem counterintuitive, but is a direct result of the speaker, positioned in this secondary pressure zone, coupling better with the room, becoming part of the room, or the room becoming an extension of the speaker.
Another advantage of this mid-room speaker placement approach, which may also seem counterintuitive, is how much more efficiently it makes use of the available living space in the room. Remember that the speakers are to be placed in the middle of that side wall pressure zone. This means that the speakers should be quite close to the side walls (and toed in considerably to achieve focus in the center of the sound stage). With the listening position quite near the rear wall, almost the entire room is open space!
If you have a dedicated listening room this side benefit may be unimportant, but here is an extreme example of how useful this can be in a multi-use environment. For a 15 month period a few years ago, because of renovations to much of my house, my entire family of four had to substantially live in my listening room. A multi-use room requires many speaker placement compromises, yes?
No.
In fact, because my electronics were near my listening position near the rear wall, I did not need to move even a single component to accommodate the family! From a use of space perspective everything is out of the way.
Here is a related tip: in the mid-room speaker placement approach the half of the room which is behind the speakers is not supercritical with respect to the placement of furnishings. So in multi-use rooms if one end of the room (the end with the listening position) can be primarily for audio use, the other end can be fairly happy used for other things. In my example above, in the open space behind the speakers we needed to install a temporary kitchen, dining area, a bed, a sofa, and a TV. I am not saying that this had no effect on the room acoustics, but it wasn't too bad.
A related benefit for rooms with irregular shapes or L's: if you can position the system with the irregularity behind the speakers this will minimize the acoustic impact of the irregularity. You can see this in Diagram 3 below.
The best thing you can do for your system costs no money. Just try moving your speakers approximately half way into the room, quite near the side walls, with plenty of toe in.
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First phase acoustic treatment: Cathedral Sound Acoustic Panels
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Use Link in text below to enlarge.
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How can we best treat our primary pressure zones?... the corners. Remember that our walls, the ceiling, and the floor will multiply pressure where they meet. This effect is most pronounced at the ceiling where there are no furnishings, etc. to break up this process of acoustic energy collection.
I feel a little like a broken record writing again about this new product, but from an acoustic perspective it borders on being a new paradigm. Our excitement about the new Cathedral Sound Acoustic Panels is because they address the primary pressure zones - the corners - and they do it better than anything else we have come across. Furthermore they are one of the very few acoustic treatment products that are effective down to 20 Hz (and below).
These 2 charts above, (click here for larger view of graphs) independently prepared by Rives Audio in a typical room, demonstrate the impact of a set of 4 panels on the deep bass frequencies. (Note that the second scale is reduced in the vertical axis to better illustrate the effect.)
Because these panels are "tuned" to low frequencies by the nature of their construction, they are particularly effective at reducing problems associated with "standing waves," which can cause boomy bass in some areas in the listening room, and anemic bass response in other locations in the same room. And when you can control bass standing waves, not only is the low frequency "foundation" better controlled, the midrange and higher frequencies can also "breathe" more easily. Not only is bass more tuneful with greater impact, the midrange (and dialog) is more articulate and dynamic, and sound stage size and layering is significantly improved. (You will understand this concept if have a well-integrated subwoofer in your system, or have upgraded the signal, and/or AC cables to your subwoofer. It is not so much what these improvements do for the bass, although this is certainly significant, as it is what they do for the midrange and high frequencies.)
Note: these Panels only work in one location - the corners of the room, especially near the ceiling. And they will ALWAYS work in this location, very effectively equalizing the pressure buildup, even for deep bass. They don't do it the old fashion way with absorption. Other acoustic products using this old school absorption approach, if effective to 20 Hz, must be at least 6ft (1.8m) tall, or you can trade off girth for height, eg. 4ft (1.2m) height and 2ft (.6m diameter). Instead the Cathedral Sound Panels make use of the ages old "Venturi effect," a restricted flow = reduced pressure concept, which helps common devices from carburetors to swimming pool filters function. And these panels fit beautifully into our concept of working with the room, rather than against it, as they are effectively "activated" by the pressure buildup naturally occurring in the corners, rather than trying to gobble it up with absorption.
These are small, light weight, and contain no damping materials, so will not interfere with any of the other acoustic treatment products we will be discussing in parts 2 and 3. Perfect for our extreme high end applications, but also the best single thing anyone can do acoustically regardless of their system set-up, for two channel stereo or home theater. If there is a "must have" product in room acoustics. this is it. $179.95 per pair in black or off-white. ($158/pr on special in February.)
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These Panels should be used symmetrically,
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...meaning either one in each corner of the room, or two in each corner of the room. Use two in each corner for larger rooms, systems playing louder, and/or systems capable of producing very deep bass. See diagram #2.
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For L - shaped or other irregular rooms,
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...treat all of the corners in the "acoustic space." See diagram #3.
This first phase approach to acoustic treatment is so straight forward, with no trial and error needed, that it may seem too good to be true. It is for real.
We will stop here for now. Second and third step acoustic treatment, irregular rooms, ASC TubeTraps, Echobusters , and the Shakti Hallograph to come. Stay tuned!
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For additional information on these offers and frequent updates speak with your Cable Company consultant, or visit our websites: www.fatwyre.com and www.ultrasystem.com. For hundreds of specials on used and demo cables, visit www.usedcable.com.
Or call us Mon.- Fri. 10 -6; Sat. 11-5 Eastern time on 800-328-9973 (or 215-862-4870). Fax: 215-862-4871
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